Method for predicting dynamic behavior characteristics of a vehicle using screw theory

• US 20040006410A1
• Filed: 05/19/2003
• Published: 01/08/2004
• Est. Priority Date: 07/08/2002
• Status: Active Grant

• Current Assignee: Hyundai Motor Company (Hyundai Motor Group)
• Original Assignee: Hyundai Motor Company (Hyundai Motor Group)
• Inventors: Lee, Unkoo
• Granted Patent: US 6,766,225 B2
• Time in Patent Office: Days
• US Class Current: 701/1
• CPC Class Codes: B60G 17/0182 involving parameter estimation, e.g. observer, Kalman filter
• CPC Class Codes: B60G 2206/99 Suspension element selection procedure depending on loading or performance requirements, e.g. selection of damper, spring or bush
• CPC Class Codes: B60G 2600/1873 Model Following
• CPC Class Codes: B60G 2800/012 Rolling condition
• CPC Class Codes: B60G 2800/70 Estimating or calculating vehicle parameters or state variables
• CPC Class Codes: B60G 2800/87 System configuration based on vehicle type or model
• CPC Class Codes: B60G 2800/912 Attitude Control; levelling control
• CPC Class Codes: G06F 30/15 Vehicle, aircraft or watercraft design
• CPC Class Codes: G06F 30/20 Design optimisation, verification or simulation optimisation, verification or simulation of circuit designs G06F30/30

Abstract

A vehicle model is developed for a quasi-static analysis. The quasi-static analysis is performed for the vehicle model under a cornering condition in which a specific lateral force acts. A finite screw axis is determined based on a rigid body displacement of the vehicle model with respect to the ground through the quasi-static analysis. A fixed screw axis surface formed by a migration of the finite screw axis is also determined. The gradients of screw parameters with respect to lateral forces when the vehicle model behaves in an initial cornering state are calculated. Roll behavior is then estimated based on the fixed screw axis surface and gradients of screw parameters.

Claims

1. A method for predicting dynamic behavior characteristics of a vehicle, comprising:

developing a vehicle model for a quasi-static analysis;

performing the quasi-static analysis for the vehicle model under a cornering condition in which a specific lateral force acts;

determining a finite screw axis based on a rigid body displacement of the vehicle model with respect to the ground through the quasi-static analysis;

determining a fixed screw axis surface formed by a migration of the finite screw axis;

calculating gradients of screw parameters with respect to the lateral force when the vehicle model behaves in an initial cornering state; and

estimating roll behavior based on the fixed screw axis surface and gradients of screw parameters.

2. The method for predicting dynamic behavior characteristics of claim 1, wherein a body of the vehicle model is coupled to a contact patch through a spring such that a tire displacement caused by a vertical load can be expressed, wherein the contact patch is configured such that there is no vertical movement, and an equilibrium of lateral forces acting on the vehicle model exists without a structural restraint in a lateral direction.

3. The method for predicting dynamic behavior characteristics of claim 2, wherein the equilibrium of lateral forces is realized by applying a lateral force that increases at a predetermined rate at a center of gravity of the vehicle model, and by applying corresponding lateral forces to the contact patch.

4. The method for predicting dynamic behavior characteristics of claim 1, wherein the vehicle model is structurally restrained in a forward/rearward direction to facilitate determination of a moment equilibrium according to a force equilibrium.

5. The method for predicting dynamic behavior characteristics of claim 2, wherein a front wheel is configured to be restrained and a rear wheel is configured to undergo a forward/rearward movement such that a wheel base change that is brought about during roll behavior by a forward/rearward movement of the contact patch caused by geometries of the front and rear wheels can be reflected in the analysis.

6. The method for predicting dynamic behavior characteristics of claim 5, wherein a forward/rearward displacement of a front contact patch is measured while bumping and rebounding the vehicle in a state of removing all forward/rearward restraints, and a value obtained by a sine function approximation is used as a front wheel displacement restraint condition.

7. The method for predicting dynamic behavior characteristics of claim 1, wherein in the quasi-static analysis, when comparing a plurality of results of the quasi-static analysis for different vehicle models, a camber change tendency and a toe change tendency are set as similar values between the models, and a roll center at an initial position is set to be the same in each model.

8. The method for predicting dynamic behavior characteristics of claim 1, wherein in the step of estimating roll behavior, a point where the fixed screw axis intersects a surface that passes through a center of a front wheel and is perpendicular to a vehicle driving direction is considered as a roll center of the front wheel, a point where the fixed screw axis insects a surface that passes through a center of gravity is considered as a roll center of the center of gravity, and a point where the fixed screw axis insects a surface that passes through a center of a rear wheel is considered as a roll center of the rear wheel, and wherein a tendency of change of the roll center at the three points is estimated.

9. The method for predicting dynamic behavior characteristics of claim 1, wherein the screw parameters include a first position parameter relating to a vertical migration of a center of gravity of the vehicle model, a second position parameter relating to a lateral migration of a center of gravity of the model, a first direction parameter relating to a pitch motion of the vehicle model, a second direction parameter relating to a yaw motion of the vehicle model, and a pitch parameter relating to a cornering speed.

10. A method for predicting dynamic behavior characteristics of a vehicle, comprising:

determining screw parameters and gradients of the screw parameters of a fixed screw axis through an analysis of a quasi-static vehicle model; and

estimating roll behavior of the vehicle based on the determined screw parameters and the gradients of the screw parameters.

11. The method for predicting dynamic behavior characteristics of claim 10, wherein said determining comprises:

applying a lateral force that increases at a predetermined rate at a center of gravity of the quasi-static vehicle model, and simultaneously applying corresponding lateral forces at each contact patch of the quasi-static vehicle model, so that a force equilibrium in a lateral direction and a moment equilibrium exist; and

determining the screw parameters and the gradients of the screw parameters of a fixed screw axis based on motions of the quasi-static vehicle model with respect to the ground.

12. The method for predicting dynamic behavior characteristics of claim 10, wherein the screw parameters include a lateral position parameter that relates to a lateral position of the fixed screw axis, and wherein in the step of estimating roll behavior, a center of gravity of a vehicle is estimated to lower if a value of the gradient of the lateral position parameter is negative, and a center of gravity of a vehicle is estimated to rise if a value of the gradient of the lateral position parameter is positive.

13. The method for predicting dynamic behavior characteristics of claim 10, wherein the screw parameters include a vertical position parameter that relates to a vertical position of the fixed screw axis, and wherein in the step of estimating roll behavior, it is estimated that a lateral migration of a center of gravity of the vehicle decreases and a roll angle decreases if a value of a gradient of the vertical position parameter is negative.

14. The method for predicting dynamic behavior characteristics of claim 10, wherein the screw parameters include a lateral direction component of a unit direction vector of the screw axis, and wherein in the step of estimating roll behavior, it is estimated that a vehicle body slants in a forward direction if a value of a gradient of the lateral direction component is negative, and the vehicle body slants in a rearward direction if a value of a gradient of the lateral direction component is positive.

15. The method for predicting dynamic behavior characteristics of claim 10, wherein the screw parameters include a vertical direction component of a unit direction vector of the screw axis, and wherein in the step of estimating roll behavior, a yaw behavior is estimated based on a gradient of the vertical direction component.

16. The method for predicting dynamic behavior characteristics of claim 10, wherein the screw parameters include a pitch parameter relating to a translating motion of a vehicle, and wherein in the step of estimating roll behavior, it is estimated that the vehicle moves in a forward direction along the screw axis if a value of a gradient of the pitch parameter is positive, and the vehicle moves in a rearward direction along the screw axis if a value of a gradient of the pitch parameter is negative.

17. The method for predicting dynamic behavior characteristics of claim 10, wherein the quasi-static vehicle model comprises a body, and a contact patch that is coupled to the body through a spring, and wherein the contact patch is configured to have no structural restraint in a lateral direction.