| CPC B60G 17/018 (2013.01) [B60G 17/0165 (2013.01); B60G 2600/09 (2013.01); B60G 2600/17 (2013.01); B60G 2600/182 (2013.01); B60G 2600/1873 (2013.01); B60G 2600/70 (2013.01); B60G 2800/915 (2013.01)] | 12 Claims |
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1. An inertial regulation method of active suspensions based on terrain ahead of a vehicle, comprising the following steps:
S1: calculating trajectories of ground-contacted points of wheels and elevation information of ground-contacted point of each wheel when the vehicle passes through the terrain ahead of the vehicle;
according to position coordinates of the vehicle in a geodetic coordinate system measured by an inertial measurement unit and a dual-antenna GPS positioning system, and the terrain ahead of the vehicle scanned by a laser radar and a steering angle of each wheel, calculating, by vehicle kinematics, the trajectories T1, T2, . . . , Tm of all ground-contacted points of wheels when the vehicle is driving on the terrain ahead of the vehicle, wherein j=1, 2, . . . , m, and m is a number of wheels; and calculating the elevation information of each planning data point on the trajectory of ground-contacted point of each wheel by an interpolation algorithm;
S2: calculating a trajectory of center of mass and an attitude history when the vehicle passes through the terrain ahead of the vehicle with passive suspensions;
S21: according to a vehicle speed, a steering angle, a driving/braking force of each wheel and a rolling friction coefficient of the wheel on the ground, calculating, from a vehicle dynamics model, a 6-dimensional coordinate history {Xi Yi Zi αi βi γi} of a vehicle coordinate system, the trajectory of center of mass and the attitude history {XWi YWi ZWi αWi βWi γWi}T when the vehicle drives with the passive suspensions along the trajectories T1, T2, . . . , Tm of the ground-contacted points of wheels in step S1, wherein, XWi, YWi, ZWi, αWi, βWi, γWi, are three-dimensional coordinates and three-dimensional attitude angles of the center of mass of the vehicle respectively, wherein i=0, 1, 2, . . . , n, and n is the number of planned data points;
S22: taking a smoothness coefficient as ξ, performing a smoothing process crossing a start point on the trajectory of the center of mass and attitude history of the passive suspension vehicle in step S21 to obtain a smoothing function {XW(ti), YW(ti), ZW(ti), αW(ti), βW(ti), γW(ti)}T of the trajectory of the center of mass and attitude history;
S3: based on the above-mentioned smooth-processed trajectory of the center of mass and attitude history, calculating the suspension stroke history si,j and suspension supporting force history Wij when the vehicle passes through the terrain ahead of the vehicle with the active suspensions;
S31: taking the smooth-processed center of mass trajectory and attitude history of the vehicle in step S22 as inputs to calculate the stroke history si,jR and speed history si,jR of each suspension relative to the passive suspension when the vehicle passes through the terrain ahead of the vehicle with the active suspensions, wherein j=1, 2, . . . , m, and m is the number of wheels;
S32: under the conditions of the same speed of vehicle, steering angle, driving/braking force of each wheel and rolling friction coefficient of the wheel on the ground as in step S21, according to the stroke history si,jR and speed history si,jR of active suspension relative to passive suspension obtained in step S31, calculating, from a dynamics model, a stroke history si,j and a supporting force history Wij of each suspension relative to the median position when the vehicle passes through the terrain ahead of the vehicle with the active suspensions;
S4: according to the stroke history si,j and the supporting force history Wij of each suspension relative to the median position when the vehicle passes through the terrain ahead of the vehicle with the active suspensions, performing an impedance control based on force-displacement on a suspension actuator;
in the steps S21 and S32, the vehicle dynamics model and solving thereof are as follows:
establishing a fixed coordinate system OXYZ, which is fixedly connected with the ground, wherein the coordinate system takes a reference point O of the inertial measurement unit as the origin of coordinates, the front of the vehicle as a positive direction of Y axis, the right direction of the vehicle as a positive direction of X axis, and the upward direction perpendicular to the XOY plane as a positive direction of Z axis; in order to determine the position of the vehicle in the fixed coordinate system, introducing a vehicle coordinate system oxyz, which is fixedly connected with a vehicle body, wherein the vehicle coordinate system coincides with the fixed coordinate system at an initial position, and positioning coordinates in the fixed coordinate system are X, Y, Z, α, β, γ respectively;
in order to improve a calculation speed, regarding the vehicle as a rigid body, setting the weight thereof as M and the coordinate thereof in the vehicle coordinate system as W (xW,yW,zW), wherein the vehicle has m wheels and has m corresponding suspensions, the active suspension is simplified to a parallel connection of an actuator, a spring and a damper; setting the control method of active suspension as a displacement control; setting the stiffness coefficients of suspension springs respectively as KS1, KS2, . . . , KSm, and the damping coefficients of suspension dampers respectively as CS1, CS2, CSm; simplifying a tire as a parallel connection of a vertical spring and a damper, and ignoring the influence of lateral and tangential elasticity and damping of the tire on vehicle dynamics characteristics; setting the stiffness coefficients of vertical springs of all tires as KW1, KW2, . . . , KWm, and setting the damping coefficients of vertical dampers of all tires as CW1, CW2, . . . , CWm; setting the above-mentioned dampers to be viscous dampers; and setting the above-mentioned springs as nonlinear springs and approximating the springs by piecewise linear;
wherein the above is the dynamics model of the active suspension vehicle, which has 6 degrees of freedom; if the actuator in each suspension is removed, the above-mentioned dynamics model becomes the dynamics model of the passive suspension vehicle; when the suspension spring and damper are not provided in the design of partial active suspension, the suspension spring and damper in the above dynamics model of the active suspension vehicle should be omitted;
establishing a kinematic differential equation of the vehicle dynamics model by a Lagrange equation, which is expressed by matrix as follows:
[M6×6]{q6}+[C6×6]{q6}+{K6×6}{q6}={F6}
in the formula, [M6×6], [C6×6] and [K6×6] are a weight matrix, a damping matrix and a stiffness matrix respectively, all of which are 6×6 symmetric square matrices; and {F6} is a force matrix which is a 6×1 array;
taking a displacement vector of the vehicle in the fixed coordinate system as:
{q6}={X,Y,Z,α,β,γ}T
constructing a dynamics matrix based on the above kinematic differential equation as follows:
{q6}=[M6×6]−1{F6}−[M6×6]−1[C6×6]{q6}−[M6×6]−1[K6×6]{q6}
setting a state variable as:
 substituting the state variable into the dynamics matrix to obtain a state equation as follows:
 the above state equation can be solved by a fourth order Runge-Kutta method to obtain the value of the state variable {q12}.
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