Vehicle state estimation device, vehicle state estimation method, and non-transitory computer-readable storage medium

1. A vehicle state estimation device configured to be installed in a vehicle to estimate a vehicle state including a vehicle velocity, wherein the vehicle is provided with an inertial measurement sensor for acquiring an acceleration and an angular velocity and a wheel speed sensor for acquiring a wheel speed, the vehicle state estimation device comprising:

a vehicle state estimation unit that estimates the vehicle state based on the acceleration and the angular velocity acquired by the inertial measurement sensor and the wheel speed acquired by the wheel speed sensor; and

a determination unit that determines whether a wheel is in a sliding state,

wherein the vehicle state estimation unit estimates a steady-state vehicle velocity based on the wheel speed and calculates a transient vehicle velocity by time integration based on the acceleration and the angular velocity,

when the wheel is in the sliding state, the vehicle state estimation unit decides an estimated value of the vehicle velocity to be close to the transient vehicle velocity, and when the wheel is not in the sliding state, the vehicle state estimation unit decides the estimated value of the vehicle velocity to be close to the steady-state vehicle velocity,

the vehicle state includes an attitude angle of the vehicle,

the vehicle state estimation unit calculates a steady-state attitude angle based on a direction of gravity estimated by use of the wheel speed and the acceleration acquired by the inertial measurement sensor and calculates a transient attitude angle by performing time integration of the angular velocity acquired by the inertial measurement sensor, and

when the wheel is in the sliding state, the vehicle state estimation unit decides an estimated value of the attitude angle to be close to the transient attitude angle, and when the wheel is not in the sliding state, the vehicle state estimation unit decides the estimated value of the attitude angle to be close to the steady-state attitude angle,

the vehicle state estimation unit estimates the vehicle velocity and the attitude angle based on:

a velocity observer equation indicating that a relative derivative of the vehicle velocity is equal to a sum of a gravitational acceleration, the acceleration acquired by the inertial measurement sensor, a cross product of the estimated value of the vehicle velocity and the angular velocity acquired by the inertial measurement sensor, and a feedback term for providing feedback with a prescribed acceleration gain to make the vehicle velocity approach the steady-state vehicle velocity; and

an attitude angle observer equation indicating that a time derivative of the attitude angle is equal to a sum of the transient attitude angle and a feedback term for providing feedback with a prescribed attitude angle gain to make the attitude angle approach the steady-state attitude angle, and

the vehicle state estimation unit makes the acceleration gain and the attitude angle gain smaller when the wheel is in the sliding state than when the wheel is not in the sliding state.

2. The vehicle state estimation device according to claim 1 , wherein the determination unit includes at least one of an anti-lock braking system and a traction control system.

3. A vehicle state estimation method for estimating a vehicle state including a vehicle velocity of a vehicle provided with an inertial measurement sensor for acquiring an acceleration and an angular velocity and a wheel speed sensor for acquiring a wheel speed, the method comprising:

determining whether a wheel is in a sliding state;

estimating a steady-state vehicle velocity based on the wheel speed;

calculating a transient vehicle velocity by time integration based on the acceleration and the angular velocity;

when the wheel is in the sliding state, deciding an estimated value of the vehicle velocity to be close to the transient vehicle velocity, and when the wheel is not in the sliding state, deciding the estimated value of the vehicle velocity to be close to the steady-state vehicle velocity,

the vehicle state includes an attitude angle of the vehicle,

a vehicle state estimation unit calculates a steady-state attitude angle based on a direction of gravity estimated by use of the wheel speed and the acceleration acquired by the inertial measurement sensor and calculates a transient attitude angle by performing time integration of the angular velocity acquired by the inertial measurement sensor, and

when the wheel is in the sliding state, the vehicle state estimation unit decides an estimated value of the attitude angle to be close to the transient attitude angle, and when the wheel is not in the sliding state, the vehicle state estimation unit decides the estimated value of the attitude angle to be close to the steady-state attitude angle,

the vehicle state estimation unit estimates the vehicle velocity and the attitude angle based on:

a velocity observer equation indicating that a relative derivative of the vehicle velocity is equal to a sum of a gravitational acceleration, the acceleration acquired by the inertial measurement sensor, a cross product of the estimated value of the vehicle velocity and the angular velocity acquired by the inertial measurement sensor, and a feedback term for providing feedback with a prescribed acceleration gain to make the vehicle velocity approach the steady-state vehicle velocity; and

an attitude angle observer equation indicating that a time derivative of the attitude angle is equal to a sum of the transient attitude angle and a feedback term for providing feedback with a prescribed attitude angle gain to make the attitude angle approach the steady-state attitude angle, and

the vehicle state estimation unit makes the acceleration gain and the attitude angle gain smaller when the wheel is in the sliding state than when the wheel is not in the sliding state.

4. A non-transitory computer-readable storage medium, comprising a stored program, wherein the program, when executed by a processor, executes the method of claim 3 .