JP6905566B2 - Vehicle center of gravity position estimation system - Google Patents

Description

The present invention relates to a system that estimates the position of the center of gravity of a vehicle, which changes depending on luggage and passengers, by processing a signal from a position information acquisition means such as a GPS unit (including a GNSS receiver).

The position of the center of gravity of the vehicle body is always constant when the vehicle is empty with no luggage or passengers, but in actual driving, the position of the center of gravity changes depending on the load capacity and the loading position of the luggage.

In order for the autonomous driving vehicle to travel, it is necessary for the vehicle control device to calculate a target movement locus and control the vehicle to follow the movement locus. The movement locus is calculated as a locus to be followed by the position of the center of gravity of the vehicle. However, as described above, the vehicle weight and the position of the center of gravity of the vehicle change depending on the passenger's boarding and loading on the vehicle, and therefore, a means for grasping the changes is important.

As a method of detecting the position of the center of gravity, in the case of a full air suspension vehicle, a method of detecting the air pressure of the air spring of each shaft, a method of calculating the natural frequency from the suspension spring constant of each shaft and detecting it from the mass on the spring of each shaft. Furthermore, a method of equipping each axis with a load cell can be considered. However, the method using the full air suspension, the method using the natural frequency, and the method using the load cell all have structural restrictions. It lacks versatility. There is a need for a versatile and easy-to-equip method.

In Patent Document 1, the vehicle weight is estimated from the accelerator opening and the generated front-rear acceleration, the rear axle load is estimated from the air pressure of the rear axle air suspension, and the rear axle load is subtracted from the vehicle weight to obtain the front axle load. The method of estimation is shown.

Patent Document 2 describes the rear wheel brake pressure changing means for changing the rear wheel brake pressure according to the rear wheel axle weight, the front wheel brake pressure detecting means for detecting the front wheel brake pressure, and the rear wheel brake pressure changing means. Based on the relationship between the rear wheel brake pressure detecting means for detecting the brake pressure of the rear wheels on the downstream side, the detected front and rear brake pressures during braking, and the rear wheel axle weight characteristics of the rear wheel brake pressure changing means. It is disclosed that a rear wheel shaft weight estimating means for estimating the rear wheel shaft weight is provided, and the vehicle center of gravity state in the vehicle width direction is determined based on the estimated rear wheel shaft weight.

In Non-Patent Document 1, the natural frequencies of bouncing and pitching are measured, the load capacity is determined in accordance with the natural frequencies of the riding comfort model, and the sprung mass, moment of inertia, center of gravity position and each axial weight are also multiplied. It is stated that it is estimated by the comfort model formula.

Japanese Patent No. 6202700 WO2014 / 122786

"Estimating the loading state of a lateral motion model for autonomous driving heavy trucks," Fujio Paddyyama et al., Automobile Technology Open Papers, Vol.44, No.6, November 2013, No.2020134847, pp.1377-1382

According to Patent Document 1, the position of the center of gravity of the vehicle can be estimated by multiplying the wheelbase by the ratio of the front axle load and the rear axle load. However, since it is assumed that the vehicle is equipped with an air suspension, there remains a problem that the applicable vehicle structure is limited.

In the method disclosed in Patent Document 2, since it is a prerequisite to detect the brake pressure, there is a problem that the applicable range is extremely narrow. Further, in Non-Patent Document 1, the burden on the control ECU for calculating the natural frequencies of bouncing and pitching becomes large.

"Equation of change in the position of the center of gravity" derived from the simultaneous equation of "balanced equation of lateral motion when empty" and "balanced equation of lateral motion when loaded" where all the specifications are grasped The unknown numbers included in this equation, the front axis lateral slip angle and the rear axis lateral slip angle, were measured by the GPS equipped at the front axis position and the GPS installed at the rear axis position, and the "center of gravity position change length" was measured. Ask for. The obtained "center of gravity position change length" is added to the "center of gravity position when the vehicle is empty" to obtain the position of the center of gravity when the vehicle is loaded.

As a known value, the distance from the known center of gravity position of the empty vehicle is calculated from the signal from the GPS unit based on the position of the center of gravity of the empty vehicle with no passengers and no passengers on it, and the calculated value is used as the known value. The position of the center of gravity during running is estimated by adding it to the known position of the center of gravity of the empty vehicle.

Specifically, the computer includes a first GPS unit that detects the front wheel position, a second GPS unit that detects the rear wheel position, and a computer that calculates the position of the center of gravity of the vehicle based on signals from these GPS units. , The amount of change in the position of the center of gravity during running from the position of the center of gravity when the vehicle is empty is calculated based on the front wheel position side slip angle, the rear wheel position side slip angle, the vehicle weight, the vehicle speed, and the yaw rate by each of the GPS units, and the amount of change is known. I added it to the position of the center of gravity when the car was empty.
Here, the position side slip angle is not limited to the one calculated and output in each GPS unit, but also includes the one calculated by a computer based on a signal from a position information acquisition means such as a GPS unit.

According to the present invention, by using two GPS units (including a GNSS receiver) installed on the front axle and the rear axle of the vehicle, the change in the position of the center of gravity can be easily estimated without depending on a specific vehicle structure. can do.

With the active development of self-driving vehicles and the increasing demand for GPS units, the price of GPS units is expected to decline gradually, and from the perspective of control device redundancy, in the future. Is expected to be equipped with multiple GNSS receivers for one self-driving vehicle of the GPS unit. The present invention makes it possible to easily estimate the position of the center of gravity of the vehicle by arranging the GPS unit vertically above the front and rear axles.

It is explanatory drawing of the vehicle state quantity at the time of turning. It is explanatory drawing of the method of estimating the actual rudder angle of the front axle.

The vehicle center of gravity position estimation system according to the present invention includes two GPS units and a computer as essential components. The front axis position on the vehicle body center line and the rear axis position The first GPS unit and the second GPS unit are provided on the vehicle roof, and the magnitude, azimuth, and eccentric angular velocity of the speed vector with respect to the vehicle body center line at each GPS position. It has a form that can grasp.
Further, the computer may be equipped with a computer dedicated to this system, but it is sufficient to use a computer already installed for operation control or a computer built in the GPS.

In addition to the above, a wheel speed sensor is provided on the front axle to enable detection of "movement distance and speed in the front axle wheel rotation direction", and a wheel speed sensor is provided on the rear axle to enable "movement distance in the rear axle wheel rotation direction". And speed ”can be detected so that the actual steering angle of the front wheels can be grasped from the cosine of both.

Hereinafter, the problem of detecting the position of the center of gravity will be described with reference to FIG.
FIG. 1 is a simplified mechanical model in which two tires on the left and right are grouped in the center. The description of the symbols of the model specifications is as shown in the figure. A code without a subscript indicates the specifications of an empty vehicle, and a code with a subscript L indicates the specifications of a loaded vehicle.

By combining the "formula of turning motion when empty" and the "formula of turning motion when loading" where all the specifications are grasped, the position of the center of gravity changes due to loading. (Δl) can be calculated.

The equation of the turning motion when the vehicle is empty is expressed by the following equations (1), (2) and (3).

The equation of the turning motion at the time of loading is expressed by the following equations (4), (5), and (6).

m is the vehicle mass, v is the speed at the center of gravity, γ is the eccentric angular velocity (yorate), β is the vehicle lateral slip angle, βf and βr are the lateral slip angles of the front and rear axle tires, and Ccf and Ccr are the front and rear axles. Tire cornering coefficient (concept of friction coefficient), Nf, Nr are front axle and rear axle loads, g is gravity acceleration, lf, lr are distances from front axle and rear axle to vehicle center of gravity, Δl is associated with loading The change distance of the position of the center of gravity.

By substituting the equations (5) and (6) into the equation (4), the equations (7) and (8) are derived. The equations (8) to (9) are described for the purpose of explaining the equation (8).

In the above, β _fGPS and β _rGPS are the lateral slip angles detected by GPS installed at the front and rear axle positions, δ is the actual steering angle of the front wheels, and v _x is the front-rear speed obtained from the rotation sensor of the rear axle tires.
v _f wheel is the front wheel speed obtained from the rotation sensor of the front axle tire.

The above equation (9) is derived from the following equation (13) for the position side slip angle of the front wheels and the equation (14) for the position side slip angle of the rear wheels as follows.

FIG. 2 is an explanatory diagram of a method for detecting the actual steering angle of the front axle. The front wheel side slip angle and the rear wheel side slip angle that are detected together with the detection of the actual steering angle will also be described. Similar to FIG. 1, this is a simplified mechanical model in which two tires on the left and right are grouped in the center. v _fwheel is the rotational speed of the front axle wheel. Since v _x is the rotational speed of the rear wheels and the forward _{/ backward movement speed of the vehicle x-axis, the cosine of v fwheel} / v _x is equal to the actual steering angle δ of the front axle wheels. That is, the following equation (12) is obtained.

In addition, the v _Fwheel output from v _f and the front shaft a wheel rotation sensor output from GPS equipped prior-axis position, the front wheel position side slip angle (19) can be detected. Similarly, the side slip angle type (20) of the rear wheel can be detected.

Claims (4)

A first position information acquisition means such as a GPS unit that detects the front wheel position, a second position information acquisition means such as a GPS unit that detects the rear wheel position, and a position of the center of gravity of the vehicle based on signals from these position information acquisition means. It is a vehicle center of gravity position estimation system consisting of a computer that calculates
The computer is based on the front wheel position side slip angle by the first position information acquisition means, the rear wheel position side slip angle by the second position information acquisition means, the vehicle weight, the vehicle speed, and the yaw rate when traveling from the center of gravity position when the vehicle is empty. A vehicle center of gravity position estimation system characterized in that the amount of change in the position of the center of gravity is calculated and the amount of change is added to the known position of the center of gravity when the vehicle is empty to estimate the position of the center of gravity during traveling. In the vehicle center of gravity position estimation system according to claim 1, the GPS unit as the first position information acquisition means is installed vertically above the front axis, and the GPS unit as the second position information acquisition means is vertically above the rear axis. A vehicle center of gravity position estimation system characterized by being installed in. In the vehicle center of gravity position estimation system according to claim 1 or 2, the amount of change (Δl) in the center of gravity position during traveling from the center of gravity position when the vehicle is empty is calculated by using the following formula. Center of gravity position estimation system.

In the vehicle center of gravity position estimation system according to any one of claims 1 to 3, the front wheel position lateral slip angle is a front shaft position speed vector and a front wheel sensor output from a GPS unit as a first position information acquisition means. Calculated from the wheel speed detected from, the rear wheel position side slip angle is calculated from the rear shaft position speed vector output from the GPS unit as the second position information acquisition means and the wheel speed detected from the rear shaft wheel sensor. A vehicle center of gravity position estimation system characterized by

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