Inclination detector and onboard apparatus

1. An inclination detector comprising:

an inclination computing device that calculates one of or both of a road surface gradient θ1 and a pitching angle θ2 from acceleration G x in back and forth direction and from acceleration G z in up and down direction of a vehicle and from real acceleration G w in direction of travel of the vehicle, the road surface gradient being an inclination in back and forth direction of a road surface on which the vehicle is placed, and the pitching angle θ2 being an inclination in the back and forth direction of the vehicle with respect to the road surface; and

a first communication interface that transmits, to an onboard apparatus including an optical axis adjuster installed in the vehicle, a value calculated by the inclination computing device, wherein the pitching angle θ2 as the calculated value is used for controlling an angle of light output by a light of the vehicle,

wherein the inclination computing device is configured to

calculate the road surface gradient θ1 through an expression (1-2) which is derived from an expression (1-1) by linearly approximating sin −1 in the expression (1-1), where g is gravitational acceleration and γ is a predetermined coefficient,

θ1=sin −1 {(− Gx 2 −Gz 2 +Gw 2 +g 2 )/2 Gwg}   (1-1)

θ1=γ(− Gx 2 −Gz 2 +Gw 2 +g 2 )/2 Gw g   (1-2)

calculate the pitching angle θ2 through an expression (2-2) which is derived from an expression (2-1) by linearly approximating tan −1 and sin −1 in the expression (2-1), where α and β are predetermined coefficients, and

θ2=tan −1 ( Gx/Gz )+sin −1 {( Gx 2 +Gz 2 +Gw 2 −g 2 )/2 Gw /sqrt( Gx 2 +Gz 2 )}  (2-1)

θ2=α( Gx/Gz )+β{( Gx 2 +Gz 2 +Gw 2 −g 2 )/2 Gw /sqrt( Gx 2 +Gz 2 )}  (2-2)

obtain in advance the coefficients α, β, and γ to be applied to the expressions (1-2) and (2-2).

2. The inclination detector according to claim 1 , further comprising:

a second communication interface that acquires velocity in the direction of travel from a wheel speed sensor installed in the vehicle; and

a real acceleration computing device that calculates the real acceleration in the direction of travel by differentiating the velocity acquired via the second communication interface.

3. The inclination detector according to claim 1 , further comprising:

a second communication interface that acquires acceleration in any two-axis directions from a two-axis acceleration sensor installed in the vehicle, the two-axis acceleration sensor being installed in a state in which at least one axis has a tilt with respect to a horizontal plane passing through the back and forth direction and right and left direction of the vehicle and with respect to a vertical plane passing through the right and left direction and up and down direction of the vehicle; and

an acceleration converter that converts accelerations in the any two-axis directions acquired via the second communication interface to acceleration in the back and forth direction and to acceleration in the up and down direction by using mounting information of the two-axis acceleration sensor.

4. The inclination detector according to claim 1 , further comprising:

a second communication interface that acquires acceleration in the back and forth direction and acceleration in the up and down direction from a two-axis acceleration sensor which is installed in the vehicle in a state in which a first axis is parallel to the back and forth direction of the vehicle, and a second axis is parallel to the up and down direction of the vehicle.

5. The inclination detector according to claim 1 , further comprising:

a two-axis acceleration sensor that is installed in the vehicle in a state in which a first axis is parallel to the back and forth direction of the vehicle and a second axis is parallel to the up and down direction of the vehicle, and that detects acceleration in the back and forth direction and acceleration in the up and down direction.

6. The inclination detector according to claim 1 , wherein

the inclination computing device is configured to

determine whether the vehicle is running or stopped on a basis of a velocity acquired by a wheel speed sensor installed in the vehicle,

calculate the road surface gradient θ1 and the pitching angle θ2 through the expressions (1-2) and (2-2) when it is determined that the vehicle is running, and

when it is determined that the vehicle is stopped, hold the road surface gradient θ1, which has been calculated in a condition where the vehicle is running, and calculate the pitching angle θ2 by calculating or approximately calculating the following two expressions using the road surface gradient θ1 having been held and the acceleration Gx or the acceleration Gz,

Gx=−g sin(θ1+θ2) or Gz=−g cos(θ1+θ2)

where g is gravitational acceleration.

7. The inclination detector according to claim 3 , further comprising:

a sensitivity correcting device that corrects, while the vehicle is stopped and when difference between the gravitational acceleration and components of a vector of the acceleration in the back and forth direction and of a vector of the acceleration in the up and down direction is greater than a prescribed first threshold, sensitivity of the two-axis acceleration sensor in accordance with the individual accelerations and the gravitational acceleration.

8. The inclination detector according to claim 7 , wherein

the sensitivity correcting device sends information to the inclination computing unit if the difference between the gravitational acceleration and the components of the vector of the acceleration in the back and forth direction and of the vector of the acceleration in the up and down direction is greater than a prescribed second threshold that is greater than the first threshold; and

the inclination computing device substitutes a preset value for one of or both of the road surface gradient and the pitching angle when receiving the information from the sensitivity correcting device.