1. Field of the Invention
The present invention relates to a device for calculating a pitch angle for a vehicle.
2. Description of the Related Art
In general, the pitch angle .theta. for a vehicle is calculated by the following expression: ##EQU1##
where
hf is a vehicle height at a front wheel, PA1 hr is a vehicle height at a rear wheel, and PA1 w is a wheel base length. PA1 height detecting units arranged both in a front position (Pf) and in the rear position (Pr) of the vehicle, for detecting a vehicle height (hf) of the front position and a vehicle height (hr) of the rear position (Pr); and PA1 a calculating section for calculating a pitch angle of the vehicle by the vehicle heights (hf, hr) and a distance between the front position (Pf) and the rear position (Pr); PA1 wherein, on condition that the pitch angle is divided into a plurality of pitch angle ranges, the calculating section integrates periods residing in each pitch angle range and subsequently determines the pitch angle of the vehicle on a basis of the integrated periods referred as "residence time". PA1 a height detecting unit arranged in either one of a front position (Pf) and the rear position (Pr) of the vehicle, for detecting either a vehicle height (hf) of the front position or a vehicle height (hr) of the rear position (Pr); and PA1 a calculating section for calculating a pitch angle of the vehicle by the vehicle heights (hf, hr) and a distance between the front position (Pf) and the rear position (Pr); PA1 wherein, on conditions that the other of the vehicle heights (hf or hr) is established by a fixed value and that the pitch angle is divided into a plurality of pitch angle ranges, the calculating section integrates periods residing in each pitch angle range and subsequently determines the pitch angle of the vehicle on a basis of the residence time.
It is noted that in the above expression (1), changes from respective heights under the vehicle's initial condition, which will be referred as "initial values" hereinafter, are entered into the vehicle heights hf, hr, respectively. Accordingly, the pitch angle .theta. of the vehicle under the initial condition is equal to an angle of zero (0) degree.
Now, in the vehicle height, there are a long-sustained variation derived from a number of passengers, a position of passengers, a weight of loads and a position of loads, and an instantaneous variation due to an acceleration (or deceleration) of the vehicle, the vehicle's getting over the irregularities and obstacles on the road and so on. The former variation in vehicle height produces a long-term pitch angle, while the latter variation in vehicle height produces an instantaneous (short-term) pitch angle. Therefore, if the pitch angle is calculated on the basis of a detected vehicle height including the latter instantaneous variation in vehicle height, then a pitch angle obtained as a calculation result will change furiously, which is undesirable for using it in an automatic control of leveling a headlamp of the vehicle, namely, "auto-levelizer".