Process for correcting angle errors in an electronic compass in

Details Process for correcting angle errors in an electronic compass in Process for correcting angle errors in an electronic compass in

1985-10-16

1988-02-16

Chin, Gary

Boots, shoes, and leggings

364571, 364449, 33356, G01C 1738

Patent

active

047259574

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a process for correcting angle errors when establishing the driving direction of vehicles with an electronic compass. From DE-PS No. 27 54 888 it is known to establish the driving location of a vehicle in a navigation apparatus with a biaxial magnetometer, whose output signals for the compensation of magnetic interference fields in the vehicle are fed to a correction unit wherein a zero point displacement of the output signals as well as a proportional change of one of the output signals is performed. With this solution one assumes that an interference field with a defined vector is present in the vehicle which is superimposed by the earth's magnetic field which is more or less screened by the automobile body depending on the alignment of the vehicle. Since the earth's magnetic field, which is decisive for the driving direction, engages the earth's surface obliquely from above under the so-called inclination angle with respect to the horizontal, only the component is picked up by the magnetometer which is in the plane of driving during the establishment of the drive direction. One axis of the magnetometer is provided in the driving direction and the other transversely to the driving direction. In the stationary installed electronic compass, no measuring error occurs as long as the vehicle drives in a horizontal direction. However, during ascent or descent, an angle error is generated in the electronic compass during the measuring of the driving direction, which may be up to 30.degree. depending on the ascent or descent and dependent on the driving direction. If this angle error is to be avoided, the magnetometer must be provided with a cardanic suspension which is expensive and susceptible to interference, so that the axes of the magnetometer are also in one horizontal plane during ascent and descent driving. However, measuring errors are generated when driving through curves, during acceleration or braking of the vehicle.
It is therefore desireable to compensate the angle errors, which depend from the incline of the vehicle in its longitudinal axis, in a very simple manner.


SUMMARY OF THE INVENTION

The process in accordance with the invention has the advantage that measuring accuracy of the electronic compass is substantially improved by the compensation of the incline dependent angle error. It is considered to be a further advantage that the magnetometer with its associated axis can be mounted stationary in the vehicle. A cardanic suspension is eliminated.
It is particularly advantageous to establish the angle of incline from the earth's acceleration and the slope output power of a body mounted in the vehicle. In order to prevent measuring errors due to acceleration or braking of the vehicle, it is further suggested that the angle of incline (.psi.) of the vehicle be computed in the evaluation circuit of the electronic compass from the equation sin .psi.=(a'-c)/g. Thereby, a' is the total active acceleration on the body in the driving direction, c is the acceleration in the driving direction and g is the earth's acceleration. Advantageously, the acceleration of the vehicle in the driving direction c is established in the evaluation circuit from the signal changes of a drive speed transmitter.


BRIEF DESCRIPTION OF THE DRAWINGS

One exemplified embodiment of the invention is illustrated in the drawings and explained in more detail in the following description.
FIG. 1 illustrates a block diagram of an electronic compass for establishing the driving direction of a motor vehicle with incline dependent angle correction in accordance with the invention,
FIG. 2 a coordination system with an uphill driving vehicle,
FIG. 3 illustrates a vehicle with the magnet field vector measured by the magnetometer,
FIG. 4 illustrates a diagram which reflects the angle error with respect to the driving direction of the vehicle depending on the road slope,
FIG. 5 illustrates the measured and the actual north direction in the coordination system with respect to the longit

REFERENCES:
patent: 4470119 (1984-09-01), Hasebe et al.
patent: 4539760 (1985-09-01), Marchent et al.
patent: 4546550 (1985-10-01), Marchent et al.
patent: 4586138 (1986-04-01), Mullenhoff et al.
patent: 4622754 (1986-11-01), Chujo et al.

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