Geometrical instruments – Miscellaneous – Light direction
Patent
1998-05-18
2000-12-12
Bennett, G. Bradley
Geometrical instruments
Miscellaneous
Light direction
G01B 1126
Patent
active
061581321
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Motor vehicles are increasingly being equipped with aids which are designed to correct and/or prevent incorrect driving behavior on the part of the person operating the vehicle. For example, one of the measures currently available prevents locking of braked wheels. Other measures consist in providing assistance whenever a vehicle threatens to run off track as a result of a curve being taken too tightly. In order that correction moments which keep the vehicle on track can be applied in conjunction with this so-called yawing moment control system, it is important that the control system be informed of the radius within which the driver intends to operate the vehicle. This is achieved with the help of a steering angle sensor. It should also be noted that the wheel angle is not yet known when the system is switched on, i.e., when power is supplied to the system by turning the ignition key. Consequently, the actual angle of the wheels cannot be obtained by simply adding or subtracting relevant incremental angle changes. Instead, continuous absolute readings must be taken to provide the control system with precise information on the actual angle of the wheels.
It is known that the aforementioned incremental steering angle sensors, which routinely consist of two sensors, cannot provide an absolute steering angle on their own. An additional third sensor (zero point sensor) is needed to provide an absolute steering angle once the circular scanning track has completed a 360 degree rotational movement. This results from the inclusion of a marking on this absolute track which defines the zero point and which is used to calculate the measured absolute reading.
The reference signal obtained in this manner is not confirmed until an additional 360 degree rotation has been completed. Even in the event that the angle of rotation of the steering wheel is very much larger than the angle of rotation of the applicable wheel, the described procedure for obtaining an absolute wheel angle reading is not sufficient for some applications in the vehicle.
The object of the invention is to design a steering angle sensor in such a way that an absolute steering angle value can be determined with simple means and after a relatively small rotational movement.
SUMMARY OF THE INVENTION
The object of the invention is achieved by a first track that features equidistant teeth, by means of which the size of a relative angular movement can be determined, and by a second track that is used to determine the absolute angle position of the steering wheel, wherein the two tracks, which are rotatable in relation to a frame, are spatially allocated to the steering wheel, the absolute angle position of which is to be determined. Thus, in principle the invention consists in the ability to determine the absolute value of the steering angle on the basis of only two information tracks, wherein the first track is used to measure the absolute values which are detectable on the second track.
In an advantageous further development of the invention designed to provide for greater resolution of the incremental readings taken along the first track, the first track (incremental track) is measured by two sensors which scan the evenly spaced flanks of the preferably rectangular teeth along the first track. The teeth and the corresponding gaps are of identical widths. Assuming that the space between two rising flanks is 360 degrees and, consequently, the space between two successive flanks is 180 degrees, the two sensors should be arranged in successive order and 90 degrees apart. Thus, the two sensors facing the first track can generate two signals which are offset by 90 degrees; if the direction of rotation is reversed, one of these signals undergoes a 180 degree phase shift, so that the direction of rotation is also clearly detectable.
According to an advantageous further development of the invention, a single detector which scans the second track and displays the absolute value is sufficient for purposes of determining the absolute v
REFERENCES:
patent: 4625411 (1986-12-01), Kashiwagi et al.
patent: 5129725 (1992-07-01), Ishizuka et al.
patent: 5435067 (1995-07-01), Uchida et al.
patent: 5442858 (1995-08-01), Wolters et al.
Kofink Peter
Traub Harald
Bennett G. Bradley
ITT Manufacturing Enterprises Inc.
Lewis J. Gordon
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