Measuring and testing – Testing of apparatus
Reexamination Certificate
1999-04-14
2001-07-03
Williams, Hezron (Department: 2856)
Measuring and testing
Testing of apparatus
C073S118040
Reexamination Certificate
active
06253630
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a device to measure the rotational position of a steering wheel in which a rotating steering shaft connected to the steering wheel is coaxial with respect to a non-rotating steering column.
2. Description of the Currently Available Technology
On steering devices for work machines, in particular for industrial trucks, the trend is toward technical development in the direction of electrical steering. That means that there is an electrical connection between the steering wheel and the steered wheel of the truck, instead of a conventional mechanical or hydraulic connection. The rotational position of the steering wheel is measured by means of a suitable device that is connected to an electrical evaluation device. The evaluation device, as a function of the movement of the steering wheel, actuates an electric steering motor, by means of which the steering movement of the steered wheel is produced.
One of the determining factors in the operational safety and reliability of such an electric steering system is the reliable function of the device that detects and measures the rotational position of the steering wheel.
An object of the invention is to provide a simple device to measure the rotational position of the steering wheel, which device has a high degree of operational reliability and accuracy.
SUMMARY OF THE INVENTION
The invention teaches that on a surface of the steering column facing the steering shaft there is at least one electrical resistance sheet that extends in a peripheral direction of the steering column. At least two wipers associated with the resistance sheet are fastened to the steering shaft such that at all times at least one wiper is in contact with the resistance sheet at a point defined by the rotational position of the steering shaft. In an alternative embodiment, the invention also teaches that on a surface of the steering shaft facing the steering column, there is at least one electrical resistance sheet that extends in a peripheral direction of the steering shaft. Fastened to the steering column are at least two wipers associated with the resistance sheet such that at all times at least one wiper is in contact with the resistance sheet in a position defined by the rotational position of the steering shaft.
When the steering wheel is turned, at least one wiper moves along the resistance sheet. The resistance sheet and the wiper thus form a potentiometer. A constant voltage is applied between the two ends of the resistance sheet. A voltage value applied to the wiper is therefore directly a function of the rotational position of the steering wheel.
The wiper can be realized in the form of an electrical wiper contact, wherein there is an electrical connection between the wiper and the resistance sheet.
It is also possible, however, that the resistance sheet can be realized as part of a film potentiometer of the type known in the prior art. On a film potentiometer, a conductive contact film is located between the resistance sheet and the wiper and comes into contact with the resistance sheet exactly at the position under the wiper. In this arrangement, no electrical currents are conducted by the wipers, which is advantageous with regard to the location of the electrical connectors and the useful life of the device to detect the rotational position of the steering wheel.
In an additional advantageous configuration of the invention, the resistance sheet extends over a peripheral angle of less than 360 degrees, preferably less than about 260 degrees. To make it possible to determine the steering angle, the resistance sheet should extend over a peripheral angle of less than about 360 degrees. A resistance sheet from a conventional commercially available potentiometer can be used if the resistance sheet extends over a peripheral angle of approximately 250 degrees.
It is advantageous if there are exactly two wipers associated with the same resistance sheet that are offset from one another in the peripheral direction. As a result of the offset arrangement, the invention ensures that at least one wiper is always in contact with the resistance sheet. The two wipers are preferably offset from each other by about 180 degrees.
The advantage of a redundant signal generation can be achieved if there are at least three wipers associated with the same resistance sheet. When three wipers are used, an arrangement is possible in which at least two wipers are in contact with the resistance sheet at all times. These two wipers in contact with the resistance sheet always generate an unambiguous signal that reflects the rotational position of the steering wheel. It thereby becomes possible to immediately recognize erroneous measurements of the type that can occur, for example, if the device to measure the steering angle is damaged. The three wipers are appropriately offset from one another by about 120 degrees.
A redundant signal can also be generated if there are two resistance sheets that are at some distance from one another in the axial direction, with two wipers associated with each resistance sheet. At least one wiper is always in contact with each resistance sheet so that when there are two resistance sheets, two signals that are independent of each other and reflect the rotational position of the steering wheel can be generated.
The invention also provides an electrical evaluation device to determine the rotational position of the steering wheel. The evaluation device is operationally connected with the resistance sheet(s) and/or with the wipers. The evaluation device can be formed by an electronic control unit, for example, in which the rotational position of the steering wheel is converted into a steering angle for the steered wheel. An electric steering motor that produces the steering movement of the steered wheel is actuated as a function of the steering angle calculated.
It is particularly advantageous if the evaluation device comprises means to measure the full rotations of the steering wheel. With the system of resistance sheets on the steering column or on the steering shaft described above, it is not possible to generate a signal that unambiguously reflects a rotation of the steering wheel at an angle of more than 360 degrees. The number of full rotations of the steering wheel is instead counted by means of the evaluation device, so that even if the steering wheel is turned by more than 360 degrees, it is possible to have an unambiguous correspondence with the position of the steered wheel.
Additional advantages and details of the invention are explained in greater detail below with reference to the embodiment illustrated schematically in the accompanying figures wherein like references characters identify like parts throughout.
REFERENCES:
patent: 4518954 (1985-05-01), Seko et al.
patent: 5027648 (1991-07-01), Filleau
patent: 5330021 (1994-07-01), Beer et al.
patent: 2501521Al (1976-07-01), None
patent: 3907442A1 (1990-09-01), None
patent: 4131533A1 (1993-03-01), None
patent: WO9306435 (1993-04-01), None
patent: 4142992A1 (1993-07-01), None
patent: 4205421Al (1993-08-01), None
patent: 68909331T2 (1994-02-01), None
patent: 69301960T2 (1996-08-01), None
patent: 19510717A1 (1996-09-01), None
patent: 19631305 (1997-02-01), None
patent: 0389669A1 (1990-10-01), None
patent: 0660084 (1995-06-01), None
Patent Abstracts of Japan, 63-47611, P-733, Jul. 21, 1998, vol. 12/No. 259.
Fayyaz Nashmiya
Linde Aktiengesellschaft
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
Williams Hezron
LandOfFree
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