Measuring and testing – Tire – tread or roadway – Tire inflation testing installation
Reexamination Certificate
2000-01-03
2001-05-29
Kwok, Helen (Department: 2856)
Measuring and testing
Tire, tread or roadway
Tire inflation testing installation
C073S146200, C340S445000
Reexamination Certificate
active
06237403
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for determining the rotational speed of a wheel of a motor vehicle rotating about a rotational axis. The invention also relates to an air pressure control system wherein the rotational speed of a wheel of a motor vehicle is measured.
BACKGROUND OF THE INVENTION
From the state of the art, air pressure control systems are known for controlling the air pressure in tires of a motor vehicle. In these systems, an air pressure control device is included which is assigned to each wheel and these devices automatically measure the air pressure of the tires of the motor vehicle and announce at least a critical deviation from a desired air pressure to the driver of the motor vehicle. For this purpose, each air pressure control device transmits a measured pressure signal together with an individual identifier at regular intervals to a central unit of the motor vehicle. The transmission of an individual identifier together with the pressure signal is especially important because, in the air pressure control system, contactless data are transmitted from the wheel of the motor vehicle to the motor vehicle. Therefore, it must be precluded that air pressure data of a neighboring vehicle are received, for example, in heavy traffic and that erroneous announcements are made to the driver of the motor vehicle based on these data. This is made possible by the individual identifiers because the wheels of another motor vehicle would, of course, transmit different individual identifiers. In this central unit, value pairs of the form (identifier of the air pressure control device/wheel position) for each wheel of the motor vehicle are stored so that a conclusion can be drawn by a corresponding comparison in the central unit as to which identifier is transmitted with the corresponding pressure signal from which wheel position of the motor vehicle. A deviation of the transmitted pressure signal from a pregiven value at a wheel position is displayed to the driver of the motor vehicle by the central unit so that the driver can initiate suitable measures.
The embodiments show that an air pressure control system described above can only function without difficulty when the allocations (identifier of the air pressure control device/wheel position) are correctly stored in the central unit. Accordingly, it must, on the one hand, be ensured that this allocation does not change during the operation of the motor vehicle and, on the other hand, a new allocation must be provided after each change of tires on the motor vehicle. A method is known from U.S. Pat. No. 5,808,190 with which a new allocation can be undertaken after a change of tires on the motor vehicle. In order to carry out the method according to U.S. Pat. No. 5,808,190, it is necessary to determine the rotational speed of each wheel of the vehicle with the aid of a measurement value sensor which is disposed on the wheel of the vehicle and rotates therewith (for more information, see U.S. Pat. No.
5,808,190).
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method with which the rotational speed of a wheel of a motor vehicle rotating about an axis can be determined in a simple manner with the aid of a measurement value sensor which rotates with the wheel of the motor vehicle.
According to an embodiment, the object is realized in that the wheel of the motor vehicle, which is rotatably journalled about a rotational axis, contains an acceleration sensor (or measurement value sensor) which is mounted at a radial distance to the rotational axis of the wheel of the motor vehicle and has a high force sensitivity along one of its axes. This one axis is referred to in the following as the force-sensitive axis. The acceleration sensor is so aligned that the force-sensitive axis is substantially perpendicular to the rotational axis and is substantially perpendicular to the centrifugal force which acts on the acceleration sensor with a rotation of the wheel of the motor vehicle.
With an arrangement of this kind, the method for measuring the rotational speed of the rotating wheel of the motor vehicle is carried out as follows:
the motor vehicle wheel is so aligned that the rotational axis of the motor vehicle wheel extends almost horizontally;
rotation is imparted to the motor vehicle wheel;
the rotational speed of the motor vehicle wheel is determined from the frequency of the periodic measurement signal which is generated by the acceleration sensor.
As to the substantially perpendicular alignment of the force-sensitive axis of the acceleration sensor to the rotational axis of the motor vehicle wheel and to the centrifugal force, it is to be understood that the force-sensitive axis of the acceleration sensor (apart from inaccuracies which technically cannot be avoided) is aligned precisely perpendicularly to the rotational axis of the motor vehicle wheel and to the centrifugal force.
The motor vehicle wheel includes a rim and a tire. The method for measuring the rotational speed of the motor vehicle wheel is especially simple to carry out because the rotational axis of the motor vehicle wheel is always automatically almost horizontally aligned for a traveling vehicle.
The basic idea of the invention is seen in that, with the aid of the acceleration sensor, the rotational speed of the motor vehicle wheel is determined directly. The acceleration sensor rotates with the motor vehicle wheel about the rotational axis. In this way, a measurement of the centrifugal force and a determination of the rotational speed from the centrifugal force are unnecessary. This centrifugal force acts on the acceleration sensor during the rotation of the motor vehicle wheel about the rotational axis.
The advantages achieved with the invention are especially seen in that the measurement signal of the acceleration sensor is not generated with the aid of centrifugal force but instead with the aid of the gravitational force (a more precise explanation is provided in the description of the figures). The motor vehicle wheel is rotatably journalled about an axis. The acceleration sensor therefore only has to measure small forces and can therefore have a correspondingly simple configuration. A further advantage of the invention is that the method for measuring the rotational speed of the motor vehicle wheel can still be carried out when the body rotates about the rotational axis at a higher rotational speed and the centrifugal forces become very great which act on the acceleration sensor because the centrifugal forces are not applied to determine the rotational speed.
According to another embodiment, each air pressure control device of an air pressure control system is assigned an acceleration sensor which is mounted at a radial distance r to the rotational axis of the corresponding wheel and exhibits a high force sensitivity along one of its axes. The acceleration sensor is aligned in such a manner that the force-sensitive axis is substantially perpendicular to the rotational axis and is substantially perpendicular to the centrifugal force which acts on the acceleration sensor with a rotation of the corresponding wheel. With an acceleration sensor arranged in this manner, the rotational speed of the corresponding wheels can be determined and therefore the method, which is explained in U.S. Pat. No. 5,808,190, can be carried out.
According to another embodiment of the invention, the acceleration sensor exhibits a significantly lesser force sensitivity along the axis which is perpendicular to the force-sensitive axis than along the force-sensitive axis. The advantage of this embodiment is seen in that the acceleration sensor is not easily deformable by forces which act perpendicular to the force-sensitive axis such as the centrifugal force which acts on the acceleration sensor with a rotation of the motor vehicle wheel.
According to a further embodiment of the invention, the acceleration sensor is a deflecting strip which is made of a piezoelectric material. An electrical voltage is generated when such a deflecting str
Ernst Gerhard
Oldenettel Holger
Continental Aktiengesellschaft
Kwok Helen
Ottesen Walter
LandOfFree
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