Data processing: measuring – calibrating – or testing – Measurement system – Speed
Reexamination Certificate
2002-09-13
2004-10-05
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Speed
C073S146500, C324S160000
Reexamination Certificate
active
06801872
ABSTRACT:
The present invention relates to a method for determining the speed of a wheel on a motor vehicle, for which purpose an acceleration sensor is mounted on the wheel. The necessity to determine the speed of a wheel arises for motor vehicles with wheels equipped with pneumatic tyres whose pressure is to be continuously monitored also in operation of the vehicle. DE 196 08 478 A1 describes for this purpose a tyre-pressure monitoring system where each wheel of a motor vehicle is equipped with a device (hereinafter referred to as wheel-mounted electronic module) that comprises a pressure sensor, an electronic evaluation sensor connected to the pressure sensor, a transmitter, a sending antenna and a battery for supplying the wheel-mounted electronic module with current. Neighbouring the wheels, there are mounted on the vehicle body receiving antennas connected by cable to a receiver which processes and evaluates the signals transmitted to it by the receiving antennas and provides a signal to the driver when a substantial, especially a dangerous, change in pressure is observed on any of the wheels, in which case the driver is simultaneously informed on the particular location of the wheel in question.
One problem encountered in connection with such tyre-pressure monitoring systems relates to the clear assignment of the individual transmitters to the location of the respective wheel on the vehicle. The transmitters generate for this purpose a signal that is subdivided into several sections and that comprises a preamble, an identification signal, a measurement signal and a postamble. The receiver is to determine by way of the identification signal (hereinafter referred to as identifier) the location where the sending wheel is mounted on the vehicle. This is, however, possible only if the identifier and the wheel position have been clearly allocated one to the other before and if such allocation has been stored in the receiver. DE 196 08 478 A1 discloses a way how to automatically determine such allocation from the signals transmitted by the wheel-mounted electronic modules after the first assembly of wheels on the vehicle and after every change of wheels. One performs for this purpose a statistical evaluation of the intensity of the signals received. Although each receiving antenna receives signals from all transmitting wheels of the vehicle, it is assumed that, regarded statistically, the signals received from the wheel that is the nearest to the respective receiving antenna will be received with the highest intensity on average.
A similar allocation method has been known from DE 196 08 479 A1.
Another way of automatically allocating the identifiers transmitted by the wheel-mounted electronic modules to the respective wheel locations is disclosed by DE 197 35 686 A1. This document proposes to design the wheel-mounted electronic module on the respective wheel in such a way that it will determine not only the tyre pressure but also additional information on the moving state of the wheel and transmit both data by radio to the central receiver in the motor vehicle. The moving state of the vehicle is used by the receiver to derive information on the location of the respective wheel on the vehicle. To this end, any accelerations encountered on the wheel are determined by acceleration sensors provided in the wheel-mounted electronic module, and either the acceleration data is evaluated in the wheel-mounted sensors provided in the wheel-mounted electronic module, and either the acceleration data is evaluated in the wheel-mounted electronic module, in which case the result of such evaluation is transmitted to the receiver by radio, or the acceleration signals are inserted by the wheel-mounted electronic module into the signal that is to be sent out regularly and that contains a data telegram and is sent, together with such signal, by radio to the receiver where it is evaluated.
The known system permits information on the wheel position to be derived from acceleration signals obtained on the wheel in the following ways:
1. When the wheel turns, a centrifugal acceleration is encountered on the wheel the strength of which depends on the speed of the wheel. The speed of spare wheels carried with the vehicle is equal to zero, even when the vehicle is moving. Any signals that are received when the vehicle is moving and that signal a speed equal to zero or a centrifugal acceleration Z equal to zero will therefore be allocated to a spare wheel carried with the vehicle.
2. When the speed or the value of the centrifugal acceleration Z is integrated over a predetermined period of time, then the value of the integrated measurand is a measure of the distance the wheel has travelled during that period of time. Given the fact that when cornering the steered front wheels travel a longer distance than the unsteered rear wheels of a vehicle, the integrated measurand for a steered front wheel will be greater than that for an unsteered rear wheel. The identifiers contained in signals that lead to the greatest integrated measurands for the speed or the centrifugal acceleration Z can therefore be assigned to the steered front wheels of a vehicle. It has been known from DE 197 28 419 A1 to determine the speed from an alternating signal contained in the tangential acceleration signal supplied by the acceleration sensor and produced by the influence of gravitational acceleration.
b is used here to describe the acceleration in the circumferential direction of a wheel encountered during acceleration or deceleration of the vehicle. The sign of the tangential acceleration signal b permits to distinguish between right and left wheels, and can be determined already in the wheel-mounted electronic module and then transmitted to the receiver. Although differentiation between right and left wheels is, preferable, effected in the acceleration phase following the start of the vehicle, it can generally be effected also in any acceleration or deceleration phase.
The tyre-pressure monitoring systems obtainable in practice have the wheel-mounted electronic modules mounted on the wheel inside the tyre and have a hermetically sealed housing that does not permit the battery to be exchanged. The battery is therefore expected to have a service life of 5 to 10 years. This requires the current consumption of the wheel-mounted electronic module to be minimised. For this purpose, it has been known to provide the wheel-mounted electronic module with an integrated circuit that activates the pressure sensor for measurements only during first time intervals and causes the transmitter to send signals during second time intervals longer than or equal to the first time intervals, i.e. in the first time intervals when a dangerous pressure loss has been detected, otherwise in the longer second time intervals.
Known wheel-mounted electronic modules have a semiconductor-based pressure sensor integrated into an integrated circuit. An acceleration sensor can also be integrated into such an integrated circuit. However, if according to DE 197 35 686 A1 two acceleration sensors or one acceleration sensor sensitive in two axes perpendicular one to the other are to be integrated into the integrated circuit in addition to the pressure sensor, then the development and production of the integrated circuit becomes considerably more complex and expensive.
BRIEF SUMMARY OF THE INVENTION
It is, therefore, the object of the present invention to open up a less expensive way of gaining signals in the wheel-mounted electronic module from which conclusions can be drawn on the location of the wheel.
This object is achieved by a method having the features defined in claim
1
and by a method having the features defined in claim
2
. Advantageous further developments of the invention are the subject-matter of the sub-claims.
According to the invention, the speed of a wheel on which an acceleration sensor is mounted is determined as the frequency &ohgr; of an alternating signal produced by the influence of the gravitational acceleration g and contained in the acceleration si
Normann Norbert
Schulze Gunter Lothar
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