Communications: electrical – Selective – Having indication or alarm
Patent
1982-04-05
1986-01-28
Caldwell, Sr., John W.
Communications: electrical
Selective
Having indication or alarm
731465, 200 6122, B60C 2300
Patent
active
045674590
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a transmission method for variable measured values from vehicle wheels, wherein energy is transmitted to a secondary coil mounted concentrically on the wheel during variable excitation produced by a primary coil integral with the vehicle, and an information signal, which is a function of the output signal from a sensor, is fed back to a receiving coil integral with the vehicle from this secondary coil.
In a known method of this type, the energy signal is fed back to a receiving coil which is independent of the primary coil (German Pat. No. 1,946,627). This results in a considerable construction cost, since, on the one hand, two coils must be provided which are integral with the vehicle and, on the other hand, the fact that these coils must be mounted next to the wheel as a rule poses considerable problems because of the limited space available for mounting them.
The goal of the invention is to reduce the construction costs in a method of the type described hereinabove.
This goal is achieved by the information signal being fed back to the primary coil as a receiving coil.
The method according to the invention can be used with low-frequency excitation of the primary coil. The primary and secondary coils then operate as a so-called "transformer sensor". The frequency can even be raised, so that the two coils operate as a transmitter and receiver. In both cases, the advantage of the invention is that only a single coil need be mounted integrally with the vehicle.
The information signal has a higher frequency for improved differentiation of the actual excitation of the primary coil from the excitation which is produced by the fed-back information signal. An evaluation circuit can be permanently connected to the primary coil through a high-pass filter, which lets only the information signal through. The high-pass filter in this case can be connected to the power supply of the primary coil.
Alternatively, or additionally, the primary coil can be excited in a pulse fashion, and the information signal can be fed back during the spaces between the pulses. In both cases, evaluation of the information signal requires no special expenditure for measurement, since the primary coil can be excited and the information signal fed back at different times.
The cost of construction and circuitry can be further reduced by powering the sensor through a threshold value switch from a capacitor connected to the secondary coil. These elements, mounted on or in the wheel, can be combined to form a compact module.
The losses involved in transmitting energy, to the coil and feeding back the information signal to the primary coil can be kept particularly low if the primary and secondary coils have the same number of windings.
The method according to the invention can be used for example to transmit the temperature or imbalance of the wheel as a measured value. If the tire pressure is transmitted as a measured value, an abnormal (i.e., as a rule, too low) tire pressure can be determined as a function of tire temperature. In addition, as is known from German Pat. No. 1,946,627, a measured value which is a function of tire temperature can also be transmitted. The two measured values, the tire pressure and the tire temperature, can then be analyzed to determine whether the tire pressure, which is a function of tire temperature, has fallen below a set value and, if so, a warning signal can be triggered.
On the other hand, one advantageous embodiment of the invention consists in the information signal associated with the tire pressure being temperature-compensated. Since temperature has a great influence on tire pressure, a rise in pressure, which results from the temperature increase caused by the flexing of the tire, is compensated so that the set pressure which determines when the warning signal is triggered, need not be fed back as a function of this pressure rise.
If the output signal from the sensor is itself temperature-compensated, temperature-dependent components connected in series with the sensor, which wou
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Folger Josef
Fournell Hans-Dieter
Hein Hans-Rudolf
Kapfhammer Karl
Rambock Josef
Bayerische Motoren Werke Aktiengesellschaft
Caldwell Sr. John W.
Heim Michael F.
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