Electrical transmission or interconnection systems – Vehicle mounted systems – Automobile
Reexamination Certificate
2000-02-07
2001-10-30
Paladini, Albert W. (Department: 2841)
Electrical transmission or interconnection systems
Vehicle mounted systems
Automobile
C340S315000, C701S036000
Reexamination Certificate
active
06310408
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the automotive technology field. More specifically, the invention relates to a system for transmitting data between a satellite station and a central station in a motor vehicle.
In vehicle occupant protection systems in motor vehicles, for example air bag systems, seatbelt tensioning systems etc., one or more satellite stations, which are arranged for example in side regions of the motor vehicle and perform impact detection or early detection of accidents there, are provided in many cases in addition to a central station which performs impact detection. Such satellite stations transmit data to the central station when an impact or a situation where a risk of an accident is detected, with the result that the station can control suitable triggering measures. The satellite station can also be configured in such a way that it transmits messages (life signs) to the central station at regular intervals.
U.S. Pat. No. 5,712,784 (European application EP 0 693 401 A2) discloses a data transmission method in which the satellite stations are connected to the control unit of the central station via dedicated data lines. The necessary voltage supply to the satellite stations is not mentioned in any detail in that specification, but is usually provided via dedicated voltage supply lines. In the prior art method, the data are transmitted in the form of pulse-width-modulated signals which have a constant period and whose pulse duty factor represents information to be transmitted. The pules are applied directly to inputs of the central unit of the central station via the data lines. The expenditure on lines and wiring which is necessary for the transmission of data and the supply of voltage to the satellite stations is relatively high.
German published patent application DE 42 01 468 A1, upon which the instant invention is based, proposes a bus system with an integrated voltage supply for all the system subscribers, in particular for motor vehicles, in which all the bus system components are fed by a common, apparently unregulated voltage source. Each subscriber is provided with a current source which can be switched on and off. Switching them on and off enables current pulses to be generated in accordance with the data that are to be transmitted and which are fed onto the bus system.
German patent DE 42 27 577 C1 discloses a method for the bidirectional transmission of signals according to the master/slave principle. A line that connects the master and the slaves is used both for the transmission of signals and also to supply power to the slave modules. The master signal is voltage-encoded, whereas the slave signals are current-encoded. The master signal is transmitted continuously without interruption, even at times in which no data are being transmitted.
U.S. Pat. No. 4,621,170 discloses a data transmission device in which the supply voltage is made available by means of a battery. The data are superimposed in the form of current pulses which are generated by current sources which can be switched on and off.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method of transmitting data between a satellite station and a central station in a motor vehicle which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which permits a reliable transmission of data while reducing the expenditure on wiring necessary for the satellite station.
With the above and other objects in view there is provided, in accordance with the invention, a data transmission system in a motor vehicle, in particular within a vehicle occupant protection system (airbag, belt tensioner, etc.) comprising:
a central station, a satellite station, and a data transmission line connecting the satellite station to the central station for transmitting data between the two stations in the form of current pulses;
a current generator with low-pass filter characteristics feedback in the central station, the current generator having an output connected to the data transmission line for supplying power to the satellite station via the data transmission line;
a voltage amplifier for regulating the current generator, the voltage amplifier having an input connected to the data transmission line and receiving a voltage reference signal and an output coupled to a control input of the current generator.
In accordance with an added feature of the invention, there is provided a current generator in the satellite station or the central station for generating current pulses representing data to be transmitted. The data are superimposed in the form of current pulses on a quiescent voltage present on the data transmission line, preferably with a different sign.
In accordance with another feature of the invention, a window comparator is connected to the data transmission line for demodulating the data signal carried on the data transmission line.
In accordance with a further feature of the invention, a voltage regulator is provided in the satellite station, the voltage regulator having an input connected to the data transmission line and an output providing a supply voltage for the satellite station.
In accordance with again an added feature of the invention, a characteristic impedance termination connected at either end of the data transmission line. In a preferred embodiment, the characteristic impedance termination is a serial RC element.
In accordance with again an additional feature of the invention, a cutoff frequency of the low-pass control of the current generator is lower than a data transmission frequency by approximately one order of magnitude.
In accordance with a concomitant feature of the invention, the satellite station inputs the data to be transmitted into the data transmission line in encoded form, and the central station demodulates the data received from the data transmission line. In a preferred embodiment of the system, the data are transmitted in AMI-encoded pulses with positive and negative polarities.
In the system according to the invention, the data transmission line is used at the same time as a current supply line for the satellite station, with the result that no additional expenditure on lines and wiring has to be provided for this. The current supply to the supply station is provided by means of a fed-back current generator which is arranged in the central station and which is actuated by means of a regulator with low-pass filter characteristics. This ensures that the output resistance of the current generator is very high in the frequency range of the data signal which is to be transmitted, and the current generator therefore causes no distortion of the amplitude and/or phase of the transmitted data signal. As a result, a high level of data transmission quality is ensured. The current regulator is preferably embodied as a differential amplifier with voltage reference signal, with the result that the quiescent voltage on the data transmission line is kept essentially the same irrespective of the current consumption of the satellite station. Because the current generator and the voltage regulator which controls it have high impedance in comparison with the transmit data generation section of the satellite station in the frequency range which is relevant for the transmission, the data signals which are to be transmitted can simply be superposed on the quiescent voltage of the data transmission line in the form of current pulses. Owing to the high (output) resistance of the current generator, these current pulses give rise, even when they are of small magnitude, to voltage pulses which are strong and can thus easily be detected at the receiver end. These data signals can easily and reliably be demodulated at the receiver end (central station or satellite station) by means of a comparator or a window comparator.
The high impedance of the data transmission line in the high-frequency range, i.e. in the range of data transmission frequency and above, provides the further advanta
Greenberg Laurence A.
Lerner Herbert L.
Paladini Albert W.
Siemens Aktiengesellschaft
Stemer Herbert H.
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