Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1999-11-22
2001-03-20
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C280S734000, C280S735000, C280S728100, C073S432100
Reexamination Certificate
active
06205383
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the automotive field. More specifically, the present invention relates to a method and apparatus for transmitting digital data from a measurement station of an occupant protection system in a motor vehicle to an air bag control unit. The apparatus includes an air bag control unit, a measurement station connected to the air bag control unit, a direct current or direct voltage source in the air bag control unit for supplying the measurement station with a direct signal, first means in the measurement station for varying the direct signal in accordance with the data to be transmitted, and second means in the air bag control unit for detecting and evaluating changes in the direct signal as current changes. The measurement station is supplied with a direct signal from a direct current or direct voltage source of the air bag control unit and varies the direct signal in accordance with the data to be transmitted. The variations in the direct signal are then detected as current changes in the air bag control unit and evaluated.
For tripping circuits of occupant protection systems, which cause air bags or belt tensioners to be tripped in the event of an accident, for instance, signals must be transmitted from remotely located sensors (measurement stations) to a central control unit (air bag control unit). With increasing progress in the development of occupant protection systems, the associated sensors are being installed at more and more places in the vehicle. If the requisite short tripping times are to be adhered to, these remotely located sensors must be polled constantly, and the sensor signals must be transmitted reliably to the central control unit.
U.S. Pat. No. 5,712,784 to Fendt et al. (European patent application EP 0 693 401 A2) discloses a data transmission method in which pulse width modulated signals are generated by the affected remotely located sensors and are transmitted to the central control unit. The data information is encoded in the duty factor.
In a system for controlling an occupant protection device, such as an air bag, the entire system must be kept in operation for a minimum period after a collision in which the on-board electrical system and thus the energy supply to the system have been destroyed. To that end, in the air bag control unit, independent energy reserves, such as capacitors, are typically furnished for the individual circuit elements, so that this emergency operation can be assured for a minimum length of time. Such energy stores are not only expensive but also take up space.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and an apparatus for a motor vehicle occupant protection system, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which the energy reserves for emergency operation can be minimized.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of transmitting digital data from a measurement station of a motor vehicle occupant protection system to an air bag control unit, which comprises:
supplying a measurement station with a direct signal from a direct current or direct voltage source of an air bag control unit;
varying the direct signal with the measurement station in accordance with data to be transmitted;
transmitting data and thereby varying a current such that the variations cancel one another out on average over time; and
detecting and evaluating the variations in the direct signal as current changes in the air bag control unit.
According to the invention, the current consumption for data transmission from the measurement station to the air bag control unit is reduced.
In accordance with an added feature of the invention, the transmitting step comprises:
transmitting the digital data in a train of binary characters;
transmitting a logic zero by leaving the direct signal unvaried;
transmitting a logic one by selectively increasing and decreasing the direct signal by a predetermined amount, and thereby
increasing the direct signal if the direct signal had been decreased to transmit a preceding logic one; and
decreasing the direct signal if the direct signal had been increased to transmit the preceding logic one.
In accordance with an additional feature of the invention, an energy store is provided in the measurement station. The energy store is charged to increase the current and discharged to reduce the current.
In accordance with a preferred embodiment of the invention, the energy store is a capacitor.
In accordance with another feature of the invention, two switches are connected to the energy store. The switches control the charging and discharging of the energy store. The switches are thereby triggered in alternation upon successive logic one values of the data train.
In accordance with a further feature of the invention, a series resistor is connected at the air bag control unit in at least one supply line connected to the measurement station, and the method further comprises measuring a voltage drop at the series resistor for ascertaining the transmitted data.
With the above and other objects in view there is also provided, in accordance with the invention, an apparatus for transmitting digital data in a motor vehicle, specifically for performing the above-outline method. The apparatus comprises:
an air bag control unit and a measurement station connected to the air bag control unit;
a direct current or direct voltage source in the air bag control unit for supplying the measurement station with a direct signal;
a first device in the measurement station for varying the direct signal in accordance with data to be transmitted to the air bag control unit, the first device include an energy store to be charged in controlled fashion to increase the current and to be discharged in controlled fashion to decrease the current; and
a second device in the air bag control unit for detecting and evaluating changes in the direct signal in the form of current changes.
As noted above, the preferred energy store is a capacitor.
In accordance with again an added feature of the invention, the measurement station receives a supply voltage, the capacitor is connected in the measurement station such that, in an absence of data transmission, the capacitor is charged to an intermediate voltage between 0 V and the supply voltage, the first device includes a first switch and a second switch connected such that an actuation of the first switch causes the capacitor to increase the direct signal and an actuation of the second switch causes the capacitor to decrease the direct signal.
In accordance with again an additional feature of the invention, the measurement station includes a voltage regulator for deriving the supply voltage from the direct signal and a voltage divider subjected to the supply voltage, the voltage divider having a first resistor and a second resistor connected to one another at a node point acting as a center tap, the capacitor being connected between an input of the voltage regulator and the center tap of the voltage divider, the first switch being connected in parallel with the first resistor and the second switch being connected in parallel with the second resistor.
In accordance with again another feature of the invention, a common resistor connects the first and second switches to the center tap.
In accordance with again a further feature of the invention, the first device includes a trigger unit for triggering the first and second switches in accordance with the data train to be transmitted.
In accordance with a concomitant feature of the invention, the measurement station includes a sensor and a monitoring unit connected to the sensor, the monitoring unit generates the data trains to be transmitted in accordance with signals received from the sensor and forwards the data trains on to the trigger unit for transmission.
In the data transmission method known from the above-mentioned U.S.
Cuchlinski Jr. William A.
Greenberg Laurence A.
Hernandez Olga
Lerner Herbert L.
Siemens Aktiengesellschaft
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