Patent Application
20090204295
The invention relates to an electronic control unit for an airbag, which is often also referred to as an airbag ECU (“Airbag Electronic Control Unit”), having an autonomous event data recorder, which is often also called an EDR (“Event Data Recorder”).
The practice of recording vehicle and accident data in a nonvolatile memory in the vehicle shortly before, during and after an accident is becoming increasingly important. These data are intended to assist with being able to reconstruct the accident and its cause as accurately as possible. Such systems are also of interest to insurance companies who wish to use the data to determine insurance payments in the event of damage. Furthermore, legal provisions for recording accident data have been proposed by various authorities (for example the National Highway Traffic Safety Administration) and other organizations.
Existing systems are not designed to store a relatively large quantity of data. Certain components of a vehicle, for example the airbag ECUs, must have a power supply which is independent of the vehicle's power supply in the event of the vehicle's power supply failing on account of an accident. For this purpose, an “emergency power supply” is ensured in known systems with the aid of electrolytic capacitors.
However, the operation of storing a relatively large quantity of data in a nonvolatile memory can take up a relatively large amount of time, for example two seconds. A very large number of capacitors and very large capacitors would be needed to maintain the power supply for the airbag ECUs over such a long period of time, which would make the overall system appreciably more expensive.
There is therefore a need for a new concept of an airbag ECU having a data recorder unit (a so-called “event data recorder”) which manages to ensure the power supply with the smallest possible number of capacitors in the event of an accident.
One example of the invention relates to an electronic control unit for an airbag, said control unit having: a data recorder unit which has a volatile memory, a nonvolatile memory and a copy circuit, the copy circuit being designed to copy data from the volatile memory to the nonvolatile memory during a second operating phase of the control unit; a protocol unit which is designed to record vehicle and/or accident data in the volatile memory arranged in the data recorder unit during a first operating phase of the control unit; a first power supply unit which is connected to the control unit and supplies the protocol unit and further components of the control unit with power; and a second power supply unit which is connected to the data recorder unit and supplies the latter with power.
The following figures and the further description are intended to assist with better understanding of the invention. The elements in the figures should not necessarily be understood as a restriction, rather importance is placed on illustrating the principle of the invention. In the figures, the same reference symbols denote corresponding parts.
The electronic control unit for airbags (airbag ECU) is the only control device in a vehicle which has to be able to maintain its functions for a particular amount of time (that is to say autonomy time TA) when there is no external supply from the car battery. This is important, in particular, when the battery supply for the airbag ECU has broken down on account of a defect or else on account of the impact which is just occurring. In some cases, the battery is also deliberately disconnected from the vehicle electrical system in the event of an accident.
As already explained at the outset, it is necessary to store increasingly comprehensive data records in the event of an accident, which data records likewise have to be stored in a nonvolatile memory during the autonomy time independently of the external battery supply. The power supply during the autonomy time is usually ensured with the aid of electrolytic capacitors which are charged to a high voltage (higher than the battery voltage) in order to store as much energy as possible. During the autonomy time TA, the energy stored in the capacitor is discharged to the airbag ECU again via a voltage converter and the circuit components arranged in the airbag ECU are thus supplied with power.
During the autonomy time TA, the airbag ECU must perform the following functions: triggering of the airbags, logging of the vehicle and accident data to be stored (for example speed, braking acceleration, transverse acceleration, braking time, status of the lighting system and of the indicators, etc.) and storing of the logged data in a nonvolatile memory, for example an EEPROM.
The airbags are triggered during a “fire interval” TF of approximately 2 ms to 30 ms, during which the current requirement is approximately 20 A. At the same time or afterward, a so-called “protocol interval” TP begins, during which the vehicle and accident data are logged as mentioned above. In this case, the current requirement is approximately 300 mA for a protocol interval of 250 ms, for example. The maximum autonomy time TA results from the sum of the fire interval TF and the protocol interval TP.
The operation of storing the logged data in a nonvolatile memory can take up a very large amount of time, for example approximately 2 seconds or else more, in the case of the required quantities of data. Storing comprehensive vehicle and accident data considerably lengthens the required autonomy time (octuples it in the present example), as a result of which it also becomes necessary to considerably increase the capacitance of the electrolytic capacitors which ensure the power supply during the autonomy time.
The circuit arrangement comprises an electronic control unit for an airbag (airbag ECU 1) and two power supply units 30, 40. The electronic control unit 1 comprises a data recorder unit 20 which has a volatile memory 21, a nonvolatile memory 22 and a copy circuit 23. The airbag ECU has a plurality of operating phases, namely the abovementioned firing phase, the protocol phase and a recorder phase. The copy circuit 23 is designed to copy data from the volatile memory 21 to the nonvolatile memory 22 during a second operating phase (recorder phase) of the control unit 1.
The electronic airbag ECU 1 also comprises a protocol unit 10 which is designed to receive vehicle and/or accident data via an interface (for example a CAN bus interface) and store them in the volatile memory 21 of the data recorder unit 20 during a first operating phase (protocol phase) of the control unit 1. A first power supply unit 30 is connected to the control unit 1 in order to supply the protocol unit 10 and further components of the control unit 1 with power. A second power supply unit 40 is connected to the data recorder unit 20 in order to supply the latter with power, in particular when the power reserves of the first power supply unit have been used up, for example on account of damage caused by an accident, that is to say during the autonomy time TA.
The volatile memory 21 is a RAM module, for example, and the nonvolatile memory 22 is an EPROM or EEPROM, for example. The second power supply unit 40 comprises a capacitor CLER. An electrolytic capacitor whose capacitance is large enough to ensure the power supply for the data recorder unit 20 at least for the duration of the operation of copying the data from the volatile memory 21 to the nonvolatile memory 22 can be used as the capacitor, for example. This copying operation may last two seconds or more, depending on the number of data items which have to be stored. It is important to note that the second power supply unit 40 supplies only the recorder unit 20 with power during the autonomy time TA, whereas all other components can be switched off, depending on the state of the first power supply unit 30. The first power supply unit 30 must ensure the power supply for the airbag ECU 1 during the fire and protocol intervals. However, it need not be designed for the entire autonomy time including the recorder interval TR.
Separating the recorder unit 20 from the protocol unit 10 makes it possible to considerably reduce the power consumption of the airbag ECU 1 during the long recorder interval because only the recorder unit 20 has to be operating and all other components of the airbag ECU 1 can be switched off. The recorder unit contains only the essential circuit elements which are required for permanently storing the relevant vehicle and accident data. Consequently, a considerably smaller number of electrolytic capacitors are required to maintain the recorder function than if the data were directly stored by the protocol unit.
The protocol unit 10 comprises, for example, a microprocessor core and a data interface which is used to receive the data D to be stored. The interface may be, for example, a CAN bus interface which is used to receive all relevant vehicle and accident data. These data are, for example, the speed of the vehicle, acceleration values, braking time, etc.
According to the example from
This protocol phase is started by the microprocessor core 11 if an accident is detected by the airbag sensors (not illustrated). The operation of storing the vehicle and accident data in the RAM module 12 or the RAM module 21 may be effected in a very much faster manner than storing them in an EEPROM. A protocol phase is typically concluded within approximately 250 milliseconds. During this time, the first power supply unit 30 must ensure the voltage supply for the airbag ECU in the event of the battery voltage breaking down. After the protocol phase has been concluded, all components of the airbag ECU, in particular the protocol unit 10 having the microprocessor core 11, can be switched off. The switching-off operation can be effected, for example, using an undervoltage detection device 60. However, such a device is not absolutely necessary, depending on the application.
In addition to the components (volatile memory 21, nonvolatile memory 22, copy circuit 23) which have already been illustrated in
The decoupler(s) 24 is/are arranged in the signal paths between the recorder unit 20 and the other components of the airbag ECU 1 in order to avoid undesirable effects from the recorder unit 20 on the protocol unit 10, for example, during the recorder phase of the autonomy time. The decouplers 24 may be designed, for example, to interrupt the signal paths between the recorder unit 20 and the protocol unit 10 if the supply voltage VDD of the first power supply unit 30 undershoots a particular limit value, that is to say an undervoltage is detected by the undervoltage detection device 60.
As already mentioned, the copy circuit 23 is designed to copy data from the RAM 21 to the nonvolatile memory 22 during the recorder phase of the autonomy time TA. Alternatively, this nonvolatile memory 22 can also be connected to the copy circuit 23 as an external component via a serial bus 50, for example an SPI bus or an I2C bus. In this case, the external nonvolatile memory 22 is also supplied with the supply voltage VDDX. Irrespective of this, all circuit components of the airbag ECU 1, with the exception of the electrolytic capacitors, can be integrated in a single application-specific integrated circuit (ASIC).
