Device for controlling a motor vehicle occupant protection system

A device for controlling a motor vehicle occupant protection system. Such a device has a control unit with an encoder for encoding messages and a transmitter for transmitting the encoded messages in the form of output signals. The encoded messages include a first encoded message having a first number of positions and a second encoded message having a second number of positions, the first number of positions being smaller than the second number of positions. In this case, at least one of the encoded messages may be provided with an error-correction code.

BACKGROUND OF THE INVENTION
 Field of the Invention
 The invention relates to a device for controlling a motor vehicle occupant
 protection system. The device includes a control unit having an encoder
 outputting encoded messages and a transmitter for transmitting the encoded
 messages as output signals.
 Such a device is disposed separately, i.e. for example in a side part of
 the motor vehicle and is described in European Patent Application EP 0 693
 401 A2. The known device includes an acceleration sensor and a control
 unit with an encoder for encoding messages and a transmitter for
 transmitting the encoded messages in the form of signals. The messages to
 be transmitted are transmitted in pulse-width-modulated form to an
 evaluation device disposed centrally within the vehicle. Such a message
 may for example have the content: "The occupant protection system is to be
 triggered, because the recorded acceleration has exceeded a predetermined
 threshold value". Occupant protection system ignition elements connected
 to the evaluation device, such as, for example, lateral airbags, belt
 tighteners, head airbags or the like are acted upon with energy, due to an
 encoded message being transmitted without error, so that the associated
 occupant protection systems are activated. In order to recognize a
 defective transmission between a separate device and the central
 evaluation device, the duration of the period of the transmitted signals
 is compared with a theoretical period duration in the evaluation device.
 If the measured period duration and theoretical period duration are not
 concordant, the transmitted message is discarded. A defective transmission
 can be caused, in particular by electromagnetic fields acting on the data
 line.
 Since a signal representing that a message has been sent by the separate
 device is periodically sent to the central evaluation device, a defective
 signal is at least prevented from being permanently ignored. However, if
 the signals transmitted subsequently to a defective signal are also
 defective then, specifically in the case of signals that have triggering
 instructions as their content, valuable time is wasted for triggering the
 occupant protection system. In particular, the triggering of an occupant
 protection system for side-impact protection can subsequently take place
 too late and cause injuries to the occupant. Because the time required for
 the triggering of occupant protection systems for side-impact protection
 are set extremely short, within 5 msec from the commencement of side
 impact, the triggering decision should be made, since there is no crumple
 zone protecting the occupant. The triggering time cannot be obtained in
 time when several defective signals are transmitted one after the other.
 SUMMARY OF THE INVENTION
 It is accordingly an object of the invention to provide a device for
 controlling a motor vehicle occupant protection system which overcomes the
 herein afore-mentioned disadvantages of the heretofore-known devices of
 this general type, which transmits data relevant to a triggering of an
 occupant protection system and enables a secure transmission of messages
 to a remotely disposed control unit in the motor vehicle within a very
 short time.
 With the foregoing and other objects in view there is provided, in
 accordance with the invention, in a motor vehicle occupant protection
 system, an apparatus for controlling a motor vehicle occupant protection
 device, the apparatus including: a control unit having an encoder for
 encoding messages and a transmitter connected to the encoder for
 transmitting encoded messages as output signals; and the encoded messages
 include a first encoded message having a first number of positions and
 containing information relevant to safety and a second encoded message
 having a second number of positions greater than the first number of
 positions.
 With the foregoing and other objects in view there is also provided, in
 accordance with the invention, in a motor vehicle occupant protection
 system, an apparatus for controlling a motor vehicle occupant protection
 device, the apparatus including: a control unit having an encoder for
 encoding messages and a transmitter connected to the encoder for
 transmitting encoded messages as output signals; and the encoded messages
 include a first encoded message containing information relevant to safety
 and a second encoded message, each of the encoded messages having an
 information word and a control word, the information word of the first
 encoded message having a first number of positions and the information
 word of the second encoded message having a second number of positions
 greater than the first number of positions.
 With the foregoing and other objects in view there is further provided, in
 accordance with the invention, in a motor vehicle occupant protection
 system, an apparatus for controlling a motor vehicle occupant protection
 device, the apparatus including a control unit having an encoder for
 encoding messages containing information relevant to safety and a
 transmitter connected to the encoder for transmitting encoded messages as
 output signals, and the encoded messages are encoded with an
 error-correction code.
 The inventive device is based on the concept that the transmitter of the
 device operates serially and files the individual symbols of the encoded
 messages in temporal succession onto the transmission medium, preferably a
 data line. In addition, individual inventive concepts come to light using
 parallel transmission.
 According to the invention, messages with differing content/information are
 converted into encoded message words of differing length. In this case,
 the first encoded message has the first number of positions, and the
 second encoded message has the second number of positions, the first
 number being smaller than the second number. Preferably, in this case
 messages which require or suggest a triggering of the associated occupant
 protection system contain in encoded form a smaller number of positions
 than messages which exhibit, for example, information independent of
 acceleration. As a result of the small number of positions of an encoded
 message containing, for example, a triggering instruction, the same can be
 transmitted serially in an extremely short time and, moreover, can be
 evaluated extremely quickly in the control device receiving the message,
 so that the corresponding measures can be introduced immediately. Messages
 of less urgent content may have, in encoded form, a substantially larger
 number of positions and thus a larger word length. The inventive device
 also reveals advantages in particular in circumstances in which there are
 provided a large number of different messages which, in the presence of
 conventional encoding with the same number of positions for all messages,
 would require a large number of positions.
 An encoded message may include not only an information word which contains
 the sense content of the message in encoded form, but also a control word
 which controls the transmission of the encoded message. In particular in
 the case of asynchronous data transmission but also in the case of
 synchronous data transmission, the control word is necessary over and
 above the information word. As a rule, it has a position which precedes
 the information word and which is occupied by a start signal which
 characterizes the start of a following information word. Following the
 information word, there is usually a further position which is associated
 with the control word of the encoded message and which has a stop symbol,
 which characterizes the end of a transmitted information word. It is
 essential in the case of a device which generates messages encoded in this
 fashion that at least the information word has, dependent on the content
 of a message, differing lengths. In this case, if appropriate, the message
 length of the different messages (i.e. the total number of positions which
 can be occupied by symbols) may be the same, even if the one encoded
 message enjoys higher priority and its information word has only a few
 positions and the other message has a low priority and its information
 word includes many positions. The encoded message having the information
 word configured to be short may, instead, include a control word
 configured to be longer. In this case, the control word preferably
 includes a plurality of, i.e. at least two, positions intended for stop
 symbols. In this case, the start symbol for the next encoded message is
 also not correctly recognized, so that, on a permanent basis, there is a
 false synchronization between the transmitter and the receiver. For this
 reason, in particular, the encoded message has a short information word
 and a longer control word with a plurality of stop symbols. If the start
 symbol is not correctly recognized, a symbol of the following information
 word will probably be interpreted as the start symbol. As a result of the
 large number of stop symbols, it is guaranteed that, even in this case,
 the stop symbol follows the "right-shifted" erroneously interpreted
 information word, so that the synchronization between transmitter and
 receiver is again created and the start symbol of the following encoded
 message is recognized as such. The advantages of the device reside in the
 number of positions of the information word, and not in the number of
 positions of the control word. The number of positions of the information
 word is of decisive importance for the rapid transmission and evaluation
 of the message.
 According to the invention, the message to be transmitted is encoded with
 an error-correction code. Such an error-correction code has the property
 that at least a defective symbol of the encoded message can be recognized
 by the receiving device and corrected.
 In the case of an illustrative error-correction code, one individual symbol
 of a message is imaged onto a plurality of symbols to be transmitted. Thus
 in the transmitter, by way of example in the case of binary encoding, the
 symbol 0 is imaged onto three successive zeros. The receiving device forms
 a majority decision for the three received symbols. If, accordingly, at
 least two zeros of the three zeros dispatched are received, then a zero is
 interpreted as the symbol actually to be transmitted. The number of
 positions which is to be made available for a data transmission with
 error-correction code, also referred to as the Hamming distance, is
 computed on the basis of 2.multidot.n+1 with n as the number of positions
 of the symbols/positions of the original code word which are to be
 provided with an error-correction code.
 As a result of the use of the error-correction code in the formulation of
 messages of the device for controlling an occupant protection system,
 there is a considerable reduction in the probability of a loss of time
 occurring through discarding a defective encoded message by the receiving
 device. The probability of a double or multiple error in an encoded
 message, which, even in the case of the use of an error-correction code,
 would lead to a message possibly erroneously interpreted by the receiving
 device or to a message to be discarded is substantially lower than the
 probability of a single error. As a result of the application of the
 error-correction code to data transmission paths in systems for
 controlling occupant protection systems, the susceptibility of the entire
 system to interference is reduced and at the same time a triggering of the
 occupant protection systems which is temporally correct and, in particular
 in the event of side-impact recognition, is timely achieved, since, in
 comparison with multiple code word transmission, which is necessary in the
 case of code words encoded only with an error-recognition code and an
 error in each code word, a time gain can be achieved.
 According to the invention, the messages for an occupant protection system
 can accordingly be encoded with a variable code length and/or an
 error-correction code independently of one another or, advantageously,
 combined with one another.
 In accordance with an added feature of the invention, the encoded messages
 include two identical information words.
 In accordance with an additional feature of the invention, at least one of
 the messages is encoded as an information word with the first number of
 positions loaded with the error-correction code and the second number of
 positions loaded without the error-correction code.
 In accordance with another feature of the invention, the first encoded
 message is encoded with the error-correction code, and the second encoded
 message is encoded in part with and in part without the error-correction
 code.
 In accordance with a further added feature of the invention, the control
 word has at least two positions provided for a start symbol, the start
 symbol indicating a commencement of the information word.
 In accordance with a further additional feature of the invention, the
 control word has at least one reserve position to be occupied by a symbol
 and ascribed to the information word.
 In accordance with yet another feature of the invention, the control word
 has at least two further positions provided for a stop symbol, the stop
 symbol indicating an end of the information word.
 In accordance with yet another added feature of the invention, the first
 encoded message contains information having a higher priority
 classification, and the second encoded message containing information
 having a lower priority classification.
 In accordance with yet another additional feature of the invention, the
 first encoded message contains information appertaining to an indirect or
 direct triggering of an occupant protection system, and the second encoded
 message containing device condition information.
 With the foregoing and other objects in view there is lastly provided, in
 accordance with the invention, a configuration for controlling a motor
 vehicle occupant protection system, including a control unit having: an
 acceleration sensor for recording an acceleration of a motor vehicle and
 outputting an acceleration signal; an encoder receiving the acceleration
 signal for encoding messages; a transmitter connected to the encoder for
 transmitting encoded messages as output signals, the encoded messages
 including acceleration-dependent signals; and an evaluation device
 disposed spatially separated from the control unit for controlling an
 occupant protection system, the evaluation device receiving and evaluating
 the acceleration-dependent signals from the control unit and outputting a
 trigger signal.
 In accordance with a concomitant feature of the invention, there is an
 ignition device disposed spatially separated from the control unit and
 connected to an ignition element of the occupant protection system, the
 ignition device receiving the trigger signal for triggering the ignition
 element.
 Other features which are considered as characteristic for the invention are
 set forth in the appended claims.
 Although the invention is illustrated and described herein as embodied in a
 device for controlling a motor vehicle occupant protection system, it is
 nevertheless not intended to be limited to the details shown, since
 various modifications and structural changes may be made therein without
 departing from the spirit of the invention and within the scope and range
 of equivalents of the claims.
 The construction and method of operation of the invention, however,
 together with additional objects and advantages thereof will be best
 understood from the following description of specific embodiments when
 read in connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring now to the figures of the drawing in detail and first,
 particularly, to FIG. 1 thereof, there is shown a symbolic message N,
 which is to be transmitted by a device 1 (FIG. 7) for controlling a motor
 vehicle occupant protection system via a suitable transmission medium, for
 example an electrical or optical data line, or alternatively in
 non-contact fashion, to a receiving device which is disposed at a
 spatially remote location. According to FIG. 7, the device 1 can be
 configured as a separate sensor unit, which includes an acceleration
 sensor 11 to record transverse accelerations of a vehicle and a control
 unit 12 having a non-illustrated evaluator, an encoder 121 and a
 transmitter 122. The transverse accelerations of the vehicle caused by an
 impact are evaluated in the evaluator. If, for example, the transverse
 acceleration exceeds a predetermined threshold value, the appropriate
 message N is to be transmitted via a data line 2 to an evaluation device
 3, disposed centrally in the vehicle, as a receiving device. The
 corresponding message N is encoded in the encoder 121. Via the transmitter
 122, the encoded message CN is output serially onto the data line 2. The
 evaluation device 3 is, for example, disposed at a vehicle drive shaft
 tunnel and includes a receiver and decoder to receive and decode the
 transmitted encoded messages CN. If, for example, in addition to the
 message containing a triggering instruction there is also information
 present indicating that the corresponding vehicle seat is occupied, a
 triggering instruction configured as an encoded message is transmitted by
 the evaluation device 3 via a further data line 2 to an ignition device 4.
 The ignition device 4 includes a receiver and decoder, so that the
 transmitted triggering instruction can be received and decoded. If the
 triggering instruction is recognized as such by the ignition device 4,
 then the same activates an ignition element of the associated occupant
 protection system.
 According to FIG. 7, the encoding specifications proposed according to the
 invention can be used for the transmission of messages on the data lines 2
 between separate devices 1 and the evaluation device 3 and/or between the
 evaluation device 3 and the ignition devices 4. In the case of the latter
 possibility, the evaluation device 3 is to be regarded as the device
 according to the invention, which includes a control unit having an
 encoder and a transmitter which, according to the invention, transmits
 edited messages to the ignition device 4. It is understood that, in those
 circumstances, the impact recognition is not dependent upon separate
 acceleration sensors, but, by way of example, an acceleration sensor is
 disposed, together with the evaluation device 3, within the same control
 unit.
 Examples of messages to be transmitted from a device constructed as a
 separate sensor unit to a central evaluation device are:
 Acceleration g has exceeded a threshold value S1 (N&gt;S1, see FIG. 1),
 Device is operational,
 Device inoperative+established error.
 Examples of messages to be transmitted from a device configured as the
 central evaluation unit to a separate ignition device are:
 Execute ignition,
 Device is operational,
 Device defective+error code.
 In the encoder of the device, such messages N are converted by an encoding
 specification C into encoded messages/message words (FIG. 1). An encoded
 message usually includes an information word IN for the content of the
 actual message and a control word ST for control of the data transmission.
 According to FIG. 1, the encoded message CN includes a total of M
 positions, from position m=1 to position m=M. Of those, the information
 word has I positions, from position i=1 to position i=I, and the control
 word ST has S positions, from position s=1 to position s=S. The first and
 the last position m=1 and m=M of the encoded message CN associated with
 the control word ST are occupied by a start symbol, e.g. zero, and a stop
 symbol, e.g. one, respectively. In the serial asynchronous transmission
 mode, an encoded message CN which has been compiled in this manner by the
 device is decoded, in the receiver device, in the following manner: in the
 transmitted data stream, a negative flank (edge) from one to zero, just
 from the stop symbol to the start symbol, is recognized and interpreted as
 the start of a new information word IN. Following the start symbol 0,
 there is a predetermined number I of positions for the information word
 IN, which are stored and decoded. Thereupon, the stop symbol "one" is
 awaited. When the stop symbol is recognized, then an attempt is again made
 to recognize the start symbol "zero" which characterizes the start of
 another information word IN.
 FIG. 2 shows an information word IN, encoded in conventional manner,
 according to a) and an associated information word IN, encoded according
 to the invention with an error-correction code FKC, according to b). The
 information word IN according to b) is output by the transmitter of the
 device to the line. Each symbol to be transmitted of one of the three
 positions i=1 to 3 of the information word according to a) is imaged,
 after application of the error-correction code FKC, by three positions.
 The process for decoding a thus encoded information word IN according to
 b) has been discussed in the introduction to the description (majority
 decision, etc.). It is understood that it is also possible for any other
 error-correction code to be used.
 Preferably, in the interests of a transmission and evaluation which saves
 as much time as possible, only the information word IN of an encoded
 message CN according to a) is imaged by the application of an
 error-correction code onto an information word IN to be transmitted, by
 way of example according to b). With regard to the interference immunity
 of the entire system, an error-correction code can also be applied to the
 symbols of the control word of the encoded message CN.
 The information word IN according to b) of FIG. 2, which is formed after
 application of an error-correction code FKC, from the information word IN
 according to a), together with the associated control word ST having a
 start symbol zero at the position s=1 and a stop symbol one at the
 position s=2, is shown in FIG. 5 as an encoded message CN1. According to
 FIG. 5, the associated control word ST can, however, also be configured in
 such a manner that a plurality of positions s=2 to s=7 for stop symbols
 are provided; see encoded message CN2.
 According to FIG. 3, two information words IN1 and IN2 are shown in a),
 with an illustrative binary symbol occupation. In this case, each
 information word has six positions i=1 to i=6. The information word IN1
 includes a message to trigger the associated occupant protection system.
 The information word IN2 includes, as a message, a status signal of the
 processor of the device, which, in its priority, is of lower rank than the
 message "trigger". According to the invention, the two messages are not
 encoded, in accordance with a), with the same number of positions, but
 according to b) with a different number of positions. In this case, the
 higher-priority message is represented by an information word IN1 having
 by way of example only two positions i=1 and i=2, and the lower-priority
 message by an information word IN2 having seven positions i=1 to i=7. In
 this case, an occupation of the first two positions i=1 and i=2 of the
 transmitted information word with a one identifies that the following five
 positions are also associated with the information word and need to be
 taken into consideration in the evaluation. All other symbol combinations
 for the first two positions of the information word reveal to the
 receiving device that no further positions in the data stream are to be
 ascribed to the information word IN.
 FIG. 4 shows the encoded messages CN1 and CN2 which are associated with the
 information words IN1 and IN2 according to b) of FIG. 3 and which, besides
 the information words IN, contain the control words ST.
 According to FIG. 6, the inventive proposals to reduce triggering times and
 to increase the interference immunity are associated with one another in
 an extremely advantageous manner. By way of example, two encoded messages
 CN1 and CN2 are shown. In this case, the encoded message CN1 contains a
 message classified as being of higher priority, in particular an
 acceleration-dependent, trigger-influencing message, and the encoded
 message CN2 contains a message classified as being of lower priority, e.g.
 a status report or an error code. In this case, the encoded message CN1
 has a six-position information word IN, which is loaded with an
 error-correction code and was derived from an originally two-position
 information word with the symbols "00". The control word ST has a total of
 10 positions. Of these, the positions s=1 and s=2 of the control word ST,
 which precede the information word IN are intended for the start symbol
 (zero). The control positions s=3 to s=10 which follow the information
 word IN are in each instance occupied by a one. In this case, the position
 s=3 is configured as a so-called reserve position and the positions s=4 to
 s=10 are provided for the stop symbol (one). If only a single start symbol
 for each encoded message is provided, then in the case of a defectively
 transmitted start symbol the receiving device usually interprets a symbol
 of the information word IN as the start symbol. A defective
 synchronization of the transmitter with the receiver is the consequence.
 As a result of this, it is advantageous to provide at least one further
 start symbol/start position ahead of the information word IN of each
 encoded message CN, so that in the event of a defectively transmitted
 first start symbol at the position s=1 and a correctly transmitted second
 start symbol at the position s=2, it is possible to initiate an
 evaluation, displaced merely by one position, of the information word. If
 only the symbol at the position s=2 is recognized as start symbol, then
 the positions i=2 to i=6 and the reserve position s=3 are interpreted as
 information word IN in place of the position i=1 to i=6. In this case, as
 a consequence of the error-correction code, for example, the positions i=1
 to i=3 are occupied by identical symbols and the positions i=4 to i=6 by
 identical symbols. In the worst case with the information word IN
 erroneously interpreted by one position, the position i=4 is not equal to
 the position i=3 and the position s=3 is not equal to the position i=6.
 Thus, both the first three positions i=2 to i=4 of the erroneously
 interpreted information word IN and also the second three positions i=5,
 i=6 and s=3 of the information word IN exhibit an error, which, if the
 transmission is in other respects error-free, is however recognized by the
 evaluation device and corrected. Even if the first start signal of an
 encoded message is not recognized, on this basis the probability of a
 correct interpretation of the message by the receiving device is
 nevertheless guaranteed. If the first start position s=1 is not recognized
 and the second start position s=2 is recognized, the position of the
 control word ST which is designated as reserve position s=3 is associated
 with the information word IN and is in the first instance capable of
 unrestricted occupation by the inventive device. Preferably, this
 reference position is occupied by the symbol which also occupies those
 positions of the information word with which the reference position is
 read together as a unit if the first start symbol is not recognized, i.e.
 in the example according to FIG. 6 after the occupation of the position
 i=5 and i=6. In this way, an error correction possibility for the start
 symbol is made available through an indirect route.
 The control positions s=4 to s=10 represent stop symbols, the redundancy of
 which is just as expedient as the redundancy of the start positions.
 As compared with the encoded message CN1, the encoded message CN2 in FIG. 6
 has lower priority and thus has a greater total number of positions M of
 the encoded message CN and a larger number of positions I of the
 information word IN than the encoded message word CN1
 (M(CN2)=24&gt;M(CN1)=16; I(CN1)=6&lt;I(CN2)=12). In contrast to the information
 word IN of the coded message CN1, the information word IN of the encoded
 message CN2 is occupied with a symbol combination ("000111" with error
 correction or "01" without error correction), which supplies to the
 receiving device an indication that further positions of the encoded
 message CN2 are to be ascribed to the information word IN. These further
 positions i=7 to i=12 contain the actual information of the encoded
 message CN2. In this case, these positions may be loaded with an
 error-correction code, but do not need to be so loaded. According to the
 example in FIG. 6, the inventive device would be able to generate three
 curtailed encoded messages according to the encoded message CN1 which are
 classified as being of higher priority. If the second portion of the
 information word IN with the positions i=7 to i=12 is encoded in
 error-correction code, then four low priority messages may be represented
 using these six positions. If error-correction code is not desired, then
 messages classified as being of low priority can be represented with
 2.sup.6, assuming in each instance binary encoding.
 With the above versions, the number of positions and the number of
 redundant positions (error correction) of an encoded message are optimized
 with respect to a rapid data transmission of messages classified as being
 of higher priority, with high interference immunity at the same time.
 The encoded message CN2 classified as being of lower priority also includes
 two start positions. Accordingly, the position s=3 of the control word
 which follows the first portion i=1 to i=6 of the information word IN is
 to be considered as the above-mentioned reserve position. The control
 position s=4 contains a stop symbol. In this case, the position s=5 and
 s=6 are again provided on a redundant basis for the start symbol zero. The
 control position s=7 which follows the second portion i=7 to i=12 of the
 information word IN is provided as a further reserve position for the
 further portion of the information word i=7 to i=12, before the control
 positions s=8 to s=12 represent stop bits for the entire encoded message
 CN2.
 To increase the interference immunity of the data transmission, it may be
 provided that, in spite of the use of error-correction code, encoded
 messages are repeatedly sent out, in order to be able to detect dual or
 multiple errors occurring even with a low probability. Furthermore, it may
 be provided that within an encoded message, i.e. in particular between the
 start symbol and the stop symbol, the information word containing the
 actual information is sent on a redundant basis. The first information
 word is then compared with the second information word of an encoded
 message in the receiving device and, in the event of divergence, the
 transmitted message is discarded. The redundant information word
 transmission can in particular be provided advantageously in the case of
 messages classified as being of higher priority; that is to say, messages
 which, for example by reason of their short word length, require only a
 short transmission time.
 The invention has indeed been presented for use with binary codes, but is
 applied in analogous fashion in the case of multi-stage codes. The
 invention permits an extremely variable construction of its hardware and
 software, and also of the resources of the receiving device.