Device for protecting the passengers in a motor vehicle

The invention relates to a device for occupant protection in a motor vehicle.

A known device (WO 96/09942 A) has an impact sensor arranged in a front region of the motor vehicle and a control unit arranged in a central region of the motor vehicle for controlling an occupant protection means. The impact sensor has either several mechanical acceleration switches, which are sensitive to different accelerations, which provide a switching signal when a fixed acceleration is exceeded. Alternatively, an acceleration sensor providing an analog acceleration signal is provided as an impact sensor. The switching signals or the analog acceleration signal are supplied to the central control unit. The occupant protection means is triggered by the control unit when the signal evaluated by a processor of the control unit of a acceleration sensor arranged centrally in the control unit has a predetermined profile. Individual operating states of the occupant protection means, such as, for example, individual stages of an airbag, are then selected as a function of the signal of the impact sensor.

When an electronic acceleration sensor is used as an impact sensor, disturbing variables acting on the line between the impact sensor and the control unit can considerably distort the sensitive analog signal delivered by the impact sensor. On the other hand, an extremely high computing power is to be provided in the processor of the control unit in order to evaluate the analog signal.

In addition, the processor must cope with a large number of other data intensive tasks such as an evaluation of signals of centrally located acceleration sensors or else an evaluation of signals from other devices connected to the control unit such as, for example, a device for occupant and / Or child identification. When mechanical acceleration switches are used as impact sensors, a larger signal-to-noise ratio is given during the switching signal transmission. However, such acceleration switches are complex and cost-intensive components to be manufactured, and in particular they do not permit a precise temporal evaluation of the acceleration acting on the front vehicle area.

DE 38 11 217 A1, which is the closest to the subject matter of the present invention, shows and describes an electronic device for occupant protection in a motor vehicle with a plurality of sensors, each of which is connected via an evaluation circuit and an interface with a star- Central control unit. The signals detected by means of the sensors are already processed in the evaluation circuits and transmitted to the central control unit via the interfaces. The central control unit has a further sensor whose signals it evaluates together with the transmitted signals and, as a function thereof, activates retaining means which are connected via interfaces via a further line to the central control unit.

It is an object of the invention to provide a device for occupant protection in a motor vehicle which can nevertheless provide a high-resolution assessment of the accident occurrence despite a small expenditure.

The object is achieved by the features of claim 1.

An evaluator-preferably in the form of a microprocessor with associated memories or in the form of an integrated circuit arrangement-as well as an interface, is assigned to the impact sensor arranged in the front region of the motor vehicle. Impingement sensor, assigned evaluator - referred to in the following as the evaluator - and interface form an impact sensor unit which is preferably arranged as an electrical control unit in a housing. The swapped evaluator is provided for the impact sensor signal delivered by the impactor. Depending on the evaluation of the impact sensor signal, a code signal is supplied from the impact sensor unit via the interface to the central control unit. An interface for receiving the code signal is provided in the central control unit. Furthermore, the central control unit has an acceleration sensor and an evaluator for an acceleration signal provided by the acceleration sensor. The occupant protection means assigned to the device is controlled by the evaluator of the control unit (hereinafter referred to as a central evaluator), which is preferably designed as a microprocessor with associated memories, as a function of the evaluated acceleration signal and the code signal. The acceleration sensor and the impact sensor are in this case in particular designed for detecting a front impact.

The device according to the invention has the advantage that the central control unit does not have to provide excessive computing power. This has the advantage, in particular, that if the existing central control units are expanded without a displaced impact sensor, just the software of the previous central control unit, but not its hardware, must be changed by this impact sensor. The central control unit is not flooded by analog signals, which must be discretized before further processing. The flared impact sensor unit directs only selected code signals with a relatively low throughput to the central control unit. On the other hand, however, despite the relatively low-dimensioned computing power of the central control unit, it is not necessary to dispense with the use of a displaced electronic acceleration sensor and its information in the analog impact signal.

With the device according to the invention, an impact can be detected very early in an impact. The impact sensor already provides a significant impact sensor signal at a point in time at which the centrally arranged acceleration sensor does not yet register an impact. An estimation of the further course of the accident, and thus of the forces acting on the occupants, as well as its advance, is made possible at an early point in time so that an adapted airbag triggering is made possible.

According to advantageous refinements of the invention in claims 2 to 5, the swapped evaluator at least takes over the discretization or the analog-digital conversion of the analog impact sensor signal. The resolution of the converter may preferably be selected to be greater than seven bits, with digital code signals having discretized values ​​being transmitted approximately at intervals of between 0.01 and one millisecond. Preferably, however, the measured impact sensor signal is also processed to be filtered and / or integrated. Such an impact signal may also be derived in another manner from the received impact sensor signal, for example, by averaging over short time intervals, by incorporating past values ​​of the impact sensor signal or the like. In this way, an impact signal is determined, which is as free as possible of disturbing influences and as far as possible as far as possible the impact in the front vehicle area. In this case, the impingement signal can be derived from the impact sensor signal before the analog-to-digital conversion or also after the analog-to-digital conversion. Through these measures, the central control unit receives the most important information in a compressed form without overloading its computing capacity.

A temporal evaluation of the impact sensor signal is carried out by the external evaluator. In this case, the swapped evaluator preferably supplies code signals via the interface to the central control unit to the approximately following message: The speed sequence determined in the front motor vehicle region as a result of an impact is low, and its maximum values ​​are also reached in a relatively large time interval.

The additional evaluation of the time profile of the impact sensor signal and the influence of the information obtained therewith into the code signals transmitted to the central control unit also reduces the rake load on the central control unit by the impact sensor unit.

Further advantageous further developments of the invention are characterized in the remaining claims.

Embodiments of the invention and its further developments are explained in more detail below with reference to the drawing. Show it:<dl tsize="7" compact="compact"><dt>FIG</dt><dd>The spatial arrangement of the device according to the invention in a motor vehicle,</dd><dt>FIG</dt><dd>A block diagram of an impact sensor unit,</dd><dt>FIG</dt><dd>A block diagram of a central control unit,</dd><dt>FIG</dt><dd>An analog impulse signal over time and its discretized values ​​at the determined sampling times,</dd><dt>FIG</dt><dd>A triggering matrix for a multi-stage occupant protection means as a function of the code signals transmitted by the impact sensor unit and the evaluation of the central acceleration signal.</dd></dl>

FIG. 1 shows the spatial arrangement of the device according to the invention in a symbolically illustrated motor vehicle. A central control unit 3 is mounted centrally in the vehicle, for example on the vehicle tunnel. Sensitivity axes of centrally arranged acceleration sensors 32 and 33 are symbolically indicated by double arrows. The control unit 3 has an acceleration sensor 32 for vehicle longitudinal accelerations and an acceleration sensor 33 for vehicle transverse accelerations. A pertinent impact sensor unit 1 arranged in the front region of the motor vehicle is electrically connected to the control unit 3 via a data line 2. The control unit 3 is connected via ignition leads 4 to ignition elements 511 and 512 for a first and a second inflation stage of a driver airbag 51 as well as ignition elements 521 and 522 for a first and a second inflation stage of a passenger airbag 52 as an occupant protection means 5.

The single arrow next to the impact sensor unit 1 indicates that the impact sensor unit 1 has an impact sensor, in particular an acceleration sensor, which is sensitive to accelerations in the vehicle direction indicated by the arrow, that is to say for vehicle longitudinal delays such as in the case of a front or an inclined impact Vehicle.

FIG. 2 shows an impact sensor unit 1 according to the invention with an impact sensor 12, an evaluator 13 comprising a microprocessor 131 and a diagnostic unit 132 constructed as a logic unit, as well as an interface 11. The impact sensor 12, designed as an electronic acceleration sensor, for accommodating vehicle delays supplies its impact sensor signal a to the microprocessor 131 , Which analog-to-digital converts the impact sensor signal a with a relatively high resolving power, and preferably compares the thus formed impact signal with several threshold values. If the impact signal exceeds one of the threshold values, a corresponding code signal co is output via the interface 11.

Alternatively, an impact signal can be obtained from the impact sensor signal a, eg by amplification and filtering or integration in an analog circuit arrangement, which is then converted analog-to-digital. If the analog-digital-converted impact signal is transmitted directly via the interface, an analog-to-digital converter with low resolution is recommended.

Instead of the previously described microprocessor or the above-described analog circuit arrangement, the out-mounted evaluator 131 can be integrated as a one-chip solution together with the impact sensor 12.

However, a code signal co can not be output via the interface 11 only if the impact sensor signal or the impact signal exceeds a predetermined threshold value. Preferably, the dynamics, ie, the time profile of the impact sensor signal or the impact signal, are taken into account for generating a code signal co. Preferably, a corresponding message as a code signal co is transmitted via the interface 11 and the data line 2 connected to the interface 11 to the central control unit 3 as a function of a period of time within which a fixed threshold value is exceeded by the impact signal. In this case, a past time interval, ie, in particular, a time window of constant length, which moves along with a progressive time, is preferably checked for the dynamics of the impact sensor signal or of the impact signal. For example, a first code signal is generated if a first value range has been traversed by the impact signal within the time window, whereas a second code signal, on the other hand, has been traced within the time window during a second larger value range.

The interface 11 defines the physical and functional prerequisites for the controlled data transmission between the impact sensor unit 1 and the control unit 3. The control unit 3 according to FIG. 3 receives the such code signal co from the data line 2 via an interface 31 and at least directs the information contained in the code signal co to one Evaluator 34 further. The evaluator 34 also receives acceleration signals b and c of a longitudinal acceleration sensor 32 and a transverse acceleration sensor 33, respectively. Furthermore, the evaluator 34 receives signals from a further interface 35, to which devices for child seat and / or occupant and / or weight detection are preferably connected. The central evaluator 34 evaluates the received signals, for example, it forms an overall speed reduction by a difference between the determined speed reduction and the centrally determined speed reduction, and ignites an ignition element of an occupant protection means connected via an ignition line 4 by switching on a controllable output stage 37 By means of a control signal ST, if, for example, the total speed reduction exceeds a threshold value. Through the control of the output stage 37, the connected ignition element is acted upon with energy from an energy source 36 and thus at least partially releases an occupant protection means assigned to the ignition element. The diagnostic unit 132 checks the functionality of the impact sensor 12, the algorithm unit 131 and the interface 11 with suitable diagnostic routines / measurements.

If it is determined that the impact sensor unit 1 is defective, a further operating mode of the device according to the invention is preferably switched over in which the assigned occupant protection means can be triggered by the central evaluator alone on the evaluation of the acceleration signal of the central acceleration sensor.

FIG. 4 shows, for example, an impact signal X, described in conjunction with FIG. 3, over time t, the impact signal X not only representing an integrated impact sensor signal, but also a measure of the speed reduction of the front vehicle body determined from the impact sensor signal. As a result of the impact, the speed reduction at early times is greater than at late times. The bars shown represent the analog-digital-converted impact signal X in the swapped evaluator 13. The instants t₀ to t₇ Characterize sampling times. The limit values ​​G₀ to G₆ Characterize individual discretization stages, wherein in each case a check is made as to whether the analogue impact signal X of a particular discretization stage G_i Exceeded. On the basis of the discretized impact signal<i>x</i> The severity and the temporal course of the detected impact will be evaluated by the evaluating evaluator. On the basis of these conclusions, fixed code signals are transmitted to the central control unit.

FIG. 5 shows a triggering strategy which is stored as software or hardware in the central evaluator and which initiates triggering decisions for individual stages of an occupant protection means as a function of the measured impact sensor signal of the displaced impact sensor and the acceleration signal of the central acceleration sensor.

The evaluation carried out by the central evaluator of the acceleration signal delivered by the central acceleration sensor is applied horizontally. A central impact signal for the speed reduction of the passenger cell is derived from the acceleration signal of the central acceleration sensor 32 after its analog-to-digital conversion. This speed reduction as a relevant central impact signal is subsequently compared with different threshold values, whereby each threshold value can be variable and in particular impact-dependent or constant. If the central impact signal exceeds a first low threshold value, the variable LEV1 is set, if the central impact signal exceeds a further threshold value which is greater than the first threshold, the variable LEV2 is set, the central impact signal exceeds a third very high threshold value, The variable LEV3 is set.

For the evaluation of an impact by the impact sensor unit, 4 messages are provided in the form of code signals col to co4. In this case, the signal col represents that a weak speed reduction, which has also been achieved only slowly, has been determined, the code signal co2 for a medium-rated speed set-up which has been reached relatively slowly, the code signal co3 for a high speed reduction, Continuous time interval, and the code signal co4 for a high speed degradation which was achieved in a very short time. With the code signals co formed in this way, not only the strength of an impact but also its dynamics are evaluated in the impact sensor unit.

The matrix according to FIG. 5 makes statements about the conditions and if so which stage of the assigned occupant protection means is to be triggered. The occupant protection means is two-stage. Its first stage, which fills a small volume of the airbag or the air bag with a low gas pressure, is activated with a control signal ST1, its second stage, which activates a larger air bag volume and usually is more aggressively inflated over the first stage, Control signal ST2 activated. If a triggering of no stage is required on the basis of the evaluation, an entry NO is found in the matrix according to FIG.

The interpretation of the matrix according to FIG. 5 is only to be illustrated with a few examples: If, for example, the impact sensor unit detects a strong, fast impact (co4), the central control unit only has a weak impact (LEV1) The front car body is deformed in the middle, but the longitudinal beams of the vehicle, which transmit the impact to the central control unit, have not yet been hit. However, the deformation is evaluated as so serious that the airbag is to be activated on its first stage (ST1), in particular against the background that, in the foreseeable future, a strong energy reduction will also take place via the vehicle longitudinal carriers. On the other hand, if the impact sensor unit detects, for example, a weak speed reduction, which is only slowly reached (co1) and if the central control unit detects a considerable speed reduction (LEV3), then no triggering (NO) occurs. It is to be assumed that in the case of no delay, or only a slight deceleration, and a strong central deceleration, there is only a grounding of the vehicle on the ground caused, for example, by the passage of a sleding hole, in which a triggering of protective means is not required.