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Following introduction of the airbag for the front-seat passenger, safety and actuarial considerations made it necessary to detect whether the front-seat passenger’s seat is oc- cupied or not. Otherwise, when an accident occurs and both front airbags are deployed, unnecessary repair costs result if the passen- ger seat is unoccupied.

The development of the so-called "Smart Bags" marked an increase in the demand for the ability to detect occupation of the dri- ver-seat and front-passenger seat. The smart bag should feature variable deployment adapted to the actual situation and occupa- tion of the seats. In certain situations, airbag triggering must be prevented when deploy- ment would be injurious to one of the vehi- cle’s occupants (for instance, if a child is sit- ting in the seat next to the driver, or a child’s safety seat is fitted). This led to further de- velopment of the "simple" seat-occupation detection to form the "intelligent" Occupa- tion Classification (OC). In addition, the automatic detection of a child’s safety seat is integrated as a further sensory function. This can detect whether the seat is occupied

or not, provided the seat is equipped with transponders.

Design and construction

A so-called sensor mat and ECU incorpor- ated in the vehicle’s front seats (Figs. 1 and 2) registers the information on the person in the seat and sends this to the airbag ECU. These data are then applied when adapting the restraint-system triggering to the current situation.

Operating concept

Measuring concept

This relies upon the classification of passen- gers (OC) according to their physical characteristics (weight, height, etc.), and applying this data for optimal airbag deploy- ment. Instead of directly "weighing" the per- son concerned, the OC system primarily applies the correlation between the person’s weight and his/her anthropometric1_{) char-}

acteristics (such as distance between hip- bones). To do so, the OC sensor mat mea- sures the pressure profile on the seat surface. Evaluation indicates first of all whether the seat is occupied or not, and further analysis permits the person concerned to be allo- cated to a certain classsification (Fig. 3). 94 Force sensors and torque sensors Occupant classification (OC) and detection of child’s safety seat

Fig. 1 1 ECU Fig. 2 1 OC-ECU 2 Airbag ECU 1

Sensor mat with OC-ECU

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Installation of the OC sensor mats in the front seats

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Sensor technology

Basically, the OC sensor mat comprises pres- sure-dependent FSR resistance elements (FSR: Force-Sensitive Resistance), the infor- mation from which can be selectively evalu- ated. A sensor element’s electrical resistance drops when it is subjected to increasing mechanical load. This effect can be regis- tered by inputting a measuring current. The analysis of all sensor points permits defi- nition of the size of the occupied seat area, and of the local points of concentration of the profile.

A sensing antenna and two receive antennas in the OC sensor mat serve to implement the child’s safety-seat detection function. During the generation of a sending field, transponders in the specially equipped child’s seats are excited so that they impose a code on the sending field by means of mod- ulation. The data received by the receive antenna and evaluated by the electronic cir- cuitry is applied in determining the type of child’s seat and its orientation.

ECU

The ECU feeds measuring currents into the sensor mat and evaluates the sensor signals with the help of an algorithm program which runs in the microcontroller. The re- sulting classification data and the informa-

tion on the child’s safety seat are sent to the airbag ECU in a cyclical protocol where, via a decision table, they help to define the trig- gering behaviour.

Algorithm

Among other things, the following decision criteria serve to analyse the impression of the seating profile:

Distance between hip-bones:

A typical seating profile has two main im- pression points which correspond to the distance between the passsenger’s hip-bones.

Occupied surface:

Similarly, there is a correlation between the occupied surface and the person’s weight.

Profile coherence:

Consideration of the profile structure.

Dynamic response:

Change of the profile as a function of time.

Force sensors and torque sensors Occupant classification (OC) and detection of child’s safety seat 95

Fig. 3

a Seating profile b Diagram

A Child with distance between hip-bones

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B Adult with distance between hip-bones X2 20 X1 X2 40 60 Weight 10 0 14

Distance between hip-bones

18 22 cm a A B B b 80 100 kg A X1 X2

Seat profile of the human body (a), with assignment of the distance between hip-bones to the person’s weight (b)

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Measured quantities

Flow measurement is only required at a few points on the vehicle:

To register the delivered fuel quantity, and in particular to measure the amount of air drawn in for combustion.

Fuel-flow measurement

On electronically controlled fuel-injection systems, the fuel quantity is metered to the IC engine precisely (without specific flow measurement), either intermittently or con- tinuously. The required fuel quantity is in- jected precisely thanks to the evaluation of such variable/adjustable parameters as injec- tion duration, setting of the metering unit, injection pressure, fuel temperature etc.

The fuel-flow meters were developed principally during periods of intense fuel scarcity and were used on the IC engines of the time, which were not yet electronically controlled. They indicated the fuel con- sumption in liters for a given distance of 100 km (60 miles). The difference between the fuel delivered from the tank and the amount of fuel which flowed back to it (whereby, particularly at idle, the amount of fuel returned to the tank was considerable) was applied as the basis for calculating the amount of fuel that had actually been used (Problem: This was the difference between two large quantities).

Since there is presently no actual necessity for such fuel flow meters, and since they are practically no longer in use, no further space will be devoted to them here.

Airflow measurement

As such, the often-used term "air quantity" is incorrect because it does not stipulate whether volume or mass is concerned. Since the chemical processes involved in fuel com- bustion are clearly based on mass relation- ships, the measurement must apply to the mass of air drawn in or the mass of super- charged air. In other words, the "air mass". At least on IC engines, the air-mass flow rate is the most important load parameter. The

sensors which are used for measuring air quantity or gas flows in general are also referred to as "anemometers".

Depending upon engine power, the aver- age maximum air-mass flow rate to be mea- sured is between 400 and 1200 kg/h. Due to the low air requirements at engine idle, the ratio of minimum to maximum flow is 1:90...1:100. The severe emissions and fuel- consumption requirements dictate accu- racies of 1...2% of the measured value. Re- ferred to the measuring range, this can easily correspond to a measuring accuracy of 10–4_,

a figure which is unusually high for the automobile.

The air though, is not drawn in continu- ously by the engine, but rather in time with the opening of the intake valves. Particularly with the throttle wide open (WOT), this leads to considerable pulsation of the air- mass flow, also at the measuring point which is always in the intake tract between air filter and throttle valve (Fig. 1). Intake-manifold resonance leads to the pulsation in the manifold sometimes being so pronounced that brief return flows can occur. This ap- plies in particular to 4-cylinder engines in which there is no overlap of the air-intake phase and the charge phase. An accurate flow meter must be capable of registering these return flows with the correct direction. 96 Flow meters Measured quantities

Flow meters