Abstract:
An air-pressure sensor for side-impact sensing, and a pressure-entry channel, which conveys the air pressure to a pressure-sensor element. The pressure-entry channel has multiple angles.

Description:
BACKGROUND INFORMATION  
       [0001]    A pressure sensor for side-impact sensing in which a channel allows the air to flow directly onto a sensor element is described in German Patent Application No. DE 199 23 985. The sensor element can be protected by a diaphragm. The channel is realized with the aid of a plurality of housing components. 
       SUMMARY OF THE INVENTION  
       [0002]    The air-pressure sensor for side-impact sensing according to the present invention has the advantage over the related art that the pressure-entry channel has multiple angles. This prevents the entry of all types of media or makes such entry more difficult. In particular, the dynamics in the transmission of the pressure increase in the event of a crash are not affected. 
         [0003]    An air-pressure sensor is screwed onto a panel in the side door of a vehicle via two holding brackets. The opening of the pressure-entry channel is always oriented such that a pressure increase in the wet zone of the door is able to be detected. The task of the entry channel is to ensure the transmission of the pressure increase in the wet region of the door to the surface of a pressure-measuring element, preferably a pressure diaphragm. The pressure diaphragm is also to be protected from media influences as much as possible, which means the ingress of dust, water and oil. The normal conditions in the wet region of the side door of a vehicle must not affect the functioning of the pressure sensor over the service life. All currently provided pressure sensors with an application area in crash sensor systems have the problem of allowing only very limited protection of the sensor diaphragm against contact by media. Tests have shown that some of the conventional entry channel designs allow spray water or dust to be transmitted to the sensor element virtually unhindered. One possibility for protecting the diaphragm from media theoretically is the passivation with the aid of silicon gels. However, a silicon gel on the diaphragm leads to an increased acceleration sensitivity of the system. 
         [0004]    Therefore, the design approach according to the present invention is provided, and the pressure-entry channel has a plurality of angles. In this way, there is no direct or indirect flight path for media particles that are able to travel up to the pressure-measuring diaphragm via a single reflection or no reflection. According to the present invention, the multiple angles require the spray water droplets or other media particles to be reflected at the wall of the housing lid at least three times in order to reach the interior of the sensor and thus the diaphragm. As a result, the occurrence of a transport process for media particles, reflected multiple times, is less likely by an order of magnitude than the mostly straight flight of a media particle. The dynamics of the pressure increase are ensured by sufficient clearance of the walls. 
         [0005]    Furthermore, the design of the present invention makes it possible to prevent the intrusion of wire. This satisfies the so-called IPX3 protection category. 
         [0006]    It is especially advantageous that the pressure-entry channel has three 90° angles. This is a very efficient angling for the purpose of preventing the ingress of media. 
         [0007]    The pressure-entry channel is preferably formed by a hollow cylinder on the housing of the air-pressure sensor and a lid having at least two openings, the lid being mounted above the hollow cylinder. Thus, the hollow cylinder is part of the pressure-entry channel, which, for example, guides the pressure increase onto the sensor element. Due to the lid that surrounds this hollow cylinder and which itself has at least two openings, the pressure is able to penetrate the space defined by the lid and the hollow cylinder. To penetrate the hollow cylinder, the pressure must be reflected at the walls of the hollow cylinder and the lid multiple times. This provides an efficient protection against the ingress of media to the pressure-sensor diaphragm. 
         [0008]    Furthermore, it is advantageous that at least one opening of the at least two openings is at least partially open in the upward direction in the mounted state in order to prevent icing up of at least this upper opening and to ensure the operability of the air-pressure sensor in this manner. 
         [0009]    The lid has preferably four openings and is also provided with an affixation plate, which has a bore hole for the hollow cylinder, so that the hollow cylinder is able to penetrate the lid through this bore hole. The affixation plate is permanently joined to the housing. This may be implemented by, for example, a type of welding or bonding or screwing. Other affixation means are also possible here. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  shows a block diagram of a safety device in a motor vehicle. 
           [0011]      FIGS. 2   a  and  2   b  show a representation of the air-pressure sensor with regard to its lid in the installed and de-installed state. 
           [0012]      FIG. 3   a  shows a sectional view through the air-pressure sensor according to the present invention. 
           [0013]      FIG. 3   b  shows an additional exploded view of the air-pressure sensor according to the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  schematically elucidates the configuration of a safety device in a vehicle that utilizes the air-pressure sensor according to the present invention. Vehicle FZ has a central air bag control device ECU. If air bag control device ECU itself has sensors such as acceleration or rate-of-rotation sensors, the usual installation location is the vehicle tunnel. If these sensors are not provided in control device ECU, then other installation locations in the vehicle may be selected as well. 
         [0015]    Control device ECU receives signals from acceleration sensors UFS 2  installed on the vehicle front, acceleration sensors PAS 4  installed on the vehicle sides, and pressure sensors PPS 1  installed in side components, preferably doors, of the vehicle, as a function of which control device ECU triggers personal protection means such as air bags or belt tighteners, which are not shown. 
         [0016]    More or fewer than the sensors shown there may be installed. In particular, it is possible to use four air-pressure sensors per vehicle. Acceleration sensors PAS 4  are used, for instance, to subject the decision made on the basis of the air-pressure signal to a plausibility check. The acceleration sensors may be placed in the B-column as usual. 
         [0017]      FIG. 2   a  shows the air-pressure sensor in the installed state. A lid  20  is mounted above a hollow cylinder  21  of the housing of the air-pressure sensor, an affixation plate  23  being permanently joined to housing  22 , for example by welding. Hollow cylinder  21  is visible through an opening  24 . 
         [0018]      FIG. 2   b  shows an exploded view of the air-pressure sensor according to the present invention. Lid  20  with bottom plate  23  and opening  24  is now separated from housing  22  having hollow cylinder  21 . Element  36  is a silicon seal. This seal  36  separates the electronics space in the interior of the sensor from the region of the pressure-sensor chip, which is in contact with the outside via the air in the pressure channel. With that, protection from atmospheric humidity is realized. 
         [0019]      FIG. 3   a  shows a sectional view of the air-pressure sensor according to the present invention. Lid  31  is permanently mounted on housing  39  via a base plate  38 . Lid  31  and housing  39  thus form air-pressure sensor  30 . Lid  31  has openings  32  and  34  through which a pressure increase is able to penetrate the interior of the air-pressure sensor. Lower opening  34 , in particular, may ice up in the process. The change in air pressure exposes itself in the channel formed by the hollow cylinder and lid  31  into hollow cylinder  33  to a sensor element. 
         [0020]      FIG. 3   b  shows an additional exploded view of the air-pressure sensor according to the present invention. A lid  31  is affixed on housing  39  above hollow cylinder  33 , which is part of housing  39 . To this end, base plate  38  is then permanently joined to the air-pressure sensor in the corresponding depression in housing  39 . The hollow cylinder can be seen through opening  32 . This completes the production of air-pressure sensor  37 .