Flow detector with a housing

[0001] This application claims the priority of European application 08006853.9, filed Apr. 4, 2008, as well as of U.S. provisional application 61/123,487 filed Apr. 9, 2008, the disclosure of both of which is incorporated herein by reference in its entirety.

[0002] The invention relates to a flow detector with a housing, an inlet and an outlet. It also relates to an assembly of such a flow detector and a support plate.

[0003] An embodiment of such a flow detector is shown in US 2004/0118218. It comprises a housing having opposite first and second sides. An inlet and an outlet for the fluid are arranged at the first side of the housing. The inlet and outlet are connected by means of a flow channel arranged in the housing. A sensor chip is located at a side of the flow channel and measures the flow therein. At the second side of the housing, electrical connectors are provided for connecting the flow detector to an external system. The connectors extend from the second side of the housing and can e.g. be soldered into a printed circuit board. The connectors are held in a filler material of glass, which, however, may be damaged when mechanical strain is exerted to the housing.

[0004] It is therefore an object of the present invention to provide a flow detector of this type with higher mechanical stability.

[0005] In a first aspect of the invention, this object is achieved by a flow detector comprising

[0006] a housing having opposite first and second sides,

[0007] an inlet and an outlet for said fluid arranged at the first side of said housing,

[0008] a flow channel arranged in said housing and connecting said inlet and said outlet,

[0009] a sensor chip arranged at said flow channel and adapted to measure said flow in said flow channel,

[0010] electrical connectors connected to said sensor chip for connecting said flow detector to an external system, wherein said connectors extend from the second side of said housing, and

[0011] a plurality of tongues, in addition to said connectors, extending away from the second side of said housing for mechanically mounting said housing to an external support.

[0012] In a second aspect of the invention, this object is achieved by a flow detector comprising

[0013] a housing having opposite first and second sides,

[0014] a hood formed by a single plastic piece and forming said first side of said housing,

[0015] an inlet and an outlet for said fluid arranged at the first side of said housing, wherein said inlet and said outlet are integrally attached to said hood and extend away from said hood,

[0016] a flow channel arranged in said housing and connecting said inlet and said outlet,

[0017] an internal printed circuit board arranged in said hood,

[0018] a sensor chip arranged on said internal printed circuit board at said flow channel and adapted to measure said flow in said flow channel,

[0019] electrical connectors connected to said sensor chip for connecting said flow detector to an external system, wherein said connectors extend from the second side of said housing and are mounted to said internal printed circuit board, and

[0020] a plurality of tongues, in addition to said connectors, integrally connected to said hood and extending perpendicularly to said internal printed circuit board away from the second side of said housing for mechanically-mounting said housing to an external support.

[0021] In a third aspect of the invention, the object is achieved by an assembly of a flow detector for measuring a flow of a fluid and a support plate, said assembly comprising

[0022] a housing having opposite first and second sides, with said second side lying against a surface of said support plate,

[0023] an inlet and an outlet for said fluid arranged at the first side of said housing and extending in a direction perpendicular to said support plate,

[0024] a flow channel arranged in said housing and connecting said inlet and said outlet,

[0025] a sensor chip arranged at said flow channel and adapted to measure said flow in said flow channel,

[0026] electrical connectors connected to said sensor chip connecting said flow detector to said support plate, wherein said connectors extend from the second side of said housing into said support plate, and

[0027] a plurality of tongues, in addition to said connectors, extending perpendicularly to said support plate and away from the second side of said housing into openings in said support plate for mechanically mounting said housing to said support plate.

[0028] Accordingly, a plurality of flexible tongues is provided, in addition to the connectors, extending away from the second side of the housing, i.e. extending into a direction away from said housing. These tongues can be used for mechanically mounting the housing to an external support, i.e. a support external to said housing, such as to the printed circuit board mentioned above. Accordingly, mechanical strain can now be received by the tongues, which allows the detector to withstand additional strain.

[0029] Advantageously, the tongues have free ends suited for insertion into openings of the external support. Advantageously, they have a comparatively thin neck and a comparatively thick head, with the neck extending from the second side of the housing to the head. Such tongues allow to anchor the detector in suitably sized holes of the support and to hold it therein against pulling forces perpendicular to the support surface. However, in an alternative embodiment, the tongues may also have constant or tapering diameter if they are to secure the device against lateral movements.

[0030] In a further advantageous embodiment, one or more pegs are provided at the second side of the housing, in addition to the connectors and the tongues. These pegs project perpendicularly from the second side of the housing. The diameter of the pegs remains constant or decreases with increasing distance from the second side of the housing. Such pegs allow to secure the detector in suitably sized holes of the support and to hold it therein against shearing forces parallel to the support surface.

[0031] Advantageously, the housing comprises a hood forming its first side, with the tongues and/or pegs being integrally attached to the same. Such a design allows to transfer mechanical strain from the first side of the housing (such as exerted by tubes attached to the inlet and outlet) directly to the support.

[0041] The detector of FIGS. 1-6 comprises a housing generally denoted by 1 having a first side 2 (FIG. 3) formed by a first, substantially flat surface of the housing and a second side 3 (FIG. 1) formed by a second, substantially flat surface of the housing. An inlet 4a and an outlet 4b (FIG. 3) project from first side 2, each formed by a hollow stub suited for being connected to a tube guiding the fluid. A series of electrical connectors 5, each formed by a metal pin 6, project perpendicularly from second side 3 of housing 1 (FIG. 1).

[0042] As can best be seen from FIG. 2, housing 1 comprises a hood 7, which forms first side 2. Hood 7 is a single plastic piece e.g. manufactured by injection molding. Hood 7 carries at least two, advantageously four tongues 8, which extend from second side 3. They serve to mechanically mount housing 1 to a support or support plate 10, such as an external printed circuit board, as shown in FIG. 5. Support or support plate 10 is external to housing 1, i.e. not an integral part thereof. Second side 3 of housing 1 rests against a surface of support plate 10.

[0043] The tongues 8 as well as inlet 4a and outlet 4b are integrally attached to hood 7, i.e. hood 7, tongues 8, inlet 4a and outlet 4b are a single piece of material.

[0044] As can be seen e.g. from FIG. 3, the subs of inlet 4a and outlet 4b extend parallel to the tongues 8, namely in a direction perpendicular to the surface of the second side 3 of housing 1 as well as perpendicular to support plate 10.

[0045] As can be seen from FIG. 2, hood 7 forms a recess 11, which receives a plate 12, e.g. a printed circuit board. To distinguish this printed circuit board from the external printed circuit board formed by plate 10, it is called the internal printed circuit board.

[0046] As can be seen from FIGS. 4 and 5, plates 10 and 12 are arranged parallel to each other. Plate 12 carries on a first side 13 thereof, a sensor chip 14. Sensor chip 14 is e.g. a thermal flow sensor such as described in US 2002/0043710. The backside of sensor chip 14 lies flush against plate 12, while the front side of sensor chip 14, which carries the flow sensing elements, is facing a flow channel 16 that connects inlet 4a with outlet 4b. Plate 12 also carries the connectors 5, i.e. the connectors 5 are mounted to plate 12. The connectors 5 project from a second side 14 of plate 12. Leads on plate 12 as well as bond wires are used to electrically connect the connectors 5 to contact pads on sensor chip 14.

[0047] Plate 12 forms part of the second side 3 of housing 1. It is held in recess 11 by a frame 17, which is also inserted into recess 11 and has been welded to its walls. Frame 17 pushes against second side 14 of plate 12, thereby holding it in place. A sealing ring 18 of an elastic material, such as silicone, is arranged between frame 17 and plate 12 for preventing the fluid from exiting at second side 3 of housing 1. Sealing ring 18 in particular covers a gap 19 between the outer rim of plate 12 and the inner walls of hood 7 for sealing the same. Sealing ring 18 obviates the need for a fluid tight seal right at the rims of flow channel 16—such a seal would be difficult to achieve, in particular in the region of sensor chip 14.

[0048] Flow channel 16 is formed as a groove extending along an inner side of a wall 20 of hood 7. Wall 20 forms first side 2 of housing 1. Flow channel 16 is covered by plate 12 and sensor chip 14.

[0049] The design of the inner side of wall 20 is best seen from FIG. 6. Apart from the groove forming flow channel 16, wall 20 further comprises a recess 21, which serves to provide room for the bond wires and a protective glob used to connect sensor chip 14 to plate 12.

[0050] As can be seen from FIG. 6, flow channel 16 extends in a plane parallel to first side 2 of housing 1. It has a first end 23 connected to inlet 4a and a second end 24 connected to outlet 4b. First end 23 and/or second end 24, advantageously both of them, are looped around at least 180° of inlet 4a and outlet 4b, respectively. In this context, “looped around at least 180°” means that, the path of the end section is wound at least around 180° of the circumference of the inlet and outlet, respectively.

[0051] This allows to increase the actual length of flow channel 16, which in turn decreases the risk of turbulences at the location of semiconductor chip 14.

[0052] Hood 7 of housing 1 is further provided with screw holders for receiving attachment screws or attachment pins, which allow, if necessary, to mount housing 1 more securely to a support. In the embodiment shown here, two types of screw holders are provided, which will in the following be called “first screw holders” and “second screw holders”. The first screw holders 26 extend parallel to first side 2 and second side 3 of housing 1, while the second screw holders 27 extend perpendicular thereto. Thus, the first screw holders are structured to hold a screw parallel to first side 2 and second side 3, while the second screw holders are structured to hold a screw perpendicular thereto. To allow to mount the same housing 1 in two different orientations, namely with side 3 parallel to a support 10, such as shown in FIG. 5 (where the second screw holders 27 can be used to attach hood 7 to base 10), or with side 3 perpendicular to support 10, such as shown in the embodiment of FIG. 8 (where the first screw holders 26 can be used to attach hood 7 to base 10).

[0053] As can be seen, the embodiment shown here has a total of four screw holders, namely one first and one second screw holder on a third side 30 of housing 1 (FIG. 3), and one first and one second screw holder on a fourth side 31 of housing 1, with third side 30 being opposite to fourth side 31 and both of them being perpendicular to first side 2 and second side 3 of housing 1.

[0054] A larger number of screw holders could be provided as well, in particular for large housings 1.

[0055] Each first screw holder is formed by a first through-hole through hood 7 and each second screw holder 27 is formed by a second through-hole through hood 7. The through-holes are adapted to e.g. receive a screw or pin. In order to achieve a compact design, the first through-hole and the second through-hole on the same side of housing 1 intersect.

[0056] As mentioned, the tongues 8 serve to anchor housing 1 in support 10 and to secure it against pulling forces. For this purpose, each tongue 8 is provided with a thin neck 34 and a thicker head 35 (FIG. 1). Neck 34 extends between hood 7 of housing 1 and head 35. Head 35, whose maximum diameter exceeds the diameter of neck 34, is wedge-shaped and tapered towards its end 36 facing away from housing 1. Hence, each tongue 8 can easily be inserted into suitably positioned and sized openings 37 in support 10 (see FIG. 5), where they snap in once that head 35 has passed fully. Hence, the heads 35 form hooks that hold housing 1 tightly in support 10, securing it against pulling forces.

[0057] For inserting the tongues 8 into the holes 37 of support 10, the tongues need to be deformed laterally. To facilitate such a deformation, each tongue is mounted in a recessed section 38 of the side walls of hood 7, as shown in FIGS. 1 and 3, which allows to increase the length of neck 34, thereby making it more resilient.

[0058] As can best be seen from FIG. 6, the tongues are arranged “with rotational asymmetry in respect to any axis of rotation extending through the first and second side of the housing”. This is to be understood such that there is no axis of rotational symmetry perpendicular to the first and second side 2, 3 of housing 1. In other words, on a support 10 parallel to first and second side 2, 3, the detector can be mounted in a single orientation only if the tongues 8 are to be inserted into the openings 37. Thereby it can be assured that the measured signal has the correct sign and the connector 5 is oriented properly. In the embodiment of FIG. 6, this is achieved by placing one tongue closer to the longitudinal axis 40 of housing 1 than the other tongues.

[0059] The resilience of the necks 34 facilitates the insertion of the tongues 8 into the holes 37, but it renders the tongues 8 poorly suited to withstand lateral forces against housing 1. In addition to this, the holes 37 in support 10 must have a larger diameter than the necks 34 for allowing passage of the heads 35, which can give rise to lateral play of the fully inserted housing 1. Hence, in addition to the tongues 8, housing 1 comprises at least one, advantageously at least two, pegs 41 projecting perpendicularly from second side 3. These pegs 41 can best be seen in FIGS. 1 and 6. Each peg 41 has a diameter that remains substantially constant or decreases with increasing distance from second side 3 of housing 1, such that it can be inserted tightly into a suitably sized hole 42 of support 10 (FIG. 5). The pegs 41 are therefore able to secure housing 1 against lateral movements in respect to support 10.

[0060] The pegs 41 are, as the tongues 8, integrally attached to hood 7.

[0061] As mentioned, the connectors 5 are formed by a plurality of pins 6. In the embodiments shown here, the pins 6 are arranged in a single line. They project perpendicularly from second side 3 of housing 1.

[0062] If the detector is to be mounted in the position of FIG. 5, the pins 6 are advantageously straight such that they can be inserted into suitable openings in position 10.

[0063] If, however, the detector is to be mounted on a support 10 perpendicular to first side 2 and second side 3, angled pins 6′ have to be used, as shown in FIGS. 7 and 8. These angled pins have a first section 10a extending substantially perpendicularly from second side 3 of housing 1 and a second section 10b extending at a right angle to first section 10a.

[0064] While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practised within the scope of the following claims.