Flow rate meter

A flow rate meter which serves to measure a quantity of air aspirated by an internal combustion engine via an air intake tube. The flow rate meter includes a housing, in which a flow conduit having a measuring body is disposed, the measuring body being pivotable about a bearing shaft in accordance with the flow of the medium counter to a restoring force and being joined via at least one strut to a damping body, which in the form of a movable wall defines a damping chamber with respect to the flow conduit. A retaining groove is embodied in the damping chamber wall and is form-fittingly engaged by a retaining section of an elastic stop body. A stop section of the stop body protrudes into the damping chamber and limits the movement of the damping body.

BACKGROUND OF THE INVENTION 
The invention is directed to a flow rate meter. A flow rate meter is 
already known in which, when the flow rate meter is used in the intake 
tube of an internal combustion engine, an elastic stop which intercepts 
the measuring body is provided in order to damp recoiling in the intake 
tube. In this apparatus, the danger still exists that in unfavorable 
cases, deformation of the measuring body will still take place. 
Furthermore, these stops have an unfavorable effect on the flow behavior 
and cause pressure losses. 
OBJECT AND SUMMARY OF THE INVENTION 
The flow rate meter according to the invention has the advantage over the 
prior art that if the flow direction of the medium to be measured suddenly 
changes counter to the measuring direction, the movement of the measuring 
body beyond its zero position is braked and damped by a stop body without 
harmfully deforming the measuring body. Furthermore, the stop body neither 
unfavorably affects the flow behavior nor causes pressure losses. 
Advantageous further embodiments of the flow rate meter disclosed are 
possible. It is particularly advantageous for a retaining groove to be 
engaged in a form-fitting manner by the stop body, with a retaining 
section thereof, while a stop section of the stop body protrudes into the 
damping chamber. As a result, the retaining body is easily mounted, and 
additional securing means are not required.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the flow rate meter shown in the drawing, the quantity of air aspirated 
by an internal combustion engine, for example, flows in the direction of 
the arrow 1 via a flow conduit 3 embodied in the housing 2 to the 
individual cylinders of the engine, not shown. A measuring body 5, of the 
flow rate meter is embodied for instance as a flat plate, having the same 
shape as the flow conduit at the zero position of the measuring body, is 
disposed in the flow conduit 3 and is pivotably supported about a bearing 
shaft 6, which is supported on one side of the flow conduit 3 in the 
housing 2. The cross section of the flow conduit increases downstream of 
the opening which permits air to flow by the measuring body as the air 
flow moves the measuring body. To enable this pivoting, a hub 7 is joined 
to the bearing shaft 6, and a damping body 8 is joined to the hub 7 and is 
engaged by one end of at least one strut 9 with the other end of the strut 
connected to the back side of the measuring body 5. The damping body 8, 
which is likewise embodied as a flat plate, serves to damp the effect of 
pulsations in the medium and likewise extends pivotably about the bearing 
shaft 6 in a damping chamber 10, which is defined with respect to the flow 
conduit 3 by the damping body 8, in the form of a movable wall. The 
deflection of the measuring body 5 in the measuring direction is caused by 
a quantity of air approaching from the direction of the arrows 1, and 
takes place counter to the spring force of a spiral spring engaging the 
bearing shaft 6 but not shown in the drawing. The angular position of the 
measuring body 5 or in other words of the bearing shaft 6 may be picked up 
electrically, for instance, by a potentiometer as a measure of the 
quantity of air flowing past the measuring body 5,. A fixed housing wall 
12 surrounds and contacts the hub 7 in such a manner that in the pivoting 
range of the measuring body 5 a leakage gap 13 formed between the hub 7 
and the housing wall 12 communicates on the one hand with the damping 
chamber 10 and on the other with the flow conduit 3 downstream of the 
measuring body 5, so that because of the equal pressure at both ends of 
the leakage gap 13, no air flow takes place in the leakage gap 13. The 
strut 9 between the measuring body 5 and the damping body 8 is spaced 
apart radially from the housing wall 12. 
Because of recoiling in the intake tube, a relatively high pressure can 
occur in the intake tube, causing a movement of the measuring body 5 
counter to the normal air flow direction 1. This movement of the measuring 
body 5 counter to the measuring direction must be retarded and damped in a 
suitable manner, in order to prevent damage to the flow rate meter. 
To this end, in accordance with the invention an elastic stop body 16 is 
supported on the damping chamber wall 15 in such a manner that when the 
medium is not flowing the damping body 8 rests on the stop body 16. In 
this position, the measuring body 5 is retained in its zero position. In 
the event of a forceful closing movement of the measuring body 5, caused 
by occasional intake tube recoiling, the stop body 16, which is made for 
instance from rubber or plastic, effects a damped stopping of the movement 
of the damping body 8 within allowable values and causes an overswing on 
the part of the damping body 8 and the measuring body 5 beyond the zero 
position without any attendant damage. The stop body 16 has a stop section 
17 protruding into the damping chamber 10 at its end, in the vicinity of 
but outside the flow conduit 3, and a retaining section 19 which 
form-fittingly engages a retaining groove 18 in the damping chamber wall 
15. With its rear surface 20 remote from the damping body 8, the stop 
section 17 of the stop body 16 is supported on a support protrusion 21 of 
the housing 2. The stop body 16 is retained in the retaining groove 18 
because the transition 22 between the stop section 17 and the retaining 
section 19 of the stop body 16 is narrowed in the same manner as is the 
opening 23 of the retaining groove 18 toward the damping chamber 10 as 
compared with the adjoining area of the retaining groove. The damping 
behavior of the stop body 16 can be adapted to requirements by appropriate 
selection of its material and shape. The disposition of the stop body 16 
outside the flow conduit 3 in accordance with the invention has the 
advantage that no additional pressure drop takes place, and the stop body 
16 can simply be inserted form-fittingly into the retaining groove 18 
parallel to the bearing shaft 6 during mounting, and a change in the 
position of the stop body 16 parallel to the bearing shaft 6 is prevented 
by the cover (not shown) of the flow rate meter, which in the mounted 
state lies parallel to the plane of the drawing and covers the flow 
conduit and the damping chamber. 
The foregoing relates to a preferred exemplary embodiment of the invention, 
it being understood that other variants and embodiments thereof are 
possible within the spirit and scope of the invention, the latter being 
defined by the appended claims.