Arrangement and method for fixing a travel sensor in a vacuum brake power booster

A vacuum brake power booster (1) has an electric travel sensor (3) for monitoring the position of a movable wall (4) furnishing the boosting power of the brake power booster. The travel sensor (3) is mounted by a sensor receptacle (2) which is made of plastic material and which is sealed off with respect to the booster housing (10) by means of a seal. In order to assure effective sealing by creating a constant degree of compression of the seal (7) despite different material thicknesses of the booster housing (10), angled tabs (12) are formed against which locking projections (11) are abutted.

BACKGROUND OF THE INVENTION 
The invention is related to a vacuum brake power booster of a known type 
having a booster housing, preferably made of sheet or plate metal and with 
an electrical travel sensor for monitoring the position of a movable wall 
furnishing the boosting power, the sensor fixed in an opening providing in 
the booster housing by means of a sensor receptacle which is formed with 
locking projections extending out from the periphery of the opening and 
which is sealed off with respect to the booster housing by means of an 
elastic seal. 
A reliable sealing of the sensor receptacle with respect to the booster 
housing is of prime importance for a smooth functioning of the brake power 
booster. A force acting on the seal is required which leads to a 
deformation of that seal and depends in part, on the thickness of the 
material of which the booster housing is formed. In order to eliminate the 
effect of the material thickness, a two-part sensor receptacle has been 
devised whose parts are coupled to each other by means of a threaded 
connection so as to be adjustable. The considerable manufacturing and 
assembly costs of this complex, prior-art sensor receptacle is a 
disadvantage. 
It is therefore, the object of the present invention to improve a vacuum 
brake power booster by providing a sensor receptacle allowing manufacture 
and assembly at low cost but which is universally applicable for different 
material thickness of the booster housing. 
SUMMARY OF THE INVENTION 
According to the invention, this object is achieved in that means are 
provided for the booster housing opening which ensure a constant 
compression of the seal notwithstanding different material thicknesses of 
the booster housing. 
These means are constituted by partially formed angled tabs which interact 
with locking projections. The height of the angled tabs corresponds 
preferably to the distance between an annular surface on the sensor 
receptacle serving as an abutment surface for the external marginal range 
of the opening, and the front surface of the locking projections which 
interact with the internal periphery of the opening. 
In order to ensure a correct positioning of the sensor receptacle during 
mounting, a radial recess or groove may be provided in the periphery of 
the opening, which in the assembled condition accommodates a guide 
projection being molded to the sensor receptacle. 
Further details and advantageous features of the invention will be revealed 
by the following description of one embodiment, making reference to the 
accompanying drawing.

DETAILED DESCRIPTION 
The assembly which is illustrated in the drawing is composed of a vacuum 
brake power booster 1 whose booster housing 10 of formed metal is 
subdivided by an axially movable wall 4 into a vacuum chamber 15 and a 
ventable power chamber 16. An electrical travel sensor 3 is provided in 
order to monitor the position of the movable wall 4. The booster housing 
half which defines the vacuum chamber 15 and which is shown on the left, 
is furnished at its bottom with an opening 8 (FIG. 2). A sensor receptacle 
2, preferably made of plastic material, is inserted which accommodates the 
travel sensor 3 mentioned above. As will be appreciated in particular from 
FIGS. 2 and 4, the sensor receptacle 2 is provided, in a part projecting 
into the interior space of the booster housing 10, with a plurality of 
locking projections 11, which in the assembled condition of the sensor 
receptacle 2 within the booster housing 10 extend radially outwardly of 
the opening 8. 
An efficient sealing of the sensor receptacle 2 with respect to the booster 
housing 10 is provided by an elastic seal, preferably in the form of an 
O-ring 7, which is clamped in between the outer surface of the booster 
housing 10 and a facing annular surface 17 on the sensor receptacle 2. 
In order to fix the travel sensor 3 within the sensor receptacle 2, the 
sensor receptacle 2 is provided in with a radial circumferential groove 9 
a portion positioned outside the booster housing 10 which groove 9 
accommodates a retaining ring 6 securing the travel sensor 3. A sealing 
ring 5 is positioned within the sensor 3 with respect to the sensor 
receptacle 2. 
In order to ensure an effective sealing of the sensor receptacle 2 with 
respect to the booster housing 10, the O-ring 7 must be subjected to the 
effect of a constant compressive force which force has to be the same 
despite of different metal thicknesses of the formed booster housing 10. 
To obtain this effect, a plurality of partially formed tabs 12 (FIGS. 2, 
3) are provided at the booster housing 10 disposed about the periphery of 
the opening 8 which interact with the locking projections 11 of the sensor 
receptacle 2 and which so ensure a uniform compression of the O-ring 7. In 
this configuration, the height of the formed tabs 12 corresponds 
preferably to the distance between an annular surface 18 which is formed 
on the sensor receptacle 2 and which abut against the surface around the 
periphery of the opening 8 in the mounted condition. The front surface 19 
of each of the locking projections 11 are abutted against the outside of 
the formed tabs 12. 
In order to locate the sensor receptacle 2 in the correct orientation when 
mounting the sensor receptacle 2 is furnished with a radial guide 
projection 14 which is accommodated by a groove 13, which is provided in 
the periphery of the opening 8. This locates the locking projections 11 in 
alignment with the formed tabs 12.