Measuring and testing – Engine detonation – Specific type of detonation sensor
Reexamination Certificate
1999-06-02
2001-04-24
Kwok, Helen (Department: 2856)
Measuring and testing
Engine detonation
Specific type of detonation sensor
C073S654000, C073S702000
Reexamination Certificate
active
06220078
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a vibration pickup with a pressure sleeve.
Vibration pickups of the above mentioned general type are known in the art. One of such vibration pickups with a pressure sleeve is disclosed for example in the German patent document DE 195 24 147.9. It is formed as a knock sensor for monitoring the operation of an internal combustion engine in a motor vehicle. The pressure sleeve is joined through an abutment region fixedly to a component which causes vibrations, for example a motor block of the internal combustion engine.
The vibrations to be detected are knock noises of the internal combustion engine during the operation. They are transmitted through a pressure sleeve to a piezo-ceramic disk as a sensor element, with intermediately located contact disks and insulating disks which allow picking up of a signal, so as to form an evaluatable electrical output signal.
This type of mounting or clamping of the sensor element on the pressure sleeve and the mounting of the pressure sleeve on the vibrating component has a great influence on the manufacture. The clamping of the sensor element together with a plurality of individual components, for example with a spring and a seismic mass is performed in the known vibration pickup with a threaded ring which is screwed on the corresponding thread of the pressure sleeve and directly abuts on the seismic mass.
The clamping of the components on the pressure sleeve is a substantial cost factor. All components must be firmly compressed with a defined mechanical pre-tensioning and remain so. When the pre-tensioning changes, also the transmission characteristic line changes and the evaluation becomes more difficult.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a vibration pickup which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated in a vibration pickup with a pressure sleeve, a sensor element and a spring, in which between the inner periphery of the ring-shaped spring and the outer wall of the pressure sleeve a wedge ring is arranged so that its wedge-shaped tipped side is mounted axially and it clamps the spring in its end position and also holds simultaneously the components with the sensor element under an axial pre-tensioning.
When the vibration pickup is designed in accordance with the present invention, it can be produced with relatively simple manufacturing steps and at the same time has a great strength. With the wedge ring arranged between the ring-shaped spring and the wall of the pressure sleeve, a reliable connection of the components of the pressure sleeve is provided in a simple manner.
The wedge ring with its wedge-like tipped side clamps in its end position the spring radially and simultaneously provides an axial pre-tensioning required for the sensor element in simple and reliable manner.
It is especially advantageous when the wedge ring is axially slotted. Thereby, an insertion is possible with great manufacturing tolerances. This embodiment has the advantage that during final injection molding of the arrangement, synthetic plastic can penetrate through the slots into the inner region between the pressure sleeve and the seismic mass.
The above mentioned intermediate spaces are produced when in accordance with another embodiment of the present invention at least three wedges are arranged between the inner periphery of the ring-shaped spring and the outer wall of the pressure sleeve. They are inserted with their wedge-shape tipped side axially and in their end position clamp the spring radially in the same way as in the first embodiment. The wedges can be formed in an advantageous manner as circular segments, wedges with straight contour, or wedge pins.
In order to guarantee the stability of the connection between the pressure sleeve and the wedge ring or the wedge, the wedge ring or the wedge are composed of a material, with which after clamping of all components of the vibration pickup, the spring and the barb on the pressure sleeve are kneaded in the wedge ring or the wedge. Such a good fixing of the wedge ring or the wedge means that the characteristic line of the vibration pickup over a service life can be maintained very stable.
An especially good seat of the wedge ring or the wedge is obtained when the gripping surface of the wedge ring or the wedge on the pressure sleeve has a rough surface contour. For example a groove, a thread or a wafer pattern can be provided, with which a fixed seat even in condition of high shaking movements of the vibration pickup can be guaranteed in a simple manner.
In accordance with a further alternative embodiment of the invention, in advantage manner a ring with an inner thread and a wedge-shape projection is mounted between the inner periphery of the ring-shaped spring and the outer wall of the pressure sleeve. It is turned in axially with its wedge-shape tipped side and in its end position radially clamps the spring as in the above described embodiment. With this embodiment the clamping of the components is guaranteed by the thread, since here no self-locking projection can be provided by the wedge shape. The lower wedge-shaped tip of the ring serves first of all for centering of the components on the pressure sleeve. Thereby also a relatively flat angle of the wedge-shape of the flat angle is possible.
The wedge-shaped tip of the ring of the above mentioned embodiment can be straight or for example has a substantially concave, convex, parabolic or hyperbolic contour.
In a deviation from the above described embodiment, a ring with an inner thread and a step projection can be mounted between the inner periphery of the ring-shaped spring and the outer wall of the pressure sleeve. With its tip side having at least one step it is turned-in axially, and radially clamps the spring in its end position and therefore centers it in advantageous manner. Metal, for example steel can be selected as a material for the wedge ring, the wedges or the ring with an inner thread.
In accordance with a preferable embodiment, the wedge ring or the wedges are composed of synthetic plastic. This has the additional advantage that the electrical insulation of the sensor element from the pressure sleeve is simultaneously provided. The originally required upper insulation disk on the sensor element can be dispensed with. Since the signal pickup can be withdrawn directly from the metallic seismic mass, also the upper contact disc can be spared.
When in the inventive vibration pickup a wedge ring of synthetic plastic is used, the acoustic properties of the vibration pickup are also improved. The structure-born noise which reaches the vibration pickup from outside can be coupled by the bottom support of the vibration pickup and in this way by the screwing can be substantially dampened from above through the insertion of the synthetic plastic wedge ring or the wedges.
The wedge ring or the wedges can be welded after the mounting without additional holding means in a simple manner, in particular by laser welding. With the above described arrangement of the wedge ring or the wedges, a pre-tensioning is provided, which makes possible an intermediate measurement of the vibration pickup. Then after the completed welding, the injection molding with the synthetic plastic mass provides a final vibration-fixed mounting.
In an advantageous embodiment, the vibration pickup is formed as a knock sensor for vibrations on a motor block of an internal combustion engine.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 4
Brammer Hartmut
Krebs Holger
Schmidt Wolfgang
Kwok Helen
Robert & Bosch GmbH
Striker Michael J.
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