Measuring and testing – Engine detonation – Specific type of detonation sensor
Patent
1996-08-01
1998-04-28
Chapman, John E.
Measuring and testing
Engine detonation
Specific type of detonation sensor
G01L 2322
Patent
active
057446989
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to an improvement on accelerometric sensors, and more particularly on sensors of the piezoelectric type used to detect and measure the piston knock of internal combustion engines.
Currently, accelerometric sensors of the non-resonating type are used to measure the piston knock of internal combustion engines, making it possible to measure the intensity of the vibrations which occur in the cylinder heads of the engine as a result of this phenomenon. The advantage of these types of sensors resides in their frequency response curve, which has an area in which their sensitivity is substantially constant as a function of the frequency. This usable range is limited to the higher frequencies because of the non-linearity generated by the resonance frequency of the sensor on its mount. But electronic control of engines requires measurement of the vibrations which reveal the presence of piston knock over a wider and wider range of frequencies.
For example, an accelerometric sensor known from the European patent 0 184 666, as shown in FIG. 1A, which represents the state of the art, is constituted by a base 10 in the form of a bushing 11 which ends in a flange 12 on which are stacked a piezoelectric washer 2 placed between two connecting disks 3 and a seismic mass 4, which stack is prestressed by an elastic washer 5 and a nut 6 screwed onto the bushing. Sensors of this type, which are widely used in automotive electronics, typically have a resonance frequency on the order of 12 to 15 Khz, which limits the measurement of piston knock to frequency ranges lower than 10 Khz. Various solutions have been proposed for raising the resonance frequency of this type of sensor to higher frequencies. Some examples which may be cited are the use of greater prestressing on the stack, which has the drawback of causing accelerated aging of the piezoelectric crystal, which reduces the reliability of the sensor, or the use of more rigid materials such as beryllium for the base plate, which increases the cost of the sensor, or even the application of a layer of grease, adhesive or polymer between the sensor and the surface on which it is mounted, which involves an added operation that is difficult to control.
SUMMARY OF THE INVENTION
The object of the present invention is to propose a solution which is simple, economic and easy to implement industrially.
This object of the invention is achieved by means of an accelerometric sensor of the type constituted by a base having the form of a bushing extended by a flange whose upper surface defines a shoulder on which are stacked at least one piezoelectric washer, connecting disks and a seismic mass, and whose lower surface is in contact with a part to be measured. According to the invention, the lower surface of the flange has a central recess such that the average diameter of the load distribution on the contact surface is greater than or equal to the average diameter of the shoulder.
According to a first embodiment of the present invention, the contact surface between the lower surface of the flange and the part has an annular shape whose internal diameter is greater than the external diameter of the bushing, and whose average diameter is at least equal to the average diameter of the shoulder.
According to one characteristic of this embodiment, the lower surface of the flange has a recess coaxial to the bushing with a diameter larger than the external diameter of the bushing.
According to a second embodiment of the present invention, the lower surface of the flange has a concavity coaxial to the bushing which extends across at least part of its surface.
The sensor according to the invention is intended to be mounted on a part by means of a bolt passing through the bore of the bushing. According to a remarkable characteristic of the invention, the area of the contact surface is determined in such a way as to avoid any permanent plastic deformation of the opposing surfaces due to the pressure exerted by the b
REFERENCES:
patent: 4961338 (1990-10-01), Komurasaki
patent: 5440933 (1995-08-01), Brammer et al.
Chapman John E.
Greenberg Laurence A.
Lerner Herbert L.
Siemens Automotive S.A.
LandOfFree
Accelerometric sensor for measuring the piston knock of an inter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Accelerometric sensor for measuring the piston knock of an inter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Accelerometric sensor for measuring the piston knock of an inter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1533593