Piezo multilayer sensors are used as energy converters to generate electrical energy from mechanical energy. If the mechanical energy is present in the form of wide band mechanical vibrations, it is difficult to couple these to the piezo sensor in the optimal manner.
Conventional devices are energy converters, which use mechanical lever transmission with a constant transmission ratio V=constant. The vibration acts from outside on the housing G, shown in
A conventional mechanical transmitter converts the movements and forces as follows:
with
xIn Deflection acting on the mechanical transmitter
xOut Deflection generated by the mechanical transmitter
FIn Force acting on the mechanical transmitter
FOut Force generated by the mechanical transmitter. The force amplitude FPiezo, which acts during an external vibration of amplitude x with a frequency f (ω=2πf) of the housing G on the energy converter, is expressed as follows:
with
k Stiffness of the piezo converter
x Amplitude of the vibration stroke
ω Angular frequency of the vibration
m Vibrating mass
FPiezo Resulting force on the piezo converter.
To adapt this apparatus in the optimal way to this vibration x*sin(ωt), the lever transmission Vmax must be selected in accordance with the following condition:
This condition states that, for a given vibrating mass m and given converter stiffness k, the optimal transmission ratio Vmax depends on the frequency ω of the vibration. This means that with a changing vibration frequency w the mechanical lever transmission V would also have to be adapted accordingly, in order exert a maximum force on the piezo element and thereby an optimal conversion into electrical energy.
One potential object is to provide an apparatus which, for a wide range of frequencies and amplitudes of mechanical vibrations, brings about an effective adaptation to a piezo sensor energy.
The inventors propose methods and devices in which a transmission ratio (V) is variably provided. The transmission ratio is the ratio of the deflection of the vibrating mass to the extension of a piezo actuator by this deflection.
Specifically, the inventors propose that a seismic mass or vibrating mass is clamped between at least two piezo sensor units in a housing frame or housing. In particular the piezo sensor units and the vibrating mass are arranged along a straight line. The vibrating mass is especially positioned in the center between the piezo sensor units allowing it to vibrate.
In accordance with a further advantageous embodiment a piezo sensor unit is a piezo sensor clamped into a spring.
In accordance with a further advantageous embodiment the piezo sensor is a piezo multilayer sensor.
In accordance with a further advantageous embodiment the spring is a tubular spring.
In accordance with a further advantageous embodiment the vibrating mass is able to be deflected at right angles to a longitudinal direction.
In accordance with a further advantageous embodiment a transmission ratio of a deflection of the vibrating mass is inversely proportional in relation to the frame. With this apparatus the transmission ratio of the deflection of the seismic mass is inversely proportional in relation to the frame of the suspension.
In accordance with a further advantageous embodiment an effective stiffness of the vibrating mass spring system is proportional to the square of a deflection. Because of the geometrical circumstances, the lengthening of a spring characterizing the reset forces of the piezo sensor units is proportional to the square of the deflection. The result is that the effective stiffness of the mass spring system is proportional to the square of the deflection. Thus a further advantage emerges in addition to the increased efficiency of the energy conversion of wide band vibrations brought about by the proposals. The stiffness increasing with the vibration amplitude means that the vibrating mass is progressively braked and any possible extreme mechanical shocks are moderated. This means that the position transformation is more robust in relation to extreme mechanical shocks which could damage the piezo materials used.
In accordance with a further advantageous embodiment the springs are essentially subjected to tensile stress. In this way, with a heavy load, the piezo converters clamped under pretension are entirely without pre-tension in the worst case. This is a further reason for the position transformation being more robust in relation to extreme mechanical shocks, which could damage the piezo materials used.
In accordance with a further advantageous embodiment the piezo sensors are pre-tensioned and only subjected to compressive forces. The clamped piezo converters are thus never subjected to tensile stress. Tensile forces can lead to tears and thereby to failure of the piezo converters.
In accordance with a further advantageous embodiment the piezo sensors are fixed in a construction designed for pressure comprising spring sleeves engaging in one another and pre-stressed accordingly. In this way the possibility referred to of the piezo converter with too high a deflection no longer being fixed free from pre-stressing in the tubular spring is circumvented by the construction designed for pressure comprising spring sleeves engaging in one another and pre-stressed accordingly being used for fixing the converter.
These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.
The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).
This application is based on and hereby claims priority to International Application No. PCT/EP2009/055724 filed on May 12, 2009 and German Application No. 10 2008 029 374.1 filed on Jun. 20, 2008, the contents of which are hereby incorporated by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2009/055724 | 5/12/2009 | WO | 00 | 12/20/2010 |