Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2001-06-04
2003-02-04
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
Reexamination Certificate
active
06513383
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an acceleration sensor for detecting an acceleration operating on a vehicle, and an acceleration detecting system using the acceleration sensor.
BACKGROUND ART
An acceleration sensor is widely used with an occupant protection device such as an airbag and a seat-belt tensioner. Generally, the acceleration sensor is provided on a floor tunnel in a vehicle room together with a control unit, detects an acceleration operating on a vehicle through the floor tunnel, and gives an analog signal representative of the acceleration to the control unit. The control unit decides based on the acceleration signal from the acceleration sensor and a collision decision threshold value whether to drive the occupant protection device, and controls the occupant protection device according to the decision.
By the way, when an impact of collision is absorbed by a crush of a collision part of the car body, it can be assumed that a collision acceleration transmitted to the floor tunnel is weakened. In such a case, an acceleration detected by the acceleration sensor provided on the floor tunnel is small. In particular, a collision, such as an offset collision or an oblique collision, tends to cause a case in which the acceleration transmitted to the floor tunnel is weakened. Because of this, from the viewpoint of providing the acceleration sensor near a collision part, providing the acceleration sensor at a front part of the vehicle can be considered. However, according to this, since the acceleration sensor must be provided near an engine of the vehicle, the acceleration sensor is placed under a state of directly receiving a great variation of temperature. Hence, a conventional acceleration sensor detecting an acceleration as an analog signal can not be provided.
Therefore, an object of the present invention is to provide an acceleration sensor which can be provided near an engine of an automobile.
Another object of the present invention is to provide an acceleration detecting system using the acceleration sensor.
DISCLOSURE OF INVENTION
An acceleration sensor in claim
1
comprises: a piezo-electric element for detecting an acceleration; an amplifier circuit for inputting voltage outputs of both ends of said piezo-electric element, and for giving a differential amplification signal, which is obtained by differentially amplifying the voltage outputs of both ends of said piezo-electric element, as a sensor output; a bias resistor circuit provided at an input side of said amplifier circuit; a capacitor inserted in parallel with said piezo-electric element in order to lower a lower cut-off frequency without increasing resistance values of said bias resistor circuit; temperature compensation means for adjusting gain of said amplifier circuit so that an output-temperature characteristic of said piezo-electric element is compensated; and a reference voltage circuit for giving a reference potential to said amplifier circuit and said bias resistor circuit.
According to a composition like this, the output fluctuations of the piezo-electric element due to variations in ambient temperature are compensated by the gain adjustment of the amplifier circuits by means of the temperature compensation means. Accordingly, even when the acceleration sensor is provided in a place with extreme ambient temperature variations such that it directly receives heat from a vehicle engine, the sensor output of the acceleration sensor does not fluctuate by variations in ambient temperature. Also, by inserting the capacitor in parallel with the piezo-electric element, the composite capacity is increased. By this, the lower cut-off frequency can be lowered without increasing resistance values of the bias resistor circuit.
In the acceleration sensor of claim
2
having a connection with the composition of claim
1
, a capacity of said capacitor is set so that resistors of said bias resistor circuit become values that can be used in a normal atmosphere and so that the lower cut-off frequency becomes a low value in which velocity variations can easily be detected. By this, the acceleration sensor can give a lower frequency component, and thereby the sensor output that facilitates a collision decision can be given. Also, it is not necessary to set resistors of the bias resistor circuit to such high resistance values that cannot be used in an ordinary atmosphere. Further, migration in the piezo-electric element, occurring by setting the resistors of the bias resistor circuit to high resistance values, can be prevented.
In the acceleration sensor of claim
3
having a connection with the composition of claim
1
, said amplifier circuit has a first non-inverting amplifier circuit for non-inversion amplifying one voltage of said piezo-electric element, a second non-inverting amplifier circuit for non-inversion amplifying the other voltage of said piezo-electric element, and a differential amplifier circuit for differentially amplifying outputs of said first and second non-inverting amplifier circuits; and said temperature compensation means is a single temperature compensation element for adjusting gains of said first and second non-inverting amplifier circuits. In the acceleration sensor of claim
4
having a connection with the composition of claim
3
, said first non-inverting amplifier circuit has a first operational amplifier, one input terminal of the first operational amplifier being connected to one end of said piezo-electric element, and the other input terminal of the first operational amplifier being connected to an output terminal of the first operational amplifier through a first resistor; said second non-inverting amplifier circuit has a second operational amplifier, one input terminal of the second operational amplifier being connected to the other end of said piezo-electric element, and the other input terminal of the second operational amplifier being connected to an output terminal of the second operational amplifier through a second resistor; and said temperature compensation element is inserted between the other input terminal of the first operational amplifier and the other input terminal of the second operational amplifier, and decreases the gains of the first and second operational amplifiers when temperature rises and increases the gains when temperature drops. According to compositions like these, since the gains of the first and second non-inverting amplifier circuits are adjusted by the single temperature compensation element, decrement in the number of elements and simplification of circuit composition can be achieved.
In the acceleration sensor of claim
5
having a connection with the composition of claim
4
, said first and second resistors are set so that a drop in voltage outputs of said piezo-electric element due to the parallel insertion of said capacitor to said piezo-electric element can be supplemented by the gains of said first and second non-inverting amplifier circuits. By this, since the drop in the voltage outputs of said piezo-electric element is supplemented, it is possible to obtain a desired sensor output.
In the acceleration sensor of claim
6
having a connection with the composition of claim
5
, said differential amplifier circuit has an operational amplifier, one input terminal of the operational amplifier receiving the output of said second non-inverting amplifier circuit and the reference potential of said reference voltage circuit, and the other input terminal of the operational amplifier receiving the output of said first non-inverting amplifier circuit; and said reference voltage circuit has a reference voltage buffer amplifier for matching with output impedances of said first and second non-inverting amplifier circuits, and gives the reference potential to at least said differential amplifier circuit by way of the reference voltage buffer amplifier. By this, since a common mode rejection ratio of the differential amplifier circuit becomes large, an influence of offset voltage due to the gain increment of the first and second non-invertin
Ishizuka Hideki
Naganuma Hiroshi
Okano Masami
Bosch Electronics Corporation
Moller Richard A.
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