JPH0645896Y2 - Accelerometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an accelerometer for detecting acceleration.

[Conventional technology]

Conventionally, a pendulum device is generally used for this type of accelerometer, and the acceleration is detected by utilizing the fact that a slight relative displacement of the pendulum is proportional to the acceleration. Among such accelerometers, those using a piezoelectric material exhibiting a piezoelectric effect are widely used as means for detecting relative displacement in that they are small and lightweight.

[Problems to be solved by the invention]

However, this type of accelerometer has a mechanical element called a pendulum device as a main part, and sufficient maintenance is required to maintain stable accuracy. In addition, the output due to the natural vibration of the pendulum device hinders the measurement of acceleration. Further, since the accelerometer based on piezoelectric detection has a high impedance, there is a problem that electric noise is easily picked up.

[Means for Solving the Problems]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention provides a generally hermetically-closed hollow housing arranged so that its longitudinal direction coincides with the acceleration direction, and respective through holes formed on the upper surfaces of both ends of the hollow housing. And a flow sensor that is arranged in the hollow housing at approximately the center between the respective through holes and that measures the flow velocity of the air flowing in the hollow housing, and the acceleration based on the predetermined relationship from the detection output of this flow sensor. And means for calculating

[Action]

When acceleration is applied, the air inside the hollow housing flows in the direction opposite to the acceleration direction due to the inertia of the air. Since there is a through hole on the upper surface of both ends of the hollow housing that communicates with the outside, air is sucked in through the leading hole for acceleration, and air is discharged through the trailing hole in the rear. Continue as long as there is. Since this flow velocity has a correlation with the acceleration, the acceleration can be measured from the output of the flow sensor.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing the configuration of an accelerometer according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a cylindrical hollow housing whose both end surfaces are closed and which is hermetically formed. The hollow housing 1 is arranged so that its longitudinal direction coincides with an acceleration measuring object holding the acceleration sensor, for example, an acceleration direction (arrow A) applied to a vehicle. The hollow housing 1 is provided with conduction holes 1a and 1b on the upper surfaces, which are the side surfaces in the direction perpendicular to the longitudinal direction on both ends in the longitudinal direction. Hollow housing 1
The inside and the outside communicate with each other only through these two conduction holes.

A flow sensor 2 is fixedly arranged inside the hollow housing 1 at a substantially central portion between the through holes 1a and 1b. The flow sensor 2 measures the flow velocity of gas (usually air) flowing inside the hollow housing 1.
Reference numeral 3 is a detection circuit connected to this sensor. The flow sensor 2 and the detection circuit 3 are well-known techniques, and are disclosed in, for example, Japanese Patent Laid-Open No. 61-88532, and the outline thereof is shown in FIG.

FIG. 2 is a perspective view of a known flow sensor, and a tunnel-shaped space is formed in the center of the silicon substrate 31 so that the windows 32 and 33 communicate with each other. This space space can be formed by an anisotropic silicon etching technique. On the surface of the sensor portion 34, two sets of temperature measuring resistance elements 11 and 17 made of permalloy or the like and a heater element 35 arranged between them are formed, and these surfaces are protected by a thin silicon nitride film. Reference numerals 12 and 18 are resistance elements for measuring the ambient temperature and are used when configuring a temperature correction circuit and the like.

Since the sensor portion 34 has a space formed below it, it is thermally insulated from the silicon substrate 31 and has a thin film shape, so that the heat capacity is extremely small. When a current is passed through the heater element 35 to heat it to a constant temperature, the temperature of the air above it rises. If there is a gas flow in the direction of arrow B, the temperature-increased air flows in the direction of arrow,
The temperature measuring resistance element 11 on the upstream side of the air flow is cooled, and the temperature measuring resistance element 17 on the downstream side is heated. Therefore, resistance changes occur in the temperature measuring resistance elements 11 and 17 due to temperature changes, and if the amount of change is detected by the bridge circuit, an electric signal proportional to the flow velocity of the airflow can be obtained.

The detection circuit 3 includes a circuit for driving the heater element 35, a circuit for detecting the flow velocity from the resistance change of the temperature measuring resistance elements 11 and 17, and the like.

In FIG. 1, reference numeral 8 is an arithmetic circuit for calculating the acceleration from the detection output of the flow sensor 3 based on a predetermined relationship.

Next, the operation of the accelerometer configured as described above will be described.

When acceleration is applied in the direction of arrow A in FIG.
Due to its inertia, the air inside the air moves relative to the housing 1 in the direction of the arrow B opposite to the arrow A. Therefore, the air pressure in the housing 1 near the conduction port 1a becomes lower than that in the outside, and the air flows into the housing 1 through the conduction port 1a. At the same time, the air pressure in the housing 1 near the conduction port 1b becomes higher than that of the outside, and the air flows out from the conduction port 1b to the outside.

As a result, the air flows into the housing 1 from the conduction port 1a and flows out from the conduction port 1b, whereby an air flow in the direction of the arrow B is generated in the housing 1, and this flow velocity is detected by the flow sensor 2
Detected by.

The flow velocity detected by the flow sensor 2 is sent from the detection circuit 3 to the arithmetic circuit 8 as an electric signal corresponding to the flow velocity. In the arithmetic circuit 8, the acceleration is detected based on the table table pre-calibrated by the input flow velocity signal.

FIGS. 3 and 4 are sectional views of a housing of another embodiment, and FIG. 3 shows a throttle portion 1c provided in the central portion of the housing 1 and a flow sensor 2 fixedly arranged on the throttle portion 1c. is there.

In FIG. 4, a wall 1d is provided inside the central portion of the housing 1, a detour 1e is provided across the wall 1d, and the flow sensor 2 is fixedly arranged in the detour 1e.

Even with such a configuration, the same operational effects as the embodiment of FIG. 1 can be obtained.

Needless to say, the air inside the hollow housing remains stationary during the uniform velocity motion.

[Effect of device]

As explained above, according to the accelerometer of the present invention,
Since the flow sensor detects the flow velocity of the airflow flowing in the housing based on the acceleration and produces the acceleration value from this detection output, there is no need for a mechanical structure such as a conventional pendulum device. A stable output can always be obtained, and an error due to natural vibration unlike the pendulum device is eliminated.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the accelerometer according to the present invention, FIG. 2 is a perspective view showing a specific appearance of the flow sensor 2, and FIGS. 3 and 4 are views of the housing of FIG. It is sectional drawing which shows another Example, respectively. 1 ... Housing, 1a, 1b ... Conduction hole, 1c ... Drawing part, 1
d ...... wall, 1e ... detour, 2 ... flow sensor, 3 ...
Detection circuit, 8 ... Arithmetic circuit, 11, 17 ... Resistance temperature measuring element, 31 ... Silicon substrate, 35 ... Heater element.

Claims (1)

[Scope of utility model registration request] 1. A generally hermetically-closed hollow housing arranged so that its longitudinal direction coincides with the acceleration direction, and through holes formed on the upper surfaces of both ends of the hollow housing, respectively. A flow sensor, which is arranged substantially in the center between the through holes and measures the flow velocity of the air flowing in the hollow housing, and a means for calculating acceleration based on a predetermined relationship from the detection output of the flow sensor. An accelerometer characterized by that.