JPS6129767A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To enable the detection of acceleration by providing the displacing member made of a shape memory alloy which receives the following weight as well as by containing freely movably a weight inside a housing and by the variation in the resistance value corresponding to the displacement of the displacing member thereof. CONSTITUTION:An acceleration sensor 1 has a housing 2, the cases 2a, 2b of which are combined at flanges 4, 5 and a containing chamber 6 is made. The air is circulated then between the outer part of the housing 2 and the containing chamber 6 via a ventilaitn aperture 7. A weight 8 is contained freely movably on one end side of the containing chamber 6 and a displacing member 9 is provided as well between the weight 8 and case 2b. On the other hand when the sensor 1 is accelerated in the arrow mark direction, a reverse force to the acceleration is acted on the weight 8 and the displacing member 9 is displaced in the right direction together with the weight 8. Now since the resistance value of the shape memory alloy is in proportion to the variable the acceleration can be found by measuring the resistance value of the member 9 via lead wires 10a, 10b.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sensor that detects the acceleration of a moving object such as an automobile, and is used, for example, to control a compressor of an air conditioner for an automobile.

(Prior art) Electrical detection of acceleration is well known, and for example, Japanese Utility Model Application Publication No. 58-27772 discloses a method using a differential transformer. One end of a leaf spring is fixed, a rod serving as a displacement member is supported at the other end of the leaf spring, and a differential transformer is provided around this rod, so that the Rondo is displaced in response to acceleration. The acceleration is detected by converting the signal into an electrical signal using a differential transformer.

(Problems to be Solved by the Invention) However, in such a configuration, the displacement of the displacement member is converted into an electric signal by a differential transformer separate from the displacement member. A space for accommodating both the displacement member and the displacement-to-electrical converter must be formed in the housing, which makes it difficult to downsize, and the structure is complicated and expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide an acceleration sensor that is capable of capturing the displacement of the displacement member itself as an electrical signal, is easily miniaturized, and has a simple structure.

(Means for Solving the Problems) The gist of the present invention is to store a weight movably in a housing, provide a displacement member made of a shape memory alloy to receive the weight, and provide a displacement member made of a shape memory alloy to receive the weight. The purpose is to detect acceleration based on a change in resistance value corresponding to the change in resistance value.

(Function) Therefore, when a moving object such as a car to which the acceleration sensor is attached accelerates, the weight receives an inertial force commensurate with this acceleration, and the displacement member made of a shape memory alloy is displaced together with the weight. Here, it is known that when a shape memory alloy is displaced, its electrical resistance value changes proportionally. Therefore, the acceleration of the moving body can be detected by measuring the resistance value of the displacement member.

(Embodiment) An embodiment of the present invention is shown in FIGS. 2a and the right case 2b have respective flange portions 4,
The cases 2a and 2bg constitute a storage chamber 6.

A large number of ventilation holes 7 are formed in the left case 2a, and air flows between the outside of the housing 2 and the storage chamber 6 through the ventilation holes 7, so that the temperature of the storage chamber 6 is the same as the outside temperature. It is intended to be. Further, in this storage chamber 6, a spherical weight 8 made of an insulating material is movably stored at one end thereof, and a displacement member 9 is provided between the weight 8 and the right case 2b. It is being

This displacement member 9 is made of Ni-Ti alloy, Cu-Z
It is made of a shape memory alloy such as n-A1 alloy, and both the shape of the parent phase (austenite phase) and the shape of the martensite phase are coiled, but when the martensite phase reversely transforms to the parent phase, the shape changes to the left in the figure. The reverse transformation start temperature (Af point) is set at around 30° C. in this example. A ring portion 9a is formed at one end of the displacement member 8, and the weight 8 is fitted into the ring portion 9a so that the displacement member 9 receives the weight. Case 2a
is in contact with the inner wall of However, at this time, the displacement member 9
If the phase is martensite, the length of the displacement member 9 is set so that the pressing force of the displacement member 9 does not act on the weight. Further, both ends 9b and 9c of the displacement member 9 are inserted into a groove 10 formed along the longitudinal direction of the case 2a to prevent rotation in the circumferential direction.
.

One ends of leads 3slOa and 10b are connected to 9C by, for example, soldering. The lead m1Oa.

The other end of the housing 10b passes through the case 2b and is drawn out to the outside of the housing 2, and the drawn-out portion is fixed by a fixing part 12 formed by pouring resin into a recess 11 formed in the case 2b. ing.

In the above configuration, when the weight 8 is accelerated in the direction of the arrow in FIG.
At the same time, the displacement member 9 is displaced to the right. The acceleration α in this case is proportional to the inertia force, and the displacement amount X of the displacement member 9 is proportional to the inertia force, so the acceleration α is proportional to the displacement amount X. Here, as shown in FIG. 3, since the resistance value Ω of the shape memory alloy is proportional to its displacement amount X, the acceleration α is eventually proportional to the resistance value Ω, and the displacement member 9
The acceleration α can be determined by measuring the resistance value Ω through the lead wires 10a and 10b.

However, the resistance value Ω in this case becomes constant when the ambient temperature is below the reverse transformation start temperature (As point), that is, when the shape memory alloy is in the martensitic phase, and the reverse transformation starts. Then, as the displacement member 9 tries to displace to the left in the figure, a leftward force is applied from the displacement member 9 to the weight 8, and the weight 8 and the displacement member 9 will not be displaced unless a large acceleration occurs. , as shown in FIG. 4, when the surrounding temperature reaches or exceeds the Af point, the temperature becomes T.

As Tz changes, the resistance value Ω also changes from Ω to Ω2. Ω
It changes like 3. Therefore, the acceleration sensor 1 in this embodiment can detect not only acceleration but also ambient temperature.

In the above embodiment, the displacement member 9 made of a shape memory alloy is provided only on one side of the weight 8, but it can also be provided on the other side to detect acceleration in both directions. A bias spring may be provided that applies a pressing force in a direction opposite to the direction of displacement.

FIG. 5 shows an application example in which the acceleration sensor 1 described above is used in a thermostat that controls a compressor in an automobile air conditioner. an output voltage V1 corresponding to a change in the resistance value of the acceleration sensor 1, and an output voltage V2 of the temperature sensor 13, which is configured from a heat-sensitive element such as a thermistor and detects the temperature of the evaporator.
is input to the adder 14. The output voltage (2) of the adder 14 changes in accordance with vI+2, is input to a comparator 15, and is compared with a reference voltage V set by a variable resistor 16 in the comparator 15. The output of the comparator 15 becomes "L" when V3>v4, turning off the transistor 17, demagnetizing the electromagnetic coil 18 of the electromagnetic clutch of the compressor, and stopping the drive of the compressor. On the other hand, ■3〈. When V4 is high, the transistor 17 is turned on to excite the electromagnetic coil 18i of the electromagnetic clutch of the compressor, thereby driving the compressor.

Therefore, now the output voltage v determined by the evaporator temperature
2 and the reference voltage V4 set by the variable resistor 16 is constant, the intermittent operation of the compressor is determined by the acceleration sensor 1.
When the acceleration of the vehicle increases, the resistance value of the acceleration sensor 1 increases and the output voltage V1 also increases.
When the acceleration exceeds a predetermined value, the output voltage 3 of the adder 14 finally exceeds the reference voltage, the output of the comparator 15 is reversed, and the drive of the compressor is stopped, so-called acceleration cut control is performed, and the compressor is stopped. To improve the acceleration of an automobile by reducing the load on the driving engine.

However, during the so-called cool-down period when the temperature inside the vehicle exceeds 30°C, as shown in Figure 4, the resistance value of the acceleration sensor 1 is small even for the same acceleration, and its output voltage V, This system ensures that the compressor continues to operate unless the vehicle accelerates considerably, allowing the vehicle interior to continue to be cooled and preventing passengers from feeling uncomfortable during acceleration. It is.

(Effects of the Invention) As mentioned above, according to the present invention, acceleration is detected using the property of a shape memory alloy that changes its resistance value with respect to displacement. By measuring the resistance value of the alloy displacement member, the acceleration can be determined immediately, and there is no need for any means to convert the mechanical displacement into an electrical signal. Therefore, the acceleration sensor can be downsized, and Its structure can be simplified and an inexpensive acceleration sensor can be used. Furthermore, compared to a device using a microswitch, it has the advantage of being able to linearly detect acceleration, and has the advantage of widening its range of applications.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an acceleration sensor according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line A-A in FIG. Figure 4 is a diagram showing the characteristics of the change in resistance value with respect to acceleration when temperature is used as a parameter in the same acceleration sensor. It is a circuit diagram showing an example of application used in a thermostat to control. ■... Acceleration sensor, 2... Housing, 7...
Ventilation hole, 8... Weight, 9... Displacement member made of shape memory alloy. 2 Figure 1 Figure 3 U-luck! Technique (G)−→−

Claims (1)

[Claims] 1. A weight is movably housed in the housing, and a displacement member made of a shape memory alloy is provided to receive the weight, and acceleration is detected by a change in resistance value corresponding to the displacement of the displacement member. An acceleration sensor featuring: 2. The acceleration sensor according to claim 1, wherein the housing has a vent hole formed therein.