Gas flow type angular velocity sensor

Abstract: A gas flow type angular velocity sensor which is capable of reliably sensing an angular velocity while accurately controlling the working gas flow with temperature compensation by using a pair of heat wires as a gas flow sensor without providing any additional gas flow sensor in the sensor body wherein a an angular velocity sensing bridge circuit is provided at its current supply source with a connected in series therewith temperature compensating circuit which is composed of a pair of series or parallel resistance elements: one is a thermosensitive resistance element disposed in a gas path and the other is a reference resistance element disposed outside the gas path.

Description: BACKGROUND OF THE INVENTION The present invention relates to a gas flow type angular velocity sensor which is capable of detecting a deflection of a gas flow in a gas path when an angular velocity acts on the sensor body by sensing a change of resistance in each of paired thermosensitive resistance elements disposed in the gas path. There has been known such a gas flow type angular velocity sensor for sensing an angular velocity acting on its body, wherein gas is forced by a pump through a nozzle port into a gas path toward a pair of thermosensitive resistance elements (heat wires) arranged at the right and the left in the gas path and a change of differential resistance in the paired heat wires, which is produced when the gas flow is deflected to the left or the right by the action of an angular velocity applied to the sensor body, is detected by an unbalanced output of an angular velocity sensing bridge circuit which includes, in its respective arms, the above-mentioned paired thermosensitive resistance elements and paired reference resistance elements. This type of angular velocity sensor, however, has a drawback that its detecting accuracy may vary with a change of the flow rate of gas in the gas path because the sensor is designed to determine a deflection of the gas flow by sensing a differential change of resistance in the paired thermosensitive resistances. Recently, there has been also developed a gas rate sensor of the type which body portion is composed of a gas path with a pair of heat wires arranged therein and is manufactured by semiconductor micro-machining on the basis of IC technology. Usually, the sensor has a small volume of its gas path and its detecting accuracy, therefore, may be greatly affected even by a very small fluctuation of the gas flow. Accordingly, Japan laid-open patent publication No. 5-2026 proposes to provide an angular velocity sensor with a flow sensor (additional thermosensitive resistance) in a nozzle portion of the sensor body to detect a flow rate of gas through the nozzle port and to control the operation of a gas injection pump so as to maintain a constant gas flow rate. This solution, however, requires the provision of an additional flow sensor element in the angular velocity sensor body, which complicates the construction of the sensor body. The sensitivity of the sensor to a change of the gas flow rate may vary with a change of the gas temperature. Therefore, it is also necessary to make the temperature compensation together with the control of the gas flow rate. From EP 0 324 620 A1 there is known an angular velocity sensor of the gas flow sensor type. This known angular velocity sensor comprises a bridge circuit which has in its arms two thermosensitive heat wires in contact with the flowing gas and two reference resistors of known resistance. A further reference resistor of known resistance is connected in series with the bridge circuit. A voltage across the further reference resistor is used by an arithmetic processor to calculate resistance values of the thermosensitive heat wires. Different temperature-to-resistance characteristics of both thermosensitive heating wires are compensated for by arithmetic operations performed in the arithmetic processor. These arithmetic operations are based on the previously calculated resistance values of the thermosensitive heat wires. Thus, in the angular velocity sensor according to EP 0 324 620 A1 only offset signals caused by the different temperature-to-resistance characteristics of the thermosensitive members are compensated for. However, the dependence of the sensitivity of the sensor on the temperature is not compensated for. Also, the sensitivity of the sensor to a change of the gas flow rate still varies with a change of the temperature. Therefore, it is an object of the invention to provide a gas flow sensor type angular velocity sensor which is capable of accurately sensing an angular velocity acting on its sensor body while controlling the rate of gas flowing through the sensor (without providing an additional flow sensor). According to the invention, there is provided a gas flow sensor type angular velocity sensor for sensing an angular velocity acting on a sensor body by an unbalance output of an angular velocity detecting bridge circuit which has, in its arms, paired thermosensitive resistance elements disposed at the left side and the right side in a gas path in the sensor body and paired reference resistance elements disposed at the outside of the gas path, said output appearing when resistances of the paired thermosensitive resistance elements change when a flow of gas directed toward said thermosensitive resistance elements deflects by the action of the angular velocity on the sensor body, characterized in that a temperature compensating circuit composed of a pair of series-connected or parallel-connected thermosensitive resistance element and reference resistance element is attached to the angular velocity detecting bridge circuit in series with a power supply of the angular velocity detecting bridge circuit, and in that a flowrate control bridge circuit is provided having in its arms the angular velocity detecting bridge circuit, the temperature compensating circuit and further paired reference resistance elements, and in that a gas flow control circuit connected to the flowrate control bridge circuit is further provided for operating a pump so as to maintain a constant gas flow rate in the gas path. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a perspective view showing, by way of example, construction of a body of a gas flow type angular velocity sensor embodying the present invention. Fig. 2 is a plan view of a lower semiconductor substrate of the sensor body shown in Fig. 1. Fig. 3 is a front sectional view of the sensor body shown in Fig. 1. Fig. 4 shows a configuration of an angular velocity detecting circuit of the gas flow type angular velocity sensor. Fig. 5 shows an example of a sensitivity characteristic of an angular velocity sensor relative to a change of gas flow. Fig. 6 shows a basic configuration of a circuit for gas flow control. Fig. 7 shows another example of the sensitivity characteristic of an angular velocity sensor relative to an output of a bridge circuit for gas flow control. Fig. 8 shows an example of the temperature coefficient characteristic curves of a bridge resistance R B and a heat wire resistance Rth relative to a bridge circuit current I B in the circuit shown in Fig. 6. Fig. 9 shows a configuration of a gas flow control circuit portion according to the present invention. Fig. 10 shows an example of the temperature coefficient characteristics of a bridge circuit resistance R B and a temperature compensating circuit resistance relative to a bridge circuit current I B in the circuit shown in Fig. 10. Fig. 11 is a view showing another configuration of a gas flow control circuit portion according to the present invention. In the drawings, 1 is a lower semiconductor substrate, 2 is an upper semiconductor substrate, 3 is a nozzle hole, 4 is a gas path, 51 and 52 are paired heat wires (thermosensitive resistance elements), 81 and 82 are cold wires (reference resistance elements), 91 is a power supply (constant-current source), 10 is an angular velocity detecting bridge circuit, 11 is an amplifier, 12 is a temperature compensating circuit, 13 is a gas flowrate control bridge circuit and 16 is a miniature pump. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be now described by way of example and with reference to the accompanying drawings. Figs. 1 to 3 shows a general construction of a miniature sensor body of a gas-flow type angular velocity sensor, which is manufactured by micro-machining on semiconductor substrates. The sensor body is constructed in such a way that a lower semiconductor substrate 1 having a half nozzle port 31 and a half groove 41 etched thereon and an upper semiconductor substrate 2 having a half nozzle port and a half groove 41 etched thereon are bonded to each other so as to precisely couple the half ports 31 and the half grooves 41 to form a nozzle port 3 and a gas path 4 in the assembled body. The lower semiconductor substrate 1 has a bridge portion 6 etched thereon whereon a pair of heat wires 51 and 52 are formed by patterning. Electrode portions 7 are formed by patterning at both sides of the paired heat wires 51 and 52. Fig. 4 is an illustrative of a configuration of an angular velocity detecting circuit of the gas flow type angular velocity sensor. This circuit is consisted of an angular velocity detecting bridge circuit 10 which includes, in its arms, paired heat wires 51 and 52 arranged in the sensor body and paired cold wires 81 and 82 serving as reference resistance elements disposed outside the sensor body and which is provided with a power supply (constant current source) 9 and an amplifier 11 for amplifying an output voltage Vr of the bridge circuit 10. The gas flow type sensor having a thus constructed sensor body can electrically detect a deflection of a laminar flow of inert gas (e.g., N 2 or Ar) constantly injected by a miniature pump (not shown) into the gas path 4 through the nozzle hole 3 and directed toward the paired heat wires 51 and 52 disposed therein. When the gas flow in the gas path 4 deflects to the left or the right by the action of an angular velocity applied to the sensor body, the paired heat wires 51 and 52 change their resistances and the bridge circuit 10 produces an unbalanced output corresponding to a differential change of thermosensitive outputs of the paired heat wires 51 and 52. This is a detection signal of an angular velocity. However, the sensor for detecting a deflection of a gas flow in its body by sensing a differential change of resistances of the paired heat wires 51 and 52 may change its sensitivity of angular velocity detection when the gas flow rate changes as shown in Fig. 5. The sensitivity characteristic of the sensor relative to a change of the gas flow rate varies with a change of the working temperature. For instance, it varies by a value of ΔS when a temperature of gas flow at acting point "f" changes from 25%C to 80%C. The present invention, therefore, provides that a temperature compensating heat wire 121 is disposed at a place free from the affection of the gas flowing in the gas path 4 in the sensor body as shown in Fig. 2 and is connected to a bridge circuit 10 in series with the power supply 9 thereof as shown in Fig. 6, and then a circuit of connected in series cold heat wires (reference resistance elements) 131 and 132 and the bridge circuit provided with the series heat wire 121 are connected in parallel with each other to form a flowrate control circuit 14' of the double bridge type wherein the angular velocity detecting bridge circuit 10, the temperature compensating heat wire 121 and the cold wires 131 and 132 form respective arms of a bridge circuit. An output Vf of the flowrate control bridge-circuit 14' is transferred as a gas flowrate detection-signal to a gas flowrate control circuit 15 which according to the detection signal controls a drive of the miniature pump 16 for injecting the gas into the gas path 4 to maintain a constant gas flowrate in the gas path. In the shown embodiment, the temperature compensating heat wire 121 is formed in the sensor body at a place where it can sense a temperature of the sensor without being affected by the gas flowing in the gas path 4, for example, on a portion 18 formed across a groove 17 etched on a lower semiconductor substrate 1 as shown in Fig. 2. In the case where the sensor body and the miniature pump are placed in a container filled with pressure gas to circulate the gas through the sensor body by the pump, it is desirable to provide an opening through which the groove 17 communicates with the outside of the sensor body in order to keep the same pressure in the gas path and the groove 17. In the flowrate control bridge-circuit 14', the angular velocity detecting bridge-circuit 10 is also used as a flow sensor. Accordingly, it is necessary to eliminate the possibility of changing the angular velocity detecting accuracy due to the effect of a temperature change, i.e., to match the temperature coefficient of a resultant resistance RB of the angular velocity detecting bridge-circuit 10 with that of resistance Rth of the temperature compensating heat wire 121 so that the sensitivity characteristic of the angular velocity sensor versus the output Vf of the flowrate control bridge-circuit 14' may not vary with a change of temperature and the constant detection accuracy can be maintained at the acting point "f" of the gas flow. The resultant resistance R B of the angular velocity detecting bridge circuit 10 can be calculated according to the following equation: R B = Rcw · Rhw/(Rcw + Rhw) where Rhw is a series resistance of heat wires 51 and 52 for detection of an angular velocity and Rcw is a series resistance of cold wires 81 and 82. If a series resistance of cold wires 131 and 132 in the flowrate control bridge-circuit 14' is expressed as Rref, R B is much less than Rref (i.e. R B << Rref). Consequently, in the current I= I B + Iref that flows through the flowrate control bridge circuit 14', there is a relation of I B >> Iref. If the angular velocity detecting bridge-circuit 10 and the temperature compensating heat wire 121 are independent from each other in circuitry, the temperature coefficient of the heat wire 121 can be controlled by changing a current flowing through the heat wire 121 to attain a desired temperature. In case of the flowrate control bridge circuit 14' having its configuration shown in Fig. 6, the resultant resistance R B of the angular velocity detecting bridge-circuit 10 and the resistance Rth of the temperature compensating heat wire 121 have different temperature coefficients of resistance, which may cause a difference between temperature characteristics of the bridge circuit 10 and the heat wire 121 in relation to the current I B commonly flowing through them. This means that matching the temperature coefficients of the bridge circuit 10 and the heat wire 121 can be achieved only at a specified current value I B1 at a point whereat their temperature characteristics meet with each other. If a gas flow type angular velocity sensor is designed according to a specified design value, it is impossible to control the sensitivity of the sensor by changing a current I B to be supplied to the angular velocity detecting bridge-circuit 10. Accordingly, the present invention devises that the flowrate control bridge-circuit 14' is provided with a temperature compensating circuit 12 consisting of a cold wire (reference resistance element) 122 connected in parallel with the temperature compensating heat wire 121 as shown in Fig. 9. The cold wire 122 is formed of the same material (e.g., platinum) by the same process that the heat wire 121 is formed. With the temperature compensating circuit 12 of the heat wire 121 and the cold wire 122 connected in parallel with each other, it is possible to set any desired temperature coefficient of resistance irrespective of a current supplied to the temperature compensating circuit 12 by selectively setting a resistance ratio between the heat wire 121 and the cold wire 122. The setting range runs from a temperature coefficient of resistance in the heat wire 121 at a current Ith flowing therein to a temperature coefficient of resistance in the cold wire 122. The temperature compensating circuit 12 has a configuration similar to the angular velocity detecting bridge-circuit 10 and, therefore, its temperature characteristic relative to the common current I B is similar to that of the angular velocity detecting bridge circuit 10 as shown in Fig. 10. Accordingly, the temperature dependency of the output Vf of the flowrate control bridge-circuit 14' is eliminated and, thereby, the gas flow rate can be constantly controlled according to the output Vf irrespective of the sensor body temperature. The adjustment of the current I B for optimizing the sensitivity of the sensor can be achieved free from the temperature influence. While the preferred embodiment is described it is to be understood that the invention is not limited thereto but may be otherwise variously embodied. For instance, as a temperature compensating circuit may be adopted a circuit of thermosensitive resistance elements 121 and 122 connected in series with each other. The present invention can be applied to a sensor of the type which is intended to detect a change of heat distribution by the action of a momentum, e.g., an acceleration acting on the sensor body by using a bridge circuit comprising a heat wire and a cold wire together with reference resistance elements. It is also possible to construct a flowrate control bridge circuit 14 not to be of the double bridge type but be such that the angular velocity detecting circuit 10 and the temperature compensating circuit 12 are connected in series and a reference voltage corresponding to a middle potential is applied to the connecting point of the circuits. As be apparent from the foregoing description, the gas flow type angular velocity sensor according to the present invention is featured by its construction that an angular velocity detecting bridge-circuit provided with a temperature compensating circuit connected thereto in series with a constant current source and a circuit of a pair of reference resistance elements connected in series are connected in parallel with each other to form a double bridge type flowrate control bridge-circuit which has, in its arms, the angular velocity detecting bridge circuit, the temperature compensating circuit and the paired reference resistance elements, and said temperature compensating circuit is composed of a thermosensitive resistance element and a connected in parallel thereto reference resistance disposed the outside of a gas path, thereby allowing paired heat wires for sensing an angular velocity to work as a flow sensor (without using an additional flow sensor in the sensor body) with temperature compensation. Accordingly, the flow rate of gas in the gas path can be accurately controlled with stable temperature compensation to optimally stabilize the sensitivity of the angular velocity sensor.

Claims: A gas flow sensor type angular velocity sensor for sensing an angular velocity acting on a sensor body by an unbalance output of an angular velocity detecting bridge circuit (10) which has, in its arms, paired thermosensitive resistance elements (51, 52) disposed at the left side and the right side in a gas path in the sensor body and paired reference resistance elements (81, 82) disposed at the outside of the gas path, said output appearing when resistances of the paired thermosensitive resistance elements (51, 52) change when a flow of gas directed toward said thermosensitive resistance elements (51, 52) deflects by the action of the angular velocity on the sensor body, characterized in that a temperature compensating circuit (12) composed of a pair of series-connected or parallel-connected thermosensitive resistance element (121) and reference resistance element (122) is attached to the angular velocity detecting bridge circuit (10) in series with a power supply of the angular velocity detecting bridge circuit, and in that a flowrate control bridge circuit (14) is provided having in its arms the angular velocity detecting bridge circuit (10), the temperature compensating circuit (12) and further paired reference resistance elements (131, 132), and in that a gas flow control circuit (15) connected to the flowrate control bridge circuit (14) is further provided for operating a pump so as to maintain a constant gas flow rate in the gas path.

Inventors: DOI MIZUHO, FUEKI NOBUHIRO, NISHIO TOMOYUKI, DOI, MIZUHO, FUEKI, NOBUHIRO, NISHIO, TOMOYUKI, DOI, MIZUHO, C/O KABUSHIKI KAISHA HONDA, FUEKI, NOBUHIRO, C/O KABUSHIKI KAISHA HONDA, NISHIO, TOMOYUKI, C/O KABUSHIKI KAISHA HONDA
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1995
Main classification: G01P9
IPC codes: B81B3, G01P9, G01P1