Gas flow type angular velocity sensor

Abstract: The specification discloses an angular velocity sensor of the type wherein a flow of gas forced by a pump into a gas path in the sensor body (9) through a nozzle hole and directed toward a pair of thermosensitive resistance elements provided in the gas path is deflected by the action of an angular velocity and the deflection of the gas flow is sensed by means of the thermosensitive resistance elements, and which is further provided with a thermostatically-controlled gas path (10) with heating means (11) for keeping the gas flow at a constant temperature with no affection of ambient temperature variations and also provided with a gas path for absorbing pulsations of the gas flow caused by pumping operations.

Description: BACKGROUND OF THE INVENTION The present invention relates to a gas flow type angular velocity sensor which is capable of electrically sensing a deflection of a gas flow, which is caused by the action of an angular velocity applied to the sensor body. Japanese laid open patent publication No. 4623/89 describes such a gas flow type angular velocity sensor in which gas is forced into a gas path in the sensor body through a nozzle hoie to flow therealong toward a pair of heat wires, each being composed of a thermo-sensitive resistance element. When an angular velocity is applied to the sensor body, the gas flow is deflected and, accordingly, a difference between thermosensitive outputs of two heat wires is produced and picked up for determining therefrom a direction and a magnitude of the angular velocity acting on the sensor body. Since the above-mentioned angular velocity sensor is designed to determine an angular velocity by sensing a very small differential change of heat radiation of two heat wires (i.e., thermosensitive resistances), temperature variation of the gas flow may affect the detecting accuracy of the sensor. For this reason, the conventional gas flow type sensor is mounted in a thermostat capable of keeping temperature therein at a constant level without being affected by ambient temperature variations. Recently, there has been also developed a gas rate sensor of the type that its body portion composed of a gas path with a pair of heat wires arranged therein is manufactured by semiconductor micro-machining on the basis of IC technology. This is disclosed in Japanese laid open patent publication No. 29858/92. However, in contrast to a conventional gas rate sensor having a relatively large volume of a gas path which is enough to absorb pulsation and fluctuation of the gas flow produced by a pump that alternately sucks and exhausts gas, the gas rate sensor having a smaller volume of gas path cannot absorb the above-mentioned pulsation or fluctuation of the gas flow, which appears as a noise component in the sensor's output. This results in lowering the accuracy of angular velocity measurement. The above-mentioned prior arts have the following problems to be solved: 1) The first problem is that the thermostat containing a sensor body requires the provision of heating means of relatively large output power so as to evenly heat up the inner space of the thermostat. It also takes time to heat up the thermostat until its inside temperature rises to a constant level, at which the sensor can accurately measure an angular velocity. Furthermore, the response of the thermostat temperature control is somewhat insufficient to prevent the possible affection of ambient temperature variations. 2) The second problem, which is solved by the present invention, arising in using a small-sized sensor having a reduced volume of a gas path is that pulsing gas flows created by pumping operations cannot be absorbed in the gas path and therefore produce noise components which may be induced into outputs of the sensor. SUMMARY OF THE INVENTION On the basis of the fact that a gas flow type angular velocity sensor not mounted in a thermostat can accurately sense a deflection of a gas flow therein by use of thermosensitive elements if the gas forced into the gas path in the sensor body through a nozzle hole could be always kept at a constant temperature, the applicant has developed such a gas flow type angular velocity sensor that is provided at the upper stream side of its nozzle portion with a thermostatically-controlled gas path the wall of which is evenly heated and kept at a constant temperature. The present invention concerns a gas flow type angular velocity sensor wherein a pump and a gas path are communicated with each other by means of, for example, a bent path or a path having a plurality of internally formed fins for damping a pulsation flow of gas supplied by the pump. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a block diagram showing a structure of a gas flow type angular velocity sensor. Fig. 2 is a cross-sectional plan view showing an example of a thermostatically-controlled gas path. Fig. 3 is a view, partly in cross-sectional plan and partly in vertical cross-section, of another example of a thermostatically-controlled gas path. Fig. 4 is a cross-sectional plan view showing another example of a thermostatically-controlled gas path. Fig. 5 is a view, partly in cross-sectional plan and partly in vertical cross-section, of a further example of a thermostatically-controlled gas path. Fig. 6 is a cross-sectional plan view showing another example of a thermostatically-controlled gas path. Fig. 7 is a temperature characteristic diagram of gas flow measured at control positions of the thermostatically-controlled gas path shown in Fig. 6. Fig. 8 is a sectional front view of a gas flow type angular velocity sensor. Fig. 9 is a perspective view of a body of a gas flow type angular velocity sensor. Fig. 10 is a plan view of a lower semiconductor substrate of the sensor body shown in Fig. 9. Fig. 11 is a sectional view taken along the plane A-A of Fig. 9. Fig. 12 is a perspective view of a angular velocity sensor body of the present invention incorporating an thermostatically-controlled gas path of bent form integrally formed therein. Fig. 13 is a plan view of a lower semiconductor substrate of the sensor body shown in Fig. 12. Fig. 14 is a sectional side view showing a bent gas-path with a connected thereto miniature pump. Fig. 15 is a characteristic diagram showing results of measurements of noise components included in outputs of sensors, one having a bent gas-path and other having no bent gas-path. Fig. 16 is a sectional side view showing a bent gas-path with a connected thereto miniature pump in another embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The discussion of Figures 1-11 does not form part of the present invention and is provided for background information only. Fig. 1 shows a structure of a gas flow type angular velocity sensor, which body includes a nozzle portion 2 and a gas path 1 with a pair of heat wires arranged therein and is further provided with a thermostatically-controlled gas path 4 which is directly connected at one end to the upper stream side of the nozzle portion 2 and at the other end to a gas-feeding pump 3. This thermostatically-controlled gas path 4 is provided with a heater 5 for heating the wall thereof, a temperature sensor 6 for measuring an actual wall temperature and a controller 7 for turning on and off the heating power supply to the heater 5 to actually maintain the wall temperature at the constant value. The sensor having thus thermostatically-controlled gas path 4 of suitably selected length can realize that gas discharged from the pump 4 enters into the thermostatically-controlled gas path 4 and flows therealong, being heated by the heating wall surface; the gas gets about the same temperature as that of heating wall at the exit thereof and then enters into the gas path 1 through the nozzle 2. This ensures that gas is always regulated at a constant temperature before entering into the gas path of the sensor body. Fig. 2 shows a straight-form thermostatically-controlled gas path which is simple but must have a large length necessary for heating gas flow therein at a constant exit temperature. Accordingly, as shown in Fig. 3, a gas path having a plurality of branches (two branches in the shown case) 41 and 42 is formed in one thermostatically-controlled block 4 which has an increased efficiency of heating a gas flow therein and also has a shorter length. The sensor of a reduced size is easy to mount in a saved space. In Fig. 4, there is shown a further shortened thermostatically-controlled block 4 in which a thermostatically-controlled gas path is made in the bent form. In this case, the gas heating efficiency is especially improved because a turbulent gas flow is produced at every turns of the bent path in the thermostatically-controlled block 4 which is accordingly shortened in length. Fig. 5 shows another example of a thermostatically-controlled gas path 4 having a plurality of inwardly projecting fins 8, which can increase the gas heating efficiency and therefore realize further shortening of its block length. Fig. 7 shows a result of temperature measurements at points F1 - F5 of a thermostatically-controlled gas-path 4 of bent form shown in Fig. 6 when nitrogen gas of about 23°C was forced to flow through the above-mentioned bent path which wall had been previously heated and maintained at a temperature of 83°C. The thermostatically-controlled path 4 of the bent form has an inlet and an outlet both formed in the upper wall portion. In Fig. 7, curves A, B and C represent characteristics obtained at gas flows of 50, 100 and 200 SCCM respectively. In every case, the gas temperature measured at point F5 near to the outlet (OUT) is about the same as that of the wall of the thermostatically-controlled bent gas-path. When a gas flow is evenly distributed to "n" branches of a thermostatically-controlled gas path as shown in Fig. 3, each branch may be of 1/n in length for allowing 1/n of gas to flow therethrough. Accordingly, the resistance to the gas flow in full length of the gas path is reduced to a very small value of about 1/n 2 . This makes it possible to reduce discharging pressure of the pump 3 necessary for feeding the gas into the thermostatically-controlled gas path. The thermostatically-controlled gas path 4 having a plurality of internally projecting fins 8 as shown in Fig. 5 may also have the same advantage as mentioned above. Fig. 8 shows an embodiment of a gas flow type angular velocity sensor which is composed of semiconductor substrates manufactured by use of micro-machining technology. In Fig. 8, the angular velocity sensor comprises a sensor body 9 for detecting a deflection of a gas flow forced into a gas path through a nozzle portion by use of a pair of heat wires arranged in the gas path; a thermostatically-controlled gas path 10 made within a semiconductor substrate by use of micro-machining technology, which is provided at its bottom with a heater substrate 11 and is directly connected to the nozzle portion of the sensor body; a miniature pump 12 for supplying gas into the thermostatically-controlled gas path 10; an IC chip 13 which includes an angular velocity detecting circuit, a detecting signal amplifier circuit and a heater drive control circuit for driving the heater substrate 11 so as to maintain the wall temperature of the thermostatically-controlled gas path 10 at a constant value by regulating wall temperature measured by a temperature sensor (not shown); a ceramic substrate 14 with wiring patterns formed thereon for mounting all above-mentioned components at predetermined positions thereon; and a can-type package 15 which contains the ceramic substrate 14 with all installed thereon components and is filled with gas medium such as helium, nitrogen or likes. In the can-type package, the miniature pump 12 intakes gas from the inner open space of the package and feeds it into the sensor body 9 through the thermostatically-controlled gas path 10 to create a circulation of gas medium. This produces thermally stabilized gas flow to the sensor body. Referring now to Figs. 9 - 11, an example of a sensor body 9 formed on semiconductor substrates by using micro-machining technology will be described in detail. The sensor body is constructed in such a way that a lower semiconductor substrate 91 having a half nozzle hole 161 and a half groove 171 etched thereon and an upper semiconductor substrate 92 having a half nozzle hole 162 and a half groove 172 etched thereon and are joined with each other so as to make both half holes and half grooves matched to form a nozzle 16 and a gas path 17 in sensor body. The lower semiconductor substrate 91 has also a bridge portion 18 etched thereon across the etched half groove 171 of the gas path 17. A pair of heat wires 191 and 192 are formed by pattern etching of a layer of heat wire material (e.g., platinum) deposited on the bridge portion 18, and electrodes 20 are formed by like method one at each side of the paired heat wires. The thermostatically-controlled gas path 10 (not shown) is constructed in such a way that a lower semiconductor substrate having a half groove etched thereon and an upper semiconductor substrate having a half groove etched thereon are joined together with their half grooves matched to form a gas path 10. It is obviously understood that the above-described device is applied not only to a gas flow type angular velocity sensors formed on semiconductor substrates by micro-machining method but also to gas flow type angular velocity sensors manufactured by general machining methods. Figs. 12 and 13 show an embodiment of the present invention. A gas flow type angular velocity sensor is provided wherein a bent gas-path 23 for damping a pulsing gas flow is formed integrally with a sensor body 9 on semiconductors by micro-machining technology. DE-A-3 112 259 discloses a gas flow type angular velocity sensor which, due to it's construction, has a bent gas path. However the single bend of this sensor is not enough to damp a pulsing gas flow. Lower and upper semiconductor substrates 21 and 22, each of which has a half hole 161 of a nozzle hole 16 etched thereon, a half groove 171 of a gas path 17 etched thereon and an etched half groove 231 of a bent path 23, are joined together so as to precisely form the nozzle 16, the gas path 17 and the bent path 23 in one integral unit. The upper semiconductor substrate 22 has an upper inlet hole 24 for inducing gas into the bent path 23. The lower semiconductor substrate 21 has also an etched thereon bridge portion 18 across the etched half groove 171 of the gas path 17. A pair of heat wires 191 and 192 are formed by pattern etching of a layer of heat wire material (e.g., platinum) deposited on the bridge portion 18, and electrodes 20 are formed by like method one at each side of the paired heat wires. Fig. 14 shows an embodiment of a gas flow type angular velocity sensor wherein a miniature pump 25 being drivable by a piezoelectric element is directly connected at its discharge port to an inlet port of a bent gas path 23 integrally formed in a sensor body 9 so as to supply gas (e.g., helium) into the bent path. The gas is supplied by the miniature pump 25 into the bent gas path 23 wherein the gas flow is damped enough to eliminate noise components such as pulsation flows due to pumping operations, and then a stabilized flow is injected into the gas path 17 of the sensor body 9. Fig. 15 is a characteristic diagram showing results of measurements of noise components included in outputs of sensors, one having a bent path (curve A) and other having no bent path (curve B). As apparent from the diagram, the provision of the bent path 23 can effectively reduce noise components in the sensor outputs. It is, of course, possible to separately form the sensor body 9 and the bent path 23 and then join them together. As shown in Fig. 16, it is also possible to produce a stabilized gas flow without pulsation or the like noise components in a gas path 17 by providing a bent path 23 at a gas outlet 26 of the gas path 17 (not at nozzle side 16) and directly connecting its outlet 27 to a suction port of a miniature pump 25 by which gas is drawn out from the bent path 23 and discharged into an open loop of gas circulation. In both cases of Figs. 14 and 16 the miniature pump 25 is installed at the upper wall surface of the bent gas-path 23. However, it is simply understood that the bent path 23 may have its outlet or inlet opening at any side or bottom wall surface whereon the miniature pump 25 is desired to be installed. The provision of a gas path having a plurality of inwardly projecting fins (not shown) is also effective to damp pulsing gas flows produced by pumping operations. This assures to supply a stabilized gas flow into the gas path in the sensor body. The advantage of the gas flow type angular velocity sensor according to the present invention is that the noise components such as pulsing gas flows due to pumping operations can be effectively eliminated in a gas-flow pulsation damping path provided between a pump and a gas path of the sensor body, thereby a stabilized gas flow is induced in the gas path of the sensor body and its deflection is accurately determined without fluctuation of the sensor's output.

Claims: A gas flow type angular velocity sensor, comprising: a sensor body (9), a gas path (17) provided in a first portion of said sensor body (9), a pair of thermosensitive resistance elements in said gas path (17), the resistance of said thermosensitive resistance elements being changeable in accordance with a deflection of a flow of gas forced by a pump into the gas path (17) of the sensor body (9) through a nozzle (16), and an angular velocity being determined from the resistance change of the thermosensitive resistance elements, a gas flow pulsation damping path (23) provided in a second portion of said sensor body (9) and communicating with said gas path (17), said gas flow pulsation damping path (23) providing a substantially bent flow path for said gas, characterized in that said bent gas flow pulsation damping path (23) is defined by a plurality of inwardly projecting fins formed on an internal wall of said second portion of the sensor body (9). Gas flow type angular velocity sensor as claimed in claim 1, characterized in that said first portion and said second portion of said sensor body (9) constitute a unitary sensor body (9). Gas flow type angular velocity sensor as claimed in claim 1, characterized in that said first and said second portion of said sensor body (9) are provided separately from each other and are connectable to each other in order to provide a communication between said gas path (17) and said gas flow pulsation damping path (23). Gas flow type angular velocity sensor as claimed in one of claims 1 to 3, characterized in that said gas flow pulsation damping path (23) with respect to a flow direction of said gas is provided in an upstream direction of said gas path (17). Gas flow type angular velocity sensor as claimed in one of claims 1 to 3, characterized in that said gas flow pulsation damping path (23) with respect to a flow direction of said gas is provided in a downstream direction of said gas path (17).

Inventors: HANO TSUYOSHI, IKEGAMI MASAYUKI, YAMAKAWA HIROSHI, HANO, TSUYOSHI, IKEGAMI, MASAYUKI, YAMAKAWA, HIROSHI, Hano, Tsuyoshi, c/o Kabushiki Kaisha, Ikegami, Masayuki, c/o Kabushiki Kaisha, Yamakawa, Hiroshi, c/o Kabushiki Kaisha
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1993
Main classification: G01P9
IPC codes: G01P9, G01P1