GAS RATE SENSOR

Abstract: The gas rate sensor in the present invention is provided with a holder assembly (1) having a metallic holding portion for holding flow sensors and the like and a cylindrical casing (2) containing the holder assembly (1) and heater wires (3) which are wound around the outside thereof, wherein the outer periphery of the holding portion is provided with a plural number of projections (1b) which are brought into compressive contact with the inner periphery of the casing (2) for enabling pressurization of the holder assembly (1) into the casing (2) and wherein a temperature detection element (9) is disposed in a gas flow passage between the holder assembly and the casing (2) for performing energizing control of the heater wires (3).

Description: The present invention relates to a gas rate sensor for maintaining especially gas temperature constant. Conventional gas rate sensors contain a holder assembly having a flow sensor in a hermetic; metallic casing and a gas flow is injected towards a thermosensitive element in the flow sensor to detect the angular velocity (the rate) on the basis of variation in the sensor output produced when the gas flow is deviated by the effect of the angular velocity movement exerted from the outside. Because variation in the ambient temperature may, in this case, exert adverse effect on the detection precision, a proposal has been offered to wind heater wires around the outside of the casing containing the holder assembly to maintain the casing and the inside thereof at a constant temperature. FIG. 6 illustrates a structural diagram showing the main portion (main body) of a conventional gas rate sensor provided with heater wires in this type. In the drawing, a numeral 1 denotes a holder assembly containing a flow sensor and the like in the inside and a numeral 2 denotes a metallic casing containing the holder assembly 1 with the inside of the casing being hermetic. Heater wires 3 are helically wound around the outside of the casing 2 through the intermediary of an insulator and a thermister 4 which is a temperature detection element is attached to the outer surface of the casing 2 by means of an adhesive. Thermosensitive elements 5a and 5b and a piezo plate 6 constituting the flow sensor are held in the holder 1a of the holder assembly 1. Gas from an exhaust port 7 passes, as given in an arrow mark in the drawing, through a portion between the holder assembly 1 and the casing 2 to define a gas flow passage from a nozzle 8 at the end of the holder assembly 1 to the inside of the holder. In the main body of the gas rate sensor thus constructed, inside of the casing being hermetic, a constant gas flow is injected from the nozzle 8 towards the thermosensitive elements 5a and 5b of the flow sensor and is deviated when the effect of the angular velocity movement is exerted from the outside. In this case, the degree of the angular movement can be detected by detecting variation in the output of the flow sensor. Conduction of the heater wires 3 is controlled by the detection signal of the thermister 4 and the temperatures of and in the casing 2 are maintained constant by means of the feedback control whereby the casing 2 acts as a thermostat. For this reason, even if the ambient temperature has varied, no effect is exerted on the holder assembly 1 whereby a high degree of detection precision can be obtained. A device similar to the gas rate sensor of figur 6 is known from FR-A 24 79 473. The casing of this device has three projections or protuberances arranged at circumferentially equal intervals and projected toward the diametrical center of the casing and axially extending. When a sensor body is mounted within the casing, axial gas flow passages are defined between adjacent ones of the protections and associated outer peripheral surfaces of the remaining part of the holder assembly. In this embodiment a temperature sensor may be mounted in the inner wall of the casing, which may be connected to a suitable switch means, so that the switch means performs a repeated switching action in response to a detected temperature signal supplied thereto from the sensor so as to keep the temperature within in casing at a desired value. However, both prior art embodiments, i. e. the prior art as shown in figur 6 of this application as well as the prior art in accordance with the FR-A 24 79 473 involve the same disadvantages. Because the above gas rate sensor is merely so constructed that the holder assembly 1 is inserted into the casing 2, however, the contact area of the holder 1a with the casing 2 is small and temperature control is performed while detecting the temperatures of the casing 2 and the heat wires 3 by means of the thermister 4. Accordingly, there are problems in that the temperature of the structure in the holder assembly 1 slowly rises and stabilizes, resulting in poor detection characteristics and the fixing member of the holder assembly 1 is required. Meanwhile, known cited references are U.S. Patent Nos. 3,587,328 dated June 28, 1971, 3,628,371 dated December 21, 1971, 4,020,699 dated May 3, 1977, 4,020,700 dated May 3, 1977 and 4,026,159 dated May 31, 1977. It is an object of the present invention to provide a gas rate sensor which rapidly rises and stabilizes the temperature of the structure in the holder assembly and which has few parts. Accordingly, the gas sensor in the present invention is provided with a holder assembly having a metallic holder for holding a flow sensor and the like and cylindrical casing containing the holder assembly and having heater wires wound around the outside thereof. The outer periphery of the holder is provided with a plural number of projections which are brought into compressive contact with the inner peripherical surface of the casing to press the holder assembly into the casing. A gas flow passage between the holder assembly and the casing is provided with a temperature detection element to perform energizing control of the heater wires. Such a structure enables containing the holder assembly in the casing without any fixing member and simultaneously increases both contact areas thereby improving detection characteristics. The wall thickness of those part of the casing against which the projections of the holding portion are pressed is 1/10 or less the diameter of this part thereby easily providing a structure of reasonal detection characteristics. In a preferred embodiment the casing is made of iron or an iron alloy. In another preferred embodiment the difference between the diameters on the two ends of the outer periphery of the casing is zero or 1/10 or less the diameter. The inner surface thereof has a stepped portion defining a first and second axially dislocated portion having different diameters. The temperature detection elements are arranged not only in the inside of the casing but also in contact with the heater wires to control the heater wires based on detection signals from these temperature detection elements thereby preventing the extreme overshot of the heater wire temperature. FIGS. 1 (a) and (b) illustrate a structural diagram showing one embodiment of the invention and a cross-sectional view taken along the lines A-A, respectively. FIGS. 2 (a) and (b) illustrate a longitudinal cross-sectional view and a side view showing the detail of the holder assembly in FIG. 1 respectively. FIG. 3 illustrates a cross-sectional view showing the external shape of the casing in FIG, 1. FIGS.4 (a) and (b) illustrate a plan view and a side view showing a state at which a thermister is attached to the holder assembly. FIG. 5 illustrates a diagram explaining the deflecting effect of the casing. FIG. 6 illustrates a longitudinal cross-sectional view of a conventional gas rate sensor. One preferred embodiment of the invention will now be described with reference to the accompanying drawings. FIG. 1 illustrates diagrams giving one embodiment of the present invention, in which FIG.1 (a) is a partially cut-away structural diagram thereof and FIG.1 (b) is a cross-sectional view taken along the lines A-A. In the drawing, the holder portion 1a of a holder assembly 1 is made of a metal of good thermal conduction such as aluminum, copper, or an alloy thereof and contains a flow sensor and a piezo plate in the inside thereof. The holder portion 1a is provided with a plurality of (three in the drawing) projections which are brought into compressive contact with the inner circumference of a casing 2. The metallic casing 2 is provided with a stepped portion 2a as a stopper portion, for housing the holder assay 1 at a predetermined position. The outside of the casing 2 is provided with heater wires 3 wound therearound, in which a thermister 4 is arranged as a temperature detection element. A gas (helium) flow passage between the holder assembly and the casing 2 is provided with a thermister 9 for temperature control. FIG. 2 illustrates diagrams showing the detail of the holder assembly 1, wherein FIG. 2(a) is a longitudinal cross-sectional view thereof and FIG. 2(b) is a side view thereof. The holder assembly 1 contains nozzles 8 for producing the streamline flow of the helium gas in the inside thereof and, in addition, an concentric sleeve 1g which is rate-sensed by the streamline flow, a flow sensor-attaching portion, 1c, and a pump chamber 1d, all of which are subjected to high precision processing. A flow sensor and a piezo plate are mounted in assembling the above. The outer periphery of the holder portion 1a is provided with three projections 1b having contacting surfaces when they are pressed into the casing 2, convex wall surfaces 1h for contacting the flowing gas divided by these projections 1b with the inner wall surfaces of the casing 2 to the utmost, a screw hole of a thermister 9 for detecting the gas temperature, the relieving groove and the inserting hole of the respective lead wires from the thermister 9 and the flow sensor, and a jet hole 1f for rendering the gas from the piezo plate in a constant direction. The outer diameter of the pump chamber 1d in which the piezo plate is disposed is maximum because of a stepped portion 1e as a stopper when the piezo plate is pressed into and housed in the chamber. FIG. 3 illustrates the external shape of the casing 2, which is in the form of a cup and has a deformed, triangular flanged portion 2b (refer to FIG. 1(b)) in the opening. The inner diameter on the opening side thereof is maximum for housing the pump chamber of the above-described holder portion 1a and a stepped portion 2a is provided between the portion of the maximum diameter and the contact point of the projected portion 1b in the holder assembly 1. The outer periphery is cylindrical or with a difference between the diameters on the two ends of the casing 2 in the amount of 1/10 or less of the diameter defining a taper portion between both cylindrical parts. The thickness of the portion into which the holder portion 1a of the holder assembly 1 is pressed is 1/10 or less of the diameter of this portion. A portion of the outer periphery is provided with a plane 2c for attaching the above-described temperature-controlling thermister 4 thereto and heater wires 3 are helically wound around the outer periphery including the thermister 4. FIGS.4 (a) and (b) illustrate a plan view and a side view showing respectively, a state in which the temperature-controlling thermister 9 is attached to the holder assembly 1 (refer to FIG. 1). A metallic fix plate 10 having a piercing hole is secured to the holder assembly 1 by means of a screw 11 and a glass terminal 12 connected to a led wire 13 is secured to the piercing hole. The thermister 9 is connected to the end of the glass terminal by means of soldering. Such an attaching structure enables arrangement of the thermister 9 at a predetermined position in the gas flow passage at any time. In the gas rate sensor constructed as described above, a flow sensor is provided in the holder assembly 1 which is housed in the inside of the casing 2 as with conventional cases and a constant amount of gas flow is blown from the nozzle (8) toward the thermosensitive element of the flow sensor. Effect of angular velocity movement exerted from the outside on the gas rate sensor deviates the gas flow, resulting in variation in the output value of the flow sensor in such a case. Accordingly, detection of the variation in the output of the flow sensor may notify the magnitude of the angular velocity. In this case, variation in the temperature in the casing 2 caused by variation in the ambient temperature may affect the detection precision. Accordingly, the heater wires 3 are wound around the outside of the casing 2 to perform feedback control by means of a control circuit (not shown). Two thermisters 4 and 9 detect the temperature of the heater wire and the atmospheric temperature in the casing 2 to perform energizing control of the heater wires 3 according to these detection temperatures. Because superimposed information obtained by these two thermisters 4 and 9 performs temperature control, the heater wire temperature is moderately overshot to compensate the time lag of the atmospheric temperature elevation in the casing 2 with regard to the temperature elevation of the heater wires 3. For this reason, the rising characteristics of the temperature elevation is improved to rapidly attain a stable condition and the extreme overshot of the heater temperature is simultaneously suppressed. In such a way, trouble such as blow of a temperature fuse can be avoided and adverse effect on an electronic circuit is also relieved. In assemblage, the holder assembly 1 can be secured only by pressing the holder assembly 1 into the casing 2 with no securing members such as a ring screw (a plate end) or punch caulking operation required whereby the number of assemblage and cost can be reduced. As given by dotted lines in FIG. 5, in this case, pressing the holder assembly 1 deflects the casing 2, but the holder portion 1a of the holder assembly 1 can easily be pressed with pressurized force in a degree that causes no deformation thereof. Accordingly, the inner contact surface of the projected portion 1b of the holder portion 1a with the casing 2 need not be processed with extremely high precision. Because deflection of the casing 2 occurs less frequently with increased thickness thereof, the thickness on the portion is 1/10 or less the pressed diameter. The holder assembly 1 is pressed utilizing the deflecting effect of the casing 2 and contact area of the holder assembly 1 with the casing 2 is large, such that the heat of the casing 2 is rapidly transferred to the holder assembly 1 whereby the gas is heated from both sides of the casing 2 and the holder assembly 1. The holder portion 1a is so formed that the gas efficiently flows along the inner walls of the casing 2 and structures such as a flow sensor and a piezo plate in the holder assembly 1 rapidly follow the gas flow thermally, whereby the temperatures of these structures rapidly rise and are stabilized, resulting in improvement in the detection characteristics. Because the outer periphery of the casing 2 is cylindrical or in the form of a single, low taper of 1/10 or less the diameter without a concave or convex portion or a curved portion (with regard to the axial direction), winding of the heater wires can easily be operated and thermal conduction from the heater wires to the casing 2 is satisfactory. In addition, the thermister 9 is disposed in the gas flow passage between the holder assembly 1 and the casing 2, such as the real-time detection of the gas temperature is possible for performing high-degree temperature control. The thermisters 4 and 9 disposed inside and outside the casing 2 may be connected either in series or parallelly.

Claims: A gas rate sensor provided with a holder assembly (1) having a holding portion for holding a flow sensor and the like and a cylindrical casing (2) for housing the holder assembly (1) by means of a plural number of projections (1b), whereby on the outside of the casing (2) heater wires (3) are wound, and with a temperature detection element, characterized in that the projections (1b) are arranged at the outer periphery of the holding portion (1a) and are provided with a peripherical contact surface area, in that the wall thickness of those parts of the metallic casing (2) against which the projections (1b) of the metallic holding portion (1a) are pressed, is 1/10 or less the diameter of this part whereby the deflection of the casing (2) provides a large compressive contact area between the contact surface on the projections (1b) and the casing (2) such that the heat of the casing is rapidly transferred to the holder assembly (1), and in that the temperature detection element (9) is disposed in the flow passage of the gas between the holder assembly (1) and the casing (2) thereby performing the energizing control of the heater wires (3). A gas rate sensor in accordance with Claim 1, characterized in that the casing (2) is made of iron or an iron alloy, in that the outer periphery of the casing is cylindrical or tapered so that the difference between the diameters on the two ends of the outer periphery of the casing (2) is zero or 1/10 or less of the diameter, and in that the inner surface has a stepped portion (2a) defining a first and a second axially dislocated portion having different diameters. A gas rate sensor in accordance with Claim 1 or 2, with another temperature detection element (4) being provided at the heater wires (3), characterized in that the energizing control of the heater wires (3) is performed on the basis of the detection signal from both temperature detection elements (9, 4). A gas rate sensor in accordance with Claim 1 to 3, characterized in that the gas flow passage is provided between the convex wall surfaces (1h) devided by three projections (1b) disposed on the outer periphery of the holder assembly (1) and the wall surfaces of the casing (2).

Inventors: OBARA, KAZUFUMI, OKAZAKI, KUNIO, SHIRAISHI, MASARU, TAKAHASHI, FUMITAKA C/O K.K. HONDA GIJUTSU, TAKAHASHI, MASAYUKI, TANABE, TOHRU, YORIMOTO, KOJI
Applicants: HONDA GIKEN KOGYO KABUSHIKI KAISHA, STANLEY ELECTRIC CO., LTD.
Application year: 1988
Main classification: G01P9
IPC codes: G01P9