Gas rate sensor

The gas rate sensor in the present invention is provided with a holder assembly having a metallic holding portion for holding flow sensors and a cylindrical casing containing the holder assembly and heater wires which are wound around the outside thereof. The outer periphery of the holding portion is provided with a plural number of projections which are brought into compressive contact with the inner periphery of the casing for enabling pressing of the holder assembly into the casing. A temperature detection element is disposed in a gas flow passage between the holder assembly and the casing for performing energizing control of the heater wires.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a gas rate sensor for maintaining 
especially gas temperature constant. 
(2) Description of the Prior Art 
Conventional gas 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 this 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. 
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. Pat. 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. 
SUMMARY OF THE INVENTION 
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 a 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 casing is made of iron or an iron alloy with the outer periphery having 
a single taper of an axial diameter which is the same or within 1/10 and 
with a step among the two different diameter portions inside thereof and 
these different diameter portions. The thickness of the pressing portion 
into which the holding portion of the holder assembly is pressed is made 
not more than 1/10 the diameter of the pressing portion thereby easily 
providing a structure of reasonal detection characteristics. 
The temperature detection elements are arranged not only in the inside of 
the casing but also in the heater wires to control the heater wires based 
on detection signals. from these tempature detection elements thereby 
preventing the extreme overshot of the heater wire temperature.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 illustrates diagrams giving one embodiment of the present invention, 
in which FIG. 1(a) is a partically cutaway 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 assembly 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 assemby 1, 
wherein FIG. 2(a) is a longitudinal cross-sectional view thereof and FIG. 
(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 eccentric 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, convey 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. 
1b)) 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 in the form of a taper 
of 1/10 or less the diameter and the thickness of the portion into which 
the holder portion 1a of the holder assembly 1 is pressed 1/10 or less the 
diameter in the 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) illustrates 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 lead 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 of 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 establishes 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 temperatrure 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 parallel.