Patent Application
20100183046
The present invention relates generally to a temperature sensor to be installed in an exhaust system of internal combustion engines.
There are known so-called exhaust temperature sensors which measure the temperature of exhaust gas flowing through a path such as the inside of a catalytic converter or an exhaust pipe of automobile exhaust emission control device using a thermo-sensitive device.
A thermister whose electric characteristics are sensitive to the temperature is disposed inside a bottomed cylindrical metallic cover. In order to enhance the thermally sensitive response of the thermister surrounded by the metallic cover, an insulating material which is good at thermal conductivity is disposed in a space formed between an inner circumferential surface of the metallic cover and an end surface of a sheath pin so that after received by the metallic cover, the heat of exhaust gas is transmitted to the thermister through the insulating material. An electric signal produced by the thermister whose electric characteristics are sensitive to the temperature is transmitted through electrode wires to a control device in which the temperature is to be measured.
Such a temperature sensor is disclosed in patent documents 1 and 2. The temperature sensor, as illustrated in
An internal combustion engine in which the temperature sensor usually vibrates during running thereof. Such vibration is transmitted from the exhaust pipe 800 to the sheath pin 505 of the temperature sensor through the boss 704 and the rib 601. Specifically, the rib 601 and the sheath pin 505 are welded together, so that the vibration is transmitted from the rib 601 directly to the sheath pin 505.
Consequently, the vibration of the sheath pin 505 becomes strong (high frequency and great amplitude), which may cause the temperature sensitive portion to vibrate at high acceleration.
An excessive stress may, thus be exerted on the top end of the sheath pin 505, the thermister 505 disposed on the top of the sheath pin 505, or a welded between the sheath pin 505 and the rib 601.
The excessive stress on the thermister 501 may result in breakage of the thermister 501 or disconnection of the elecdtrode wire 502 of the thermister 505. The excessive stress on the weld between the sheath pin 505 and the rib 601 may result in cracks or breakage of the sheath pin 505.
Therefore, in
Patent Document 1: Japanese Patent First Publication No. 2002-350239
Patent Document 2: Japanese Patent First Publication No. 2006-47273
The structure of Patent document 1 or 2, however, face the problem that it is impossible to bring the resonance frequency of the top end of the temperature sensor out of the resonance frequency band of the vibration of the exhaust pipe, thus resulting in possibility of the breakage of the thermister 501 or the disconnection of the electrode wires 502.
When the rib 601 is prolonged toward the top end to increase the resonance (primary) frequency of the sheath pin 505, it will cause the resonance to be about 500 times, so that the stress acting on the electrode wires 502 located on the top end side of the temperature sensor to be increased greatly. This result in a difficulty in avoiding the disconnection of the electrode wires 502.
The present invention was made in order to solve the prior art problems. It is an object to provide a temperature sensor which reduces the transmission of vibration and is excellent in durability.
In order to achieve the above object, the present invention, as recited in claim 1, is a temperature sensor including a temperature sensitive device which is disposed in a flow path through which fluid flows and whose electric characteristic changes as a function of temperature of the fluid in the flow path, signal lines connected at top end sides thereof to said temperature sensitive device through electrode wires and at base end sides thereof to lead wires for connection with an external circuit, a sheath member retaining the signal lines therein, and a holding member which holds an outer circumferential surface of said sheath member directly or indirectly through another member, characterized in that a resonance (primary) frequency at a top end of the temperature sensor against acceleration in a radius direction of the temperature sensor is 480 Hz or less.
There was a conventional technical idea of increasing the resonance (primary) frequency at the top end of the temperature sensor to avoid the resonance arising from external vibration. However, the present invention was based on a technical idea opposite the conventional one. Specifically, the decrease in transmission of vibration to the top end of the temperature sensor is achieved by decreasing the resonance (primary) frequency at the top end of the temperature sensor down to 480 Hz or less, thereby avoiding the breakage of the thermister 501 or disconnection of the electrode wires 502 even when the temperature sensor resonates.
The invention, as recited in claim 2, is characterized in that said resonance (primary) frequency is 380 Hz or less against the acceleration in the radius direction of the temperature sensor.
This ensures the durability further and avoids the disconnection of the electrode wires for an increased period of time.
The invention, as recited in claim 3, is characterized in that if a protruding length that is a distance between an inner circumference of said flow path and a top end of the temperature sensor on an axis of the temperature sensor is defined as L1, and a held length that is a distance between a top end of a portion of said sheath member which is held by the holding member directly or indirectly and the top end of the temperature sensor is defined as L2, a relation of L1<L2 is satisfied.
The protruding length L1 is changed frequently according to the object or intended purpose. For instance, the protruding length L1 is changed greatly between when the temperature of a central portion of the flow path is to be measured and when the temperature of an inner edge of the flow path is to be measured. Consequently, when L1<L2, the resonance (primary) frequency at the top end of the temperature sensor depends upon the protruding length L1 as long as a condition such as the diameter of the sheath member is constant. In other words, when the protruding length L1 is short, it will result in an increase in the held length L2, so that the resonance (primary) frequency at the top end of the temperature sensor will become great.
However, in the present invention, the held portion of the sheath member is designed to be located at the base end of the holding member, thereby permitting the held length L2 to be increased sufficiently even when the protruding length L1 is short, which results in a great decrease in resonance (primary) frequency at the top end of the temperature sensor regardless of the protruding length L1.
The breakage of the electrode wires and the temperature sensitive device located at the top end side of the temperature sensor caused by the resonance is, therefore, avoided.
The invention, as recited in claim 4, is characterized in that if a diameter of a portion of the protruding length L1 which holds said temperature sensitive device is defined as a sensor outer diameter D, the sensor outer diameter D is 3.2 mm or less, and the held length L2 is 75 mm or more.
This enables the resonance (primary) frequency at the top end of the temperature sensor to be decreased below 480 Hz as the sensor outer diameter D is decreased and the held length L2 is increased, thereby avoiding the disconnection of the electrode wires.
The invention, as recited in claim 5, is characterized in that said temperature sensitive device is disposed inside a metallic cover.
This shields the temperature sensitive device from the atmosphere of exhaust gas to avoid the reduction-caused deterioration of the temperature sensitive device.
The invention, as recited in claim 6, is characterized in that the temperature sensitive device is characterized as being implemented by a thermister.
This realizes the temperature sensor which is high in measurement accuracy.
The invention, as recited in claim 7, is characterized in that the temperature sensitive device is embedded in a fixing member supplied inside a top end of said metallic cover.
This avoids collision of the temperature sensitive device with the metallic cover so that it is broken when the temperature sensor vibrates following external vibration. Further, the temperature sensitive device is secured by the fixing member inside the metallic cover, thus reducing the vibration of the temperature sensitive device caused by the resonance. This decreases the stress acting on the electrode wires which is developed by the resonance of the temperature sensitive device.
The invention, as recited in claim 8, is characterized in that the temperature sensitive device is sealed by glass.
In high-temperature environments, the metallic cover is oxidized, so that the concentration of oxygen within the metallic cover drops. It is, thus, necessary to avoid the reduction-caused deterioration arising from removal of oxygen from the temperature sensitive device. The reduction-caused deterioration of the temperature sensitive device is, therefore, avoided by sealing the temperature sensitive device using the glass. This ensures the stability in the measurement accuracy of the temperature sensitive device.
Embodiments of an exhaust temperature sensor 1 (temperature sensor) according to the invention will be described below based on drawings.
The exhaust temperature sensor 1 is applied as a sensor to measure the temperature of exhaust gas emitted from an automotive engine and to be installed in, for example, an exhaust pipe of automobiles.
As illustrated in
In this specification, the lower side and the upper side of
The temperature sensitive portion 10 is exposed to the exhaust gas and sensitive to the temperature of the exhaust gas.
The thermister 101 is preferably used as the temperature sensitive device to make the exhaust temperature sensor easily which has a high measurement accuracy.
The thermister 101 is preferably disposed inside the temperature sensitive portion cover 104 to shield the thermister 101 from the exhaust gas, thereby avoiding the deterioration of the thermister 101.
A fixing member is preferably disposed between the thermister 101 and the temperature sensitive portion cover 104 to avoid collision of the thermister 101 with the temperature sensitive portion cover 104 when the exhaust temperature sensor vibrates, so that the thermiaster 101 oscillates. This avoids the damage to the thermister 101 and disconnection of the electrode lines 102 of the thermister 101.
As the fixing material, material which is excellent in thermal conductivity may be used to accelerate the transmission of heat outside the temperature sensitive portion cover 104 to the thermister 101, thereby achieving the exhaust temperature sensor which is excellent in response.
Further, the temperature sensitive portion cover 104 preferably uses alloy such as Inconel that is excellent in oxidation resistance, thereby avoiding the oxidation of the temperature sensitive portion cover 104 and avoiding a change in characteristic of the thermister 101 arising from a decrease in concentration of oxygen in the temperature sensitive portion cover 104. The oxidation of the temperature sensitive cover 104 usually results in a drop in concentration of oxygen in the cover. This may cause the oxygen to be removed from the thermister 101 to compensate for the drop in the concentration of oxygen, thereby changing the characteristics of the thermister 101. This is avoided by making the temperature sensitive portion cover 101 by the anti-oxidation metal.
As the anti-oxidation metal, there is, for example, stainless steel or Inconel
In the thus constructed temperature sensitive portion 10, the sheath pin 105 which corresponds to a sheath member is inserted and disposed at an end thereof.
The sheath pin 105 is cylindrical and made of Inconel. The sheath pin 105 is secured to the temperature sensitive portion cover 104 by crimping or laser-welding. The sheath pin 105 may be press-fitted or resistor-welded into the temperature sensitive portion cover 104.
The thermister 101 is preferably sealed by a glass material. This reduces the deterioration of the temperature sensitive device and makes it excellent in durability.
The sheath pin 105 has the signal lines 103 disposed therein and insulates and protects them. The sheath pin 105 includes the two signal lines 103 made of stainless steel, an insulating portion made of insulating powder such as such as magnesia which is disposed around the signal lines 103, and an outer tube portion made of stainless steel covering the outer circumference of the insulating portion.
Next, the case 20, as illustrated in
The case 20 includes a rib 201 coupled to the outer periphery of the sheath pin 105, a protection tube 202 welded to the outer periphery of the rib 201, and the lead wires 203 connected electrically to the base end of the sheath pin 105.
In
As illustrated in
The top end surface of the rib 201 is seated firmly on the inner peripheral surface of the boss 301 to hermetically seal the exhaust gas flowing inside the exhaust pipe 400.
The thus constructed exhaust temperature sensor 1 outputs an exhaust gas temperature signal, as produced by the thermistor 101, to an external circuit (e.g., an ECU) not shown through the lead wires 203 to detect the temperature of the exhaust gas.
The fixing of the rib 201 and the protection tube 202 is achieved by placing a portion of the outer circumferential surface of the rib 201 in abutment with the inner circumferential surface of the protection tube 202 and welding the outer circumferential surface of the protection tube 202.
The sheath pin 105 is fit in a central hole of the rib 201. The sheath pin 105 and the rib 201 are welded together at a contact between the inner circumferential surface of the rib 201 and the outer circumferential surface of the sheath pin 105.
The holding member, as referred to in this specification, is the substantially integrated member made by laser-welding the rib 201 and the protection tube 202. A held portion of the sheath member is a contact between the sheath member and the rib 201 disposed around the outer periphery of the sheath pin 105.
The features of the exhaust temperature sensor 1 according to the embodiment of the invention will be described below.
The fixing of the rib 201 and the protection tube 202 is, as illustrated in
The sheath pin 105 is fit in the central hole of the rib 201. The sheath pin 105 and the rib 201 are welded together at the contact between the inner circumferential surface of the rib 201 and the outer circumferential surface of the sheath pin 105.
The vibration applied externally to the exhaust temperature sensor 1 is transmitted to the contact (i.e., the held portion) between the inner circumferential surface of the rib 201 and the outer circumferential surface of the sheath pin 105 to induce the vibration and the resonance to which the sheath pin 105 has the contact as a fixed end is subjected. The resonance, as referred to herein, is the characteristic vibration of each member such as the sheath pin 105 having energy which arises from vibration applied thereto.
In this invention, the resonance (primary) frequency at the top end of the exhaust temperature sensor 1 is specified 480 Hz relative to the acceleration of the exhaust temperature sensor 1 in a radius direction thereof.
The reduction in transmission of vibration to the top end of the exhaust temperature sensor 1 may be achieved by bringing the above resonance frequency below 480 Hz. Even when the resonance occurs at the exhaust temperature sensor 1, it avoids the breakage of the thermister 501 or disconnection of the electrode wires 502. The resonance frequency is preferably set to 380 Hz or less, thereby enabling the exhaust temperature sensor 1 which has a high degree of durability and vibration resistance. The vibration resistance is ensured, especially when the exhaust temperature sensor 1 is used in an exhaust system which is to vibrate greatly or required to be prolonged.
Note that the resonance (primary) frequency at the top end of the exhaust temperature sensor 1 may be measured using a laser Doppler oscillometer.
The adjustment of the resonance (primary) frequency at the top end of the exhaust temperature sensor 1 may be achieved by selecting a relation between a protruding length L1 and a held length L2 where the protruding length L1 is, as can be seen in
The inner circumference surface of the exhaust pipe 400 on the axis f the exhaust temperature sensor 1, as referred to above, is an intersection a between an imaginary line (a broken line in
The top end of the held portion, as referred to above, is an end A of the held portion in which the rib 201 and the sheath pin 105 are welded, that is, portions of the rib 201 and the sheath pin 105 which are placed in constant contacting abutment with each other. In this embodiment, the protruding length L1 is also a distance between an end of a tapered portion of the rib 201 o the base end side and the top end of the temperature sensitive portion 10 (i.e., a length of a portion of the exhaust temperature sensor 1 protruding into the exhaust pipe 400).
In this embodiment, the protruding length L1 and the held length L2 preferably have a relation of L1<L2.
The resonance frequency at the top end of the exhaust temperature sensor 1 may be decreased by prolonging the held length L2 as much as possible relative to the protruding length L1, thereby avoiding the disconnection of the electrode wires 102.
The relation among the resonance frequency of the exhaust temperature sensor 1, the protruding length L1, and the held length L2 was checked by heat/resonance durability texts, as illustrated in
As illustrated in
The tests were performed for different values, as listed in table 1, of a sensor outer diameter D that is a diameter of the sheath pin 105 which is the holding member holding the thermister 101 within the protruding length L1 and the held length L2. Results of the tests are shown in table 1 and
Note that the resonance was measured by the above described laser Doppler oscillometer. In the tests, the protruding length L1 was smaller than the held length L1 by 20 mm (L1=L2−20).
Particularly, it is advisable that the sensor outer diameter D be 3.2 mm or less, and the held length L2 be 75 mm or more. This, as can be seen from
It is also found that samples Nos. 25 and 26 in which the held length L2 is as long as 75 mm, but sensor outer diameter D is more than 3.2 mm exceed 480 Hz in the resonance frequency and do not satisfy the target time.
It is also found that samples Nos. 5-8, 14-16, 23, and 24 in which the resonance frequency is 380 Hz or less have improved durability against the disconnection of the electrode wires 102 which is two times longer than the target time or more.
When the sensor outer diameter D is 3.2 mm or less, and the held length L2 is 85 mm or more, the resonance (primary) frequency will be 380 Hz or less.
In the above described embodiment, the rib 201 and the sheath pin 105 are designed so that they placed in direct contact with each other and welded together at the contact therebetween, but however, they may be, as illustrated in
For instance, the temperature sensitive portion cover 104 is so fixed as to cover a portion of the outer circumferential surface of the top end of the sheath pin 105, but the longer temperature sensitive portion cover 104, as illustrated in
In the structure of
The protection tube 204 may be, as illustrated in
The protection tube 202 may also be, as illustrated in
The glass material 107 which has the heat resistance may also be, as illustrated in
The structures may be modified in various ways without departing from the principle of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-107517 | Apr 2007 | JP | national |
| 2008-103995 | Apr 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/057405 | 4/16/2008 | WO | 00 | 3/17/2010 |
