JP2005274554A - Gas detecting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas detecting system using shieldless lead wires, and reducing a cost and an effect due to a noise. <P>SOLUTION: The gas detecting system 1 has the lead wire 53 on the pump side, the common lead wire 54 and the lead wire 55 on the measurement side. Although the lead wires comprise the shieldless lead wire, the effect due to the noise can be reduced, and a degradation of the detection precision of a gas and an element resistance can be inhibited since the lead wires are twisted and tied. Although the gas detecting system 1 generates the noise by carrying a current to a ceramic heater 41, the effect due to the noise generated by carrying the current to the ceramic heater 41 can be reduced, and the degradation of the detection precision of the gas and the element resistance can be inhibited since the lead wires 53, 54, 55 connected to three sensor elements are twisted and tied and coverings for covering the lead wires mutually contact. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas detection system used for air-fuel ratio control of an internal combustion engine for automobiles, for example.

Conventionally, a sensor element in which an oxygen pump cell and an oxygen concentration measurement cell are stacked is known as a sensor element for detecting a specific gas component in a measurement target gas.
The oxygen pump cell and the oxygen concentration measuring cell are formed by sandwiching an oxygen ion conductive solid electrolyte layer between a pair of electrodes, and the sensor element is between the oxygen pump cell and the oxygen concentration measuring cell. A hollow measurement chamber into which a measurement target gas is introduced is provided.

  Also, a gas detection system comprising such a sensor element, a plurality of lead wires connected to the electrodes of the sensor element, and a control unit electrically connected to the plurality of electrodes of the sensor element via the lead wires Is known (see Patent Documents 1 to 3).

  The control unit controls the oxygen concentration in the measurement chamber to be constant by flowing a current through the oxygen pump cell so that the output voltage of the oxygen concentration measurement cell becomes a constant value, and the measurement target gas from the current value flowing through the oxygen pump cell. The process which measures the oxygen concentration in is performed.

The sensor element includes a sensor element having a plurality of electrodes provided on an oxygen ion conductive solid electrolyte body, and a lead wire connected to the electrode of the sensor element. A gas detection system is also known that detects the internal resistance value of a sensor element (solid electrolyte body) based on an electrical signal output via a lead wire at that time or a current (voltage). To Patent Document 4).

Such a gas detection system is used, for example, for applications that detect specific gas components (oxygen, NOx, etc.) contained in exhaust gas such as automobiles. An automobile is equipped with many electrical devices (ignition coils, generators, etc.) that are noise sources, and shield wires are generally used as an example of measures against such noise. The shield wire is a lead wire having a shield portion made of a metal material that covers the periphery of the core wire in an electrically insulated state. By connecting the shield portion to the ground line, the influence of external noise on the core wire is achieved. Can be reduced. That is, by using a shield wire, it is possible to suppress the influence of external noise, and it is also possible to suppress a decrease in gas detection accuracy due to noise. Further, by using a shielded wire that can suppress the influence of such external noise, the detection accuracy when detecting the internal resistance value of the sensor element can be improved.
Japanese Patent Laid-Open No. 10-048180 JP-A-10-142194 JP 2003-185626 A JP 2000-081414 A

However, since the above shielded wire is more expensive than a general lead wire, there is a problem that the gas detection system configured using the shielded wire is expensive.
In contrast, the use of lead wires that do not have shields (hereinafter also referred to as unshielded lead wires) can suppress price increases, but they are controlled by sensor elements due to the effects of noise. The electric signal flowing between the two parts fluctuates, which causes a problem that the gas detection accuracy is lowered. In addition, by using unshielded lead wires, the electrical signal flowing between the sensor element and the resistance detection unit that detects the internal resistance value is affected by noise, and the detection accuracy of the internal resistance value is increased. The problem that it falls will arise.

Therefore, the present invention has been made in view of such problems, and an object thereof is to provide a gas detection system capable of reducing the cost by using a lead wire having no shield part and reducing the influence of noise. .
Another object of the present invention is to provide a gas detection system that can accurately detect the internal resistance value of a sensor element using a lead wire that does not have a shield portion.

  In order to achieve this object, the invention according to claim 1 is directed to an oxygen pump cell in which an oxygen ion conductive solid electrolyte layer is sandwiched between a pair of electrodes, and a pair of oxygen ion conductive solid electrolyte layers. An oxygen concentration measurement cell sandwiched between electrodes, and a measurement chamber into which a measurement target gas is introduced between the oxygen pump cell and the oxygen concentration measurement cell, and the oxygen pump cell and the oxygen concentration measurement cell are stacked. The sensor element, a plurality of lead wires connected to the plurality of electrodes of the sensor element, and the output voltage of the oxygen concentration measurement cell is a constant value electrically connected to the plurality of electrodes of the sensor element via the lead wires. And a control unit that controls the oxygen concentration in the measurement chamber to be constant by passing an electric current through the oxygen pump cell, wherein the plurality of leads have a plurality of electrodes facing the measurement chamber. At least one common lead wire to be connected is included, and the common lead wire is electrically insulated from at least one lead wire other than the common lead wire among the plurality of lead wires. The gas detection system is provided in a form having a contact portion.

  In this gas detection system, at least one lead wire other than the common lead wire among the plurality of lead wires and the common lead wire have a portion in contact with each other in an electrically insulated state. Has been. In other words, of the plurality of lead wires, at least two lead wires including at least the common lead wire have a portion in contact with each other in an electrically insulated state.

  And according to the measurement results (FIGS. 4 and 5 described later) of the measurement conducted by the present inventor, all the lead wires are arranged by arranging at least two or more lead wires in contact with each other. It can be seen that fluctuations in the electrical signal (current) due to the influence of noise can be suppressed as compared with the case where they are arranged apart from each other.

  For this reason, even when a lead wire having no shield portion (unshielded lead wire) is used as the lead wire, the influence of noise can be suppressed, and there is no need to use an expensive shield wire.

  Therefore, according to the gas detection system of the present invention, it is possible to use a lead wire that does not have a shield portion, so that an increase in cost due to the use of the shield wire can be avoided, and at least two wires including a common lead wire can be avoided. The influence of noise can be reduced by bringing the lead wires into contact with each other. Further, since noise resistance as a gas detection system is improved, it is possible to provide a low-cost gas detection system that can appropriately cope with an increase in noise sources due to an increase in various electric devices in an automobile.

  In order to effectively reduce the influence of noise, the lead wire electrically connected to the electrode located outside the measurement chamber of the oxygen concentration measurement cell and the common lead wire are brought into contact with each other, or all the lead wires are brought into contact with each other. It is preferable to make it.

  According to another aspect of the present invention, as described in claim 2, the heater unit that heats the oxygen pump cell and the oxygen concentration measurement cell of the sensor element, and an electrical signal output through a plurality of lead wires including a common lead wire are provided. And a heater control means for detecting the internal resistance value of the oxygen concentration measurement cell based on the detected temperature and controlling the amount of heat generated by the heater unit so that the detected internal resistance value becomes a predetermined target resistance value. It is good to apply to.

  That is, when a heater unit that generates heat by current application is provided, noise may be generated due to the current supplied to the heater unit and connected to a plurality of electrodes in the oxygen pump cell and oxygen concentration measurement cell of the sensor element. The lead wire may be affected by noise due to the current flowing to the heater section.

  Therefore, in the gas detection system having the heater part, the effect of the present invention of reducing the influence of noise on the conducting current of the lead wire can be further exhibited by applying the present invention. That is, by configuring the gas detection system so that at least two lead wires including at least the common lead wire are in contact with each other in a state of being electrically insulated from each other, a remarkable effect regarding noise countermeasures can be obtained. It is possible to suppress a decrease in gas detection accuracy.

  Furthermore, in the present invention, among the lead wires connected to the sensor element, at least two lead wires including at least the common lead wire are brought into contact with each other to reduce noise, so that the internal resistance of the oxygen concentration measurement cell is reduced. The value detection accuracy is also improved. Thereby, the internal resistance value of the oxygen concentration measurement cell can be accurately detected, and the heat generation amount of the heater portion (the current value supplied to the heater portion) can be appropriately controlled based on the internal resistance value.

  Next, in the above gas detection system, as described in claim 3, a bundling member for bundling a plurality of lead wires is provided, and the common lead wire is bundled with other lead wires by the bundling member. Then, it is good to contact with other lead wires.

  That is, when bringing a plurality of lead wires into contact with each other, by binding the plurality of lead wires using a bundling member, at least a portion where the lead wires contact each other can be formed, and the influence of noise can be reduced. .

  As the binding member, for example, an adhesive tape, a binding band, or the like can be used. By using a plurality of binding members, a plurality of lead wires are bound at regular intervals. A large area of the contact portion can be secured, and the noise reduction effect can be improved. In addition, a glass tube or a corrugated tube can be used as the binding member.

  In the gas detection system described above, as described in claim 4, the common lead wire may be brought into contact with the other lead wire by being bound in a form to twist with the other lead wire.

  When bringing a plurality of lead wires into contact with each other, at least a contact portion where the lead wires are in contact with each other can be formed by bundling the lead wires in a twisted manner, and the influence of noise can be reduced.

  In addition, the bundling configuration in which the lead wires are twisted together can bundle a plurality of lead wires without using a bundling member, so that an increase in the number of parts can be prevented by omitting the bundling member. Therefore, it is possible to suppress an increase in the cost of parts as a whole system.

  In addition, as described above, in order to heat the sensor element, the heater part may be provided integrally or close to the sensor element. However, the order (current level) of the electric signal flowing through the heater part is determined by the sensor element. It is larger than the current level of the electric signal flowing through. Therefore, in order to effectively improve the noise resistance of the sensor element, do not bind the lead wire of the heater part to the lead wire including the common lead wire of the sensor element or twist it to the lead wire of the sensor element. Thus, it is preferable that the lead wire of the sensor element is in a non-contact state.

  Furthermore, in the above-described gas detection system, as described in claim 5, the common lead wire may be in contact with all the other lead wires.

  As described above, by bringing the common lead wire into contact with all the other lead wires connected to the sensor element, it is possible to suppress fluctuations in current due to the influence of noise without using shield wires for all the lead wires. Further, in the gas detection system, lead wires having no shield part can be used for all the lead wires, and a greater cost reduction effect can be obtained.

  Moreover, the invention according to claim 6 as another solving means made for achieving the object includes an oxygen ion conductive solid electrolyte body and a plurality of electrodes formed on the solid electrolyte body. A sensor element, a plurality of lead wires connected to a plurality of electrodes of the sensor element, and a resistance detection unit that detects an internal resistance value of the sensor element based on an electrical signal output through the plurality of lead wires A gas detection system, wherein each of the plurality of lead wires is disposed in a form having a portion in contact with any one of the other lead wires in an electrically insulated state. It is a detection system.

  In this gas detection system, a plurality of lead wires through which an electric signal for detecting the internal resistance value of the sensor element flows are all in contact with one of the other lead wires in an electrically insulated state. It is arrange | positioned with the form which has. In this way, by bringing one of the plurality of lead wires into contact with any other lead wire, compared to the case where the plurality of lead wires are all separated, the current due to the influence of noise is reduced. Variations can be suppressed. Therefore, even when a lead wire that does not have a shield part (unshielded lead wire) is used as the lead wire, the influence of noise can be suppressed. Therefore, according to the gas detection system of the present invention, the internal resistance value of the sensor element can be accurately detected without using an expensive shield wire.

  Next, in the above-described gas detection system, as described in claim 7, a bundling member for bundling a plurality of lead wires is provided, and the plurality of lead wires are bound by a bundling member. May be in contact with any other lead.

  In other words, at the time of bringing a plurality of lead wires into contact with each other, by binding a plurality of lead wires of the sensor element using a bundling member, at least a portion where the lead wires come into contact with each other can be formed, thereby reducing the influence of noise. Can do. According to the gas detection system of the present invention, the internal resistance value of the sensor element can be accurately detected via the lead wire by reducing the influence of noise in this way. The specific form and material of the binding member are as described above.

  Moreover, in the above-described gas detection system, as described in claim 8, each of the plurality of lead wires is bundled in a form in which each of the lead wires twists with another lead wire, so Contact with the lead wire.

  When bringing a plurality of lead wires into contact with each other, at least a contact portion where the lead wires are in contact with each other can be formed by bundling the lead wires in a twisted manner, and the influence of noise can be reduced. According to the gas detection system of the present invention, the internal resistance value of the sensor element can be accurately detected via the lead wire by reducing the influence of noise in this way.

  In addition, as described above, in order to heat the sensor element, the heater part may be provided integrally or close to the sensor element. However, the order (current level) of the electric signal flowing through the heater part is determined by the sensor element. It is larger than the current level of the electric signal flowing through. Therefore, in order to effectively improve the noise resistance of the sensor element, do not bind the lead wire of the heater section to the lead wire including the common lead wire of the sensor element or twist it with the lead wire of the sensor element. Thus, it is preferable that the lead wire of the sensor element is in a non-contact state.

(Embodiment 1)
Hereinafter, as a first embodiment to which the present invention is applied, a gas detection system 1 including a full-range air-fuel ratio sensor will be described with reference to the drawings. The gas detection system of the first embodiment detects the oxygen concentration contained in the exhaust gas of the internal combustion engine, and the detection result of the oxygen concentration is used to control the air-fuel ratio of the internal combustion engine.

FIG. 1 is a system configuration diagram illustrating a schematic configuration of the gas detection system 1.
The gas detection system 1 includes a full-range air-fuel ratio sensor element 10, a sensor control circuit 31 connected to the full-range air-fuel ratio sensor element 10, a ceramic heater 41 for heating the full-range air-fuel ratio sensor element 10, and a ceramic heater 41. The heater voltage supply device 43 connected to the is provided. In addition, the gas detection system 1 includes three lead wires (pump-side lead wire 53, common lead wire 54, and measurement-side lead wire) for electrically connecting the full-range air-fuel ratio sensor element 10 and the sensor control circuit 31. 55).

  The heater voltage supply device 43 and the sensor control circuit 31 each start to operate in synchronization with a sensor activation signal input from the outside when the entire region air-fuel ratio sensor element 10 is activated.

  First, as shown in FIG. 1, the full-range air-fuel ratio sensor element 10 has porous electrodes 13 and 14 on both plate surfaces (front side plate surface and back side plate surface) of the solid electrolyte body 12, and oxygen (O2). The oxygen pump cell 11 (hereinafter also referred to as the Ip cell 11) for performing the pumping of the solid electrolyte body 16 has porous electrodes 17 and 18 on both plate surfaces (the front plate surface and the back plate surface), depending on the oxygen concentration. A gas which is an oxygen concentration measurement cell 15 (hereinafter also referred to as a Vs cell 15) that generates an electromotive force and is a space provided between the oxygen pump cell 11 and the oxygen concentration measurement cell 15 and into which a gas to be measured is introduced. Provided between the detection chamber 19, the gas diffusion porous layer 21 disposed in the path for introducing the gas to be measured into the gas detection chamber 19, the oxygen concentration measurement cell 15 and the shielding layer 23, and stores oxygen. With an oxygen reference chamber 25 as a space That.

  Note that the porous electrode 14 of the oxygen pump cell 11 and the porous electrode 17 of the oxygen concentration measurement cell 15 are disposed so as to face the gas detection chamber 19. The solid electrolyte bodies 12 and 16 and the shielding layer 23 are mainly formed of partially stabilized zirconia in which yttria is solid-solved as a stabilizer, and the porous electrodes 13 and 14 are mainly formed of platinum. .

  The sensor control circuit 31 has a known circuit configuration, and includes a pump current drive circuit 33, a voltage output circuit 35, a measurement current supply circuit 37, a resistance value detection circuit 38, a reference voltage comparison circuit 39, A minute current supply circuit 40 is provided.

  Among these, the minute current supply circuit 40 supplies a minute current Icp from the porous electrode 18 side of the oxygen concentration measurement cell 15 to the porous electrode 17 side. When the minute current supply circuit 40 energizes the minute current Icp, oxygen is pumped into the porous electrode 18 side (oxygen reference chamber 25), and the porous electrode 18 functions as an internal oxygen reference source. The voltage output circuit 35 detects an electromotive force Vs generated between the porous electrodes 17-18 of the oxygen concentration measurement cell 15 when the minute current supply circuit 40 energizes the minute current Icp. The reference voltage comparison circuit 39 holds a predetermined reference voltage (450 [mV] in the present embodiment) inside, and compares the electromotive force Vs detected by the voltage output circuit 35 with the reference voltage. And the comparison result is notified to the pump current drive circuit 33. The pump current drive circuit 33 controls the pump current Ip that flows through the oxygen pump cell 11 based on the comparison result received from the reference voltage comparison circuit 39.

The oxygen concentration measurement cell 15 in the entire region air-fuel ratio sensor element 10 is provided for monitoring the atmosphere inside the gas detection chamber 19, and between the porous electrodes 17-18 of the oxygen concentration measurement cell 15, An electromotive force Vs corresponding to the oxygen concentration in the gas detection chamber 19 is generated. In addition, the oxygen pump cell 11 out of the entire range air-fuel ratio sensor pumps or pumps oxygen (O ₂ ) into the gas detection chamber 19 in accordance with the pump current Ip supplied from the pump current drive circuit 33.

That is, in the full-range air-fuel ratio sensor element 10, the electromotive force Vs of the oxygen concentration measurement cell 15 becomes a constant value (450 [mV]), that is, the air-fuel ratio of the gas detection chamber 19 becomes the stoichiometric air-fuel ratio. In addition, oxygen (O ₂ ) is pumped or pumped into the gas detection chamber 19 using the oxygen pump cell 11.

  In the full-range air-fuel ratio sensor element 10 configured in this way, the current value and current direction of the pump current Ip flowing through the oxygen pump cell 11 change according to the oxygen concentration in the gas to be measured. Based on the measurement result, the oxygen concentration in the gas to be measured can be detected. In the present embodiment, a voltage (detection signal) proportional to the amount of the pump current Ip is output from the sensor control circuit 31 to an engine control device (not shown), and the engine control device is based on this detection signal. The oxygen concentration of the gas to be measured is detected.

  The full-range air-fuel ratio sensor element 10 can detect the oxygen concentration in the exhaust gas, for example, by being disposed in the exhaust pipe of the internal combustion engine. Since there is a correlation between the oxygen concentration in the exhaust gas and the air-fuel ratio, the air-fuel ratio of the internal combustion engine can be measured by using the detected oxygen concentration.

  The sensor control circuit 31 includes a resistance detection circuit 38. The resistance detection circuit 38 is a porous electrode 17− when the measurement current Irpvs for measuring the resistance value is supplied from the measurement current supply circuit 37. The electrical resistance value (internal resistance value) Rpvs between the porous electrodes 17-18 in the oxygen concentration measurement cell 15 is detected based on the amount of change in the voltage value between 18 and according to the detected electrical resistance value Rpvs. A resistance value signal (voltage signal) Sr is output to the heater voltage supply device 43. Here, the measurement current supply circuit 37 supplies a measurement current Irpvs (for example, −1.22 [mA]) having a constant current value to the oxygen concentration measurement cell 15 and includes a switching element. When the electric resistance value Rpvs of the oxygen concentration measurement cell 15 is measured, the switching element is driven based on a command signal from the engine control device, and the measurement current Irpvs flows to the oxygen concentration measurement cell 15 side for a predetermined time. To do. The resistance detection circuit 38 is a peak hold circuit for holding the peak value of the voltage change at the time of measuring the electric resistance value Rpvs.

  The heater voltage supply device 43 detects and detects the temperature Tc of the entire region air-fuel ratio sensor element 10 (specifically, the oxygen concentration measurement cell 15) based on the resistance value signal Sr from the sensor control circuit 31. The voltage applied to the ceramic heater 41 is controlled based on the temperature Tc.

  Note that there is a correlation between the temperature Tc in the oxygen concentration measurement cell 15 of the full-range air-fuel ratio sensor element 10 and the electric resistance value Rpvs, and the temperature Tc of the full-range air-fuel ratio sensor is calculated based on the electric resistance value Rpvs. It is possible to detect.

  When the applied voltage VH is applied from the heater voltage supply device 43, the ceramic heater 41 generates a heat generation amount corresponding to the magnitude of the applied voltage VH, and heats the entire region air-fuel ratio sensor element 10. The heater voltage supply device 43 includes a microcomputer. As an internal process of the microcomputer, the temperature Tc of the full-range air-fuel ratio sensor element 10 becomes a normal temperature (for example, 800 [° C.]) higher than the activation temperature (for example, 600 [° C.]). Then, the magnitude of the voltage VH applied to the heater based on the resistance value signal Sr from the sensor control circuit 31 so that the electric resistance value Rpvs of the oxygen concentration measurement cell 15 becomes the target resistance value Rta corresponding to this normal temperature. A temperature control process for adjusting the temperature is executed. As a result, the oxygen pump cell 11 and the oxygen concentration measurement cell 15 are heated to the activation temperature or higher, and the entire region air-fuel ratio sensor element 10 enters an activated state in which oxygen can be detected. The temperature control process executed by the microcomputer provided in the heater voltage supply device 43 may be executed by adopting a known method, and specifically disclosed in Japanese Patent Application Laid-Open No. 2003-185626. Therefore, further explanation will be omitted.

  Next, three lead wires (pump-side lead wire 53, common lead wire 54, and measurement-side lead wire 55) for electrically connecting the full-range air-fuel ratio sensor element 10 and the sensor control circuit 31 will be described. .

  The pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 are core wires made of a metal material (for example, copper, gold, stainless steel alloy, etc.) (specifically, the core wire is a plurality of fine wires made of a metal material). And a covering portion made of an insulating material (for example, resin, rubber, etc.) covering the periphery of the core wire. The pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 are not shielded wires provided with a shield portion made of a metal material for shielding the core wire, but are configured as unshielded lead wires. .

  One end of the pump-side lead wire 53 is electrically connected to the porous electrode 13 of the oxygen pump cell 11, and the other end is electrically connected to the metal terminal 52 of the connection connector 51.

  One end of the common lead wire 54 is branched and is electrically connected to the porous electrode 14 of the oxygen pump cell 11 and the porous electrode 17 of the oxygen concentration measuring cell 15, and the other end is a metal terminal of the connection connector 51. 58 is electrically connected.

  One end of the measurement-side lead wire 55 is electrically connected to the porous electrode 18 of the oxygen concentration measurement cell 15, and the other end is electrically connected to the metal terminal 59 of the connection connector 51. .

  When the connection connector 51 is connected to the connection connector 32 of the sensor control circuit 31, the porous electrodes 13, 14, 17, 18 of the entire region air-fuel ratio sensor element 10 and the sensor control circuit 31 have three leads. They are electrically connected via wires (pump side lead wire 53, common lead wire 54, measurement side lead wire 55).

Next, a perspective view of the three lead wires (pump side lead wire 53, common lead wire 54, measurement side lead wire 55) and connection connector 51 is shown in FIG.
As shown in FIG. 2, the pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 have their ends connected to metal terminals 52, 58, 59, and the metal terminals 52, 58, 59 is housed inside the connection connector 51.

  In addition, the pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 are bundled in a twisted form (twist form) and are in contact with other lead wires, and are connected from the connection connector 51 to the entire region air-fuel ratio. It is arranged over the sensor element 10. In addition, since each core wire is covered with the coating | coated part, each core wire will be in the state electrically insulated mutually, and it is arrange | positioned in the state which the coating | coated parts contact. In FIG. 2, the illustration of the pair of lead wires connected to the ceramic heater 4 is omitted, but the lead wires connected to the ceramic heater 4 are also metal terminals accommodated in the connection connector 51. Are connected to each. However, the lead wire connected to the ceramic heater 4 is not bound in a form twisted to any of the pump side lead wire 53, the common lead wire 54, and the measurement side lead wire 55.

  Here, when the energization is performed via the pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 between the full-range air-fuel ratio sensor element 10 and the connection connector 51, the lead wire arrangement state is different. A description will be given of a measurement test performed for examining the influence of external noise on the current waveform for six patterns. Of the six patterns, three patterns are wiring states to which the present invention is applied, and the other three patterns are conventional wiring states.

  As a measurement result, the current waveform of the current flowing through the measurement-side lead wire 55 among the three lead wires is shown in FIGS. FIG. 4 shows the measurement results for the three patterns in the wiring state to which the present invention is applied, and FIG. 5 shows the measurement results for the three patterns in the conventional wiring state.

  The wiring state to which the present invention is applied is as follows: (1) When three unshielded lead wires are bundled in the twisted form and arranged in a state where the lead wires are in contact with each other (hereinafter also referred to as a first measurement pattern). .), (2) Three binding bands are arranged at substantially equal intervals without twisting the three unshielded lead wires, and the lead wires are bound and arranged so that the lead wires are in contact with each other. In the case (hereinafter also referred to as a second measurement pattern), (3) two unshielded lead wires (common lead wire 54 and measurement side lead wire 55) are bundled in a twisted form so as to be in contact with each other on the pump side. Measurement was performed on three patterns when only the lead wires 53 were disposed apart (hereinafter also referred to as a third measurement pattern).

  In addition, as a conventional wiring state, (4) when three unshielded lead wires are arranged in parallel with a predetermined interval in a non-contact state (hereinafter also referred to as a fourth measurement pattern), 5) The measurement-side lead wire 55 is formed by using a shield wire, the other two wires are formed by unshielded lead wires, and the lead wires are arranged in parallel with a predetermined interval in a non-contact state. In the case (hereinafter also referred to as the fifth measurement pattern), (6) When all three lead wires are formed of shield wires, and the lead wires are arranged in parallel with a predetermined interval in a non-contact state. Measurement was performed on three patterns (hereinafter also referred to as a sixth measurement pattern).

  For the first measurement pattern, the measurement result is shown in FIG. 4A, for the second measurement pattern, the measurement result is shown in FIG. 4B, and for the third measurement pattern, FIG. Shows the measurement results. Moreover, about a 4th measurement pattern, a measurement result is shown to Fig.5 (a), about a 5th measurement pattern, a measurement result is shown to FIG.5 (b), and about a 6th measurement pattern, FIG.5 (c). Shows the measurement results.

  For each pattern, three lead wires are arranged in the vicinity of a noise generating source (specifically, an ignition coil that is connected to a spark plug and supplies a high voltage to the ignition timing), and the measurement side lead wire The measurement test was carried out by measuring the fluctuation state of the current waveform flowing through 55.

  More specifically, a part of each of the lead wires connecting the full-range air-fuel ratio sensor element 10 and the connection connector 51 is arranged in the vicinity of an ignition coil mounted on a gasoline engine (6 cylinders) having a displacement of 3000 [cc]. The current waveform that flows through the measurement-side lead wire 55 by driving the full-range air-fuel ratio sensor element 10 using the above-described sensor control circuit 31 while being arranged and operated at no load and at an engine speed of 3000 [rpm]. This was performed by measuring the fluctuation state of each of the six patterns. The pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 were each formed using a lead wire having a length of about 80 [cm].

  As shown in FIGS. 4 and 5, at least two lead wires are in contact with each other (first measurement pattern, second measurement pattern, and third measurement pattern). Each lead wire is in non-contact with each other ( It can be seen that the noise component is reduced compared to the fourth measurement pattern, the fifth measurement pattern, and the sixth measurement pattern.

  According to this measurement result, when the lead wires are arranged in contact with each other, fluctuations in current due to the influence of noise can be suppressed compared to when the lead wires are arranged in a separated state. I understand. In addition, when the lead wires are arranged in contact with each other, even if unshielded lead wires are used, the noise reduction effect can be obtained equivalently or better than when shielded wires are used. I understand that.

  Further, according to the measurement result of the third measurement pattern, not only when all three lead wires are brought into contact, but also when the common lead wire 54 and the measurement-side lead wire 55 are brought into contact with each other, the influence of noise. It can be seen that it can be suppressed more satisfactorily.

  In addition, in addition to the above six patterns, the inventor of the present application makes contact with the pump-side lead wire 53 and the measurement-side lead wire 55, or makes contact with the pump-side lead wire 53 and the common lead wire 54. The same measurement was performed on the two patterns in order to examine the influence of noise.

  According to the measurement results of the measurement test, when the pump-side lead wire 53 and the common lead wire 54 are brought into contact with each other as compared with the case where the pump-side lead wire 53 and the measurement-side lead wire 55 are brought into contact with each other, the common It was found that the two patterns when the lead wire 54 and the measurement-side lead wire 55 are in contact with each other can more effectively suppress the influence of noise.

  Therefore, when the pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 are brought into contact with each other for the purpose of noise reduction, at least two lead wires including at least the common lead wire 54 are brought into contact with each other. It is desirable to arrange in.

  Further, the contact portion between the lead wires is not limited to the case where all the regions in the region from the entire region air-fuel ratio sensor element 10 to the connection connector 51 are in contact with other lead wires, but the entire region air-fuel ratio sensor element 10 From the measurement results of the measurement test separately conducted by the inventor of the present application, it is possible to reduce the influence of noise even when contact is made in at least a part of the region from the connector to the connector 51.

  In this embodiment, the gas detection chamber 19 corresponds to the measurement chamber described in the claims, the sensor control circuit 31 corresponds to the control unit, and the ceramic heater 41 corresponds to the heater unit. The sensor control circuit 31 and the heater voltage supply device 43 correspond to the heater control means, the solid electrolyte body 12 and the solid electrolyte body 16 correspond to the solid electrolyte layer, and the resistance detection circuit 38 corresponds to the resistance detection unit. Yes.

  As described above, in the gas detection system 1 of the present embodiment, the pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 are composed of unshielded lead wires, but the lead wires twist together. Since they are bundled in a form, the influence of noise can be suppressed, and a decrease in gas detection accuracy can be suppressed. In addition, since the gas detection system 1 does not use a shielded wire, the cost can be reduced. Furthermore, as described above, since the lead wires are bundled in a twisted form, the influence of noise is suppressed, and the electrical resistance value (internal resistance value) of the sensor element (specifically, the oxygen concentration measurement cell 15). ) Reduction in Rpvs detection accuracy can be suppressed.

  Moreover, the gas detection system 1 of this embodiment is provided with the ceramic heater 41 which generate | occur | produces heat by current supply, Noise may generate | occur | produce due to the current supply to the ceramic heater 41, and the noise is on the pump side. The current flowing in the lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 may be affected.

  On the other hand, the pump-side lead wire 53, the common lead wire 54, and the measurement-side lead wire 55 are bundled in a twisted manner, and the covering portions come into contact with each other. The influence of noise to be reduced can be reduced, and the deterioration of the gas detection accuracy and the detection accuracy of the electric resistance value (internal resistance value) Rpvs of the sensor element (oxygen concentration measurement cell 15) can be suppressed.

(Embodiment 2)
Next, as a second embodiment to which the present invention is applied, a gas detection system 100 including a limiting current type air-fuel ratio sensor (hereinafter simply referred to as an A / F sensor) as an oxygen concentration sensor will be described with reference to the drawings. Note that the gas detection system of the second embodiment is also mounted on the internal combustion engine.
In FIG. 6, the gas detection system 100 includes an A / F sensor. From this A / F sensor, oxygen in the exhaust gas is applied in accordance with application of a voltage commanded from a microcomputer (hereinafter simply referred to as a microcomputer) 130. A linear air-fuel ratio detection signal corresponding to the concentration is output. The microcomputer includes a CPU as a central processing unit that executes various known arithmetic processes, a ROM that stores a control program, a RAM that stores various data, and the like, and a bias control circuit 140 and a heater control circuit 160 according to a predetermined control program. Is controlled.

FIG. 7 is a cross-sectional view showing a schematic configuration of the A / F sensor. As shown in FIG. 7, the A / F sensor protrudes toward the inside of the exhaust pipe 125, and mainly includes a cover 123 formed with a plurality of gas introduction holes, the A / F sensor element 110, and the heater unit 120. It is configured.
The A / F sensor element 110 includes a solid electrolyte body 115 mainly composed of zirconia formed in a bottomed cylindrical shape, a porous outer electrode 111 made of platinum formed on the outer surface of the solid electrolyte body 115, and a solid A porous inner electrode 113 made of platinum formed on the inner surface of the electrolyte body 115 and a porous diffusion resistance layer 117 made of alumina, spinel or the like formed on the outer side of the outer electrode 111 are constituted. The heater unit 120 is housed in the A / F sensor element 120 and heats the A / F sensor element 110 (solid electrolyte body 115) to a predetermined temperature (target temperature) by the heat generation.

  In the A / F sensor configured as described above, the A / F sensor element 110 generates a limit current corresponding to the oxygen concentration in a lean region from the stoichiometric air-fuel ratio. Further, in the region richer than the theoretical air-fuel ratio, the concentration of unburned gas such as carbon monoxide (CO) and hydrocarbon (HC) changes substantially linearly with respect to the air-fuel ratio, and the A / F sensor element 110 Generates a limiting current according to the concentration of CO, HC, etc.

  In FIG. 1, a bias command signal Vr for applying a voltage to the A / F sensor element 110 is input from the microcomputer 120 to the D / A converter 133, and is converted into an analog signal Va by the D / A converter 133. And input to the bias control circuit 140. From the bias control circuit 140, either the air-fuel ratio detection voltage or the element resistance detection voltage is applied to the A / F sensor element 110.

  In addition, the bias control circuit 140 detects a sensor current that flows along with application of a voltage to the A / F sensor element 110 with a current detection circuit (resistance detection circuit) 150, and the current detected by the current detection circuit 150. A value analog signal is input to the microcomputer 120 via the A / D converter 135. The heater unit 120 disposed inside the A / F sensor element 110 is controlled by the heater control circuit 160. That is, the heater control circuit 160 executes heat generation control (energization control) of the heater unit 160 to control the element temperature of the A / F sensor element 110. Note that the bias control circuit 140 and the heater control circuit 160 including the current detection circuit 150 may be configured by a known circuit configuration, and thus description thereof is omitted.

  In the gas detection system 100, when an A / F is detected, a positive applied voltage is applied to the A / F sensor element 110, so that an electrical signal (sensor) from the A / F sensor element 110 corresponding to the applied voltage. Current) is output, the air-fuel ratio is obtained from the electrical signal. On the other hand, at the time of detecting the internal resistance (element resistance) of the A / F sensor element 110, a negative applied voltage having a predetermined time constant consisting of a predetermined frequency signal is applied to correspond to the applied voltage. An electrical signal (sensor current) is detected from the A / F sensor element 110. Then, the internal resistance value of the A / F sensor element 110 is detected by dividing the applied voltage by the sensor current at that time.

  Here, also in the gas detection system 100 of the second embodiment, the first lead wire 171 is connected to the inner electrode 113 of the A / F sensor element 110, and the second lead wire 173 is connected to the outer electrode 111, The first lead wire 171 and the second lead wire 173 are connected to the current detection circuit 150, respectively. The first lead wire 171 and the second lead wire 173 are configured to include a core wire made of a metal material and a covering portion made of an insulating material that covers the periphery of the core wire, as in the first embodiment. The lead wire is composed of an unshielded lead wire that does not have a shield portion made of a metal material for shielding the core wire.

  Also in the second embodiment, although not shown in detail, the two first lead wires 171 and the second lead wires 173 are bound in a twisted form (twist form) as in the first embodiment. The lead wires are arranged in contact with each other. In addition, since each core wire is covered with the coating | coated part, each lead wire 171 and 173 will be in the state which mutually insulated the core wire, and is arrange | positioned in the state which the coating | coated parts contact.

  As described above, in the gas detection system 100 of the second embodiment as well, although the first lead wire 171 and the second lead wire 173 are composed of unshielded lead wires, the lead wires 171 and 173 are twisted together. Since they are bundled, the influence of noise can be effectively suppressed, and a decrease in detection accuracy of the air-fuel ratio and detection accuracy of the internal resistance value in the A / F sensor element 110 can be suppressed. Moreover, since the gas detection system 100 does not use a shielded wire, the cost can be reduced.

  The gas detection system 100 according to the second embodiment also includes the heater unit 120, and noise may be generated due to energization of the heater unit 120. The current flowing through the two lead wires 173 may be affected. On the other hand, since the first lead wire 171 and the second lead wire 173 are bundled in a twisted form and the covering portions are in contact with each other, the influence of noise generated due to energization to the heater portion 120 is reduced. From this point of view, it is possible to suppress a decrease in the air-fuel ratio detection accuracy and the internal resistance value detection accuracy in the A / F sensor element 110.

As mentioned above, although embodiment of this invention was described, this invention can take a various aspect, without being limited to said Embodiment 1,2.
For example, the form of bundling between lead wires is not limited to the form of bundling in a twisted form, but a plurality of lead wires using an adhesive tape 57 that is one of the bundling members as shown in FIG. It is also possible to take a form of binding the two. By using such a binding member, a plurality of lead wires can be easily bound, and the complexity of the binding work can be reduced.

In addition to the adhesive tape 57, examples of the binding member include a binding band, an insulating tube, a glass tube, and a corrugated tube.
It is also possible to adopt a bundling form in which a plurality of lead wires are twisted together and then bundled using a bundling member.

  Note that, when the lead wires are bundled only in a twisted form, there is no need for a bundling member, so that there is an advantage that the number of parts can be reduced as a whole system and material cost can be reduced.

  Further, as a form not using the bundling member, a form in which a plurality of lead wires are bundled like a so-called flat cable can be adopted in addition to the form of twisting each other.

  Further, the sensor element is a full-range air-fuel ratio sensor element having two cells of the oxygen concentration measurement cell and the oxygen pump cell shown in the first embodiment, or a one-cell type sensor composed of one solid electrolyte body shown in the second embodiment. The sensor is not limited to other elements, and other sensor elements (NOx sensor element, CO sensor element, etc.) can also be used.

  More specifically, it has a first oxygen pumping cell and an oxygen concentration measurement cell in which an oxygen ion conductive solid electrolyte layer is sandwiched between a pair of electrodes, and communicates with the measurement target gas side via the first diffusion rate limiting layer. And a second oxygen pumping cell in which an oxygen ion conductive solid electrolyte layer is sandwiched between a pair of electrodes, and communicated with the first measurement chamber via a second diffusion rate limiting layer. The present invention may be applied to a NOx sensor (NOx sensor element) including two measurement chambers. In this NOx sensor, a current is supplied to the first oxygen pumping cell so that the output voltage of the oxygen concentration measuring cell becomes a constant value, so that the oxygen concentration in the first measuring chamber is controlled to be constant and the second oxygen pumping is performed. By applying a constant voltage in the direction of pumping oxygen from the second measurement chamber to the cell, it is possible to detect the nitrogen oxide concentration (NOx concentration) in the measurement target gas from the current value flowing through the second oxygen pumping cell. .

  In the NOx sensor having such a structure, since the current flowing through the second oxygen pumping cell is as weak as 1 [mA] at the maximum, the gas detection accuracy tends to be lowered due to the influence of noise caused by electric equipment mounted on the vehicle. However, as in the present invention, a plurality of lead wires connecting the electrodes constituting the NOx sensor and the control unit for detecting the NOx concentration and detecting the internal resistance value of the oxygen concentration measurement cell are twisted together. In other words, it is possible to effectively improve the gas detection accuracy by bringing the lead wires into contact with each other in an electrically insulated state. Furthermore, the detection accuracy of the internal resistance value of the oxygen concentration measuring cell can be improved.

  In addition, it is desirable that the contact between the lead wires is performed in a region that is relatively susceptible to noise in the region from the sensor element to the control unit. Even if it exists, the influence of noise can be reduced appropriately.

1 is a system configuration diagram illustrating a schematic configuration of a gas detection system 1 according to a first embodiment. In the gas detection system 1 concerning Embodiment 1, it is a perspective view of the pump side lead wire 53, the common lead wire 54, the measurement side lead wire 55, and the connection connector 32 which were bundled together in the form which twists. It is a perspective view of a pump side lead wire, a common lead wire, a measurement side lead wire, and a connection connector that are bound using a binding member. It is a measurement result of the measurement test implemented in order to investigate the influence which external noise has on a current waveform about three patterns of the wiring state to which this invention (Embodiment 1) is applied. It is a measurement result of the measurement test implemented in order to investigate the influence which external noise has on a current waveform about three patterns of the conventional wiring state. FIG. 4 is a system configuration diagram illustrating a schematic configuration of a gas detection system 100 according to a second embodiment. In the gas detection system 100 concerning Embodiment 2, it is sectional drawing which shows schematic structure of an A / F sensor (A / F sensor element 110).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,100 ... Gas detection system, 10 ... Full range air-fuel ratio sensor element, 11 ... Oxygen pump cell, 15 ... Oxygen concentration measurement cell, 19 ... Gas detection chamber, 31 ... Sensor control circuit, 32 ... Connection connector, 38 ... Resistance detection Circuit, 41 ... Ceramic heater, 43 ... Heater voltage supply device, 53 ... Pump side lead wire, 54 ... Common lead wire, 55 ... Measurement side lead wire, 57 ... Adhesive tape, 110 ... A / F sensor element, 120 ... Heater 115, solid electrolyte body, 140, bias control circuit, 150, current detection circuit (resistance detection circuit), 160, heater control circuit, 171, first lead wire, 173, second lead wire.

Claims (8)

An oxygen pump cell comprising an oxygen ion conductive solid electrolyte layer sandwiched between a pair of electrodes; and an oxygen concentration measuring cell comprising an oxygen ion conductive solid electrolyte layer sandwiched between a pair of electrodes, the oxygen pump cell comprising: A sensor element formed by stacking the oxygen pump cell and the oxygen concentration measurement cell in a form including a measurement chamber into which a measurement target gas is introduced between the oxygen concentration measurement cell and
A plurality of lead wires connected to the plurality of electrodes of the sensor element;
An oxygen is electrically connected to the plurality of electrodes of the sensor element via the lead wires, and a current is passed through the oxygen pump cell so that an output voltage of the oxygen concentration measurement cell becomes a constant value. A control unit for controlling the concentration to be constant;
A gas detection system comprising:
The plurality of lead wires include at least one common lead wire connected to the plurality of electrodes facing the measurement chamber,
The common lead wire is disposed in a form having a portion in contact with at least one lead wire other than the common lead wire in an electrically insulated state among the plurality of lead wires;
A gas detection system. A heater unit for heating the oxygen pump cell and the oxygen concentration measurement cell of the sensor element;
An internal resistance value of the oxygen concentration measurement cell is detected based on an electrical signal output through the plurality of lead wires including the common lead wire, and the detected internal resistance value becomes a predetermined target resistance value. Heater control means for controlling the amount of heat generated by the heater section,
The gas detection system according to claim 1, comprising: A bundling member for bundling a plurality of lead wires is provided,
The common lead wire is brought into contact with another lead wire by being bound to the other lead wire by the binding member;
The gas detection system according to claim 1 or 2, characterized by the above. The common lead wire is brought into contact with the other lead wires by being bound in a form twisted with the other lead wires;
The gas detection system according to any one of claims 1 to 3, wherein: The common lead is in contact with all of the other leads;
The gas detection system according to any one of claims 1 to 4, wherein: A sensor element comprising an oxygen ion conductive solid electrolyte body and a plurality of electrodes formed on the solid electrolyte body;
A plurality of lead wires connected to the plurality of electrodes of the sensor element;
A resistance detector that detects an internal resistance value of the sensor element based on an electrical signal output via the plurality of lead wires;
A gas detection system comprising:
The plurality of lead wires are all arranged in a form having a portion that is in an electrically insulated state from any other lead wire,
A gas detection system. A bundling member for bundling a plurality of lead wires is provided,
The plurality of lead wires are bundled from the bundling member, so that any of them is in contact with any other lead wire,
The gas detection system according to claim 6. The plurality of lead wires are all in contact with other lead wires by being bundled in a form that twists with other lead wires,
The gas detection system according to claim 6 or 7, characterized by the above.