JP2006307750A - Sensor controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor controller capable of integrally controlling the driving of a sensor outputting, as weak electric signals, the state of the detected state of exhaust gases and a device requiring a large capacitance for driving in the form of a single controller. <P>SOLUTION: The weak electric signals output from an NOx sensor 60 installed in the route of an exhaust pipe 30 on the downstream side of a catalyst 40 is input into this sensor controller 100. Since the sensor controller 100 is connected to an ECU 90 through a bidirectional serial communication cable 210, it is disposed near the NOx sensor 60 to prevent a detection accuracy from being lowered by noise. Further, since an added injection 54 is drivingly controlled by the sensor controller 100, the signal cable in which a large current for the driving flows is unnecessary to be wired up to the ECU 90. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sensor control device that controls driving of a plurality of exhaust sensors attached to an exhaust passage of an internal combustion engine.

Exhaust gas discharged from automobiles contains nitrogen oxides (NOx) in addition to carbon monoxide (CO) and hydrocarbons (HC). In recent years, a process for reducing and discharging harmful nitrogen oxides into harmless gas has been performed. For example, a NOx selective reduction catalyst (SCR) is installed in the exhaust passage in the exhaust passage of the exhaust gas discharged from the engine, and urea water as a reducing agent solution is injected into the exhaust gas and then passed through the catalyst. A system for reducing NOx to harmless gases such as carbon dioxide (CO ₂ ) and nitrogen (N ₂ ) has been proposed (see, for example, Patent Document 1).

  In addition, a system in which a NOx storage reduction catalyst is installed to reduce the NOx emission amount has been proposed. The NOx occlusion reduction catalyst has a characteristic of storing NOx when the air-fuel ratio of the exhaust gas is lean, and reducing and releasing the stored NOx when the air-fuel ratio becomes rich. In the system using this catalyst, fuel is injected into the exhaust gas so that the air-fuel ratio becomes intermittently rich during lean operation, and NOx stored in the NOx storage reduction catalyst is reduced to harmless gas and discharged. Processing is performed.

  In an internal combustion engine equipped with such a system, a plurality of sensors are attached around a NOx storage reduction catalyst or a NOx selective reduction catalyst provided in an exhaust passage, or a DPF. Specifically, at least one of a full-range air-fuel ratio sensor, a temperature sensor, a pressure sensor, and the like (collectively referring to these sensors for detecting a state related to exhaust gas, hereinafter referred to as “exhaust sensor”), It is attached upstream or downstream of the catalyst. Further, a NOx sensor for measuring the NOx concentration in the exhaust gas is attached to the downstream side of the catalyst.

These exhaust sensors and NOx sensors are connected to and controlled by an engine control device (hereinafter referred to as “ECU”) that performs various controls related to engine driving such as air-fuel ratio control and ignition control. The ECU is usually installed at a position away from the exhaust passage, such as near the engine room, and is connected to the exhaust sensor via a long signal cable. However, some exhaust sensors can only output the detected exhaust gas status (for example, temperature and concentration of a specific gas) as a weak electrical signal due to its characteristics, and are affected by noise and resistance loss due to signal cables. If received, there is a risk of degrading detection accuracy. Therefore, it is effective to dispose the sensor control device that controls the driving of the exhaust sensor in the vicinity of the exhaust sensor mounting position while being provided separately from the ECU, and to control the sensor control device by the ECU. (For example, refer to Patent Document 2).
JP-A-10-33948 JP-A-11-304758

  By the way, in a drive circuit for driving an injection device for injecting fuel into exhaust gas in a system using a NOx storage reduction catalyst or an injection device for injecting urea into exhaust gas in a system using a NOx storage reduction catalyst, A current capacity larger than the current capacity for drive control of the exhaust sensor is usually required. When the drive circuit of the injection device is provided in the ECU, there is a possibility that the ECU will be increased in size and there is a possibility that the amount of generated heat will increase, so there is a need to provide a structure for dissipating heat. . Further, as described above, since the ECU is installed at a position away from the exhaust passage, there is a high possibility that the signal cable that electrically connects the ECU and the injection device is deteriorated or disconnected. For this reason, the signal cable requires specifications for preventing large current leakage, voltage drop, and heat generation due to deterioration and disconnection, and there is a problem that it is difficult to reduce the cost.

  The present invention has been made in order to solve the above-described problems. It is preferable to drive a sensor that outputs a detected state of exhaust gas as a weak electric signal or a device that requires a large current capacity for driving. An object of the present invention is to provide a sensor control device that can be integrated and controlled as one control device.

  In order to achieve the above object, a sensor control device according to a first aspect of the present invention is provided downstream of the position of a catalyst provided in an exhaust passage of an internal combustion engine in the exhaust gas flow direction, and is circulated through the exhaust passage. And a weak signal output sensor that outputs a detection result as an electric signal having a maximum current value of 1 mA or less or a maximum voltage value of 100 mV or less, and the weak signal output sensor. A weak signal output sensor drive control circuit for controlling the driving of the output sensor and outputting a sensor signal corresponding to the electric signal obtained from the weak signal output sensor, and the position of the catalyst in the exhaust passage or the position thereof Catalyst purification liquid injection that is provided upstream of the exhaust gas in the flow direction and injects a purification liquid into the exhaust passage for assisting purification of exhaust gas by the catalyst. A catalyst purification liquid injection device drive control circuit for controlling the drive of the catalyst purification liquid injection device based on the received drive signal, and a sensor signal received from the weak signal output sensor drive control circuit, A microcomputer that outputs the drive signal for driving the catalyst purification liquid injection device to the catalyst purification liquid injection device drive control circuit, and an engine that is connected to the microcomputer and controls the internal combustion engine by bidirectional serial communication And a communication circuit for performing communication with the control device.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, in addition to the weak signal output sensor, at least one exhaust sensor attached around the catalyst. And an exhaust sensor drive control circuit that is provided corresponding to the exhaust sensor and outputs a sensor signal corresponding to an electrical signal obtained from the exhaust sensor to the microcomputer.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the invention, the weak signal output sensor measures the NOx concentration in the exhaust gas flowing through the exhaust passage. This is a NOx sensor in which the maximum current value of the electric signal output is 1 mA or less.

  According to a fourth aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the microcomputer has an abnormality in driving the catalyst purification liquid injection device. An abnormality determination means for determining whether or not an abnormality signal is output to the engine control device using the communication circuit when the abnormality determination means determines that an abnormality has occurred. To do.

  According to a fifth aspect of the present invention, in addition to the configuration of the first aspect, the distance between the engine control device and the sensor control device is the sensor control device. The sensor control device is installed in the internal combustion engine so as to satisfy a relationship that is longer than a distance between the device and the weak signal output sensor.

  In the sensor control device according to the first aspect of the present invention, a weak signal output sensor that outputs a detection result relating to the state of the exhaust gas as an electrical signal having a maximum current value of 1 mA or less or a maximum voltage value of 100 mV or less, and catalyst purification liquid injection A weak signal output sensor drive control circuit and a catalyst purification liquid injection device drive control circuit, each of which is a drive control circuit with the device, and communicates with the engine control device by bidirectional serial communication. Each can be arranged at a distance from the control device. That is, since the weak signal output sensor and the weak signal output sensor drive control circuit can be arranged close to each other, the signal cable that electrically connects the two can be set to be short overall, and noise and signal can be set. There is no possibility that the detection accuracy related to the exhaust gas state will be lowered due to the influence of resistance loss of the cable. Similarly, since the catalyst purification liquid injection device and the catalyst purification liquid injection device drive control circuit can be arranged close to each other, the deterioration due to the routing of the signal cable as in the case where they are arranged apart from each other. And the risk of disconnection or the like can be reduced.

  Then, independent of the engine control device, a weak signal output sensor drive control circuit and a catalyst purification liquid injection device drive control circuit are integrated into a sensor control device, so that the engine control device can be increased in size and structure. Can be prevented from becoming complicated. In addition, since communication between the sensor control device and the engine control device is performed by bidirectional serial communication, it is possible to prevent a reduction in communication accuracy between the two. Furthermore, since serial communication is used, the number of signal lines constituting the signal cable can be reduced.

  Further, in the sensor control device of the invention according to claim 2, in addition to the configuration of the invention of claim 1, at least one exhaust sensor and an exhaust sensor drive control circuit for driving the exhaust sensor And. Therefore, it is not necessary to perform drive control by the engine control device for the exhaust sensor in addition to the weak signal output sensor, and the processing load of the engine control device can be reduced. Further, since the exhaust sensor is also disposed at a position close to the installation position of the weak signal output sensor, the exhaust sensor drive control circuit can be disposed close to the exhaust sensor. As a result, the signal cable that electrically connects the two can be set to be short overall, and there is no possibility of degrading the detection accuracy related to the exhaust gas state due to noise or resistance loss of the signal cable. .

  Further, in the sensor control device of the invention according to claim 3, in addition to the configuration of the invention according to claim 1 or 2, the NOx sensor having a maximum current value of the output electric signal of 1 mA or less is specified as the weak signal output sensor. Is. Since the current value of the electrical signal output from the NOx sensor is very small as described above, if the exhaust gas purifying device of the present invention is disposed in the vicinity of the NOx sensor, the signal cable through which the electrical signal flows can be shortened. Thereby, there is no possibility that the detection accuracy of the NOx sensor is lowered due to the influence of noise or resistance loss of the signal cable.

  Further, in the sensor control device of the invention according to claim 4, in addition to the configuration of the invention according to any one of claims 1 to 3, whether or not an abnormality has occurred in the drive of the catalyst purification liquid injection device by the abnormality determination means. When an abnormality occurs, an abnormality signal is output to the engine control device using the communication circuit. Since the sensor control device includes such an abnormality determination unit, it is not necessary to provide an external device, a sensor, or the like for failure diagnosis of the catalyst purification liquid injection device, and the manufacturing cost can be reduced. Further, it is not necessary for the engine control apparatus itself to perform a failure diagnosis process for the catalyst purification liquid injection apparatus, and the processing load on the engine control apparatus can be reduced.

  Further, in the sensor control device of the invention according to claim 5, in addition to the effect of the invention according to any of claims 1 to 4, the value of the electric signal output from the weak signal output sensor to the sensor control device is Although it is very small and easily affected by noise, etc., communication is performed between the engine control device and the sensor control device by bidirectional serial communication, so communication with high signal communication accuracy even if the distance between the two is long It can be performed. As a result, the three members are arranged in a state where the distance between the sensor control device and the engine control device is increased with respect to the distance between the weak signal output sensor and the weak signal output sensor drive control circuit. If the position is determined, the degree of freedom of the arrangement position can be increased while maintaining the signal communication accuracy, and the influence of noise or the like in the output of the weak signal output sensor can be effectively reduced.

  DESCRIPTION OF EMBODIMENTS Embodiments of an exhaust gas purification control apparatus including a sensor control apparatus embodying the present invention will be described below with reference to the drawings. First, a schematic configuration around an exhaust system of an internal combustion engine 1 including an NOx sensor 60, an additional injector 54, and a sensor control device 100 as an example of an exhaust gas purification control device will be described with reference to FIG. FIG. 1 is a diagram showing a schematic configuration around an exhaust system of the internal combustion engine 1.

  An internal combustion engine 1 shown in FIG. 1 includes a piston 21 and a cylinder 22, an engine 20 for driving an automobile, an exhaust pipe 30 for releasing exhaust gas discharged from the engine 20 to the outside of the vehicle, and an exhaust pipe 30. A catalyst 40 provided on the path, a sensor control device 100 that drives and controls an exhaust sensor provided around the catalyst 40, and an ECU (engine control device) that communicates with the sensor control device 100 by bidirectional serial communication 90. The internal combustion engine 1 is configured to control the air-fuel ratio in a predetermined lean region (for example, A / F = 22) based on a command from the ECU 90 and realize lean combustion in the engine 20.

  The catalyst 40 provided on the path of the exhaust pipe 30 is a NOx occlusion reduction catalyst in the present embodiment, occludes NOx when the air-fuel ratio of the exhaust gas is lean, and occludes NOx when the air-fuel ratio becomes rich. It has a characteristic of reducing and releasing. Although not shown, the catalyst 40 includes an oxidation catalyst and a DPF (diesel particulate filter, particulate removal filter) for removing soot in the exhaust gas. The exhaust pipe 30 corresponds to the “exhaust passage” in the present invention.

  Next, the internal combustion engine 1 includes a full-range air-fuel ratio sensor 55, a first temperature sensor 56, a second temperature sensor 59, a first pressure sensor 52, and a second pressure sensor 58 described later as exhaust sensors. The NOx sensor 60 is also provided as a weak signal output sensor that detects the oxygen concentration and NOx concentration in the exhaust gas and outputs a weak signal. These exhaust sensors and the like are connected to the sensor control device 100 via analog signal cables provided individually.

  The full-range air-fuel ratio sensor 55 is a sensor for detecting the oxygen concentration in the exhaust gas over a wide area, and outputs a current value that changes according to the oxygen concentration to the sensor control device 100. On the path of the exhaust pipe 30, the full-range air-fuel ratio sensor 55 is provided at a position near the engine 20 (combustion chamber) on the upstream side of the catalyst 40.

  The first temperature sensor 56 and the second temperature sensor 59 manage the activation temperature of the catalyst 40, and manage the temperature of exhaust gas when performing incineration removal (refreshing) of the soot accumulated in the DPF. It is a sensor. The resistance value changes in accordance with the detected temperature of the exhaust gas, and the resistance value is detected by the sensor control device 100. The first temperature sensor 56 and the second temperature sensor 59 are provided on the upstream side and the downstream side, respectively, on the path of the exhaust pipe 30 so as to sandwich the catalyst 40 therebetween.

  Further, a second pressure sensor 58 is provided on a passage of a bypass 57 that connects the upstream side and the downstream side of the exhaust pipe 30 so as to straddle the catalyst 40. The second pressure sensor 58 detects a differential pressure between the pressure on the upstream side and the pressure on the downstream side of the exhaust pipe 30 and outputs it to the sensor control device 100. Based on the detection result of the second pressure sensor 58, determination of clogging of the DPF and detection of failure of the DPF are performed.

  Next, the NOx sensor 60 provided on the downstream side of the catalyst 40 on the path of the exhaust pipe 30 is a sensor for detecting the oxygen concentration and the NOx concentration in the exhaust gas that has passed through the catalyst 40. The NOx sensor 60 outputs two types of current values, that is, a current value that changes according to the oxygen concentration in the exhaust gas and a current value that changes according to the NOx concentration in the exhaust gas, to the sensor control device 100. . Note that the NOx sensor 60 and the NOx sensor control circuit 140 to be described later may be any one that adopts a known configuration, and specifically, can adopt the structure disclosed in Japanese Patent Application Laid-Open No. 11-304758. Therefore, further detailed description is omitted. The NOx concentration detected by the NOx sensor 60 is generally several tens to several hundred ppm, and the current value corresponding to the NOx concentration is a weak current having a magnitude of 0.1 to several hundreds (μA). The NOx sensor 60 corresponds to the “weak signal output sensor” in the present invention.

  Further, the internal combustion engine 1 includes an additional injector 54 for injecting fuel as a purification liquid that promotes purification of the catalyst 40 with respect to the exhaust gas. The additional injector 54 is provided to inject fuel into the exhaust gas passing through the exhaust pipe 30 to make the air-fuel ratio rich. The additional injector 54 is located upstream of the exhaust air pipe 30 with respect to the entire region air-fuel ratio sensor 55. It is arranged with the injection port facing inside. The additional injector 54 is also electrically connected to the sensor control apparatus 100, and a driving voltage for driving is applied. The additional injector 54 is connected to a fuel supply pipe 53 for supplying fuel to be injected from a fuel tank (not shown). The fuel supply pipe 53 is provided with a control valve 51 electrically connected to the sensor control device 100, and opening / closing control is performed by the sensor control device 100. The additional injector 54 corresponds to the “catalyst purification liquid injection device” in the present invention.

  Further, a first pressure sensor 52 is provided between the control valve 51 of the fuel supply pipe 53 and the additional injector 54. The first pressure sensor 52 detects the pressure of the fuel supplied to the additional injector 54 and outputs a voltage value corresponding to the pressure to the sensor control device 100.

  In such an internal combustion engine 1, the signal cable connecting the weak signal output sensor that outputs a weak electric signal such as the NOx sensor 60 and the sensor control device 100 has a decrease in detection accuracy due to the influence of resistance loss, noise, and the like. In order to prevent this, it is desirable to be 2 meters or less. For this reason, in the present embodiment, the sensor control device 100 is arranged within a radius of 1 meter from the arrangement position of the catalyst 40.

  On the other hand, ECU90 is normally arrange | positioned in the engine room vicinity etc. of a motor vehicle. For this reason, the distance between the sensor control device 100 and the ECU 90 is longer than the distance between the exhaust sensor and the sensor control device 100. For this reason, the sensor control device 100 and the ECU 90 are electrically connected by the bidirectional serial communication cable 210 so that the signal can be exchanged between the two. In the present embodiment, the international standard protocol CAN (Controller Area Network) standardized as ISO11898 is used as the communication protocol.

  Next, the internal configuration of the sensor control device 100 will be described with reference to FIG. FIG. 2 is a block diagram showing an internal configuration of the sensor control apparatus 100. As shown in FIG.

  As shown in FIG. 2, the sensor control device 100 includes a CPU 111 that controls the sensor control device 100, a RAM 113 that temporarily stores various data, a catalyst purification program that will be described later, and a catalyst in a casing (not shown). A microcomputer 110 having a ROM 112 in which initial values and threshold values of variables used in the purification program are stored is provided.

  Note that the CPU 111, the ROM 112, and the RAM 113 of the microcomputer 110 have known configurations. The ROM 112 is provided with various storage areas not shown, and a catalyst purification program (to be described later), various coefficients used in the catalyst purification program, calculation formulas, and the like are stored in a predetermined storage area. Similarly, various storage areas not shown are also provided in the RAM 113, and when the catalyst purification program is executed, the catalyst program, various variables used in the catalyst program, timer count values, etc. are temporarily stored in a predetermined storage area. Is remembered.

  The sensor control device 100 is provided with a control circuit for controlling the NOx sensor 60, each exhaust sensor, the additional injector 54, etc., and is connected to the microcomputer 110, respectively. Specifically, a temperature sensor input circuit 120, a pressure sensor input circuit 130, a NOx sensor control circuit 140, an air-fuel ratio sensor control circuit 150, and driver circuits 160 and 170 are provided, and an exhaust sensor and an additional injector 54 corresponding to each of them are provided. Etc. are connected. The sensor control device 100 is provided with a communication circuit 180. Further, the sensor control device 100 is provided with a power supply circuit 190 for reducing the voltage supplied from the external power supply 200 to a potential used in the microcomputer 110 and each circuit. The driver circuits 160 and 170 are supplied with voltage (potential VBAT) from the power source 200. Note that a control circuit for controlling each of the exhaust sensors, specifically, the temperature sensor input circuit 120, the pressure sensor input circuit 130, and the air-fuel ratio sensor control circuit 150 are the “exhaust sensor drive control circuit” according to the present invention. Is equivalent to.

  Based on the resistance values of the first and second temperature sensors 56 and 59, the temperature sensor input circuit 120 transmits a sensor signal corresponding to the temperature of the exhaust gas detected by each sensor to the microcomputer 110. The pressure sensor input circuit 130 receives a sensor signal corresponding to the injected fuel pressure detected by the first pressure sensor 52 based on the voltage value output from the first and second pressure sensors 52 and 58, and the second pressure sensor 58. A sensor signal corresponding to the differential pressure between the upstream side and the downstream side of the catalyst 40 in the exhaust pipe 30 detected in step S is transmitted to the microcomputer 110. One of the signal lines of the first and second temperature sensors 56 and 59 and the first and second pressure sensors 52 and 58 is grounded.

  The NOx sensor control circuit 140 controls the NOx sensor 60 based on an instruction from the microcomputer 110, and according to each of the oxygen concentration in the exhaust gas and the NOx concentration based on the current value output from the NOx sensor 60. The sensor signal is transmitted to the microcomputer 110. The air-fuel ratio sensor control circuit 150 controls the entire region air-fuel ratio sensor 55 based on an instruction from the microcomputer 110, and responds to the oxygen concentration in the exhaust gas based on the current value output from the entire region air-fuel ratio sensor 55. The sensor signal is transmitted to the microcomputer 110. The NOx sensor control circuit 140 corresponds to the “weak signal output sensor drive control circuit” in the present invention.

  The driver circuit 170 is supplied with the voltage VBAT from the power supply 200, and controls the voltage applied to the control valve 51 based on an instruction from the microcomputer 110, thereby controlling the opening and closing of the control valve 51. The control valve 51 is grounded. Further, the driver circuit 160 is supplied with the voltage VBAT from the power source 200 via the additional injector 54, and controls the voltage applied to the additional injector 54 based on an instruction from the microcomputer 110, thereby performing injection control of the additional injector 54. ing. The driver circuit 160 is connected to a current detection circuit 161 that is grounded. The current detection circuit 161 monitors a current value when the driver circuit 160 controls the additional injector 54 in a catalyst purification program described later. When an abnormality occurs, an abnormality signal is output to the microcomputer 110, whereby the sensor control apparatus 100 can perform a failure diagnosis (OBD: On Board Diagnostics). The driver circuit 160 corresponds to the “catalyst purification liquid injection device drive control circuit” in the present invention.

  The communication circuit 180 is a circuit for performing bidirectional communication with the ECU 90 (see FIG. 1) via the bidirectional serial communication cable 210. As described above, the communication circuit 180 is configured to transmit signals including various information to the ECU 90 and to receive signals including various information from the ECU 90 using the protocol CAN.

  Among the control programs executed in the sensor control apparatus 100 having such a configuration, a catalyst purification program for detecting the state of the catalyst 40 for purifying exhaust gas and refreshing the catalyst 40 will be described below with reference to FIGS. This will be described with reference to FIG. FIG. 3 is a flowchart of the main routine of the catalyst control program. FIG. 4 is a flowchart of a subroutine of the catalyst control program. FIG. 5 is a flowchart of a subroutine of the catalyst control program. Hereinafter, each step of the flowchart is abbreviated as “S”.

  In the microcomputer 110, before the catalyst purification program is executed, a process for storing n (for example, 500) lean retention times Tl (n) in a predetermined storage area of the RAM 113 is executed. The lean retention time Tl (n) corresponds to the duration of time until the catalyst 40 enters the NOx occlusion saturation state immediately after the refresh in the lean air-fuel ratio state, and is a determination index for determining the deterioration state of the catalyst 40. It becomes.

  The catalyst 40 of the internal combustion engine 1 stores NOx when the air-fuel ratio of the exhaust gas is in a lean state. The catalyst purification program of the present embodiment reduces and releases NOx by injecting fuel into the exhaust gas and making the air-fuel ratio rich when the NOx occlusion of the catalyst 40 becomes saturated. Thus, a series of processes for refreshing the catalyst 40 is performed.

  When the catalyst purification program shown in FIG. 3 is executed, it is first determined whether or not the catalyst downstream side exhaust gas temperature Te2 detected by the second temperature sensor 59 is higher than the catalyst activation temperature Teth1 (for example, 150 ° C.). Is performed (S1). While the catalyst downstream side exhaust gas temperature Te2 is equal to or lower than the catalyst activation temperature Teth1, standby is performed by repeating S1 (S1: NO). Then, when the catalyst downstream side exhaust gas temperature Te2 becomes higher than the catalyst activation temperature Teth1, it is determined that the catalyst 40 is in an active state, that is, a state where NOx can be occluded and reduced (S1: YES), and the process proceeds to S2.

  Next, a subroutine for fuel injection processing (Rich spike injection processing) for controlling the air-fuel ratio of the exhaust gas to be rich is executed (S2). As shown in FIGS. 4 and 5, in the Rich spike injection process, first, a request for a CDR (target injection amount of fuel set on the ECU 90 side) value is made to the ECU 90 (S20). The CDR value request signal output from the CPU 111 is transmitted to the ECU 90 via the bidirectional serial communication cable 210 by the communication circuit 180. When ECU 90 receives the CDR request signal, ECU 90 transmits the CDR value to sensor control device 100.

  The sensor control device 100 returns to S20 until the CDR value is not yet received, and repeatedly requests the ECU 90 for the CDR value (S21: NO, S20). When the CDR value is received from the ECU 90 (S21: YES), the CDR value is multiplied by a predetermined coefficient L, and the injection line pressure as the fuel pressure in the fuel supply pipe 53 detected by the first pressure sensor 52 is obtained. A value (L × CDR / g (Pinj)) divided by a predetermined function g (Pinj) corresponding to the sensor output Pinj is calculated. This calculation result is stored in the RAM 113 as the fuel injection time TCDR of the additional injector 54, and “1” is stored as an adjustment value M for adjusting the injection time TCDR described later (S22). Then, a calculation based on the duty ratio calculation function f (TCDR) stored in the ROM 112 is performed, and the calculation result is stored as an additional injector drive duty ratio Dinj for determining the drive power of the additional injector 54 (S23). .

  Next, a drive voltage is applied to the control valve 51 from the driver circuit 170 to open the valve, and fuel pressure is applied to the additional injector 54 (S25). Then, power is supplied from the driver circuit 160 to the additional injector 54 based on the additional injector drive duty ratio Dinj, whereby driving of the additional injector 54 is started (S26), and fuel is injected into the exhaust gas.

  Next, it is confirmed whether or not a Shut-off (driving stop) signal is received from the ECU 90 (S27). If the Shut-off signal has been received (S27: YES), the power supply to the additional injector 54 is stopped and the drive is stopped (S51), and the valve is closed by the drive of the control valve 51 (S52). Returning to the main routine of FIG.

  If the Shut-off signal has not been received (S27: NO), the current detection circuit 161 performs an abnormality diagnosis of the driver circuit 160 by the determination processing of S30 to S33 shown in FIG. First, in S30, standby is performed by repeating S30 until the timing at which the additional injector driver drive signal voltage Vinj (voltage applied to the additional injector 54) becomes High level (S30: NO). When the additional injector driver drive signal voltage Vinj becomes the High level (S30: YES), the additional injector drive current Iinj (current flowing through the additional injector 54) is compared with the additional injector wiring abnormality determination threshold THhigh stored in the ROM 112. (S31). When the additional injector drive current Iinj is equal to or less than the additional injector wiring abnormality determination threshold THhigh (S31: NO), an additional injector wiring abnormality signal is output to the ECU 90 assuming that the current at the high level is abnormal (S35). . The additional injector wiring abnormality signal output from the CPU 111 is transmitted to the ECU 90 via the bidirectional serial communication cable 210 by the communication circuit 180. Then, as shown in FIG. 4, the drive of the additional injector 54 is stopped (S51), and the control valve 51 is closed (S52), and the process returns to the main routine of FIG. On the other hand, as shown in FIG. 5, if the additional injector drive current Iinj is larger than the additional injector wiring abnormality determination threshold value THhigh (S31: YES), the process proceeds to S32 because there is no problem with the current at the high level.

  In S32, standby is performed by repeating S32 until the timing at which the additional injector driver drive signal voltage Vinj becomes the Low level (S32: NO). When the additional injector driver drive signal voltage Vinj becomes the Low level (S32: YES), the additional injector drive current Iinj is compared with the additional injector wiring abnormality determination threshold THlow stored in the ROM 112 (S33). When the additional injector drive current Iinj is equal to or greater than the additional injector wiring abnormality determination threshold THlow (S33: NO), an additional injector wiring abnormality signal is output to the ECU 90, assuming that there is an abnormality in the current at the low level. (S35). The additional injector wiring abnormality signal output from the CPU 111 is transmitted to the ECU 90 via the bidirectional serial communication cable 210 by the communication circuit 180. Then, as shown in FIG. 4, the drive of the additional injector 54 is stopped (S51), and the control valve 51 is closed (S52), and the process returns to the main routine of FIG. On the other hand, as shown in FIG. 5, if the additional injector drive current Iinj is less than the additional injector wiring abnormality determination threshold THlow (S33: YES), it is determined that there is no problem with the current at the low level, and the process proceeds to S40 shown in FIG. . Each of the determination means in S30 to S33 corresponds to “abnormality determination means” in the present invention.

  In the process of S40 to S50 in FIG. 4, the adjustment (adjustment) of the injection amount of the fuel injected from the additional injector 54 is performed. First, the output (air-fuel ratio sensor A / F output) Uaf from the air-fuel ratio sensor control circuit 150 based on the current value corresponding to the oxygen concentration in the exhaust gas detected by the full-range air-fuel ratio sensor 55 is stored in the ROM 112. The rich A / F setting lower limit value THrich (for example, 10) is compared (S40). If the air-fuel ratio sensor A / F output Uaf is larger than the rich A / F setting lower limit value THrich (S40: YES), then it is compared with the rich A / F setting upper limit value THlean (for example, 13.5) stored in the ROM 112. (S41). If the air-fuel ratio sensor A / F output Uaf is smaller than the rich A / F setting upper limit value THlean (S40: YES), the process proceeds to S42 assuming that the oxygen concentration in the exhaust gas is within the normal range.

  In S42, it is confirmed whether or not the output current value NIp1 corresponding to the oxygen concentration in the exhaust gas after passing through the catalyst 40 detected by the NOx sensor 60 is less than the rich spike end determination threshold value THrs (S42). When the current value NIp1 is equal to or greater than the rich spike end determination threshold value THrs (S42: NO), the rich fuel is used for the reduction of NOx stored in the catalyst 40, and all of the NOx is not reduced. (The catalyst 40 is not refreshed). Therefore, the process returns to S27, and the fuel injection from the additional injector 54 is continued while the additional injector drive duty ratio Dinj remains unchanged. If the current value NIp1 corresponding to the oxygen concentration in the exhaust gas after passing through the catalyst 40 is less than the rich spike end determination threshold value THrs (S42: YES), it is determined that NOx is all reduced and the catalyst 40 is refreshed. Then, the drive of the additional injector 54 is stopped (S51), and the control valve 51 is closed (S52), and the process returns to the main routine of FIG.

  In S40 of FIG. 4, when the air-fuel ratio sensor A / F output Uaf becomes equal to or less than the rich A / F setting lower limit value THrich (S40: NO), the constant β preset and stored in the ROM 112 is injected. Subtraction (M−β) from the adjustment value M for adjusting the time TCDR (“1” is stored when the processing of S43 or S45 is performed for the first time), and the result is the new adjustment value. It is stored as M (S45). On the other hand, when the air-fuel ratio sensor A / F output Uaf becomes equal to or greater than the rich A / F setting upper limit value THlean in S41 (S41: NO), the constant α previously set and stored in the ROM 112 is the same as described above. It is added to the adjustment value M (M + α), and the result is stored as a new adjustment value M (S43).

  Then, the adjustment value M whose value has been changed by the process of S43 or S45 is compared with each of the upper limit value Mmax and the lower limit value Mmin of the adjustment value M that is preset and stored in the ROM 112 (S46). First, the adjustment value M is compared with the upper limit value Mmax, and if it is less than the upper limit value Mmax, it is further compared with the lower limit value Mmin. If the adjustment value M is larger than the lower limit value Mmin (S46: YES), it is determined that the adjustment value M is within the normal value range, and the adjustment value M and the injection time TCDR whose values are updated in S43 or S45, Multiplied by (M × TCDR). The injection time TCDR updated by the calculation result is stored as a new injection time TCDR (S47). As the injection time TCDR is updated, the calculation based on the duty ratio calculation function f (TCDR) is performed again in the same manner as in S23, and the calculation result is stored as the additional injector drive duty ratio Dinj (S48). Since the electric power supplied from the driver circuit 160 to the additional injector 54 follows the additional injector drive duty ratio Dinj, the amount of fuel injected from the additional injector 54 is changed by this process. Then, the process returns to S27, and the subsequent processing is continued.

  Incidentally, in S46, when the adjustment value M becomes equal to or higher than the upper limit value Mmax, or when the adjustment value M becomes equal to or lower than the lower limit value Mmin (S46: NO), there is a problem in adjusting the injection amount of the additional injector 54. Is determined, and an additional injector abnormality signal is output to the ECU 90 (S50). The additional injector abnormality signal output from the CPU 111 is transmitted to the ECU 90 via the bidirectional serial communication cable 210 by the communication circuit 180. Then, as shown in FIG. 4, the drive of the additional injector 54 is stopped (S51), and the control valve 51 is closed (S52), and the process returns to the main routine of FIG.

  When the Rich spike injection process (S2) shown in FIG. 3 is completed, the process proceeds to S5, and the output current value NIp1 from the NOx sensor control circuit 140 is 0 mA or less while the air-fuel ratio of the exhaust gas after passing through the catalyst 40 remains rich. If the current value NIp1 is 0 mA or less, the standby is performed by repeating S5 (S5: NO). If it is determined that the current value NIp1 is greater than 0 mA and the exhaust gas after passing through the catalyst 40 has become lean (S5: YES), the lean time counter Tlean stored in the RAM 113 is set to “0”. At the same time, the lean time counter Tlean starts counting (S6).

  Next, the NOx determination in which the output current value NIp2 from the NOx sensor control circuit 140 based on the current value according to the NOx concentration in the exhaust gas after passing through the catalyst 40 detected by the NOx sensor 60 is stored in the ROM 112 in advance. It is compared with the value Ip2th (S7). While the concentration of NOx is low and the output current value NIp2 is equal to or less than the NOx determination value Ip2th (S7: NO), NOx is occluded by the catalyst 40 and NOx is not detected downstream from the catalyst 40. And S7 is repeated to wait. When the output current value NIp2 becomes larger than the NOx determination value Ip2th (S7: YES), the process proceeds to S9.

  In S9, for the n lean retention times Tl (n) stored in the RAM 113, the data stored as the second lean retention time Tl (2) is set as the first lean retention time Tl (1). The storing process is executed. Similarly, the data stored as the nth lean holding time Tl (n) in the order of the third and fourth are set as the (n−1) th lean holding time Tl (n−1). The storing process is performed. Note that the data stored as the first lean retention time Tl (1) before this processing is executed is discarded.

  When these data migration processes are completed, the count value of the lean time counter Tlean is stored as the nth lean holding time Tl (n). That is, the count value of the lean time counter Tleane that has started counting in S6 is stored as the latest lean holding time Tl (n).

  In this manner, the lean retention time, that is, the time until the NOx occlusion is saturated after the catalyst 40 is refreshed is stored for the past n times. Here, if the average value of the lean holding time for n times and the average value of the latest lean holding time for C times are obtained and compared, it can be confirmed whether the lean holding time is shortened. In some cases, the exhaust gas contains sulfur oxides. When the sulfur oxides are adsorbed on the catalyst 40 and inhibit the NOx occlusion, the NOx occlusion amount decreases and the lean retention time is shortened. At this time, if the catalyst 40 is subjected to heat treatment, the sulfur oxide can be dissociated and the deterioration state of the catalyst 40 can be recovered. In the following process, a series of processes for determining whether or not to perform a heat treatment (CAT Burning process) on the catalyst 40 is performed.

  First, an average value TlA1 of n lean retention times stored in the RAM 113 is calculated (S10). In this process, the lean retention time average value TlA1 is calculated based on the following calculation formula and stored in a predetermined storage area of the RAM 113.

  Similarly, the average value TlA2 of the latest C lean retention times among the n lean retention times is calculated (S11). In this process, the lean retention time average value TlA2 is calculated based on the following calculation formula and stored in a predetermined storage area of the RAM 113.

なお、Ｃは、予め定められた整数値（例えば１０）であり、ｎよりも小さい値が設定されている。

C is a predetermined integer value (for example, 10), and a value smaller than n is set.

  Then, it is determined whether or not the lean retention time average value TlA2 is smaller than a value (TlA1 × K) obtained by multiplying the lean retention time average value TlA1 by a predetermined coefficient K (S12). A value (for example, 0.8) that is larger than 0 and smaller than 1 is set in the coefficient K for determination. When the lean retention time average value TlA2 is equal to or greater than the value obtained by multiplying the lean retention time average value TlA1 by the coefficient K (S12: NO), the lean retention time is not shortened, that is, the catalyst 40 is deteriorated by sulfur oxides. It is determined that it is not, and the process returns to S1.

  When the reduction and storage of NOx by the catalyst 40 are repeatedly performed (S1 to S12), the catalyst 40 gradually deteriorates due to the sulfur oxide, and the lean storage time is shortened by reducing the storage amount of NOx by the catalyst 40. It will become. When the average value TlA2 of the latest C lean retention times becomes smaller than a value obtained by multiplying the past n times of lean retention time average values TlA1 by a coefficient K (S12: YES), the processing of S13 to S18 is executed. Dissociation of the sulfur oxide from the catalyst 40 is achieved.

  First, in S13, a burning request signal (CAT Burning request signal) is transmitted to the ECU 90 to cause the catalyst 40 to perform heat treatment (a process for controlling the temperature of the catalyst 40 to a high temperature at which sulfur oxide can be removed). (S13). The burning request signal output from the CPU 111 is transmitted to the ECU 90 via the bidirectional serial communication cable 210 by the communication circuit 180.

  When the ECU 90 receives the burning request signal, the ECU 90 increases the fuel injection amount from an injector (not shown) provided on the intake side of the engine 20 by a predetermined amount, and increases the fuel ratio in the fuel mixture to make the air-fuel ratio rich. Thus, the exhaust gas temperature is raised by the reaction of the oxidation catalyst provided in the NOx storage reduction catalyst 40 to heat the catalyst 40.

  Next, whether or not the catalyst downstream side exhaust gas temperature Te2 detected by the second temperature sensor 59 is higher than a catalyst burning temperature Teth2 (for example, 600 ° C.) as a temperature at which the sulfur oxide adsorbed on the catalyst 40 can be removed. The process which judges whether is performed (S15). If the catalyst downstream side exhaust gas temperature Te2 is equal to or lower than the catalyst burning temperature Teth2 (S15: NO), S15 is repeated and the standby is performed because the catalyst 40 is not sufficiently heated.

  When the catalyst downstream side exhaust gas temperature Te2 becomes higher than the catalyst burning temperature Teth2 (S15: YES), the burning time counter Tburn stored in the RAM 113 is set to “0” and initialized, and the burning time counter Tburn is set. The count process is started (S16).

  In the next S17, a process is performed to determine whether or not the count value of the burning time counter Tburn is larger than a burning process time threshold Tth that is predetermined as a time for performing the CAT Burning process (S17). If the count value of the burning time counter Tburn is equal to or less than the burning processing time threshold value Tth (S17: NO), it is assumed that sufficient time has not passed to recover the deterioration state of the catalyst 40, and S17 is repeated and waits. Is done.

  If the count value of the burning time counter Tburn becomes larger than the burning processing time threshold value Tth (S17: YES), it is determined that a sufficient time has elapsed for the catalyst 40 to be sufficiently heated and to recover the deteriorated state. Accordingly, in the next S18, a burning end signal (CAT Burning end signal) is transmitted to the ECU 90 (S18). The burning end signal output from the CPU 111 is transmitted to the ECU 90 via the bidirectional serial communication cable 210 by the communication circuit 180. When the ECU 90 receives the burning end signal, the ECU 90 reduces the fuel injection amount from an injector (not shown) provided on the intake side of the engine 20 and reduces the fuel ratio in the fuel mixture to control the air-fuel ratio to the lean region. By doing so, the lean combustion in the engine 20 is restarted. Then, returning to S5, the respective processes of NOx occlusion and reduction by the catalyst 40 are repeatedly executed (S1 to S12).

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the present embodiment, CAN is used for communication with the ECU 90 by the communication circuit 180. However, the communication circuit 180 is not limited to this, and any communication protocol may be used. In this embodiment, a NOx occlusion reduction catalyst is used as the catalyst 40, but a NOx selective reduction catalyst may be used. In this case, urea water or ammonia may be injected from the additional injector 54 instead of fuel. Of course, as for each coefficient, etc., an optimum coefficient may be set in accordance with the NOx selective reduction catalyst.

  Further, the contents of the failure diagnosis by the sensor control device 100 may be various forms other than those described in the present embodiment. For example, diagnosis of disconnection or short circuit of the sensor, diagnosis of abnormality of the sensor element, and the like may be performed.

  Further, in the present embodiment, when executing the CAT Burning process, a burning request signal is transmitted to the ECU and the fuel injection amount of the injector on the intake side is increased by a predetermined amount from the ECU. The sensor control device 100 may be configured to perform the CAT Burning process so as to increase the fuel injection amount of the additional injector 54.

  The present invention can be applied to a sensor control device including a sensor that outputs a weak electric signal and a drive control circuit thereof.

1 is a diagram showing a schematic configuration around an exhaust system of an internal combustion engine 1. FIG. 2 is a block diagram showing an internal configuration of a sensor control device 100. FIG. It is a flowchart of the main routine of a catalyst control program. It is a flowchart of the subroutine of a catalyst control program. It is a flowchart of the subroutine of a catalyst control program.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 30 Exhaust pipe 40 Catalyst 54 Additional injector 55 Whole area air-fuel ratio sensor 60 Sensor 90 ECU
DESCRIPTION OF SYMBOLS 100 Sensor control apparatus 110 Microcomputer 140 NOx sensor control circuit 150 Air-fuel ratio sensor control circuit 160 Driver circuit 180 Communication circuit

Claims (5)

It is provided downstream of the position of the catalyst provided in the exhaust passage of the internal combustion engine in the exhaust gas flow direction, detects the state of the exhaust gas flowing through the exhaust passage, and the detection result is a maximum current value of 1 mA or less or the maximum A weak signal output sensor that outputs an electric signal having a voltage value of 100 mV or less;
A weak signal output sensor drive control circuit connected to the weak signal output sensor for controlling the driving of the weak signal output sensor and outputting a sensor signal corresponding to an electrical signal obtained from the weak signal output sensor;
Catalyst purification in which the position of the catalyst in the exhaust passage or upstream of the position of the catalyst in the flow direction of the exhaust gas is injected into the exhaust passage to purify the exhaust gas by the catalyst to assist the purification of the exhaust gas. A catalyst purification liquid injection device drive control circuit that is connected to the liquid injection device and controls the drive of the catalyst purification liquid injection device based on the received drive signal;
Based on the sensor signal received from the weak signal output sensor drive control circuit, the microcomputer that outputs the drive signal for driving the catalyst purification liquid injection device to the catalyst purification liquid injection device drive control circuit;
A sensor control device comprising: a communication circuit that is connected to the microcomputer and communicates with an engine control device that controls the internal combustion engine by bidirectional serial communication. In addition to the weak signal output sensor, at least one exhaust sensor mounted around the catalyst;
2. An exhaust sensor drive control circuit provided corresponding to the exhaust sensor and outputting a sensor signal corresponding to an electrical signal obtained from the exhaust sensor to the microcomputer. The sensor control device according to 1.   The weak signal output sensor is a NOx sensor in which a maximum current value of the electrical signal output by measuring a NOx concentration in exhaust gas flowing through the exhaust passage is 1 mA or less. The sensor control apparatus according to 1 or 2.   The microcomputer includes abnormality determining means for determining whether or not an abnormality has occurred in driving the catalyst purification liquid injection device, and when the abnormality determining means determines that an abnormality has occurred, The sensor control device according to claim 1, wherein an abnormality signal is output to the engine control device using a communication circuit. The sensor control device is connected to the internal combustion engine so that a distance between the engine control device and the sensor control device is longer than a distance between the sensor control device and the weak signal output sensor. The sensor control device according to claim 1, wherein the sensor control device is installed.

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