JP2005315152A - Secondary air supply system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly operate an air pump while protecting the air pump. <P>SOLUTION: As this secondary air supply system, a secondary air pipe 35 is connected to the upstream side of a catalyst 31 in an exhaust pipe 24, and a secondary air pump 36 is arranged in an upstream part of its secondary air pipe 35. An ECU 40 estimates the pump temperature before starting operation of the secondary air pump 36, and calculates operable time of the secondary air pump 36 on the basis of the estimated pump temperature. Whether or not to permit operation of the secondary air pump 36 is determined on the basis of the operable time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a secondary air supply system for an internal combustion engine.

  A catalyst device for purifying exhaust gas is provided in an exhaust pipe of an internal combustion engine, and in order to improve the purification efficiency of the catalyst device, a technique of supplying secondary air to the upstream side of the catalyst device by operating an air pump Has been proposed.

  Here, if the secondary air supply is insufficient, the catalyst device is not sufficiently warmed up. If the secondary air supply is excessive, the catalyst device is overheated. Therefore, there is a technique for setting the operation time of the air pump to avoid such inconvenience and operating the air pump within the operation time.

  For example, in Patent Document 1, the stop time from the stop of the internal combustion engine to the start is determined according to the temperature difference between the coolant temperature at the time of stop of the internal combustion engine and the coolant temperature at the time of the next start, and the stop time is short. When it was time, the operation time of the air pump was corrected. Further, in Patent Document 2, the start timing and end timing of the secondary air supply period are set by the engine temperature, the catalyst temperature, the intake air temperature, and the like at the time of starting the engine.

  The existing techniques including the above-mentioned Patent Documents 1 and 2 set the operation time of the air pump in order to optimize the catalyst activity and protect the catalyst device, but the following inconvenience occurs. That is, the air pump has a DC motor or the like as a constituent element, and it is necessary to operate the air pump within a predetermined operating temperature range in order to protect the air pump and achieve stable operation. However, in the existing technology, during the operation of the air pump, the temperature of the air pump rises excessively beyond the operating temperature range, resulting in inconveniences such as failure. For this reason, there is a demand for a technology that can appropriately set the operation time of the air pump in view of protecting the air pump.

In addition, it is necessary to operate the air pump in addition to the catalyst warm-up at the time of starting the engine in order to perform failure diagnosis of the secondary air system, etc. Even when the air pump is restarted, the air pump operating time is set appropriately. A technology that can be used is desired.
JP 2000-240434 A Japanese Patent No. 3351835

  An object of the present invention is to provide a secondary air supply system for an internal combustion engine that can appropriately operate the air pump while protecting the air pump.

  According to the first aspect of the present invention, the pump temperature is estimated before the operation of the air pump is started, and the operable time of the air pump is calculated based on the estimated pump temperature. Then, it is determined whether or not the operation of the air pump is permitted based on the calculated operable time. In this case, if the pump temperature before starting operation is relatively low, the operable time is relatively long, and if the pump temperature is relatively high, the operable time is relatively short. As described above, excessive temperature rise of the air pump during operation can be suppressed, and the air pump can be protected. In addition, the air pump can be appropriately operated within a desired operation time. Even when the air pump is restarted during the operation of the internal combustion engine, the operating condition of the air pump can be properly determined.

  According to a second aspect of the present invention, the time required for the pump temperature to reach the predetermined operating upper limit temperature from the estimated temperature at the time after starting the operation of the air pump may be calculated as the operable time. Thereby, the possible pump operation time can be accurately grasped each time.

  In the invention described in claim 3, the required operation time of the air pump is set each time, and the operation of the air pump is permitted when the operable time is longer than the required operation time. In this case, the air pump can be reliably operated within a desired operation request time. Further, if the air pump is operated even though the operable time is short, the air pump must be stopped and restarted immediately thereafter, and as a result, the air pump is repeatedly operated / stopped. On the other hand, according to the present invention, such inconvenience can be avoided, and deterioration of drivability due to repeated operation / stop of the air pump can be prevented.

  According to the fourth aspect of the present invention, when the failure diagnosis of the secondary air system including the air pump is performed, the time required for the failure diagnosis is set as the operation request time. Thereby, the failure diagnosis of a secondary air system can be implemented reliably. When a plurality of failure diagnosis processes are selectively performed, the operation request time may be appropriately set according to the contents of failure diagnosis each time.

  Moreover, in invention of Claim 5, pump temperature is estimated one by one according to progress of time during a pump stop. After the operation of the air pump is stopped, it is considered that the pump temperature basically decreases with the passage of time. In this case, it is possible to reliably grasp the change in the pump temperature while the pump is stopped without requiring an additional configuration such as a temperature sensor.

  In the sixth aspect of the present invention, a temperature gradient corresponding to the ambient temperature around the air pump is set, and the pump temperature is sequentially estimated according to the passage of time while the pump is stopped. Thereby, for example, when the temperature of the air pump is not easily lowered due to heat received from the surroundings, the pump temperature can be accurately grasped.

  Basically, the pump temperature continues to decrease with the passage of time while the pump is stopped, but when the temperature decreases to the intake air temperature or the cooling water temperature, the pump temperature is considered to converge in the vicinity thereof. Therefore, as described in claim 7, the pump temperature estimated according to the passage of time during the pump stop and at least one of the intake air temperature or the cooling water temperature of the internal combustion engine are compared, and the higher one is estimated as the pump temperature. Value is good.

  In invention of Claim 8, pump temperature is estimated one by one according to progress of time during a pump operation | movement. In this case, since the change in the pump temperature is sequentially estimated not only when the pump is stopped but also during the pump operation, the pump temperature can be monitored throughout the operation period of the internal combustion engine. In this case, it is preferable to set a temperature gradient according to the ambient temperature around the air pump and sequentially estimate the pump temperature according to the passage of time during the pump operation.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings. In the present embodiment, an engine control system is constructed for an in-vehicle multi-cylinder gasoline engine that is an internal combustion engine. In the control system, an electronic control unit (hereinafter referred to as ECU) is used as a center to control the fuel injection amount. And control of ignition timing. First, an overall schematic configuration diagram of the engine control system will be described with reference to FIG.

  In the engine 10 shown in FIG. 1, the intake pipe 11 is provided with a throttle valve 14 whose opening degree is adjusted by an actuator such as a DC motor, and a throttle opening degree sensor 15 for detecting the throttle opening degree. A surge tank 16 is provided downstream of the throttle valve 14, and an intake pipe pressure sensor 17 for detecting the intake pipe pressure is provided in the surge tank 16. The surge tank 16 is connected to an intake manifold 18 that introduces air into each cylinder of the engine 10. In the intake manifold 18, an electromagnetically driven fuel injection that injects fuel near the intake port of each cylinder. A valve 19 is attached.

  An intake valve 21 and an exhaust valve 22 are respectively provided at the intake port and the exhaust port of the engine 10. When the intake valve 21 is opened, a mixture of air and fuel is introduced into the combustion chamber 23. The exhaust gas after combustion is discharged to the exhaust pipe 24 by the opening operation. A spark plug 25 is attached to each cylinder of the cylinder head of the engine 10, and a high voltage is applied to the spark plug 25 at a desired ignition timing through an ignition device (not shown) including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 25, and the air-fuel mixture introduced into the combustion chamber 23 is ignited and used for combustion.

  The exhaust pipe 24 is provided with a catalyst 31 such as a three-way catalyst for purifying CO, HC, NOx and the like in the exhaust gas, and the air-fuel ratio of the air-fuel mixture is detected on the upstream side of the catalyst 31 with exhaust gas as a detection target. An air-fuel ratio sensor 32 (linear A / F sensor, O2 sensor, etc.) for detecting the above is provided. The cylinder block of the engine 10 has a coolant temperature sensor 33 that detects the temperature of engine coolant, and a crank angle that outputs a rectangular crank angle signal at every predetermined crank angle of the engine (for example, at a cycle of 30 ° CA). A sensor 34 is attached. The intake air temperature sensor 39 is provided in an air cleaner or the like upstream of the intake pipe and detects the temperature of the intake air.

  Further, as a secondary air supply system, a secondary air pipe 35 is connected upstream of the catalyst 31 in the exhaust pipe 24, and a secondary air supply device as a secondary air supply device is connected upstream of the secondary air pipe 35. An air pump 36 is provided. The secondary air pump 36 is composed of, for example, a DC motor or the like, and operates by receiving power from a vehicle battery (not shown). An on-off valve 37 that opens or closes the secondary air pipe 35 is provided downstream of the secondary air pump 36. A pressure sensor 38 that detects the pressure in the secondary air pipe 35 is provided between the secondary air pump 36 and the on-off valve 37.

  The outputs of the various sensors described above are input to the ECU 40 that controls the engine. The ECU 40 is configured mainly by a microcomputer including a CPU, a ROM, a RAM, and the like, and executes various control programs stored in the ROM, so that the fuel injection amount and ignition of the fuel injection valve 19 according to the engine operating state. The ignition timing by the plug 25 is controlled. In addition, the ECU 40 supplies the secondary air by operating the secondary air pump 36 in order to activate the catalyst 31 at the time of starting the engine early.

  Next, a control procedure for operating the secondary air pump 36 to supply secondary air to the catalyst 31 will be described. Particularly in the present embodiment, the pump temperature tpm (for example, the temperature of the brush portion of the DC motor constituting the secondary air pump 36) is estimated while the operation of the secondary air pump 36 is stopped, and the secondary air pump 36 is based on the pump temperature tpm. The operable time TA is calculated. The operable time TA is a time required for reaching the upper limit temperature (for example, 150 ° C.) of the pump operating temperature range after the operation of the secondary air pump 36 is started, and the longer the pump temperature tpm at the start of the operation, Conversely, the higher the pump temperature tpm at the start of operation, the shorter the time. The operation of the secondary air pump 36 is permitted on the condition that the operable time TA is longer than the operation request time TB required as the operation time of the secondary air pump 36.

  Further, in the present embodiment, a failure diagnosis of the secondary air supply system is performed during engine operation, and the secondary air pump 36 is reactivated during the failure diagnosis. In this case, the time required for failure diagnosis corresponds to the operation request time TB, and the operation request time TB is set corresponding to the failure diagnosis item. For example, if (1) leakage detection of the secondary air system and (2) malfunction detection of the secondary air pump 36 are set as failure diagnosis items, only (1) is performed as failure diagnosis ( It is preferable to set the operation request time TB for each time depending on whether only 2) is implemented or (1) + (2) is implemented.

  In the leak detection of (1), the on-off valve 37 is closed and the secondary air pump 36 is operated for a predetermined time (for example, about 5 seconds). Leak detection is performed based on (the detection value of the air-fuel ratio sensor 32). In the malfunction detection of (2), the on-off valve 37 is closed and the secondary air pump 36 is operated for a predetermined time (for example, about 1 second), and the pressure change at that time (detected value of the pressure sensor 38) is used. Perform pump malfunction detection.

  Next, an estimation process of the pump temperature tpm executed by the ECU 40 and an operation permission determination process for the secondary air pump 36 will be described. FIG. 2 is a flowchart showing pump temperature estimation processing, and FIG. 3 is a flowchart showing air pump operation permission determination processing. These processes are executed by the ECU 40 at a predetermined time period.

  In FIG. 2, first, in step S <b> 101, the intake air temperature ta calculated from the detected value of the intake air temperature sensor 39 and the engine water temperature tw calculated from the detected value of the water temperature sensor 33 are read. In the subsequent step S102, it is determined whether or not the secondary air pump 36 is currently operating. When the pump is operating, the process proceeds to step S103 to calculate the pump temperature base value tbase. When the pump is stopped, the process proceeds to step S104 to calculate the pump temperature base value tbase.

  At this time, in step S103, Δt1 is added to the previous value of the pump temperature tpm to calculate the current value of tbase (tbase = tpm previous value + Δt1). Δt1 is a temperature gradient that is variably set based on the intake air temperature ta and the engine water temperature tw during the pump operation, and is set, for example, with reference to a Δt1 setting map in FIG. In the map, the higher the intake air temperature or the higher the water temperature, the larger Δt1 is. By this step S103, it is possible to sequentially estimate the temperature rise with the passage of time during the pump operation.

  In step S104, the current value of tbase is calculated by subtracting Δt2 from the previous value of the pump temperature tpm (tbase = tpm previous value−Δt2). Δt2 is a temperature gradient that is variably set based on the intake air temperature ta and the engine water temperature tw when the pump is stopped. For example, Δt2 is set with reference to a Δt2 setting map in FIG. In the map, Δt2 is set to a larger value as the intake air temperature is lower or the water temperature is lower. By this step S104, it is possible to sequentially estimate the temperature decrease with the passage of time while the pump is stopped.

  After calculating the pump temperature base value tbase, in step S105, the intake air temperature ta, the engine water temperature tw, and the pump temperature base value tbase are compared, and the highest temperature among them is estimated as the pump temperature tpm.

  Next, in FIG. 3, in step S201, it is determined whether or not the secondary air pump 36 is currently stopped. In step S202, it is determined whether or not the operation of the secondary air pump 36 is permitted. If the pump is stopped and the pump operation is not permitted, the process proceeds to step S203, and the operation request time TB of the secondary air pump 36 is set. At this time, the operation request time TB is set according to the catalyst warm-up time when the engine is started. Alternatively, for example, the operation request time TB is set corresponding to the failure diagnosis item to be executed next.

  Thereafter, step S204 reads the pump temperature tpm estimated in the process of FIG. 2, and in the subsequent step S205, the operable time TA of the secondary air pump 36 is calculated based on the pump temperature tpm. For example, based on the relationship shown in FIG. 5, the operable time TA is calculated to be shorter as the pump temperature tpm is higher, and conversely, as the pump temperature tpm is lower.

  Thereafter, in step S206, it is determined whether or not the operable time TA is longer than the operation request time TB. If TA> TB, the operation of the secondary air pump 36 is permitted in step S207. If TA ≦ TB, the operation of the secondary air pump 36 is not permitted in step S208.

  After the operation of the secondary air pump 36 is permitted, step S202 becomes YES, and the operation request time TB is set in step S209. Thereby, the operation of the secondary air pump 36 is started.

  Further, during the operation of the secondary air pump 36, the process proceeds from step S201 to step S210, and it is determined whether or not the operation end timing has come. If the desired failure diagnosis or the like has been completed, or if the elapsed time from the start of operation of the secondary air pump 36 has reached the operation request time TB, an affirmative determination is made in step S210 and the process proceeds to step S208. The operation of the air pump 36 is not permitted.

  According to the embodiment described above in detail, the following excellent effects can be obtained.

  Based on the pump temperature tpm estimated during the operation stop of the secondary air pump 36, the operable time TA of the secondary air pump 36 is calculated, and the secondary air pump is compared by comparing the operable time TA and the required operation time TB in each case. It was determined whether to allow 36 operations. Thereby, an excessive temperature rise of the secondary air pump 36 during operation can be suppressed, and the air pump 36 can be protected. Further, the secondary air pump 36 can be appropriately operated within the desired operation request time TB.

  In this case, since the pump temperature changes due to heat received from the engine or the like during engine operation, in the configuration in which the operation time of the secondary air pump 36 is set from the water temperature or the like at the time of engine start as in the existing technology, The air pump 36 cannot be sufficiently protected. On the other hand, according to the present embodiment, the pump temperature is constantly monitored and the operation time of the secondary air pump 36 is set based on the pump temperature, so that the secondary air pump 36 can be sufficiently protected. Even when the secondary air pump 36 is restarted during the operation of the engine, the secondary air pump 36 can be appropriately operated. Therefore, even when the secondary air pump 36 is restarted for failure diagnosis of the secondary air system, the failure diagnosis of the secondary air system can be reliably performed while protecting the secondary air pump 36.

  Since the operation of the secondary air pump 36 is permitted on the condition that the operable time TA> the operation required time TB, there is a disadvantage that the secondary air pump 36 is unnecessarily restarted (that is, the operation / deactivation is repeated). This can be avoided, and deterioration of drivability due to unnecessary pump reactivation can be prevented.

  In addition, during the operation of the secondary air pump 36 and when the operation is stopped, the pump temperature tpm is sequentially estimated over time based on the temperature gradient set according to the water temperature and the intake air temperature each time. The change of the pump temperature tpm during the pump operation and the stop can be surely grasped without requiring an additional configuration such as the above.

  In addition, this invention is not limited to the content of description of the said embodiment, For example, you may implement as follows.

  It is also possible to set the operation request time TB as a fixed time. In this case, the fixed operation request time TB may be set based on the most severe condition (for example, the condition in which the operation time is longest) as the operation condition of the secondary air pump 36.

  When the secondary air pump 36 is restarted for failure diagnosis of the secondary air system, the shortest time period for performing the diagnosis is determined, the time period has been reached, and the operable time TA> operation request The configuration may be such that the secondary air pump 36 is allowed to restart when both the time TB is satisfied.

  In the above-described embodiment, the pump temperature tpm is continuously estimated in both cases where the secondary air pump 36 is in operation and stopped. However, instead of this, the pump is only used while the secondary air pump 36 is stopped. The temperature tpm may be continuously estimated. Also in this configuration, overheating of the secondary air pump 36 during the next pump operation can be suppressed. In this case, for example, at the operation stop timing of the secondary air pump 36, the operation upper limit temperature (for example, 150 ° C.) may be estimated as the pump temperature tpm at that time.

  When the engine is started, the pump temperature may be estimated by comparing the water temperature at the previous engine stop and the water temperature at the current engine start. At this time, if the water temperature at the time of the previous engine stop is unknown due to battery clear or the like, the allowable limit temperature of the secondary air pump 36 may be used instead.

  A temperature sensor may be attached to the secondary air pump 36, and the pump temperature may be obtained based on a detection signal of the temperature sensor. In this case, a temperature sensor is newly required, but the object of the present invention is achieved such that the air pump 36 is properly operated while the secondary air pump 36 is protected.

It is a block diagram which shows the outline of the engine control system in embodiment of invention. It is a flowchart which shows the estimation process of pump temperature. It is a flowchart which shows the operation permission determination process of a secondary air pump. It is a figure which shows the setting map of (DELTA) t1, (DELTA) t2. It is a figure which shows the relationship between pump temperature and operation possible time.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine, 24 ... Exhaust pipe, 31 ... Catalyst, 36 ... Secondary air pump, 40 ... ECU.

Claims (8)

In a secondary air supply system of an internal combustion engine that supplies secondary air to an exhaust passage of the internal combustion engine by operation of an air pump,
A pump temperature estimating means for estimating a pump temperature before starting the operation of the air pump;
Operable time calculating means for calculating an operable time of the air pump based on the estimated pump temperature;
An operation permission determining means for determining whether to permit the operation of the air pump based on the calculated operable time;
A secondary air supply system for an internal combustion engine, comprising:   2. The internal combustion engine according to claim 1, wherein the operable time calculating unit calculates a time required for the pump temperature to reach a predetermined operating upper limit temperature from the estimated temperature at the time after the operation of the air pump is started as the operable time. Engine secondary air supply system. It further comprises an operation request setting means for setting an operation request time of the air pump required each time,
3. The secondary air supply system for an internal combustion engine according to claim 1, wherein the operation permission determination unit permits the operation of an air pump when the operable time is longer than the operation request time.   4. The internal combustion engine according to claim 3, wherein a failure diagnosis of a secondary air system including the air pump is performed, and the operation request time setting unit sets a time required for the failure diagnosis as an operation request time. Secondary air supply system.   The secondary air supply system for an internal combustion engine according to any one of claims 1 to 4, wherein the pump temperature estimating means sequentially estimates the pump temperature according to the passage of time while the pump is stopped.   The internal combustion engine according to any one of claims 1 to 4, wherein the pump temperature estimation means sets a temperature gradient according to an ambient temperature around the air pump and sequentially estimates the pump temperature according to a lapse of time while the pump is stopped. Secondary air supply system.   The pump temperature estimating means compares the pump temperature estimated according to the passage of time while the pump is stopped and at least one of the intake air temperature or the cooling water temperature of the internal combustion engine, and sets the higher one as the estimated pump temperature value. Item 7. A secondary air supply system for an internal combustion engine according to Item 5 or 6.   The secondary air supply system for an internal combustion engine according to any one of claims 5 to 7, further comprising means for sequentially estimating a pump temperature in accordance with a lapse of time during operation of the pump.