Engine exhaust emission control device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to an engine exhaust gas purification device, and more particularly to promotion of activation of a catalyst for purifying exhaust gas provided in the exhaust system.

【0002】

[Conventional technology]

When a catalyst is provided in the exhaust system of an engine to purify exhaust gas, in order to promote activation of the catalyst and cause an efficient reaction, for example, as described in Japanese Patent Application Laid-Open No. 4-166608, secondary air is introduced upstream of the catalyst. And those that heat this secondary air have been conventionally known. It is also known that the catalyst itself is heated by an electric heater as described in Japanese Patent Publication No. 61-49014.

【0003】

Separately from this, as described in Japanese Patent Publication No. 62-18318, the passage length of the exhaust system silencer is made variable, and the passage length of the silencer is lengthened in the low noise region to improve the sound deadening performance. , The one that shortens the passage length of the silencer and reduces the exhaust resistance in the high output region has been conventionally known, and as described in Japanese Patent Application Laid-Open No. 2-64236, it is exhausted when the engine is started or when the temperature is low. It is known that by narrowing the downstream side of the catalyst of the system, the pressure in the cylinder is raised to raise the combustion temperature to promote engine warm-up and catalyst warm-up.

【0004】

[Problems to be Solved by the Invention]

When a variable silencer that makes the passage length of the silencer variable and a secondary air heating that heats the secondary air to promote catalyst warm-up are combined, the variable silencer exhausts pressure due to the lengthening of the passage length in the low noise region. The problem is that the amount of secondary air decreases due to the increase in (pressure in the exhaust passage), which in turn increases the air temperature and reduces the reliability of the heater and catalyst, and also causes deterioration of fuel efficiency due to excessive heating. Occurs.

【0005】

Further, when an electric heating catalyst for heating the catalyst itself by an electric heater is provided in the exhaust system and used in combination with a variable silencer, the exhaust pressure rises in a low noise region and the exhaust passes through the electric heating catalyst. The passage time of the gas changes, the rate of temperature rise changes, and the catalyst temperature fluctuates greatly, which greatly exceeds the target temperature and impairs the reliability of the catalyst, or when the target temperature is exceeded, fail judgment is made and heating control is interrupted. There is a problem that it ends up.

【0006】

Further, when the exhaust throttle control that throttles the downstream side of the catalyst of the exhaust system and the catalyst heating by the secondary air heating or the electric heating catalyst are combined, the operating times of the exhaust throttle and the secondary air heating or the catalyst heating do not match, for example. When the operation of the exhaust throttle to the exhaust pressure increasing side starts during the operation of the secondary air heating or the catalyst heating, the same problems as described above occur for each of the secondary air heating or the catalyst heating by the electric heating catalyst.

【0007】

The present invention prevents the catalyst temperature from being improperly controlled by the electric heating catalyst when the exhaust pressure rises and the reliability of the catalyst is lowered, and the heating control is interrupted due to improper fail determination. The purpose is to prevent it from being done.

【0008】

[Means for solving problems]

According to the present invention, an engine exhaust equipped with an engine control means accompanied by a change in exhaust pressure and an electric heating catalyst including a catalyst for purifying exhaust gas in the exhaust system and an electric heating means for heating the catalyst after the engine is started. The purification device is provided with a heating limiting means for limiting the heating control by the electric heating means when the engine control means operates to the exhaust pressure increasing side during the operation of the electric heating means, and the heating control by the heating limiting means is restricted. Will be gradually released over time.

【0009】

Further, it is an engine exhaust purification device provided with an engine control means for changing the exhaust pressure and an electric heating catalyst including a catalyst for purifying the exhaust gas in the exhaust system and an electric heating means for heating the catalyst after the engine is started. The engine control means is provided with a catalyst temperature detecting means for detecting the temperature of the catalyst and a feedback control means for controlling the electric heating means so that the temperature of the catalyst reaches the target temperature, and the exhaust pressure of the engine control means rises during the operation of the electric heating means. When operating to the side, the target temperature is corrected to the high temperature side.

【0010】

Here, the engine control means accompanied by a change in exhaust pressure is a variable silencer control means that changes the passage length of the silencer of the exhaust system, or an exhaust throttle control that controls the area of the passage downstream of the catalyst of the exhaust system by an exhaust throttle valve. It is a means.

【0011】

[Action]

When the engine is started, the electric heating means of the electric heating catalyst is activated, and the catalyst is heated, the passage length of the silencer is lengthened in the low noise region to improve the sound deadening performance, and the passage length is shortened in the high output region. A variable silencer control means that reduces exhaust resistance, and a throttle on the downstream side of the catalyst in the exhaust system when the engine is started or at low temperature to raise the pressure inside the cylinder and raise the combustion temperature to warm up the engine or catalyst. When the exhaust throttle control means for promoting is activated and the exhaust pressure rises, the heating control of the electric heating catalyst is restricted.

【0012】

As a result, when the variable silencer and the electric heating catalyst are combined, the fluctuation of the temperature rise rate is suppressed when the passage time of the exhaust gas passing through the electric heating catalyst changes due to the variable silencer operating to the exhaust pressure increase side. , It is possible to prevent the catalyst temperature from greatly exceeding the target temperature or the failure judgment and the interruption of heating when the target temperature is exceeded.

【0013】

Further, when the exhaust throttle control and the heating control of the electric heating catalyst are combined, the heating control of the electric heating catalyst is restricted as the exhaust throttle operates to the exhaust pressure increasing side, so that the catalyst temperature rise rate is increased. Fluctuations are suppressed, and it is possible to prevent the catalyst temperature from greatly exceeding the target temperature, or to prevent the failure judgment and interruption of heating when the target temperature is exceeded.

【0014】

[Example]

Hereinafter, examples of the present invention will be described with reference to the drawings.

【0015】

Example 1. FIG. 1 is an overall system diagram of Example 1 (reference example) of the present invention. In the figure, 1 is the engine body of the V-type engine, and the exhaust passages 2 and 3 of the left and right banks extending outward are gathered on the downstream side to form one collective exhaust passage 4, and the gathering portion thereof. A catalyst device 5 for purifying harmful components in the exhaust gas is provided immediately downstream. Then, downstream of the catalyst device 5 of the collective exhaust passage 4, switching control is performed according to the engine operating state so that the passage length is lengthened in the operating region where low noise is desired and the passage length is shortened in the operating region where high output is desired. A variable silencer 6 is installed. Reference numeral 7 denotes a switching valve that controls switching of the variable silencer 6. An air pump 8 for supplying secondary air is provided in the exhaust system, and two air passages 9 and 10 extending from the air pump 8 are connected to the exhaust passages 2 and 3 of the left and right banks, respectively. Further, a heater 11 for heating secondary air is provided between the air pump 8 and these air passages 9 and 10.

【0016】

The engine is provided with a control unit 12 composed of a microcomputer, and the control unit 12 controls the air pump 8 and the heater 11 according to the control state of the variable silencer 6. Therefore, a crank angle signal is input to the control unit 12 from the crank angle sensor 13 that detects the crank angle of the engine as engine rotation information for detecting the engine start, and a water temperature signal 2 is input from the water temperature sensor 14 that detects the engine water temperature. It is input as a determination signal for the next air heating execution condition, and a switching signal from the switching valve 7 that switches and controls the variable silencer 6 is input as information on the variable silencer control state. Then, when it is detected that the engine is started, the secondary air is supplied by the air pump 8, and the variable silencer 5 is switched to the exhaust pressure increasing side while the secondary air is heated by the heater 11. As the variable silencer 5 is switched, the heating amount of the heater 11 is reduced and the secondary air supply amount by the air pump 8 is increased.

【0017】

FIG. 2 is a time chart showing the above control of the heater 11 and the air pump 8 accompanying the control of the variable silencer 5. As shown in this time chart, the air pump 8 and the heater 11 start operating at the same time as the engine is started. Then, when the operation of the variable silencer 6 to the low noise side (exhaust pressure rising side) is started in the predetermined low noise region, the current supplied to the heater 11 is reduced by a predetermined value or applied to the air pump 8. The driving voltage is increased by a predetermined value.

【0018】

FIG. 3 is a flowchart for executing the above control of the first embodiment. This flowchart consists of each step of S101 to S108, and it is first determined in S101 whether or not the engine has started. Then, when it has not started, it ends as it is, and when it has started, it proceeds to S102 and determines whether or not the predetermined secondary air heating execution condition is satisfied. Then, if the secondary air heating execution condition is not satisfied, the process ends as it is, and if the secondary air heating execution condition is satisfied, the secondary air heating is executed in S103.

【0019】

Next, in S104, check whether the control of the variable silencer is on the exhaust pressure increase side (high exhaust pressure side). Then, if it is not on the exhaust pressure increase side, it returns to S102, and if it is on the exhaust pressure increase side, it proceeds to S105 and corrects the heater heating amount to the predetermined value decrease side (or corrects the air pump discharge amount to the predetermined value increase side). Then, S106 counts down the timer.

【0020】

Next, it is determined whether or not a predetermined time has elapsed since the timer started the countdown in S107. Then, if the predetermined time has not elapsed, the process returns to S102, and when the predetermined time has elapsed, the process proceeds to S108 to cancel the heater heating amount reduction correction (or the air pump discharge amount increase correction).

【0021】

In the above description, the heating amount of the heater 11 is reduced or the secondary air supply amount by the air pump 8 is increased as the variable silencer 5 is operated to increase the exhaust pressure. When the silencer 5 is operated to the exhaust pressure increasing side, the heating amount of the heater 11 may be reduced and the secondary air supply amount of the air pump 8 may be increased at the same time.

【0022】

Example 2. Next, Example 2 will be described in which the variable silencer and the electric heating catalyst are combined, the temperature of the catalyst outlet and the like is feedback-controlled to the target temperature, and the heating amount is reduced when the variable silencer is operated to the exhaust pressure increasing side. ..

【0023】

In the apparatus of the second embodiment, an electric heating catalyst having a built-in heater is provided, and a temperature sensor that detects the catalyst outlet temperature and outputs the catalyst temperature information to the control unit is provided. Then, as shown in the time chart of FIG. 4, the heater of the electric heating catalyst is energized at the same time as the engine is started, and feedback control to the target temperature is performed. Further, when the variable silencer operates to the exhaust pressure increase side, the correction control amount of the heater control is switched to the minus side, whereby the energization amount to the heater is instantly reduced. Further, after the correction control amount is once switched to the minus side, the minus value is gradually reduced. As a result, it is prevented that the catalyst outlet temperature deviates significantly from the target temperature due to the switching of the variable silencer. The broken line in the figure shows the changes in the catalyst outlet temperature and the heater current when such correction control is not performed.

【0024】

FIG. 5 is a flowchart for executing the control of the third embodiment. This flowchart consists of each step of S201 to S209, and it is first determined in S201 whether or not the engine has started. Then, when it has not started, it ends as it is, and when it has started, it proceeds to S202 and determines whether or not the heating execution condition of the predetermined electric heating catalyst is satisfied. Then, if the heating execution condition is not satisfied, the process ends as it is, and if the heating execution condition is satisfied, the electric heating catalyst is heated by S203.

【0025】

Next, in S204, check whether the control of the variable silencer is on the exhaust pressure increase side (high exhaust pressure side). Then, if it is on the exhaust pressure rising side, the heater heating amount is reduced by a predetermined value in S205, and if it is not on the exhaust pressure rising side, it remains as it is, and then the process proceeds to S206 to determine whether the catalyst outlet temperature is the target temperature. Then, if the catalyst outlet temperature is the target temperature, the process returns to S202 as it is, and if it is not the target temperature, the process proceeds to S207.

【0026】

In S207, it is determined whether the catalyst temperature is higher than the target temperature (plus side). Then, when the temperature is higher than the target temperature, the heater heating amount is reduced by S208, and if not, the heater heating amount is increased by S209. Then return to S202.

【0027】

Example 3. Example 3 (reference example) in which the variable silencer and the secondary air heating are combined and the temperature of the catalyst outlet or the like is feedback-controlled to the target temperature will be described next.

【0028】

In the apparatus of the third embodiment, a temperature sensor that detects the catalyst outlet temperature and outputs the catalyst temperature information to the control unit is provided. Then, as shown in the time chart of FIG. 6, the heater is energized at the same time as the engine is started, and feedback control is performed so that the catalyst outlet temperature reaches the target temperature. Further, when the variable silencer operates to the exhaust pressure increase side, the correction control amount of the heater control is switched to the minus side, whereby the energization amount to the heater is instantly reduced. As a result, it is prevented that the catalyst outlet temperature deviates significantly from the target temperature due to the switching of the variable silencer. The broken line in the figure shows the changes in the catalyst outlet temperature and the heater current when such correction control is not performed. The correction control amount when the variable silencer is operated may be switched in a plurality of stages such as two stages and three stages.

【0029】

The flowchart for executing the control of the third embodiment is the same as the flowchart of FIG. 5 in the case of the second embodiment, and corresponds to the heating of the electric heating catalyst replaced with the heating of the secondary air.

【0030】

Example 4. Another example of a case where the variable silencer and the electric heating catalyst are combined and the temperature of the catalyst outlet or the like is feedback-controlled to the target temperature will be described below as Example 4.

【0031】

In the apparatus of the fourth embodiment, an electric heating catalyst having a built-in heater is provided, and a temperature sensor that detects the catalyst outlet temperature and outputs the catalyst temperature information to the control unit is provided. Then, as shown in the time chart of FIG. 7, the heater of the electric heating catalyst is energized at the same time as the engine is started, and feedback control to the target temperature is performed. Further, when the variable silencer operates to the exhaust pressure increasing side, the target temperature is changed to the high temperature side. As a result, the heater heating amount does not fall when the variable silencer is operated, and the heating control is prevented from being interrupted by the fail determination.

【0032】

Example 5. Further, another example in the case where the variable silencer and the electric heating catalyst are combined and the temperature of the catalyst outlet or the like is feedback-controlled to the target temperature will be described below as Example 5.

【0033】

In the apparatus of the fifth embodiment, an electric heating catalyst having a built-in heater is also provided, and a temperature sensor that detects the catalyst outlet temperature and outputs the catalyst temperature information to the control unit is provided. Then, as shown in the time chart of FIG. 8, the heater of the electric heating catalyst is energized at the same time as the engine is started, and feedback control to the target temperature is performed. Further, when the heater heating amount becomes equal to or less than the fail judgment value, the fail judgment for turning off the heater is started at the same time as the engine is started, but the fail judgment is performed for a certain period of time with the operation of the variable silencer to the exhaust pressure increase side. It is forbidden. As a result, the heating control is continued even when the heater heating amount falls below the fail determination value due to the fall of the heater heating amount when the variable silencer is operated.

【0034】

Example 6. Further, another example in the case where the variable silencer and the electric heating catalyst are combined and the temperature of the catalyst outlet or the like is feedback-controlled to the target temperature will be described below as Example 6.

【0035】

In the apparatus of the sixth embodiment, an electric heating catalyst having a built-in heater is also provided, and a temperature sensor that detects the catalyst outlet temperature and outputs the catalyst temperature information to the control unit is provided. Then, as shown in the time chart of FIG. 9, the heater of the electric heating catalyst is energized at the same time as the engine is started, and feedback control to the target temperature is performed. Further, the fail determination value is reduced as the variable silencer is operated toward the exhaust pressure increase side, and the fail determination condition is relaxed. As a result, the fail determination is made due to the fall of the heater heating amount when the variable silencer is operated, and the heating control is prevented from being interrupted.

【0036】

In the above embodiment, the one provided with the variable silencer has been described, but the secondary air heating is provided in the one provided with the exhaust throttle control means for controlling the area of the passage downstream of the catalyst by the exhaust throttle valve as the engine control means accompanied by the increase in exhaust pressure. The present invention can be similarly applied to the case of controlling the above or the electric heating catalyst.

【0037】

[Effect of the invention]

Since the present invention is configured as described above, the heating control of the catalyst temperature by the electric heating catalyst becomes inappropriate when the engine control means accompanied by an increase in exhaust pressure such as a variable silencer or an exhaust throttle is operated, and the reliability of the catalyst is increased. It is possible to prevent the property from being deteriorated and the heating control from being interrupted due to improper fail determination.

[Simple explanation of drawings]

[Figure 1]

Overall system diagram of Example 1 of the present invention [Figure 2]

Time chart showing control of Example 1 of the present invention [Fig. 3]

Flow chart for executing the control of the first embodiment of the present invention [Fig. 4]

Time chart showing control of Example 2 of the present invention [Fig. 5]

Flow chart for executing the control of the second embodiment of the present invention [Fig. 6]

Time chart showing control of Example 3 of the present invention [Fig. 7]

Time chart showing control of Example 4 of the present invention [Fig. 8]

Time chart showing control of Example 5 of the present invention [Fig. 9]

Time chart showing control of Example 6 of the present invention [Explanation of symbols]

1 Engine body 5 Catalyst device 6 Variable silencer 8 air pump 11 heater 12 Control unit