JP2007040269A - Back pressure control device of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent functional failures such as oil leakage or overstress from being caused by an increase in back pressure resulting from filter pressure loss in an engine equipped with a particulate filter. <P>SOLUTION: Exhaust manifold pressure (back pressure) is calculated from a difference in pressure between on the front and back sides of the particulate filter and engine operating conditions such as a number of revolutions. When the exhaust manifold pressure (back pressure) exceeds marginal pressure, a suction air amount of the engine is restricted by decreasing supercharging pressure so as to reduce the back pressure, and a fuel injection amount is also restricted to thereby prevent an increase in temperature of exhaust gas and generation of smoke. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a back pressure control device for an engine having a particulate filter that collects particulates in exhaust gas in an exhaust passage.

Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for promoting temperature rise by increasing a back pressure with an exhaust throttle valve during filter regeneration in an engine equipped with a particulate filter.
Further, Patent Document 2 discloses that when the particulate collection amount in the particulate filter exceeds an allowable value, the exhaust pressure to be recirculated from the upstream side of the filter to the intake side is increased to increase the exhaust pressure upstream of the filter. A technique for suppressing an increase in the amount is disclosed.
JP 2003-343287 A JP 2002-138814 A

  By the way, in an engine equipped with a particulate filter, when particulates or ash accumulates on the filter and the engine is fully opened with the filter pressure loss increased, the engine back pressure rises beyond the allowable limit. Functional problems such as opening of the exhaust valve, oil leakage from the turbo oil seal, and excessive stress on the turbine blade may occur.

In addition, since regeneration of the particulate filter usually requires several minutes to several tens of minutes, the back pressure exceeds the limit pressure by operating the engine fully even after the start of filter regeneration. There was a possibility that a malfunction would occur.
The present invention has been made in view of the above problems, and in an engine equipped with a particulate filter, it is possible to prevent the occurrence of functional problems such as oil leakage and excessive stress due to an increase in back pressure due to filter pressure loss. An object is to provide a pressure control device.

  Therefore, the engine back pressure control apparatus according to the present invention is characterized in that the intake air amount of the engine is limited when the back pressure of the engine exceeds a limit pressure.

  According to the engine back pressure control device of the present invention, when the engine back pressure exceeds the limit pressure, the back pressure is forcibly reduced by restricting the amount of intake air to be smaller than usual. It is possible to prevent functional failures such as oil leakage and excessive stress from being left in a state exceeding the pressure.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram of a vehicle direct injection diesel engine (hereinafter referred to as “engine”) 1 according to an embodiment.
In the engine 1 shown in FIG. 1, the intake air from which dust has been removed by the air cleaner 2 is compressed by the compressor section 3 a of the variable nozzle turbocharger 3 (supercharger) and sent out to the intake passage 4.

An intercooler 5 is installed downstream of the compressor unit 3a, and the intake air pumped from the compressor unit 3a is cooled by the intercooler 5.
Further, an intake throttle valve 7 is installed immediately before the surge tank 6, and the intake air cooled by the intercooler 5 passes through the intake throttle valve 7 and flows into the surge tank 6, and the surge tank 6 To each cylinder via the manifold portion 8.

In the main body of the engine 1, the injector 9 is installed in the approximate center of the upper part of the combustion chamber for each cylinder.
The fuel pumped by the fuel pump 10 is supplied to the injector 9 through the common rail 11.
The injector 9 is opened by a fuel injection control signal from an electronic control unit (hereinafter referred to as “ECU”) 21 incorporating a microcomputer.

The fuel injection by the injector 9 is performed in a plurality of times. The injector 9 performs pilot injection for reducing the generated particulates in addition to the main injection for controlling the torque of the engine 1, and will be described later. Post-injection is performed to increase the exhaust temperature during regeneration of the particulate filter 12.
The pilot injection is performed with an advance angle from the main injection, and the post injection is performed with a retard angle from the main injection.

On the other hand, a turbine section 3b of the turbocharger 3 is installed in the exhaust passage 13, and a catalytic converter 14 and a particulate filter 12 are installed downstream of the turbine section 3b for exhaust aftertreatment.
Particulates in the exhaust gas are removed from the exhaust gas when passing through the particulate filter 12.

An exhaust gas recirculation pipe 15 is connected between the exhaust gas passage 13 upstream of the turbine section 3b and the intake air passage 4 (surge tank 5) downstream of the intake throttle valve 7, and an exhaust gas recirculation control is provided in the middle of the exhaust gas recirculation pipe 15. A valve 16 is interposed.
The exhaust gas recirculation control valve 16 is actuated by an exhaust gas recirculation control signal from the ECU 21 so that an amount of exhaust gas corresponding to the opening of the exhaust gas recirculation control valve 16 is recirculated to the intake passage 4 (surge tank 5). The

  The signals input to the ECU 21 include temperature sensors 31 and 32 for detecting exhaust temperatures Texhin and Texhout at the inlet and outlet of the particulate filter 12, and a differential pressure sensor for detecting the differential pressure ΔPtotal before and after the particulate filter 12. 33, an air flow meter 34 for detecting the intake air flow rate of the engine 1, a crank angle sensor 35 for detecting the rotation angle of the crankshaft, an accelerator opening sensor 36 for detecting the depression amount of the accelerator pedal, and an excess on the downstream side of the intercooler 5. Signals from a supercharging pressure sensor 37 that detects the supply pressure and a water temperature sensor 38 that detects the coolant temperature of the engine 1 are included.

The ECU 21 controls the supercharging pressure by the vane angle of the variable nozzle turbocharger 3, the preheating control by the glow plug 17, the injection amount control by the fuel pump 10 and the injector 9, and the exhaust gas recirculation control valve 16 based on the above various detection signals. Exhaust gas recirculation control and intake throttle control by the intake throttle valve 7 are performed.
Further, the ECU 21 estimates a particulate accumulation amount in the particulate filter 12 based on, for example, a detection result of the differential pressure sensor 33, and determines a filter regeneration request based on the estimation result.

If it is determined that filter regeneration is necessary, filter regeneration control is performed in which the exhaust gas temperature is raised under predetermined regeneration-permitted operating conditions to burn the particulates collected by the particulate filter 12.
Means for raising the exhaust temperature in the regeneration control include the injector 9, the variable nozzle turbocharger 3, the exhaust gas recirculation control valve 16, and the intake throttle valve 7. During the regeneration of the filter, the main injection timing and post injection of the injector 9 are included. By adjusting at least one of the timing and post injection amount, the vane angle of the variable nozzle turbocharger 3, the opening degree of the exhaust gas recirculation control valve 16, and the opening degree of the intake throttle valve 7, the exhaust temperature is raised. The particulate deposited on the particulate filter 12 is burned.

By the way, the regeneration process of the particulate filter 12 is performed when the regeneration permitting operation condition is satisfied, and the regeneration process does not rapidly proceed even when the regeneration process is started. Due to the accumulation of curate, the back pressure when the engine is fully opened may become excessively high.
Therefore, in the present embodiment, the ECU 21 performs a process for preventing the back pressure at the time of the engine fully open operation from exceeding the limit pressure due to the pressure loss of the particulate filter 12.

The flowchart of FIG. 2 shows a first embodiment of the back pressure rise prevention process.
In the flowchart of FIG. 2, in step S <b> 11, engine operating conditions such as engine rotation speed, fuel injection amount, and supercharging pressure are measured, and the differential pressure across the particulate filter 12 is determined based on the detection signal from the differential pressure sensor 33. Measure.
In the next step S12, the exhaust manifold pressure (back pressure) is calculated based on the measurement result in step S11.

  As shown in FIG. 3, there is a certain correlation between the differential pressure before and after the particulate filter 12 indicating the pressure loss of the particulate filter 12 and the exhaust manifold pressure (back pressure), and before and after the deposition of particulate ash. As the differential pressure increases, the exhaust manifold pressure (back pressure) increases. For the same differential pressure before and after, the exhaust manifold pressure (back pressure) increases as the engine speed (rpm) increases.

Therefore, a correlation (map) as shown in FIG. 3 is stored in advance, and the exhaust manifold pressure (back pressure) can be calculated from the differential pressure across the particulate filter 12 and the engine speed (rpm).
The correlation between the front-rear differential pressure and the exhaust manifold pressure (back pressure) shown in FIG. 3 indicates the characteristics when the engine 1 is fully opened.

Further, instead of setting the correlation as shown in FIG. 3 in advance, the exhaust manifold pressure (back pressure) can be obtained by thermodynamic calculation based on the measurement result in step S11.
In step S13, it is determined whether or not the exhaust manifold pressure (back pressure) calculated in step S12 is equal to or lower than a limit pressure.

The limit pressure is set and stored in advance as the maximum value of the pressure range in which functional malfunctions such as exhaust valve opening, oil leakage from the turbo oil seal, and excessive stress on the turbine blade do not occur.
Here, if the exhaust manifold pressure (back pressure) calculated in step S12 is equal to or lower than the limit pressure, the above-described functional problem does not occur and the processing for reducing the back pressure is unnecessary, and therefore the measurement in step S11. Return to processing.

  On the other hand, when it is determined that the exhaust manifold pressure (back pressure) calculated in step S12 exceeds the limit pressure, that is, because the filter pressure loss is large and the engine 1 is operated near the fully open position, the exhaust manifold pressure (back pressure) When the pressure (pressure) exceeds the limit pressure, there is a possibility that a functional failure may occur. Therefore, the process proceeds to step S14 in order to reduce the back pressure below the limit pressure.

  In step S14, by reducing the supercharging pressure by controlling the vane angle of the variable nozzle turbocharger 3, the intake air amount (exhaust flow rate) of the engine 1 is limited to a smaller amount than usual, and the exhaust manifold pressure (rear) is reduced. Pressure) is reduced below the limit pressure. At the same time, by restricting the fuel injection amount by the injector 9 to a smaller amount than usual, it is possible to prevent an excessive increase in exhaust temperature and smoke from occurring due to the restriction of the intake air amount.

  As shown in FIG. 4, when the differential pressure (pressure loss) across the particulate filter 12 increases due to the accumulation of particulates, if the intake air amount (supercharging pressure) remains at the initial setting, the engine 1 The exhaust manifold pressure (back pressure) may exceed the limit pressure during fully open operation, but the exhaust air pressure (supercharging pressure) is restricted by lowering as the front-rear differential pressure (pressure loss) increases. The manifold pressure (back pressure) can be prevented from exceeding the limit pressure.

  Accordingly, the accumulated amount of the particulates with respect to the particulate filter 12 reaches near the saturation amount, the filter pressure loss is large, and the exhaust manifold pressure (back pressure) exceeds the limit pressure when the engine 1 is fully opened. Even so, the exhaust manifold pressure (back pressure) can be prevented from greatly exceeding the limit pressure, and functional problems such as exhaust valve opening, oil leakage from the turbo oil seal, and excessive stress on the turbine blades can occur. Can be prevented.

  Also, exhaust manifold pressure (back pressure) is calculated based on detection signals used for purposes other than estimating exhaust manifold pressure (back pressure), such as engine speed, fuel injection amount, boost pressure, and differential pressure across the filter. In addition, since the exhaust manifold pressure (back pressure) is suppressed by controlling the vane angle of the variable nozzle turbocharger 3, a new device has been added to realize processing to suppress the exhaust manifold pressure (back pressure) below the limit pressure. There is no need to do.

As a means for limiting the amount of intake air, in addition to lowering the supercharging pressure, intake throttling may be performed.
Further, in the limiting process of the supercharging pressure (intake air amount) in step S14, the supercharging pressure may be reduced by a control amount corresponding to the deviation between the actual exhaust manifold pressure (back pressure) and the limit pressure. The supercharging pressure may be gradually decreased by a predetermined value set in advance.

The flowchart of FIG. 5 shows a second embodiment that is a back pressure rise prevention process that does not use the differential pressure sensor 33.
In the flowchart of FIG. 5, in step S21, engine operating conditions such as engine speed, fuel injection amount, and supercharging pressure are measured, and particulate (PM) / ash accumulation amount is estimated.

The particulate ash accumulation amount can be estimated from the travel distance of the vehicle, for example, but in addition to this, the estimated amount of the particulates according to the engine operating conditions may be integrated, and the estimation method is not limited.
In step S21, a process of reading the particulate ash deposition amount calculated by another routine for determining the filter regeneration request may be performed.

In step S22, the pressure loss (front / rear differential pressure) of the particulate filter 12 is calculated from the particulate ash accumulation amount. In the next step S23, the exhaust manifold pressure at that time is calculated based on the filter pressure loss and the engine operating conditions. (Back pressure) is calculated.
In step S24, it is determined whether or not the exhaust manifold pressure (back pressure) calculated in step S23 is equal to or lower than a limit pressure.

  If the exhaust manifold pressure (back pressure) exceeds the limit pressure, the process proceeds to step S25, and the supercharging pressure is reduced by controlling the vane angle of the variable nozzle turbocharger 3 as in step S14. By restricting the intake air amount of the engine 1 and reducing the exhaust manifold pressure (back pressure) below the limit pressure, the fuel injection amount by the injector 9 is restricted at the same time, thereby restricting the intake air amount. Prevents excessive exhaust temperature rise and smoke.

According to the second embodiment, even if the differential pressure sensor 33 is not provided, the filter pressure loss and the exhaust manifold pressure (back pressure) can be reduced without providing a dedicated sensor for detecting the exhaust manifold pressure (back pressure). ).
Further, since the estimation of the particulate ash accumulation amount is a process required for the filter regeneration process, it is not necessary to newly perform the matching of the accumulation amount estimation process when adding the back pressure control function.

The flowchart of FIG. 6 determines whether or not the differential pressure before and after the filter (filter pressure loss) detected by the differential pressure sensor 33 is equal to or less than a limit value, so that the exhaust manifold pressure (back pressure) is not calculated. The 3rd Embodiment which suppresses an exhaust manifold pressure (back pressure) below a limit pressure is shown.
In the flowchart of FIG. 6, in step S31, engine operating conditions such as engine speed, fuel injection amount, and supercharging pressure are measured, and the differential pressure across the particulate filter 12 based on the detection signal from the differential pressure sensor 33. Measure.

In step S32, it is determined whether or not the differential pressure before and after the filter (that is, the filter pressure loss) is equal to or less than a limit value.
The limit value is set and stored in advance based on the differential pressure before and after the exhaust manifold pressure (back pressure) exceeds the limit pressure when the engine 1 is operated near the fully open position.
When the differential pressure before and after the filter (filter pressure loss) exceeds the limit value, the process proceeds to step S33, where the setting of limiting the maximum supercharging pressure of the variable nozzle turbocharger 3 to be smaller than normal is performed. By limiting the intake air amount (maximum intake air amount), the exhaust manifold pressure (back pressure) does not exceed the limit pressure even when the engine 1 is fully opened, and at the same time, the fuel injection amount (maximum injection) by the injector 9 (Amount) is set to be limited in accordance with the restriction of the intake air amount, and an excessive increase in exhaust temperature and smoke are prevented due to the restriction of the intake air amount.

According to the third embodiment, the exhaust manifold pressure (back pressure) is less than the limit pressure without calculating the exhaust manifold pressure (back pressure) using the correlation between the differential pressure across the filter and the exhaust manifold pressure (back pressure). Can be limited to.
In the first to third embodiments, when the process of restricting the intake air amount (supercharging pressure) is being performed, the vehicle driver is inhaled by the increase of the exhaust manifold pressure (back pressure). It is good to warn that the amount of air (supercharging pressure) is limited.

In addition, it predicts whether or not the exhaust manifold pressure (back pressure) exceeds the limit pressure when the engine is fully opened from the differential pressure (pressure loss) before and after the filter, and the intake air amount is limited when the engine is fully opened. It is also possible to warn in advance.
Further, when processing for limiting the amount of intake air (supercharging pressure) is performed, processing for making the filter regeneration timing earlier than the initial value is performed, and the amount of intake air (supercharging pressure) is increased every time particulates accumulate. ) Can be prevented from being repeated.

  Further, the supercharging pressure in the turbocharger 3 can be controlled by controlling the exhaust amount that bypasses the turbine section 3b.

The system diagram of the engine for vehicles in an embodiment. The flowchart which shows 1st Embodiment of the back pressure raise prevention process. The diagram which shows the correlation with filter differential pressure and exhaust manifold pressure (back pressure). The diagram which shows the correlation with the amount of intake air (supercharging pressure) and exhaust manifold pressure (back pressure). The flowchart which shows 2nd Embodiment of the back pressure raise prevention process. The flowchart which shows 3rd Embodiment of the back pressure raise prevention process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 3 ... Variable nozzle turbocharger, 4 ... Intake passage, 5 ... Intercooler, 6 ... Surge tank, 7 ... Intake throttle valve, 9 ... Injector, 10 ... Fuel pump, 11 ... Common rail, 12 ... Particulate filter , 13 ... exhaust passage, 14 ... catalytic converter, 21 ... electronic control unit (ECU), 31, 32 ... temperature sensor, 33 ... differential pressure sensor, 34 ... air flow meter, 35 ... crank angle sensor, 36 ... accelerator opening sensor 37 ... Supercharging pressure sensor, 38 ... Water temperature sensor

Claims (7)

In an engine equipped with an exhaust passage with a particulate filter that collects particulates in the exhaust,
An engine back pressure control device that limits an intake air amount of the engine when the back pressure of the engine exceeds a limit pressure. 2. The engine back pressure control device according to claim 1, wherein the back pressure of the engine is calculated based on a pressure loss of the particulate filter. 2. The engine back pressure control apparatus according to claim 1, wherein the back pressure of the engine is calculated based on a differential pressure across the particulate filter. 2. The engine back pressure control device according to claim 1, wherein the back pressure of the engine is calculated based on a particulate accumulation amount in the particulate filter. 2. The engine back pressure control device according to claim 1, wherein the intake air amount is limited based on a comparison between a differential pressure across the particulate filter and a limit value. The engine according to any one of claims 1 to 5, wherein the engine includes a supercharger and restricts a supercharging pressure of the supercharger to restrict an intake air amount of the engine. Back pressure control device. The engine back pressure control device according to any one of claims 1 to 6, wherein the engine intake air amount is restricted and the fuel injection amount is restricted.