JP4735505B2 - Surge prevention control device and surge prevention control method for turbocharged engine - Google Patents

Description

  The present invention relates to an apparatus and a method for preventing the occurrence of a surge in which intake air intermittently backflows from a downstream side to an upstream side of a turbocharger compressor in an engine with a turbocharger.

  An engine having a turbocharger including a turbine installed in an exhaust passage and driven by exhaust gas and a compressor installed in an intake passage and driven by the turbine is known. The flow rate of the compressor depends on the rotational speed of the turbine or the supercharging pressure. If the compressor flow rate becomes too small and falls below the allowable minimum flow rate, a phenomenon (surge) occurs in which intake air intermittently backflows from the downstream side to the upstream side of the compressor. This surge is likely to occur when the exhaust pressure decreases in a specific operating state, such as when the fuel injection amount decreases.

Therefore, for example, in Patent Document 1, when the reduction amount per unit time of the fuel injection amount is in a specific operation state that is a predetermined amount or more, the rotation speed of the turbine is reduced from the normal time to reduce the supercharging pressure, The amount of EGR by the EGR device is reduced as compared with the normal time. By doing so, the allowable minimum value of the compressor flow rate is reduced to avoid a surge. Moreover, the backflow of the intake air through the EGR passage is prevented by closing the EGR valve.
JP-A-2005-240756

  By the way, recent engines have a diesel particulate filter (Diesel Particulate Filter; hereinafter referred to as “DPF”) that captures particulates (hereinafter referred to as “PM”) contained in exhaust gas, and an exhaust air-fuel ratio. A NOx trap catalyst for trapping nitrogen oxide NOx flowing in during lean and removing and purifying nitrogen oxide NOx trapped when the exhaust air-fuel ratio becomes rich is mounted. If the DPF continues to capture PM, it will eventually become clogged. Also, the NOx trap catalyst becomes sulfur poisoned over time. Therefore, in such a case, it is necessary to raise the exhaust gas temperature to forcibly burn and remove the accumulated PM to regenerate the DPF, or to cancel sulfur poisoning. Therefore, the fuel injection amount is increased. When the DPF is regenerated or sulfur poisoning is released, the increased fuel is returned to the original injection amount again.

  However, in the invention of the above-described Patent Document 1, since it is determined that the reduction amount per unit time of the fuel injection amount is a specific operation state that is a predetermined amount or more and surge prevention control is started, DPF regeneration control or NOx trapping is started. Every time the catalyst sulfur poisoning release control is finished and the fuel injection amount is returned to the original injection amount, useless surge prevention control is started, and the drivability deteriorates.

  The present invention has been made paying attention to such a conventional problem, and avoids unnecessary surge prevention control and prevents operability from deteriorating. Surge prevention control device and surge prevention control for an engine with a turbocharger It aims to provide a method.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

The present invention is a surge prevention control device for an engine with a turbocharger that prevents the occurrence of a surge in which intake air flows back and forth intermittently from the downstream side to the upstream side of the compressor (41) of the turbocharger (40). Surge prevention control permission judging means (step S8) for judging whether or not the surge prevention control is permitted or prohibited when the engine is decelerated or the fuel injection amount is reduced. without starting the control, have a surge prevention control starting means for starting the anti-surge control (step S13) when it is determined the authorization of the surge prevention control, the anti-surge control permission judging means, the change in the intake air amount Is less than a predetermined reference value, the surge prevention control is prohibited (steps S82 and S86) .

  According to the present invention, even when the engine is decelerated or the fuel injection amount is reduced, whether or not surge prevention control is permitted or prohibited is determined. Since the surge prevention control is started when it is determined that the prevention control is permitted, unnecessary surge prevention control can be avoided, and deterioration in drivability can be prevented.

  Hereinafter, the best mode for carrying out the present invention will be described in more detail with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment of a surge prevention control device for a turbocharged engine according to the present invention.

  The diesel engine 10 includes a turbocharger 40 including a turbine 42 installed in the exhaust passage 23 and driven by exhaust gas, and a compressor 41 installed in the intake passage 21 and driven by the turbine 42. The flow rate of the compressor 41 depends on the rotational speed of the turbine 42 or the supercharging pressure. Therefore, the flow rate of the compressor 41 is controlled by adjusting the rotational speed or supercharging pressure of the turbine 42 by controlling the opening of the variable nozzle mechanism 43.

  The diesel engine 10 is injected with fuel, which has been increased in pressure by the high-pressure pump 14 and once accumulated in the common rail 13, from the injector 12 in accordance with the injection timing.

  Part of the exhaust gas discharged from the diesel engine 10 and flowing through the exhaust passage 23 returns to the intake passage 21 via an exhaust gas recirculation device (hereinafter referred to as “EGR device”) 30. The EGR device 30 includes an EGR cooler 32 and an EGR valve 33 in the EGR passage 31. The EGR cooler 32 cools the exhaust gas recirculated from the exhaust passage 23. The EGR valve 33 is opened and closed to adjust the EGR amount. The EGR valve 33 is duty-controlled by the controller 100.

  A diesel oxidation catalyst (Diesel Oxidative Catalyst; hereinafter referred to as “DOC”) 70 is provided in the exhaust passage 23 of the diesel engine 10 and reduces particulates due to oxidation by a catalyst such as palladium or platinum. When the unburned component (hydrocarbon HC) of the fuel flows into the DOC 70, the exhaust gas that has become a high temperature due to the catalytic reaction flows out of the DOC 70.

  The DPF assembly 50 is provided further downstream of the DOC 70. The DPF assembly 50 incorporates a DPF 52 in a DPF housing 51. The DPF 52 has a porous honeycomb structure made of ceramic such as cordierite. In the DPF 52, flow paths are partitioned in a lattice shape by porous thin walls. The inlets of the respective channels are alternately sealed. In the flow path where the inlet is not sealed, the outlet is sealed. The exhaust gas that has flowed into the DPF 52 passes through the porous thin wall that partitions each flow path and is discharged downstream. PM contained in the exhaust gas is trapped and deposited on the inner surface of the porous thin wall. Although a part of the trapped PM burns in the DPF, if the DPF temperature (bed temperature) is not high, the combustion amount is small and the deposition amount is larger than the PM combustion amount. If this state continues and the DPF continues to capture PM, it will eventually become clogged. Therefore, when the PM is accumulated to some extent, the exhaust gas temperature is raised and the accumulated PM is forcibly removed by combustion.

  The differential pressure sensor 61 detects a differential pressure (pressure loss) between the upstream chamber 51 a (inlet of the DPF 52) and the downstream chamber 51 b (exit of the DPF 52) of the DPF housing 51, and outputs a differential pressure signal to the controller 100. The DPF inlet temperature sensor 62 detects the inlet temperature Tin of the DPF 52 and outputs an inlet temperature signal to the controller 100. The DPF outlet temperature sensor 63 detects the outlet temperature Tout of the DPF 52 and outputs an outlet temperature signal to the controller 100. The crank angle sensor 64 detects the rotational speed of the crankshaft 11 of the diesel engine 10.

  The accelerator position sensor 65 detects the accelerator pedal depression amount of the driver. The air flow sensor 66 detects the intake air amount. The pressure sensor 67 detects the pressure P1 on the upstream side of the turbo (compressor 41). The pressure sensor 68 detects the pressure P2 on the downstream side of the turbo (compressor 41).

  The controller 100 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface).

  The controller 100 inputs a differential pressure signal from the differential pressure sensor 61 and estimates the PM accumulation amount Mpm of the DPF 52 based on the magnitude of the differential pressure. The controller 100 determines the DPF regeneration timing based on the PM accumulation amount Mpm. The controller 100 inputs the inlet temperature signal of the DPF inlet temperature sensor 62 and the outlet temperature signal of the DPF outlet temperature sensor 63, and calculates the bed temperature of the DPF 52 based on these. Further, the controller 100 controls the injector 12 and the high-pressure pump 14 based on the input signal to adjust the fuel injection amount and the injection timing. The controller 100 adjusts the opening degree of the throttle valve 22 based on the input signal. The controller 100 performs duty control on the EGR valve 33. The controller 100 controls these to adjust the excess air ratio (air-fuel ratio) (λ control) to adjust the unburned components (hydrocarbon HC) contained in the exhaust gas, and increase the exhaust gas temperature flowing out from the DOC 70 And DPF regeneration is executed.

  Further, the controller 100 starts surge prevention control when the engine is decelerated or the fuel injection amount is reduced. However, if the engine is decelerated or the fuel injection amount is reduced, surge prevention control is always started and even unnecessary surge prevention control is performed. Therefore, it is determined whether or not the surge prevention control can be permitted when the engine is decelerated or the fuel injection amount is reduced, and the surge prevention control is started only when it can be permitted.

  Here, in order to facilitate understanding of the present invention, the knowledge of the present inventors will be described. If the DPF continues to capture PM discharged from the engine as described above, it will eventually become clogged. If PM accumulates to some extent, the amount of fuel is increased to raise the exhaust gas temperature, and the accumulated PM is forcibly removed by combustion.

  By the way, conventionally, when the reduction amount per unit time of the fuel injection amount is equal to or greater than a predetermined amount, it is determined that the specific operation state is set, and the surge prevention control is started. Therefore, the regeneration control of the DPF and the NOx trap catalyst Every time the sulfur poisoning release control is completed and the fuel injection amount is returned to the original injection amount, unnecessary surge prevention control is started. Originally, when the regeneration control of the DPF and the sulfur poisoning release control of the NOx trap catalyst are completed and the fuel injection amount is returned to the original injection amount, it is not necessary to execute the surge prevention control. However, conventionally, unnecessary surge prevention control is started in such a case, so that drivability is deteriorated.

  Therefore, the present inventors conducted day and night studies on further narrowing down the conditions under which surges can occur so as not to perform unnecessary surge prevention control.

  For example, the surge prevention control may be prohibited from the start to the end of the DPF regeneration control. However, in this way, the surge prevention control is prohibited until the surge prevention control must be executed during the regeneration of the DPF.

  Therefore, the inventors of the present invention focused on the intake air amount and the front-rear pressure of the turbo (compressor). When plotted on a graph with the horizontal axis intake air amount Qa and the vertical axis pressure ratio (P2 / P1), the surge depends on the intake air amount Qa and the front-rear pressure ratio (P2 / P1), and the boundary of surge generation (surge line) ) Was found to exist. Therefore, the surge prevention control is permitted only in the area where the surge is not generated and in the vicinity of the boundary where the surge occurs (i.e., the area where the surge is likely to occur). Therefore, it was found that unnecessary surge prevention control can be avoided by prohibiting surge prevention control.

  Based on the above, the specific operation of the surge prevention control device for the turbocharged engine according to the present invention will be described focusing on the operation of the controller 100. FIG. 2 is a main flowchart for explaining the operation of the surge prevention control device for the turbocharged engine. The controller 100 repeatedly executes this process at a DPF regeneration timing in a minute time (for example, 10 milliseconds) cycle.

  In step S1, the controller 100 detects the accelerator pedal depression amount APO. Specifically, for example, the detection is made based on the accelerator pedal depression amount detected by the accelerator position sensor 65.

  In step S2, the controller 100 determines whether or not the vehicle has been decelerated based on the accelerator pedal depression amount APO. If it is decelerated, the process proceeds to step S7, and if not, the process proceeds to step S3.

  In step S3, the controller 100 detects the fuel injection amount Qf.

  In step S4, the controller 100 determines whether or not the fuel injection amount Qf has been reduced. If the amount has been reduced, the process proceeds to step S7, and if not, the process proceeds to step S5.

  In step S5, the controller 100 resets the timer. This timer is a timer that is incremented in step S11 when deceleration and fuel reduction injection continue.

  In step S6, the controller 100 resets the permission flag Fper. The permission flag Fper is a flag that is set in step S10 when the surge prevention control is permitted.

  In step S7, the controller 100 determines whether or not the permission flag Fper is set. If it is set, the process proceeds to step S11, and if not, the process proceeds to step S8.

  In step S8, the controller 100 determines that the surge prevention control is permitted. A specific determination method will be described later.

  In step S9, if the surge prevention control is permitted, the controller 100 proceeds to step S10, and if not, temporarily exits this process.

  In step S10, the controller 100 sets a permission flag Fper.

  In step S11, the controller 100 increments the timer. This timer is a timer that counts the duration of deceleration and fuel reduction injection as described above.

  In step S12, the controller 100 determines whether or not the timer has become longer than a predetermined time. This process is temporarily exited until it becomes larger, and when it becomes larger, the process proceeds to step S13.

  In step S13, the controller 100 starts surge prevention control.

  FIG. 3 is a flowchart of a routine for determining whether or not to allow surge prevention control.

  In step S81, the controller 100 detects the intake air amount Qa.

  In step S82, the controller 100 determines whether or not the change in the intake air amount Qa is small. If it is smaller, the process proceeds to step S86; otherwise, the process proceeds to step S83. The reference value for determining whether or not the value is small is adapted in advance through experiments and stored in the ROM.

  In step S83, the controller 100 detects the pressure P2 on the downstream side of the turbo (compressor) and the pressure P1 on the upstream side, and calculates the pressure ratio (P2 / P1). The downstream pressure P2 is detected by the pressure sensor 68, and the upstream pressure P1 is detected by the pressure sensor 67.

  In step S84, the controller 100 determines whether or not it is within the surge prevention control region based on the characteristic map shown in FIG. If it is within the implementation area, the process proceeds to step S85, and if it is outside the implementation area, the process proceeds to step S86. The characteristic map is preliminarily adapted through experiments and stored in the ROM.

  In step S85, the controller 100 permits surge prevention control.

  In step S86, the controller 100 prohibits surge prevention control.

  According to this embodiment, even if the amount of decrease in the fuel injection amount per unit time is equal to or greater than a predetermined amount, the surge prevention control is prohibited when the change in the intake air amount is small. Thus, when the change in the intake air amount is small, the fuel injection amount decreased because the DPF regeneration control and the sulfur poisoning release control of the NOx trap catalyst were completed and the fuel injection amount was returned to the original injection amount. There is a high possibility that unnecessary surge prevention control is not required.

  In addition, surge prevention control is permitted only in the area near the surge generation boundary line (i.e., the area where surge is likely to occur), and in other areas there is no possibility of surge occurrence in the first place. Since the prevention control is prohibited, unnecessary surge prevention control is not performed.

  Without being limited to the embodiment described above, various modifications and changes can be made within the scope of the technical idea, and these are also included in the technical scope of the present invention.

  For example, in the said embodiment, although the diesel engine was illustrated and demonstrated, a gasoline engine may be sufficient. The reference values and characteristic maps described above are merely examples, and can be set as appropriate through experiments.

1 is a system diagram showing an embodiment of a surge prevention control device for an engine with a turbocharger according to the present invention. It is a main flowchart explaining operation | movement of the surge prevention control apparatus of an engine with a turbocharger. It is a flowchart of a routine for determining whether or not surge prevention control is permitted. It is a figure which shows an example of the characteristic map for determining whether it is in the implementation area | region of surge prevention control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 40 Turbocharger 41 Compressor 42 Turbine 43 Variable nozzle mechanism 66 Air flow sensor 67, 68 Pressure sensor Step S8 Surge prevention control permission judgment means Step S13 Surge prevention control start means

Claims (4)

A surge prevention control device for an engine with a turbocharger that prevents the occurrence of a surge in which intake air flows back and forth intermittently from the downstream side to the upstream side of the compressor of the turbocharger,
Surge prevention control permission judging means for judging permission or prohibition of surge prevention control when there is a deceleration of the engine or a decrease in the fuel injection amount;
Surge prevention control start means for starting the surge prevention control when judging the permission of the surge prevention control without starting the surge prevention control when judging the prohibition of the surge prevention control,
I have a,
The surge prevention control device for an engine with a turbocharger, wherein the surge prevention control permission determination means prohibits surge prevention control when the change in the intake air amount is smaller than a predetermined reference value . The surge prevention control permission determination means prohibits surge prevention control when the intake air amount and the front-rear pressure ratio of the turbocharger compressor are out of a predetermined region.
The surge prevention control device for an engine with a turbocharger according to claim 1. The surge prevention control starting means starts the surge prevention control when the deceleration of the engine or the reduction of the fuel injection amount continues for a predetermined time or more when the permission of the surge prevention control is determined.
The surge prevention control device for an engine with a turbocharger according to claim 1 or 2, wherein the engine is equipped with a turbocharger. A surge prevention control method for an engine with a turbocharger that prevents the occurrence of a surge in which intake air flows back and forth intermittently from the downstream side to the upstream side of the turbocharger compressor,
Surge prevention control permission determination step for determining permission or prohibition of surge prevention control when there is engine deceleration or fuel injection amount reduction;
A step of prohibiting surge prevention control when the change in the intake air amount is smaller than a predetermined reference value;
Surge prevention control start process for starting surge prevention control when judging prohibition of surge prevention control without starting surge prevention control when judging prohibition of surge prevention control;
A surge prevention control method for an engine with a turbocharger.
Vehicle exhaust purification system.