JP5991287B2 - EGR control device for internal combustion engine - Google Patents

Description

  The present invention relates to an EGR control device for an internal combustion engine.

  When an EGR mechanism (exhaust gas recirculation mechanism) is applied to an internal combustion engine in which a turbocharger is assembled, the exhaust gas downstream of the turbine wheel of the turbocharger is recirculated upstream of the compressor wheel by the EGR mechanism as shown in Patent Document 1. The

  As the turbocharger assembled to the internal combustion engine, an abradable seal layer is formed in the turbine housing surrounding the turbine wheel, and the turbocharger rotates after the start of use of the turbocharger (first operation after the completion of the production of the internal combustion engine). It is conceivable to employ a turbine wheel that wears the abradable seal layer.

  In this case, since the tip clearance between the turbine wheel and the turbine housing can be set small by wearing (shaving) the abradable seal layer with the turbine wheel as described above, the exhaust gas passing through the turbine housing can be reduced. It is possible to efficiently convert the kinetic energy into the rotational motion of the turbine wheel.

JP 2012-202265 A

  By the way, when the abradable seal layer in the turbine housing is worn by the rotating turbine wheel after the start of the use of the turbocharger, wear powder generated in association with the abradable seal layer is mixed into the exhaust gas downstream of the turbine wheel. When wear powder is mixed into the exhaust gas downstream of the turbine wheel in this way, if the exhaust gas is recirculated upstream of the compressor wheel by the EGR mechanism, the wear powder in the exhaust gas is caught in the compressor wheel and causes damage to the compressor wheel. There is a fear.

  The objective of this invention is providing the EGR control apparatus of the internal combustion engine which can suppress the damage of the compressor wheel after the start of use of a turbocharger.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
A turbocharger in which an abradable seal layer that is worn by a rotating turbine wheel is formed in a turbine housing is assembled in an internal combustion engine to which an EGR control device that solves the above problems is applied. The EGR control device also includes a control unit that controls the operation of the EGR mechanism that recirculates the exhaust gas downstream of the turbine wheel to the compressor wheel upstream of the turbocharger. This control unit prohibits the recirculation of exhaust gas from the turbine wheel downstream to the compressor wheel upstream by the EGR mechanism until a certain period of time has elapsed from the start of use of the first turbocharger after completion of manufacture of the internal combustion engine . For this reason, when the abradable seal layer in the turbine housing is worn by the rotating turbine wheel after the start of the use of the turbocharger, even if wear powder generated thereby is mixed into the exhaust downstream of the turbine wheel, the exhaust is Recirculation to the upstream side of the compressor wheel by the EGR mechanism is suppressed. Therefore, the wear powder in the exhaust gas recirculated to the upstream side of the compressor wheel is caught in the compressor wheel, thereby preventing the compressor wheel from being damaged.

1 is a schematic diagram showing a structure around an internal combustion engine to which an EGR control device is applied. The expanded sectional view which shows the structure of the boundary periphery of the turbine housing and turbine wheel in a turbocharger. The flowchart which shows the procedure which prohibits the recirculation | reflux of exhaust_gas | exhaustion by an EGR mechanism until the fixed period after the start of use of a turbocharger passes.

Hereinafter, an embodiment of an EGR control device for an internal combustion engine will be described with reference to FIGS.
As shown in FIG. 1, a turbine housing 5 provided so as to surround a turbine wheel 7 of the turbocharger 1 is connected to the exhaust passage 3 of the internal combustion engine 2 in which the turbocharger 1 is assembled. The turbine wheel 7 is fixed to one end of a shaft 8 rotatably provided on the turbocharger 1. The turbine wheel 7 is formed with a large number of blades 6 at equal intervals in the rotational direction about the shaft 8. On the other hand, a compressor housing 12 provided so as to surround the compressor wheel 14 of the turbocharger 1 is connected to the intake passage 10 of the internal combustion engine 2. The compressor wheel 14 is fixed to the other end of the shaft 8. The compressor wheel 14 is formed with a large number of blades 13 at equal intervals in the rotational direction about the shaft 8.

  In the turbocharger 1, the exhaust gas from the internal combustion engine 2 passes through the exhaust passage 3 and flows into the turbine housing 5. The exhaust gas flowing into the turbine housing 5 flows between the blades 6 of the turbine wheel 7 and then flows out from the outlet of the turbine housing 5 to the outside. When the exhaust flows between the blades 6 in the turbine housing 5, the turbine wheel 7 and the shaft 8 rotate around the center line of the coaxial 8 by the kinetic energy of the exhaust. In the turbocharger 1, the air in the portion upstream of the inlet of the compressor housing 12 in the intake passage 10 is sucked into the compressor housing 12 through the inlet, and then between the blades 13 of the compressor wheel 14. Pass through. At that time, when the compressor wheel 14 rotates through the rotation of the turbine wheel 7 and the shaft 8 described above, the air between the blades 13 is boosted by the kinetic energy of the compressor wheel 14 and then the intake passage from the outlet of the compressor housing 12. 10 is sent downstream of the same outlet.

  The internal combustion engine 2 includes an EGR passage 16 that connects the turbine wheel 7 downstream in the exhaust passage 3 and the compressor wheel 14 upstream in the intake passage 10, and an EGR that opens and closes to make the exhaust flow area in the EGR passage 16 variable. An EGR mechanism (exhaust gas recirculation mechanism) including a valve 17 is provided. In the EGR mechanism, the EGR valve 17 is fully closed, so that the exhaust downstream of the turbine wheel 7 through the EGR passage 16 is prohibited from returning to the upstream of the compressor wheel 14. Further, as the EGR valve 17 is opened from the fully closed state toward the fully opened state, the amount of recirculation of the exhaust gas downstream of the turbine wheel 7 through the EGR passage 16 to the upstream of the compressor wheel 14 increases.

  The internal combustion engine 2 is provided with a throttle valve 20 that opens and closes so as to make the gas flow area in the intake passage 10 variable, and a cooling water circuit 18 through which the cooling water of the internal combustion engine 2 flows. A water pump 19 driven to circulate is also provided.

Next, the structure around the boundary between the turbine housing 5 and the turbine wheel 7 in the turbocharger 1 will be described in detail.
As shown in FIG. 2, an abradable seal layer 9 that can be worn (cut) by the rotating turbine wheel 7 is formed on the inner surface of the turbine housing 5 corresponding to the blades 6 of the turbine wheel 7. ing. The abradable seal layer 9 has a shape in which the blade 6 side surface 9a is located closer to the center of the turbine wheel 7 than the surface of the blade 6 on the abradable seal layer 9 side before the start of use of the turbocharger 1. have. The start of use of the turbocharger 1 is after the completion of manufacture of the internal combustion engine 2 with the turbocharger 1 and after the engine 2 is assembled to a vehicle on which the internal combustion engine 2 is to be mounted. This is the time when the first driving was started.

  After the start of use of the turbocharger 1, the abradable seal layer 9 is worn (cut) by the blades 6 of the rotating turbine wheel 7, so that the turbine wheel 7 (more precisely, the blade 6) and the turbine housing The chip clearance with 5 is set small. Thus, by setting the tip clearance small, it becomes possible to efficiently convert the kinetic energy of the exhaust gas passing through the turbine housing 5 into the rotational motion of the turbine wheel 7.

Next, the electrical configuration of the EGR control device will be described.
As shown in FIG. 1, the EGR control device includes an electronic control device 21 that performs various controls of the internal combustion engine 2 and its peripheral devices. This electronic control device 21 is a CPU that executes various arithmetic processes related to the above control, a ROM that stores programs and data necessary for the control, a RAM that stores CPU arithmetic results, etc., and signals between the outside Input / output ports for input / output.

  In addition to the rotational speed sensor 22 that detects the rotational speed of the turbocharger 1, the input port of the electronic control device 21 is used to detect the operating state of the internal combustion engine 2 and the traveling state of the vehicle in which the engine 2 is mounted. Various sensors are connected. Such sensors include a crank position sensor 23 for detecting the engine rotational speed, a throttle position sensor 24 for detecting the opening (throttle opening) of the throttle valve 20, and the like. On the other hand, the output port of the electronic control device 21 is connected to a drive circuit for the EGR valve 17, a drive circuit for the throttle valve 20, a drive circuit for the water pump 19, and the like, and various devices for operating the internal combustion engine 2. The drive circuit is also connected.

  The electronic control device 21 grasps information such as the rotational speed of the turbocharger 1, the operating state of the internal combustion engine 2, and the traveling state of the vehicle based on the detection signals input from the various sensors, and according to the grasped information. Command signals are output to various drive circuits connected to the output port. Thus, the opening control of the EGR valve 17, the opening control of the throttle valve 20, the drive control of the water pump 19, and the like are performed through the electronic control device 21.

Next, the operation of the EGR control device will be described.
The electronic control unit 21 prohibits the recirculation of exhaust gas from the turbine wheel 7 downstream to the compressor wheel 14 upstream by the EGR mechanism until a certain period of time elapses from the start of use of the turbocharger 1 as the opening degree control of the EGR valve 17. Accordingly, the valve 17 is driven so that the EGR valve 17 is fully closed. For this reason, when the abradable seal layer 9 in the turbine housing 5 is worn by the rotating turbine wheel 7 after the start of use of the turbocharger 1, it is assumed that the generated wear powder is mixed into the exhaust gas downstream of the turbine wheel 7. However, it is suppressed that the exhaust gas is recirculated upstream of the compressor wheel 14 by the EGR mechanism. Therefore, the abrasion powder in the exhaust gas recirculated to the upstream of the compressor wheel 14 is caught in the compressor wheel 14, thereby preventing the compressor wheel 14 from being damaged.

  Incidentally, the initial wear of the abradable seal layer 9 by the turbine wheel 7 is completed after the start of use of the turbocharger 1 (the blade 6 and the abradable seal layer 9 are removed) during the above-mentioned fixed period in which the exhaust gas recirculation is prohibited. It is preferable to be a period until the wear powder is not generated). The determination as to whether or not such a certain period has elapsed after the start of use of the turbocharger 1 can be made, for example, through one of the following determinations [A] to [F].

  [A] Whether or not the cumulative travel distance of the vehicle has reached a value corresponding to a period required from the start to the end of the wear. The cumulative travel distance of the vehicle is obtained through the electronic control device 21 based on detection signals from various sensors that detect the travel state of the vehicle, and is stored in the nonvolatile RAM 21a (FIG. 1) of the electronic control device 21. Yes.

  [B] Whether or not the cumulative traveling time of the vehicle has reached a value corresponding to a period required from the start to the end of the wear. The accumulated traveling time of the vehicle is obtained through the electronic control device 21 based on detection signals from various sensors that detect the traveling state of the vehicle, and is stored in the nonvolatile RAM 21a of the electronic control device 21.

  [C] Whether or not the cumulative start count of the internal combustion engine 2 has reached a value corresponding to a period required from the start to the end of the wear. The cumulative number of times the internal combustion engine 2 has been started is obtained through the electronic control device 21 based on detection signals from various sensors that detect the operating state of the engine, and is stored in the nonvolatile RAM 21a of the electronic control device 21. .

  [D] The engine operating conditions such as the engine speed, the opening degree of the throttle valve 20, and the operating time of the internal combustion engine 2 are multiplied and accumulated every predetermined timing, and the accumulated value obtained in this way is the wear value. Whether or not the value corresponding to the period required from the start to the end of

  [E] Whether the responsiveness of the rotational speed of the turbocharger 1 is equal to or higher than a level that can be regarded as the end state of the wear. The responsiveness of the rotational speed of the turbocharger 1 can be expressed by an increase speed of the rotational speed of the turbocharger 1 with respect to an increase in a parameter related to the engine output such as the engine rotational speed.

  [F] Whether or not the amplitude of the rotational speed of the turbocharger 1 is less than a level that can be regarded as the end state of the wear. Incidentally, the amplitude of the rotational speed of the turbocharger 1 tends to decrease as the wear progresses and the rotational resistance of the turbocharger 1 decreases. The amplitude of the rotational speed of the turbocharger 1 can be grasped by obtaining the rotational speed of the turbocharger 1 based on the detection signal of the rotational speed sensor 22 and monitoring the rotational speed.

  FIG. 3 is a flowchart showing an EGR prohibition routine for prohibiting exhaust gas recirculation (EGR) by the EGR mechanism from the start of use of the turbocharger 1 until a certain period of time elapses. The EGR prohibition routine is periodically executed through the electronic control device 21 by, for example, a time interrupt at predetermined intervals.

  The electronic control unit 21 determines whether or not the EGR permission condition is satisfied as the process of step 101 (S101) of the routine. This EGR permission condition is for determining whether to permit or prohibit the exhaust gas recirculation by the EGR mechanism, and is referred to as “a certain period of time has elapsed since the start of use of the turbocharger 1”. Includes conditions. Then, based on the fact that all EGR permission conditions including the same condition are satisfied, an affirmative is made in S101. Accordingly, if it is determined in S101 that the EGR permission condition is satisfied, the wear powder is abated after the initial wear of the abradable seal layer 9 by the turbine wheel 7 is completed for a certain period from the start of use of the turbocharger 1. The period until no longer occurs has passed.

  If a certain period has not elapsed since the start of use of the turbocharger 1, a negative determination is made in S101 and the process proceeds to S102. Further, even if a certain period has elapsed since the start of use of the turbocharger 1, if other conditions of the EGR permission conditions are not satisfied, a negative determination is made in S101 and the process proceeds to S102. The electronic control unit 21 prohibits the recirculation of the exhaust gas by the EGR mechanism by setting the EGR valve 17 to the fully closed state as a process of S102. However, if the recirculation of exhaust gas by the EGR mechanism is prohibited between the start of use of the turbocharger 1 and the elapse of the predetermined period, the NOx emission amount of the internal combustion engine 2 may increase accordingly.

  Therefore, the electronic control unit 21 determines whether or not the predetermined period is within the process of S103. If the determination is affirmative, the NOx for suppressing the NOx emission amount of the internal combustion engine 2 is reduced as the process of S104. Perform suppression processing. In such NOx suppression processing, the cooling water discharge flow rate from the water pump 19 is increased to increase the cooling efficiency of the internal combustion engine 2 by the cooling water circuit, or the throttle valve 20 is opened to suppress the heat generation amount of the internal combustion engine 2. It may be possible to limit the value to a smaller value. If a negative determination is made in S104, the electronic control device 21 ends the EGR prohibition routine.

  On the other hand, if an affirmative determination is made in S101, it means that a certain period has elapsed since the start of use of the turbocharger 1. In this case, the process proceeds to S105. The electronic control device 21 permits the recirculation of the exhaust gas by the EGR mechanism by permitting the opening change from the fully closed state of the EGR valve 17 as the processing of S105. Furthermore, if the above-described NOx suppression process is executed as the process of S106, the electronic control device 21 ends the process.

According to the embodiment described in detail above, the following effects can be obtained.
(1) The exhaust gas recirculation by the EGR mechanism is prohibited until a certain period of time has elapsed after the start of use of the turbocharger 1. For this reason, before the initial wear of the abradable seal layer 9 by the turbine wheel 7 is finished, the exhaust gas containing the wear powder is recirculated upstream of the compressor wheel 14, whereby the wear powder is caught in the compressor wheel 14. The compressor wheel 14 can be prevented from being damaged.

  (2) Since NOx suppression processing is executed while exhaust gas recirculation by the EGR mechanism is prohibited during the predetermined period, the amount of NOx emission from the internal combustion engine 2 increases during the exhaust gas recirculation prohibition period. This can be suppressed.

In addition, the said embodiment can also be changed as follows, for example.
A plurality of determinations among the determinations [A] to [F] may be performed, and it may be determined that the predetermined period has elapsed when all of these determinations are positive.

  -It is not always necessary to execute the NOx suppression process.

  DESCRIPTION OF SYMBOLS 1 ... Turbocharger, 2 ... Internal combustion engine, 3 ... Exhaust passage, 5 ... Turbine housing, 6 ... Blade, 7 ... Turbine wheel, 8 ... Shaft, 9 ... Abradable seal layer, 9a ... Surface, 10 ... Intake passage, DESCRIPTION OF SYMBOLS 12 ... Compressor housing, 13 ... Blade | wing, 14 ... Compressor wheel, 16 ... EGR passage, 17 ... EGR valve, 18 ... Cooling water circuit, 19 ... Water pump, 20 ... Throttle valve, 21 ... Electronic control unit, 21a ... RAM, 22 ... rotational speed sensor, 23 ... crank position sensor, 24 ... throttle position sensor.

Claims (1)

EGR applied to an internal combustion engine having a turbocharger formed with an abradable seal layer that is worn by a rotating turbine wheel in a turbine housing, and returns exhaust gas downstream of the turbine wheel upstream of a compressor wheel of the turbocharger. In an EGR control device for an internal combustion engine comprising a mechanism and a control unit that controls the operation of the EGR mechanism,
The control unit prohibits recirculation of exhaust gas from the turbine wheel downstream to the compressor wheel upstream by the EGR mechanism until a certain period of time has elapsed since the first use of the turbocharger after the completion of manufacture of the internal combustion engine. An EGR control device for an internal combustion engine characterized by the above.