JP2013087687A - Secondary air supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain a backflow of exhaust gas of an internal combustion engine into a pump for supplying secondary air.SOLUTION: This secondary air supply system includes the pump 43 for repeating a cycle of discharging air from an outlet 435 by compressing or carrying the air by moving a movable part 433, a secondary air supply pipe for connecting the outlet 435 of the pump 43 to an exhaust passage of the internal combustion engine, and a stopping part for stopping the movable part 433 in the last period of the cycle when stopping the pump 43. The outlet 435 of the pump 43 is blocked up by the movable part 433, to prevent the inflow of the exhaust gas. Alternatively, a quantity of the exhaust gas flowing backward in the pump 43 is reduced by reducing the volume in the pump 43 communicating from the outlet 435 of the pump 43.

Description

  The present invention relates to a secondary air supply system.

  A technique is known that includes a pump that supplies secondary air upstream of an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine and supplies oxygen to the exhaust purification catalyst (see, for example, Patent Document 1). ).

  In such a system for supplying secondary air, a check valve is provided in the secondary air supply pipe between the pump and the exhaust passage so that the exhaust does not flow backward from the exhaust passage to the pump. For this reason, when supplying secondary air, the extra pump work for opening a check valve is needed, and when a pump is electrically driven, there exists a possibility that power consumption may increase. Further, in the case of a pump driven by a crankshaft of an internal combustion engine, it is necessary to increase the fuel supplied to the internal combustion engine in order to open the check valve. Moreover, there is a possibility that the pump generates heat and deteriorates due to an increase in work of the pump.

  On the other hand, if the check valve is not provided, the exhaust gas from the internal combustion engine may flow back into the pump when the pump is stopped. If the exhaust gas of the internal combustion engine flows backward in the pump, the inside of the pump may become dirty and the function may be deteriorated. In addition, moisture in the exhaust may condense in the pump, leading to a decrease in pump function.

JP 2003-239733 A

  The present invention has been made in view of the above-described problems, and an object thereof is to suppress the backflow of the exhaust gas of the internal combustion engine into the pump that supplies the secondary air.

In order to achieve the above object, a secondary air supply system according to the present invention comprises:
A pump that repeats a cycle in which the moving part moves to compress or convey air and discharge from the outlet;
A secondary air supply pipe connecting the outlet of the pump to the exhaust passage of the internal combustion engine;
When stopping the pump, a stop unit that stops the movable unit at the end of the cycle;
Is provided.

  For example, by controlling the discharge amount of air from the pump so that the pressure in the secondary air supply pipe is equal to or higher than the pressure in the exhaust passage, the exhaust passage can be provided without providing a check valve in the secondary air supply pipe. It is possible to prevent the exhaust gas from flowing backward to the pump. And since the work for opening a check valve is not required, it is possible to suppress deterioration in fuel consumption, increase in power consumption, and increase in pump load.

However, when the pump is stopped, the pressure in the secondary air supply pipe can be lower than the pressure in the exhaust passage. Therefore, there is a possibility that exhaust gas from the internal combustion engine flows backward into the pump. On the other hand, the stop portion stops the movable portion at the end of the cycle in which the movable portion compresses or conveys air and discharges it from the outlet. The movable part compresses or conveys air and pushes out the air from the outlet of the pump. Therefore, at the end of the discharge of the air from the pump, the volume of the space through which the air communicating from the outlet of the pump into the pump can flow Is relatively small. By stopping the movable part at such time, the exhaust of the internal combustion engine hardly flows back into the pump. Moreover, even if the exhaust gas from the internal combustion engine flows back into the pump, the amount of backflow decreases.

  The end of the cycle may be immediately before the cycle is completed or may be the time when the cycle is completed. Furthermore, it may be immediately after the cycle is completed. Further, the end of the cycle may be at the time when the air is completely pushed out by the movable part, or immediately after that. Furthermore, it is good also as a time when a movable part draws out air from an exit. Also, it may be at the end of the compression stroke. These may have a certain width. The pump may be a compressor. The movable part may push air intermittently. Moreover, you may stop a movable part immediately after discharge | emission of the air compressed or conveyed by a movable part is complete | finished.

  In this invention, the said stop part can stop the said movable part, when the volume inside the pump connected from the exit of the said pump is substantially the minimum.

  When air is discharged from the pump, the internal volume of the pump communicating from the pump outlet is gradually reduced by moving the movable part. If the movable part is stopped when this volume is minimized, the amount of condensed water generated and contamination can be minimized because even if the exhaust gas of the internal combustion engine flows back into the pump, it can be suppressed to a small amount. To the limit. It should be noted that when the volume is substantially minimum, it can include when the volume is zero. Moreover, since the same effect can be acquired also when the volume inside a pump is the predetermined range near the minimum, this range can also be included when it is substantially the minimum.

  In the present invention, the stop portion can stop the movable portion when the movable portion of the pump comes closest to the outlet of the pump.

  In other words, even if the outlet of the pump is not blocked by the movable part, the exhaust of the internal combustion engine flows into the pump because the movable part approaches the outlet and becomes resistance when the exhaust of the internal combustion engine flows backward. Can be suppressed. Further, since the volume in the pump that communicates from the outlet becomes smaller due to the movable part approaching the outlet, even if the exhaust gas from the internal combustion engine flows in, the amount can be reduced.

  In this invention, the said stop part can stop this movable part so that the outlet of the said pump may be plugged up with the movable part of the said pump.

  In some pumps, the movable part closes the outlet when the movable part approaches the outlet of the pump. In such a case, since the inflow of exhaust gas from the internal combustion engine is blocked by the movable portion, the amount of condensed water generated in the pump and the adhesion of dirt can be suppressed. If at least a part of the movable part exists on the outlet, it can be a resistance when the exhaust gas of the internal combustion engine flows into the pump, so that the inflow of exhaust gas can be suppressed. For this reason, plugging the outlet of the pump can include not only completely blocking the outlet of the pump, but also that at least a portion of the movable portion is located on the outlet.

  ADVANTAGE OF THE INVENTION According to this invention, the backflow of the exhaust_gas | exhaustion of an internal combustion engine into the pump which supplies secondary air can be suppressed.

It is a figure which shows schematic structure of the secondary air supply system which concerns on an Example. It is the flowchart which showed the control flow of the secondary air supply apparatus which concerns on an Example. FIG. 3 is a two-side view illustrating the structure of the pump according to the first embodiment. It is a figure which shows the mechanism for fixing a rotor. It is the flowchart which showed the control flow when stopping the pump which concerns on an Example. It is a figure which shows the structure of the pump by which the discharge port is provided in the outer peripheral surface of the housing similarly to the suction port. It is the figure which showed schematic structure of the pump provided with two orthogonal vanes. It is the figure which showed schematic structure of the piston pump which discharges air by the reciprocating motion of a piston. It is the figure which showed schematic structure of the Roots type pump which discharges air when two rotors rotate.

  Hereinafter, specific embodiments of the secondary air supply system according to the present invention will be described with reference to the drawings.

<Example 1>
FIG. 1 is a diagram illustrating a schematic configuration of a secondary air supply system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 may be a diesel engine or a gasoline engine.

An exhaust passage 2 is connected to the internal combustion engine 1. An exhaust purification catalyst 3 is provided in the middle of the exhaust passage 2. Examples of the exhaust purification catalyst 3 include an occlusion reduction type NOx catalyst, a selective reduction type NOx catalyst, a three-way catalyst, and an oxidation catalyst. The exhaust purification catalyst 3 may be a catalyst having an oxidation function or a catalyst that generates heat by supplying a reducing agent and air.

  A secondary air supply device 4 is provided in the exhaust passage 2 upstream of the exhaust purification catalyst 3. The secondary air supply device 4 includes an opening 41 that opens into the exhaust passage 2, a secondary air supply pipe 42, and a pump 43. The opening 41 is formed so as to have an outer diameter smaller than the inner diameter of the exhaust passage 2 and a cylindrical shape coaxial with the central axis of the exhaust passage 2. The opening 41 is connected to the pump 43 via a secondary air supply pipe 42. The pump 43 includes an electric motor, for example, and discharges air according to the number of rotations. Air is supplied to the exhaust passage 2 by operating the pump 43 to discharge air. The pump 43 may obtain a driving force from the crankshaft or the camshaft of the internal combustion engine 1. The pump 43 may control the discharge amount of air by controlling the rotation speed, and controls the discharge amount of air by adjusting the energization time and the energization stop time. It may be.

  The secondary air supply pipe 42 is provided with a secondary air pressure sensor 11 that detects the pressure in the secondary air supply pipe 42. An exhaust pressure sensor 12 that detects the pressure in the exhaust passage 2 is provided in the exhaust passage 2 between the opening 41 and the exhaust purification catalyst 3. An exhaust temperature sensor 13 for detecting the temperature of the exhaust gas flowing through the exhaust passage 2 is attached to the exhaust passage 2 downstream of the exhaust purification catalyst 3. Based on the output signal of the exhaust temperature sensor 13, the temperature of the exhaust purification catalyst 3 is detected.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 10 is connected to the sensor via an electric wiring, and an output signal of the sensor is input to the ECU 10. On the other hand, a pump 43 is connected to the ECU 10 via electrical wiring, and the pump 43 is controlled by the ECU 10.

  In this embodiment, the ECU 10 controls the pump 43 so that the pressure P1 in the secondary air supply pipe 42 is equal to or higher than the pressure P2 in the exhaust passage 2. That is, the pressure detected by the secondary air pressure sensor 11 is compared with the pressure detected by the exhaust pressure sensor 12, and the pressure detected by the secondary air pressure sensor 11 is detected by the exhaust pressure sensor 12. The pump 43 is controlled so as to be equal to or higher than the pressure to be applied.

  For example, if the pressure P1 in the secondary air supply pipe 42 is lower than the pressure P2 in the exhaust passage 2, the amount of air discharged from the pump 43 is increased or the pump 43 is operated to supply the secondary air. If the pressure P1 in the pipe 42 is equal to or higher than the pressure P2 in the exhaust passage 2, the amount of air discharged from the pump 43 is reduced or the pump 43 is stopped.

  FIG. 2 is a flowchart showing a control flow of the secondary air supply device 4 according to the present embodiment. This routine is repeatedly executed by the ECU 10 every predetermined time.

  In step S101, it is determined whether or not the pressure P1 in the secondary air supply pipe 42 is equal to or higher than the pressure P2 in the exhaust passage 2. That is, it is determined whether or not the exhaust does not flow backward in the secondary air supply pipe 42.

  If a positive determination is made in step S101, the process proceeds to step S102. In step S102, the pump 43 is stopped. In this step, the discharge amount of air from the pump 43 may be decreased. That is, since the exhaust does not flow backward in the secondary air supply pipe 42, the work of the pump 43 is reduced by stopping the pump 43 or reducing the discharge amount of air.

  On the other hand, if a negative determination is made in step S101, the process proceeds to step S103. In step S103, the pump 43 is operated. In this step, the amount of air discharged from the pump 43 may be increased. That is, since there is a possibility that the exhaust gas flows backward in the secondary air supply pipe 42, the air is discharged from the pump 43 so that the exhaust gas does not flow backward.

  In this way, by maintaining the pressure P1 in the secondary air supply pipe 42 at or above the pressure P2 in the exhaust passage 2, it is possible to suppress the backflow of exhaust gas through the secondary air supply pipe 42. Thereby, since a check valve can be abolished, fuel consumption can be improved. In addition, power consumption can be reduced. Furthermore, it can suppress that the pump 43 deteriorates.

  In the present embodiment, the secondary air pressure sensor 11 and the exhaust pressure sensor 12 are provided, but instead, the difference between the pressure in the secondary air supply pipe 42 and the pressure in the exhaust passage 2 is provided. You may provide the differential pressure sensor which detects this. Such a differential pressure sensor can also compare the pressure P1 in the secondary air supply pipe 42 with the pressure P2 in the exhaust passage 2, so that the pressure P1 in the secondary air supply pipe 42 is exhausted. The pump 43 can be controlled so as to be equal to or higher than the pressure P2 in the passage 2.

In the present embodiment, the pump 43 is controlled so that the pressure P1 in the secondary air supply pipe 42 becomes equal to or higher than the pressure P2 in the exhaust passage 2, but instead, the secondary air supply You may control the pump 43 so that the pressure P1 in the pipe | tube 42 may become larger than zero. Further, the pump 43 may be controlled so that the exhaust does not flow backward in the secondary air supply pipe 42. Here, it can be determined whether or not the exhaust gas flows backward in the secondary air supply pipe 42 based on the exhaust gas flow rate, the exhaust gas temperature, the back pressure, and the like. Further, the pump 43 can be controlled using a map obtained in advance through experiments or the like.

  By the way, since the secondary air supply device 4 according to the present embodiment does not include a check valve, if the pump 43 is stopped, the exhaust gas from the internal combustion engine 1 may flow back into the pump 43. For example, even if the pressure P1 in the secondary air supply pipe 42 is less than the pressure P2 in the exhaust passage 2 and the pump 43 is operated, if it takes time to operate, the exhaust of the internal combustion engine 1 is pumped. 43 may be reached. When the exhaust from the internal combustion engine 1 reaches the pump 43, the inside of the pump 43 may be contaminated by PM in the exhaust, or condensed water may be generated inside the pump 43. As a result, the pump 43 may be damaged or the function may be reduced.

  In contrast, in this embodiment, the pump 43 is stopped so as to suppress the inflow of exhaust gas into the pump 43.

  Here, FIG. 3 is a two-view diagram illustrating the structure of the pump 43 according to the present embodiment. The pump 43 shown in FIG. 3 is a vane pump. The pump 43 includes a rotor 432 and a vane 433 in the housing 431. The housing 431 has a cylindrical space inside. The rotor 432 is formed in a columnar shape, and the central axis thereof is arranged in parallel to the central axis of the housing 431 and shifted from the central axis of the housing 431. Both central axes are shifted so that the outer peripheral surface of the rotor 432 is in contact with the inner peripheral surface of the housing 431. The rotor 432 is driven by, for example, an electric motor or a camshaft or crankshaft of the internal combustion engine 1.

  The rotor 432 is provided with a vane 433 that is orthogonal to the central axis of the rotor 432. The vane 433 is slidably installed in a groove provided in the rotor 432. At least one end of the vane 433 reaches the housing 431. The rotor 432 rotates within the housing 431. When the rotor 432 rotates, the vane 433 is pushed by the inner peripheral surface of the housing 431 and moves in the rotor 432 in the radial direction.

  The housing 431 is provided with a suction port 434 that is an air inlet and a discharge port 435 that is an air outlet. The suction port 434 is provided on the curved surface portion in the housing 431 in a direction orthogonal to the central axis of the housing 431. Further, the discharge port 435 is provided in a plane portion in the housing 431 in a direction parallel to the central axis of the housing 431. The suction port 434 and the discharge port 435 are provided near the portion where the outer peripheral surface of the rotor 432 and the inner peripheral surface of the housing 431 are in contact with each other. A secondary air supply pipe 42 is connected to the discharge port 435. The rotor 432 rotates in a direction from the discharge port 435 toward the suction port 434 through a portion where the outer peripheral surface of the rotor 432 and the inner peripheral surface of the housing 431 are in contact with each other.

  In the pump 43 configured as described above, when the rotor 432 rotates, the tip of the vane 433 advances along the inner peripheral surface of the housing 431. The volume of the space that is communicated from the suction port 434 and is surrounded by the housing 431, the rotor 432, and the vane 433 gradually increases, whereby the suction port 434 enters the housing 431. Air is inhaled. This air is pushed by the vane 433 as the rotor 432 rotates and proceeds to the discharge port 435. When the vane 433 passes over the discharge port 435, the volume of the space formed by being surrounded by the housing 431, the rotor 432, and the vane 433 is gradually reduced. Thereby, air is pushed out from the discharge port 435. This air flows through the secondary air supply pipe 42 and is supplied to the exhaust passage 2.

  In this embodiment, when the pump 43 is stopped, the rotor 432 is stopped so that at least a part of the vane 433 is positioned on the discharge port 435. More desirably, the vane 433 stops the rotor 432 so as to block the discharge port 435. Note that the shapes of the discharge port 435 and the vane 433 may be determined so that the discharge port 435 can be blocked by the vane 433. FIG. 3 shows the time when the vane 433 is positioned on the discharge port 435.

  Here, if the exhaust port 435 is closed by the vane 433, the exhaust of the internal combustion engine 1 is suppressed from flowing into the housing 431. Further, even when the exhaust port 435 is not completely blocked by the vane 433, if at least a part of the vane 433 is positioned on the exhaust port 435, it becomes a resistance when the exhaust flows in, and therefore the inflow of exhaust Can be suppressed. Note that the discharge port 435 is blocked by the vane 433 immediately after the discharge of air from the discharge port 435 is completed. This can be said to be the end of a cycle from when the pump 43 sucks air to when it is discharged. At this time, the volume of the space in the pump 43 communicating from the discharge port 435 is the smallest.

  In order to stop the rotor 432 more reliably at the position where the vane 433 closes the discharge port 435, a mechanism for fixing the rotor 432 when the vane 433 is positioned on the discharge port 435 is provided. May be.

  Here, FIG. 4 is a view showing a mechanism for fixing the rotor 432. This mechanism includes a lock pin 436 that passes through the housing 431. The rotor 432 is provided with a hole 437 into which the lock pin 436 is fitted. When the lock pin 436 is fitted into the hole 437, the rotor 432 cannot rotate. The position of the hole 437 is determined such that the vane 433 is positioned on the discharge port 435 in a state where the lock pin 436 is fitted in the hole 437. The lock pin 436 is controlled by an electromagnetic valve 438 provided in the housing 431. The solenoid valve 438 pulls out the lock pin 436 from the hole 437 in the energized state (ON), and fits the lock pin 436 in the hole 437 in the non-energized state (OFF). The electromagnetic valve 438 is controlled by the ECU 10.

  Instead of moving the lock pin 436 forward and backward by the electromagnetic valve 438, the lock pin 436 may be advanced and retracted using hydraulic pressure.

  Further, the rotor 432 may be controlled based on the rotation angle of the rotor 432. The rotation angle of the rotor 432 can be acquired by, for example, a sensor that detects the rotation angle. Then, the rotation angle of the rotor 432 such that the vane 433 is positioned on the discharge port 435 is obtained in advance, and the motor is adjusted so that the vane 433 is positioned on the discharge port 435 when the rotor 432 is stopped. You may control. At this time, the ECU 10 may perform duty control on the motor.

  Further, the vane 433 or the housing 431 may be formed so that the gap between the vane 433 and the discharge port 435 becomes small when the rotor 432 stops. If it does so, it can control that exhaust flows backward through the crevice between vane 433 and housing 431. For example, when the rotor 432 is stopped, the gap between the discharge port 435 and the vane 433 can be reduced by causing a part of the vane 433 on the discharge port 435 to protrude toward the discharge port 435. Conversely, the discharge port 435 may protrude toward the vane 433 side.

When the discharge port 435 and the vane 433 are brought close to each other, the vane 433 may come into contact with the peripheral edge of the discharge port 435. On the other hand, you may give the coating for improving durability, and the coating for reducing friction to the location which may contact. Moreover, you may employ | adopt for the vane 433 or the discharge port 435 the shape which improves durability, or the shape which reduces friction.

  Next, FIG. 5 is a flowchart showing a control flow when the pump 43 according to the present embodiment is stopped. This routine is executed by the ECU 10 every predetermined time.

  In step S201, it is determined whether or not the pump 43 is in a stopped state. For example, when the rotor 432 is driven from the crankshaft or camshaft of the internal combustion engine 1 through the coupling, the pump 43 is stopped when the coupling is in a disconnected state. It is determined. Further, when the rotor 432 is driven by a motor, it is determined that the pump 43 is in a stopped state when power supply to the motor is stopped. Moreover, when it is in the driving | running state which does not require the pump 43, you may determine with the state which the pump 43 stops.

  If an affirmative determination is made in step S201, the process proceeds to step S202. On the other hand, if a negative determination is made, this routine is terminated.

  In step S202, it is determined whether or not the rotational speed of the rotor 432 is equal to or less than a predetermined value. The rotational speed of the rotor 432 is detected by attaching a sensor for detecting the rotational angle of the rotor 432, for example. Further, the rotational speed of the rotor 432 may be estimated based on the time elapsed since the power supply of the motor that drives the rotor 432 is stopped. This relationship can be obtained in advance by experiments or the like. The predetermined value here is a value indicating that the rotational speed of the rotor 432 has sufficiently decreased, and the rotational speed at which the lock pin 436 and the rotor 432 are not damaged even if the lock pin 436 protrudes toward the rotor 432 side. Is the upper limit.

  If an affirmative determination is made in step S202, the process proceeds to step S203, whereas if a negative determination is made, step S202 is executed again. That is, step S202 is repeatedly executed until the rotational speed of the rotor 432 becomes equal to or less than a predetermined value.

  In step S203, it is determined whether or not the discharge pressure of the pump 43 is equal to or less than a predetermined value. The discharge pressure of the pump 43 is the pressure in the secondary air supply pipe 42 and is the pressure detected by the secondary air pressure sensor 11. Further, the predetermined value here is a value indicating that the discharge pressure of the pump 43 has sufficiently decreased.

  If an affirmative determination is made in step S203, the process proceeds to step S204. On the other hand, if a negative determination is made, step S203 is executed again. That is, step S203 is repeatedly executed until the discharge pressure of the pump 43 becomes a predetermined value or less.

  In step S204, the electromagnetic valve 438 is turned off. That is, the lock pin 436 is protruded toward the rotor 432 side. At this time, since the rotor 432 is still rotating, the rotor 432 rotates with the tip of the lock pin 436 in contact with the outer peripheral surface of the rotor 432. When the hole 437 reaches the position of the lock pin 436, the lock pin 436 is fitted into the hole 437, and at the same time, the rotation of the rotor 432 is stopped. In this way, the discharge port 435 can be closed by the vane 433 when the rotor 432 is stopped. In this embodiment, the ECU 10 that processes step S204 corresponds to the stop portion in the present invention.

If the lock pin 436 is not provided and instead the stop position of the rotor 432 is adjusted by controlling the motor, the position of the rotor 432 is detected by a sensor in step S204. When the rotor 432 stops, the vane 433 is discharged from the discharge port 435.
The rotation angle of the rotor 432 is duty-controlled so as to be positioned above.

  The stop position of the rotor 432 may be adjusted using a cam or gear instead of using the lock pin 436 or performing the duty control of the motor.

  Further, in this embodiment, the position of the discharge port may be different. FIG. 6 is a view showing a structure of a pump 43B in which the discharge port 435B is provided on the outer peripheral surface of the housing 431B in the same manner as the suction port 434. Also in the pump 43B configured in this manner, if the rotor 432 is stopped so that the tip of the vane 433 closes the discharge port 435B, the exhaust of the internal combustion engine 1 can be prevented from flowing back into the pump 43B.

  As described above, according to the present embodiment, it is possible to suppress the exhaust of the internal combustion engine 1 from flowing backward into the pump 43.

<Example 2>
FIG. 7 is a diagram illustrating a schematic configuration of a pump 50 including two orthogonal vanes 51 and 52. Different parts from the pump 43 shown in FIG. 3 will be described.

  The pump 50 shown in FIG. 7 includes a first vane 51 and a second vane 52. The first vane 51 and the second vane 52 are perpendicular to the central axis of the rotor 53, and each is slidably installed in a groove provided in the rotor 53. The center part of the first vane 51 and the second vane 52 is cut according to the relative movement range of the other so as to avoid the other. Further, the discharge port 54 is provided on the outer peripheral surface of the housing 55 like the suction port 434.

  Also in the pump 50 configured as described above, if the rotor 53 is stopped so that the tip of the first vane 51 or the second vane 52 blocks the discharge port 54, the exhaust gas of the internal combustion engine 1 flows back into the pump 50. This can be suppressed.

<Example 3>
FIG. 8 is a diagram showing a schematic configuration of a piston pump 60 that discharges air by the reciprocating motion of the piston 61. A piston pump 60 is used instead of the pump 43 described in FIG. 3 of the first embodiment. Since other devices are the same as those in the first embodiment, description thereof is omitted.

  In the piston pump 60, the volume in the cylinder 62 is the largest when the piston 61 is in the lowest position, and the volume in the cylinder 62 is the smallest when the piston 61 is in the highest position. The suction port 63 is formed at a relatively low position of the cylinder 62 so as to open when the piston 61 is at a relatively low position. Further, the discharge port 64 is formed in the cylinder head 65. The piston 61 is connected to a crank 67 via a connecting rod 66. Then, when the crank 67 rotates, the piston 61 reciprocates in the cylinder 62. The crank 67 is driven by a motor, for example.

In the piston pump 60 configured as described above, air flows into the cylinder 62 from the suction port 63 when the piston 61 is at a relatively low position. When the position of the piston 61 is increased, the suction port 63 is blocked by the piston 61, and the outflow of air from the suction port 63 is suppressed. Then, the air pushed by the piston 61 as the piston 61 rises is discharged from the discharge port 64. Even in the piston pump 60 configured as described above, if the piston 61 is stopped at a relatively high position when the piston pump 60 is stopped, the volume in the cylinder 62 communicating from the discharge port 64 is compared. Therefore, even if the exhaust gas from the internal combustion engine 1 flows backward from the exhaust port 64, the amount thereof decreases. More preferably, if the piston 61 is stopped at the highest position, the volume in the cylinder 62 communicating with the exhaust port 64 becomes the smallest, and the amount of exhaust gas of the internal combustion engine 1 that flows back into the cylinder 62. Can be reduced. Thereby, it can suppress that the inside of the cylinder 62 becomes dirty, or can suppress that condensed water generate | occur | produces in the cylinder 62. Here, when the piston 61 is at a relatively high position, it can be said that the end of the cycle from when the piston pump 60 sucks in air until it is discharged.

  The same applies to any pump that compresses or conveys air by a reciprocating motion of the movable part (for example, a diaphragm pump, a swash plate pump, a plunger pump, etc.). That is, when the volume in the pump (which may be in the cylinder) leading from the discharge port becomes relatively small, or when the air is in the most compressed state, the movable part is relatively close to the discharge port. By stopping the movable part at times, the amount of exhaust gas from the internal combustion engine 1 flowing into the pump can be reduced.

<Example 4>
FIG. 9 is a diagram showing a schematic configuration of a Roots-type pump 70 that discharges air by rotating two rotors. A Roots pump 70 is used instead of the pump 43 described in FIG. Since other devices are the same as those in the first embodiment, description thereof is omitted.

  A Roots type pump 70 shown in FIG. 9 has two rotors, a first rotor 72 and a second rotor 73, in a housing 71. The two rotors 72 and 73 are configured to rotate synchronously in opposite directions. In such a Roots type pump 70, the air that has entered the housing 71 from the suction port 74 is confined in the space between the housing 71 and the rotors 72 and 73, and the exhaust port 75 side as the rotors 72 and 73 rotate. To be discharged.

  Even in the Roots type pump 70 configured as described above, when the rotors 72 and 73 are stopped, the space in the housing 71 that communicates from the discharge port 75 (the space surrounded by the housing 71 and the two rotors 72 and 73). ) Is stopped at a position where the volume is relatively small, the amount of exhaust gas flowing into the housing 71 can be relatively small, so that the amount of condensed water and the amount of dirt attached can be suppressed. it can. When the rotors 72 and 73 are located at a position where the volume of the space in the housing 71 communicating with the discharge port 75 is relatively small, the cycle of the cycle from when the roots pump 70 sucks in air until it is discharged. It can be said that it is the end. More desirably, when the rotors 72 and 73 are stopped, the volume of the space in the housing 71 (the space surrounded by the housing 71 and the two rotors 72 and 73) communicating with the discharge port 75 is minimized. By stopping at such a position (see the alternate long and short dash line), the amount of exhaust gas flowing into the housing 71 can be minimized, so that the amount of condensed water generated and the amount of dirt attached can be minimized. . The stop positions of the rotors 72 and 73 are obtained in advance by experiments or the like.

  A twin (double) screw pump in which a pair of twisted rotors are engaged, and a single screw pump in which two compression chambers are formed by two gate rotors arranged with a central axis at a right angle with respect to one screw rotor. The same applies to a scroll pump. For example, immediately after the air is exhausted from the discharge port, the volume of the space in the pump communicating with the discharge port is small, and the pump may be stopped at this time.

1 Internal combustion engine 2 Exhaust passage 3 Exhaust purification catalyst 4 Secondary air supply device 10 ECU
11 Secondary Air Pressure Sensor 12 Exhaust Pressure Sensor 13 Exhaust Temperature Sensor 41 Opening 42 Secondary Air Supply Pipe 43 Pump 431 Housing 432 Rotor 433 Vane 434 Suction Port 435 Discharge Port 436 Lock Pin 437 Hole 438 Solenoid Valve

Claims (4)

A pump that repeats a cycle in which the moving part moves to compress or convey air and discharge from the outlet;
A secondary air supply pipe connecting the outlet of the pump to the exhaust passage of the internal combustion engine;
When stopping the pump, a stop unit that stops the movable unit at the end of the cycle;
A secondary air supply system comprising:   The secondary air supply system according to claim 1, wherein the stop portion stops the movable portion when the volume inside the pump communicating from the outlet of the pump is substantially minimum.   The secondary air supply system according to claim 1, wherein the stop unit stops the movable unit when the movable unit of the pump comes closest to the outlet of the pump.   The secondary air supply system according to any one of claims 1 to 3, wherein the stop portion stops the movable portion so as to block the outlet of the pump with the movable portion of the pump.

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