JP6613132B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine provided with a catalyst type exhaust purification device, and is mainly intended for a vehicle internal combustion engine.

A three-way catalyst is generally used for purifying exhaust gas in a vehicular gasoline engine, and the catalyst is built in a catalyst case so that the exhaust gas passes through the catalyst. Catalyst is excellent performance for purification of exhaust gas, there is a problem that excessively becomes heated easily damaged.

  Therefore, it is considered to control the temperature of the exhaust gas flowing into the catalyst case so as not to become an excessively high temperature. For example, in Patent Document 1, for example, by increasing the amount of fuel injected into the internal combustion engine A technique for lowering the exhaust temperature is disclosed.

Japanese Patent Laid-Open No. 04-1437

  When the amount of fuel is increased, the heat of vaporization increases and the combustion temperature decreases, and as a result, the temperature of the exhaust gas also decreases. For this reason, there are examples that have been put into practical use as means for lowering the exhaust temperature, but since the amount of fuel that is required for the output required for the engine is consumed, the problem of deterioration in fuel consumption cannot be avoided.

  The present invention has been made in view of such a current situation, and is intended to protect the catalyst from excessively high temperatures without deteriorating fuel consumption and purification performance.

The present invention is
“In the exhaust system , a catalyst case containing a catalyst is interposed in the exhaust passage and an oxygen sensor or an air-fuel ratio sensor is provided.
A bypass passage is provided in the exhaust passage to recirculate a part of the exhaust gas from the downstream side to the upstream side of the catalyst, and when the measured or estimated value of the temperature of the catalyst is equal to or higher than a preset reference temperature , the catalyst is It is controlled so that a part of the exhaust gas that has passed is recirculated to the upstream side of the catalyst via the bypass passage. ''
In the basic configuration
“As a dangerous value for the catalyst, a dangerous temperature higher than the reference temperature related to temperature, a strong lean value and a strong rich value related to oxygen concentration are preset, and the temperature is higher than the reference temperature and lower than the dangerous temperature. When the detection value of the oxygen sensor or air-fuel ratio sensor reaches either the strong lean value or the strong rich value in the state, the exhaust gas recirculation is controlled to be stopped or suppressed.
It has the characteristics.

  The bypass passage (or exhaust passage) must be provided with an open / close valve that controls the recirculation of the exhaust gas, but the open / close valve may be a simple method such as a fully-open / fully-closed method or a method that can adjust the amount of recirculation. There may be.

  The temperature of the catalyst (or the internal temperature of the catalyst case) can be directly measured by a temperature sensor, and the dangerous temperature range can be estimated from other factors. As an estimation method, for example, the engine speed and torque (or load) are used as variables, and it is possible to estimate that the catalyst has reached an excessively high temperature when both the torque and the speed exceed a preset value. is there. The torque can be derived from the throttle opening (or intake negative pressure) and the fuel injection amount.

  The exhaust gas temperature is closely related to the engine temperature. Therefore, for example, when the cooling water temperature is replaced with the engine temperature and the cooling water temperature is lower than the preset value, the exhaust gas recirculation is started after reaching the high load / high rotation range, and the cooling water temperature is When the value is higher than a preset value, it is possible to correct the exhaust gas recirculation when the high load / medium rotation range (or medium load / high rotation) is reached.

The exhaust system of an internal combustion engine is usually provided with an oxygen sensor (O2 sensor) and an A / F (air-fuel ratio sensor) for engine control, and these sensors are generally connected to the upstream side of the catalyst. It is arranged on the downstream side, and feedback control is performed by front and rear sensors. Therefore, in the present invention, by using these sensors, (so as not to give in other words, an effect on the purification performance of the exhaust gas by the catalyst) so as not to affect the adjustment of the amount of oxygen in the catalyst, the feedback control Is done.

  The temperature of the exhaust gas decreases as it goes downstream of the exhaust passage. Therefore, there is a large temperature difference between the upstream side and the downstream side of the catalyst. The present invention utilizes this fact, and the temperature of the exhaust gas flowing into the catalyst can be lowered as a whole by recirculating the cooled exhaust gas to the upstream side of the catalyst. Thereby, the abnormal heating of a catalyst can be suppressed and damage can be prevented.

Further, since the amount of fuel is not increased, there is no problem of deterioration in fuel consumption, and since exhaust gas that has already been purified is recirculated, the purification performance of exhaust gas does not deteriorate. Rather, since a part of the exhaust gas is purified again, the purification performance is improved.
Further, in the present invention, since the exhaust gas recirculation is controlled based on the sensor, it is possible to prevent the oxygen passing through the catalyst from becoming excessive or excessive due to the exhaust gas recirculation, and to control the engine appropriately. In this way, the purification function of the catalyst can be optimized.

  The catalyst has a problem that the performance deteriorates when the temperature becomes too low.For this reason, for example, when the atmospheric air is taken in, the temperature of the exhaust gas may become too low. Since the exhaust gas at a high temperature is recirculated, it can be said that there is an advantage that excessive cooling of the catalyst can be prevented.

It is a figure which shows embodiment, (A) is a schematic diagram of the whole, (B) is sectional drawing of an example of a reflux nozzle.

(1). Description of Structure Next, an embodiment in which the present invention is applied to a vehicle internal combustion engine will be described with reference to the drawings. First, the structure will be described. In FIG. 1A, the whole is displayed. In this figure, reference numeral 1 denotes a cylinder block, reference numeral 2 denotes a cylinder head, and reference numeral 3 denotes a head cover. The internal combustion engine of the present embodiment has three cylinders, and an exhaust manifold 4 having three branch pipes is fixed to the exhaust side of the cylinder head 2.

  The branch pipes of the exhaust manifold 4 converge to one collecting pipe 5, and a catalyst case 6 is connected to the collecting pipe 5. The catalyst case 6 includes a straight portion 6a in which the catalyst 7 is incorporated, and an upper cone portion 7b is connected to the upper end of the straight portion 6a, and the lower end of the straight portion 6a is connected to the lower end of the straight portion 6a. A lower-cone-shaped lower cone portion 7c is connected. The upper cone part 7 b is connected to the collecting pipe 5 of the exhaust manifold 4, and the exhaust pipe 9 is connected to the lower cone part 7 c via a joint part 8.

The exhaust manifold 4, the catalyst case 6, and the exhaust pipe 9 constitute an exhaust passage (exhaust system) as a whole, and a silencer 10 is provided at the end of the exhaust pipe 9. A bracket 11 is fixed to the joint portion 8, and the bracket 11 is fixed to the cylinder block 1.

  The internal combustion engine of the present embodiment includes an EGR device that recirculates exhaust gas to the intake system, and the start end of the EGR pipe 12 is connected to the lower cone portion 6c of the catalyst case 6. A water-cooled EGR cooler 13 is disposed in the middle of the EGR pipe 12, and the EGR cooler 13 is provided with an inlet 14 and an outlet 15 for cooling water.

  An appropriate portion of the exhaust pipe 9 and the upper cone portion 6 b of the catalyst case 6 are connected by a bypass passage 16. In the drawing, the start end of the bypass passage 16 is positioned at the start end portion close to the joint portion 8 in the exhaust pipe 9. However, in order to recirculate the exhaust gas whose temperature has been lowered as much as possible, the exhaust pipe 9 is as downstream as possible. It is good to connect to. In consideration of cost, assemblability and the like, it can be said that the bypass passage 16 is preferably connected to the most downstream side of the exhaust pipe 9 at a portion located in the engine room. Of course, like the EGR pipe 12, it may be connected to the lower cone portion 6c of the catalyst case 6. In this case, the bypass passage 16 can be unitized with the catalyst case 6, so that the assemblability can be improved.

  An opening / closing valve 17 is provided at the start end of the bypass passage 16. As the opening / closing valve 17, for example, a waste gate valve used for an exhaust turbocharger, an EGR valve used for controlling EGR gas, or the like can be used. Therefore, there is no difficulty in implementation. The bypass passage 16 is preferably provided with a water-cooled cooler 18 similar to the EGR cooler 13. When the water-cooled cooler 18 is provided, even when the bypass passage 16 is connected to the lower cone portion 6c of the catalyst case 6 or directly below it, the exhaust gas having been cooled down can be recirculated.

  Instead of the water-cooled cooler 18, an air-cooled cooler that is cooled by the suction air of the radiator or the traveling wind of the vehicle can be provided. Alternatively, the bypass passage 16 may be configured by a plurality of pipes, or may be bent in a spiral shape or the like so that the length of the bypass passage 16 is increased, thereby providing the bypass passage 16 itself with an exhaust gas cooling action (heat radiation action). Is possible.

  The bypass passage 16 is connected to the upper cone portion 6 b of the catalyst case 6 through the reflux nozzle 19. In the partial diagram (B), an example of the reflux nozzle 19 is shown. The recirculation nozzle 19 of the present embodiment has a ball (valve element) 20 inside and a spring 21 that urges the ball 20 toward the inlet side. When the on-off valve 17 is opened, the exhaust gas resists the spring 21. Then, the ball 20 is pushed and ejected into the catalyst case 6. When the exhaust gas is not recirculated, the exhaust gas does not leak from the catalyst case 6 to the bypass passage 16.

  The reflux nozzle 19 is inclined with respect to the axis of the catalyst case 6 so as to approach the catalyst toward the tip. The exhaust gas flowing into the catalyst case 6 from the exhaust manifold 4 has a directionality that flows in the axial direction of the catalyst case 6 as shown by an arrow 23 in FIG. If the nozzle 19 is inclined, it can be said that there is no exhaust gas leak even if the reflux nozzle 19 does not have a check valve function.

Rather, the exhaust gas flowing out from the exhaust manifold 4 is presumed to cause a phenomenon (orifice action) in which the recirculation exhaust pipe 9 is sucked out of the recirculation nozzle 19, and therefore it is presumed that no exhaust gas leaks. Therefore, it can be said that it is possible to simply make an ejection hole in the upper cone portion 7b or the like of the catalyst case 7 or insert a cylinder body from which exhaust gas is ejected. It is safe to have a check valve function.

  The recirculated exhaust gas is preferably mixed with the exhaust gas flowing in from the exhaust manifold 4 as much as possible. For this purpose, the reflux nozzle 19 is preferably arranged as upstream as possible. Therefore, it is more preferable to connect the reflux nozzle 19 to the collecting pipe 5 of the exhaust manifold 4. Further, it is also possible to recirculate exhaust gas from the plurality of ejection holes by providing a plurality of ejection holes arranged in the circumferential direction on the upper cone portion 6b of the catalyst case 6 and the upper cone portion 6b of the exhaust manifold 4. In this case, not only the mixing property is further improved, but also the leakage of the exhaust gas to the bypass passage 16 can be accurately prevented by reducing the diameter of each ejection hole.

(2). Control Mode The internal combustion engine includes an ECU (Engine Control Unit) as a control device, and the on-off valve 17 is controlled by a command from the ECU. Moreover, the temperature sensor 24 is provided in the appropriate site | part of the catalyst case 6, and the temperature sensor 24 is also connected with ECU. The internal combustion engine further includes sensors such as a rotation sensor 25 for detecting the rotational speed of the crankshaft, a negative pressure sensor 26 for detecting intake negative pressure, and a water temperature sensor 27 for detecting the temperature of cooling water. Wired to the ECU. The internal combustion engine also includes a throttle valve 28 for controlling the intake air amount and an injector 29 for injecting fuel, which are also controlled by the ECU.

  Further, as a sensor for detecting the combustion state of the engine, a front oxygen sensor 30 is provided in the upper cone portion 6b of the catalyst case 6, and a rear oxygen sensor is provided in a portion of the exhaust pipe 9 downstream from the catalyst case 6. 31 is provided, and these sensors 30 and 31 are connected to the ECU. The recirculation nozzle 19 is disposed downstream of the front oxygen sensor 30 (in order to enable the front oxygen sensor 30 to accurately detect the oxygen ratio of the exhaust gas without being affected by the recirculated exhaust gas. is there.).

When the temperature sensor 24 is provided in the catalyst case 6, the temperature of the catalyst 7 can be detected directly (or approximately from the temperature of the exhaust gas). Therefore, when the detected value of the temperature sensor 24 rises to a preset reference temperature , the open / close valve 17 is opened, and the exhaust gas whose temperature has been lowered is recirculated to the upstream side of the catalyst 7. Thereby, the temperature of the exhaust gas passing through the catalyst 7 and the temperature of the catalyst can be lowered, and damage to the catalyst can be prevented.

When the detected value of the temperature sensor 24 falls to a preset value, the open / close valve 17 is closed to stop the exhaust gas recirculation. In this case, the temperature at which the opening / closing valve 17 is opened may be the same as the temperature at which the opening / closing valve 17 is closed. However, for stable control, it is preferable that the temperature at which the opening / closing valve 17 is closed is lower than the opening temperature. That is, it is preferable to close the open / close valve 17 after the temperature is lowered to a sufficiently safe area.

When the catalyst case 6 is not provided with the temperature sensor 24, the temperature of the catalyst 7 is estimated using other elements as parameters, and if it is determined that the catalyst 7 has been heated to the reference temperature from other elements, the opening / closing valve 17 is opened and controlled. For example, the engine torque (load) is estimated from one or both of the value of the negative pressure sensor 26 and the opening of the throttle valve 28, and the estimated torque value reaches a preset upper limit value, and the engine speed When reaching the preset upper limit value, it is possible to employ a control of opening and closing the on-off valve 17.

  In other words, when reaching an area such as a high load / high rotation range, the exhaust gas temperature rises and the catalyst is heated, resulting in excessive temperature rise. When this region is reached, control is performed so that the on-off valve 17 is opened. Such a combination of torque and rotation speed can be used as a basic pattern to correct with the coolant temperature and the vehicle speed. As for the vehicle speed, since the cooling performance of the catalyst case 6 by the traveling wind is high at high speeds, correction may be made so as to suppress the opening of the on-off valve 17.

  The catalyst 7 has a property of adsorbing oxygen, and in order to properly maintain the exhaust gas purification performance (nitrogen oxide decomposition performance), it is necessary to perform feedback control so that the amount of oxygen is appropriate.

  For example, at the time of fuel cut, oxygen is excessively contained in the recirculated exhaust gas (in a strong lean state). When the exhaust gas in the strong lean state is recirculated to the catalyst 7, the amount of oxygen in the catalyst 7 is reduced. There is a risk that the adjustment performance will be distorted and the purification performance will deteriorate.

Therefore, while setting a dangerous temperature higher than the reference temperature for the temperature, a strong lean value is set as a dangerous state for the oxygen concentration, the rear oxygen sensor 31 determines that the exhaust gas is in a strong lean state, and the exhaust gas is exhausted. If it is determined that the catalyst 7 has not yet reached the dangerous temperature without recirculating the gas, the exhaust gas is not recirculated or the recirculation amount is reduced, and the amount of oxygen passing through the catalyst 7 becomes appropriate. So that it is controlled.

Conversely, when the amount of oxygen passing through the catalyst 7 is too small, the purification performance is adversely affected, so that a strong rich value is also set as a dangerous state for the oxygen concentration, the rear oxygen sensor 31 detects the strong rich state, and If it is determined that the catalyst 7 has not yet reached the dangerous temperature even if the exhaust gas is not recirculated, the exhaust gas is not recirculated or the catalyst 7 passes through the catalyst 7 by suppressing the recirculation amount. Optimize the amount of oxygen to be used.

  The front oxygen sensor 30 (or front A / F sensor) is for confirming whether or not the fuel injection amount and the air amount are appropriately controlled. The front oxygen sensor 30 is as shown in the control map. By controlling the exhaust gas recirculation based on the rear oxygen sensor 31 in a state where the result is detected, the exhaust gas recirculation prevents the oxygen passing through the catalyst 7 from becoming excessive or excessive. Thus, the purification function of the catalyst 7 can be optimized while appropriately controlling the engine.

  In FIG. 1, the starting end of the bypass passage 16 indicated by a solid line is arranged upstream of the rear oxygen sensor 31, but the oxygen concentration of the exhaust gas is the same everywhere after passing through the catalyst 7. Even if the rear oxygen sensor 31 is connected upstream, there is no inconvenience in the control using the rear oxygen sensor 31.

  When the engine is in a high load state and a large amount of exhaust gas is discharged, the processing capacity of the catalyst 7 may reach a limit. In this case, purification of exhaust gas can be promoted by detecting an exhaust gas excess state from the fuel injection amount, throttle opening, and engine speed and recirculating the exhaust gas from the bypass passage 16. This control can be executed regardless of the temperature of the exhaust gas.

(3). Modification / Others In FIG. 1 (A), a modification is indicated by a virtual line (two-dot chain line). First, as a first modification, a state in which the start end of the bypass passage 16 is connected to the vicinity of the silencer 10 is displayed. In this example, the temperature of the exhaust gas is considerably lowered, so that the temperature of the exhaust gas passing through the catalyst 7 can be reliably lowered even with a small recirculation amount. Therefore, the temperature lowering effect of the catalyst 7 is excellent.

  As a second modification, a state in which the start end of the bypass passage 16 is connected to a portion of the EGR pipe 12 downstream of the EGR cooler 13 is displayed. In this case as well, the temperature of the catalyst 7 can be reliably lowered (cooled) because the temperature of the exhaust gas has dropped considerably. Further, in this example, since the EGR pipe 12 is in a state that also serves as a part of the bypass passage 16, there is an advantage that the entire engine can be made compact.

  The embodiment of the present invention has been described above, but the present invention can be embodied in various ways. For example, in the case of an internal combustion engine in which the exhaust manifold portion is built in the cylinder head, the exhaust gas can be recirculated to the exhaust manifold portion of the cylinder head. The catalyst of the present invention includes DPF of diesel engines.

  The present invention can actually be embodied in an internal combustion engine. Therefore, it can be used industrially.

2 Cylinder head 4 Exhaust manifold 5 Collecting pipe of exhaust manifold 6 Catalyst case 6b Upper cone part 6c Lower cone part 7 Catalyst 9 Exhaust pipe constituting exhaust passage 10 Silencer 12 EGR pipe 13 EGR cooler 16 Bypass passage 17 Open / close valve 18 Water cooling Type cooler 19 reflux nozzle 30 front oxygen sensor 31 rear oxygen sensor

Claims (1)

In the exhaust system , a catalyst case containing a catalyst is interposed in the exhaust passage, and an oxygen sensor or an air-fuel ratio sensor is provided.
A bypass passage is provided in the exhaust passage to recirculate a part of the exhaust gas from the downstream side to the upstream side of the catalyst, and when the measured or estimated value of the temperature of the catalyst is equal to or higher than a preset reference temperature , the catalyst is A configuration in which a part of the exhaust gas that has passed is controlled so as to recirculate to the upstream side of the catalyst via the bypass passage ,
As a dangerous value for the catalyst, a dangerous temperature higher than the reference temperature related to temperature, a strong lean value and a strong rich value related to oxygen concentration are preset, and the temperature is higher than the reference temperature and lower than the dangerous temperature. When the detected value of the oxygen sensor or the air-fuel ratio sensor reaches either the strong lean value or the strong rich value, the exhaust gas recirculation is controlled to be stopped or suppressed.
Internal combustion engine.

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