JP2006112311A - Exhaust emission control system for hybrid vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system for a hybrid vehicle, in which the amount of use of a reducing agent can be suppressed without additionally providing a bypass. <P>SOLUTION: The exhaust emission control system is provided with a NOx storage reduction catalyst, and a means for adding the reducing agent. In the system, after the reducing agent is added to the NOx storage reduction catalyst, the speed of the internal combustion engine is reduced less than that before addition of the reducing agent, or the engine is stopped, and besides when the hybrid vehicle is driven, the amount of exhaust gas passing through the NOx storage reduction catalyst is reduced less than that before addition of the reducing agent by using an electric motor as the power source. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device for a hybrid vehicle.

A technique has been proposed in which a NOx storage reduction catalyst (hereinafter referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine, and NOx in the exhaust is stored in the NOx catalyst.
By the way, when the internal combustion engine is operated in lean combustion, it is necessary to reduce the NOx stored in the NOx catalyst before the NOx stored in the NOx catalyst is saturated. Therefore, a reducing agent is added to the exhaust gas upstream of the NOx catalyst to increase the concentration of the reducing agent in the NOx catalyst and reduce the NOx stored in the NOx catalyst.

When a passage for bypassing the NOx catalyst is provided and the reducing agent is supplied to the NOx catalyst, the reducing agent is supplied to the NOx catalyst while restricting the amount of exhaust flowing into the NOx catalyst by circulating the exhaust through the bypass passage. A technique is known in which the addition amount of the reducing agent is reduced by addition (see, for example, Patent Document 1).
JP 2001-140635 A JP 2000-186536 A

  However, according to the prior art, a passage for bypassing the NOx catalyst, a bypass valve for switching the flow between the bypass passage and the NOx catalyst, and a catalyst for separately purifying exhaust when flowing the exhaust to the bypass passage are required. The cost increases with the complexity.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a technique capable of suppressing the amount of reducing agent used without adding a bypass passage in an exhaust gas purification apparatus for a hybrid vehicle. And

In order to achieve the above object, an exhaust emission control device for a hybrid vehicle according to the present invention comprises:
An internal combustion engine and / or an electric motor comprising: a NOx occlusion reduction catalyst that occludes NOx in an oxidizing atmosphere and reduces NOx in a reducing atmosphere; and a reducing agent addition means that adds a reducing agent to the NOx occlusion reduction catalyst. In an exhaust emission control device for a hybrid vehicle provided in a hybrid vehicle capable of traveling as a power source,
After adding a reducing agent to the NOx occlusion reduction catalyst, the electric motor is used as a power source when the rotational speed of the internal combustion engine is made lower than before addition of the reducing agent or the internal combustion engine is stopped and the hybrid vehicle is run. By doing so, the amount of exhaust gas passing through the NOx occlusion reduction catalyst is reduced more than before the addition of the reducing agent.

  The most important feature of the present invention is that the amount of exhaust gas flowing into the NOx storage reduction catalyst after the addition of the reducing agent to the NOx storage reduction catalyst is reduced, thereby suppressing excess oxygen from flowing into the NOx storage reduction catalyst. The purpose is to keep the reducing agent concentration high.

That is, when the rotational speed of the internal combustion engine is reduced, the amount of exhaust from the internal combustion engine is reduced, so that the amount of exhaust passing through the NOx storage reduction catalyst is reduced. When the internal combustion engine is stopped,
Since there is no exhaust from the internal combustion engine, the exhaust stays in the NOx storage reduction catalyst.

  Therefore, when the rotational speed of the internal combustion engine is reduced after the reducing agent is added to the NOx storage reduction catalyst or the internal combustion engine is stopped, a large amount of the reducing agent remains in the NOx storage reduction catalyst, and the newly supplied oxygen The amount decreases. As a result, the amount of oxygen relative to the reducing agent in the NOx storage reduction catalyst can be relatively reduced, so that the atmosphere in the NOx storage reduction catalyst can be easily maintained at a stoichiometric or rich air-fuel ratio. Therefore, the amount of addition of the reducing agent can be small, and the amount of addition of the reducing agent can be reduced. In addition, the volume flow rate of the exhaust gas that passes through the NOx storage reduction catalyst can be reduced or the volume flow rate can be made zero, so that many opportunities for the reducing agent to act on NOx can be obtained, and the NOx reduction efficiency is improved. Can be made. Furthermore, it is possible to suppress the removal of heat from the NOx storage reduction catalyst due to exhaust, and it is possible to suppress the temperature decrease of the NOx storage reduction catalyst.

  In addition, when the internal combustion engine speed is reduced or the internal combustion engine is stopped, the hybrid motor can be driven by using the electric motor as a drive source, and the output of the internal combustion engine can be reduced. By making up with the output of the electric motor, it is possible to suppress deterioration in drivability.

  Note that “reducing the amount of exhaust gas passing through the NOx storage reduction catalyst than before adding the reducing agent” includes a state in which exhaust does not flow at all after adding the reducing agent. Further, the amount of exhaust may be a volume flow of exhaust.

  In the present invention, an exhaust throttle valve for adjusting the flow rate of exhaust gas is further provided in the exhaust passage of the internal combustion engine, and the exhaust throttle valve can be closed after the reducing agent is added by the reducing agent adding means.

  Here, since the internal combustion engine rotates with inertia even if the rotational speed is reduced or stopped, it takes time to reach a desired rotational speed. Then, the amount of exhaust from the internal combustion engine gradually decreases until the desired number of revolutions is reached. During this time, exhaust flows into the NOx storage reduction catalyst, and oxygen is supplied to the NOx storage reduction catalyst. Here, by closing the exhaust throttle valve, the flow of the exhaust can be stopped, and the exhaust can be prevented from flowing into the NOx storage reduction catalyst. Thereby, it can suppress that oxygen is supplied to a NOx storage reduction catalyst.

  In the present invention, after a predetermined time from when the reducing agent is added by the reducing agent addition means, the rotational speed of the internal combustion engine is reduced from that before addition of the reducing agent or the internal combustion engine is stopped, and the hybrid vehicle is driven. In this case, the electric motor can be used as a power source.

The predetermined time may be a time required for the reducing agent to reach the NOx storage reduction catalyst after the reducing agent is added into the exhaust gas by the reducing agent addition means.
Here, when the reducing agent is added from the upstream side of the NOx storage reduction catalyst, the reducing agent flows along with the exhaust, but if there is a distance from the place where the reducing agent is added to the NOx storage reduction catalyst, the reduction is performed. It takes time for the agent to reach the NOx storage reduction catalyst. Therefore, immediately after supplying the reducing agent, the reducing agent may not yet reach the NOx storage reduction catalyst. However, after a predetermined time has elapsed from the supply of the reducing agent, the reducing agent is caused to flow further downstream, and the reducing agent can reach the NOx storage reduction catalyst. Therefore, the reducing agent can be more reliably supplied to the NOx storage reduction catalyst by reducing the rotational speed of the internal combustion engine or stopping the internal combustion engine after a predetermined time.

  In the exhaust emission control device for a hybrid vehicle according to the present invention, the amount of exhaust gas that passes through the NOx storage reduction catalyst after the addition of the reducing agent can be reduced, thereby reducing the amount of reducing agent used without adding a bypass passage. .

  A specific embodiment of an exhaust emission control device for a hybrid vehicle according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a hybrid system according to the present embodiment and an exhaust system of an internal combustion engine.
The hybrid vehicle according to the present embodiment includes an internal combustion engine 1, a power split mechanism 31, an electric motor 32, a generator 33, a battery 34, an inverter 35, an axle 36, a speed reducer 37, and wheels 38.

  The power split mechanism 31 distributes the output from the internal combustion engine 1 to the generator 33 and the axle 36. The power split mechanism 31 also has a function of transmitting the output from the electric motor 32 to the axle 36. The electric motor 32 rotates at a rotational speed proportional to the axle 36 via the speed reducer 37. The electric motor 32 can assist the output of the internal combustion engine 1 as necessary during normal operation. A battery 34 is connected to the electric motor 32 and the generator 33 via an inverter 35. The generator 33 obtains power from the internal combustion engine 1 to generate power and charge the battery 34.

  In the hybrid system configured as described above, during normal traveling, the wheel 36 is driven by rotating the axle 36 by the output of the internal combustion engine 1 or the output of the electric motor 32. Further, the wheel 36 can be driven by rotating the axle 36 by combining the output of the internal combustion engine 1 and the output of the electric motor 32. On the other hand, at the time of deceleration, the electric motor 32 is operated as a generator by the rotational force of the wheel 38, whereby the kinetic energy can be converted into electric energy and collected by the battery 34. Thus, since the kinetic energy is converted into electric energy when the vehicle is decelerated, it is possible to assist the deceleration of the vehicle.

  Next, the internal combustion engine 1 is a diesel engine having four cylinders. The internal combustion engine 1 is an engine that can be operated by lean combustion. In the present embodiment, a diesel engine will be described as an example. However, a gasoline engine can be applied as long as it can perform lean combustion.

  In the internal combustion engine 1, each cylinder is provided with a fuel injection valve 5 for injecting fuel into the cylinder. Further, an exhaust passage 2 leading to the combustion chamber is connected to the internal combustion engine 1. This exhaust passage 2 communicates with the atmosphere downstream.

A NOx occlusion reduction catalyst 4 (hereinafter referred to as NOx catalyst 4) is provided in the middle of the exhaust passage 2.
The NOx catalyst 4 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have.

By the way, when the internal combustion engine 1 is operated in lean combustion, it is necessary to reduce the NOx stored in the NOx catalyst 4 before the NOx stored in the NOx catalyst 4 is saturated.
Therefore, in this embodiment, a reducing agent addition valve 9 for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage 2 upstream from the NOx catalyst 4 is provided. Here, the reducing agent addition valve 9 is
The valve is opened by a signal from the ECU 6 to be described later, and the reducing agent is injected. The reducing agent injected into the exhaust passage 2 from the reducing agent addition valve 9 makes the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 2 rich. That is, the oxygen concentration in the exhaust is reduced. During NOx reduction, reducing agent addition control is executed so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 4 becomes rich.

  Further, an exhaust throttle valve 10 for adjusting the flow rate of the exhaust gas flowing through the exhaust passage 2 is provided in the exhaust passage 2 downstream of the NOx catalyst 4. An air-fuel ratio sensor 11 that outputs a signal corresponding to the air-fuel ratio of the exhaust gas flowing through the exhaust passage 2 is attached to the exhaust passage 2 downstream of the NOx catalyst 4 and upstream of the exhaust throttle valve 10. Yes.

  The internal combustion engine 1 configured as described above is provided with an ECU 6 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 6 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 6 outputs an electric signal corresponding to the amount of depression of the accelerator by the driver, and an accelerator opening sensor 7 that can detect the load state of the vehicle, and a crank position sensor 8 that detects the rotational speed of the internal combustion engine 1. In addition, various sensors are connected via electric wiring, and output signals of the various sensors described above are input to the ECU 6.

On the other hand, the fuel injection valve 5, the reducing agent addition valve 9, the exhaust throttle valve 10, and the like are connected to the ECU 6 through electrical wiring, and these are controlled by the ECU 6.
Further, the ECU 6 stores various application programs and various control maps.

  Here, in this embodiment, in the reducing agent addition control, the internal combustion engine 1 is stopped after a predetermined time has elapsed since the reducing agent was supplied from the reducing agent addition valve 9, and the exhaust throttle valve 10 is closed. The vehicle is driven by the electric motor 32.

  That is, as described above, when the NOx stored in the NOx catalyst 4 is reduced, the concentration of the reducing agent in the NOx catalyst 4 needs to be increased. Here, if the internal combustion engine 1 is operated after the reducing agent is added from the reducing agent addition valve 9, the exhaust gas from the internal combustion engine 1 flows into the NOx catalyst 4. When the internal combustion engine 1 is performing lean combustion, since the exhaust gas contains a large amount of oxygen, the reducing agent reacts with oxygen. Therefore, since the reducing agent for reducing NOx stored in the NOx catalyst 4 is reduced, more reducing agent is required to reduce NOx, and the fuel efficiency is deteriorated.

Further, if the amount of exhaust gas passing through the NOx catalyst 4 is large, the rate at which the reducing agent reacts with the NOx catalyst 4 is lowered, and the reduction efficiency may be lowered.
In that regard, when the internal combustion engine 1 is stopped, the exhaust gas hardly circulates in the exhaust passage 2, so that it is possible to suppress an increase in the oxygen concentration in the NOx catalyst 4. That is, it is possible to maintain a high reducing agent concentration in the NOx catalyst 4. Further, since the reducing agent remains in the NOx catalyst 4, the reduction efficiency can be improved. Furthermore, it is possible to suppress the temperature of the NOx catalyst 4 from decreasing.

Further, while the internal combustion engine 1 is stopped, the vehicle can be driven by using the electric motor 32 as the drive source.
Then, this state is maintained for several seconds, for example, which is necessary for reducing NOx. Thereafter, the internal combustion engine 1 is started and the drive source is the internal combustion engine 1, and the exhaust throttle valve 10 is opened to perform the original operation. Return to the state.

Next, the flow of reducing agent supply control according to this embodiment will be described.
FIG. 2 is a flowchart showing a flow of reducing agent supply control according to this embodiment. This routine is executed every predetermined time.

In step S101, the ECU 6 determines whether or not a NOx reduction condition for the NOx catalyst 4 is satisfied.
An example of the condition is whether the amount of NOx stored in the NOx catalyst 4 exceeds a specified amount. Here, regarding the NOx occlusion amount, the NOx occlusion amount may be obtained based on the vehicle travel distance, assuming that the NOx occlusion amount increases according to the vehicle travel distance. Alternatively, the NOx reduction condition may be established simply at predetermined time intervals.

If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, NOx is not reduced, so this routine is terminated.
In step S102, the ECU 6 adds the reducing agent into the exhaust gas from the reducing agent addition valve 9.

In step S <b> 103, the ECU 6 stops the internal combustion engine 1, closes the exhaust throttle valve 10, and causes the electric motor 32 to drive the vehicle.
In step S104, the ECU 6 determines whether it is the NOx reduction end time. Here, it is determined whether or not a sufficient time has passed to reduce the NOx stored in the NOx catalyst 4. This time is obtained in advance by experiments or the like and stored in the ECU 6.

If an affirmative determination is made in step S104, the process proceeds to step S105, whereas if a negative determination is made, the process returns to step S104.
In step S105, the ECU 6 starts the internal combustion engine 1, opens the exhaust throttle valve 10, and stops the electric motor 32.

  As described above, according to this embodiment, when the reducing agent is added to the NOx catalyst 4, the internal combustion engine 1 is stopped and the exhaust throttle valve 10 is closed to reduce the flow rate of the exhaust gas in the NOx catalyst 4. The reducing agent concentration in the NOx catalyst 4 can be kept high. At this time, the hybrid vehicle can be driven by using the electric motor 32 as a drive source.

  In the present embodiment, the internal combustion engine 1 is stopped when the reducing agent is added, but instead, the rotational speed of the internal combustion engine 1 may be made lower than before the reducing agent is added. And the fall of the output at the time of reducing the rotation speed of the internal combustion engine 1 is supplemented by the output of the electric motor 32. That is, by reducing the rotational speed of the internal combustion engine 1, the flow rate of the exhaust gas flowing through the NOx catalyst 4 can be reduced, so that the amount of oxygen relative to the amount of reducing agent can be relatively reduced, and the NOx catalyst 4 The concentration of the reducing agent inside can be increased. Further, since it takes time for the reducing agent to pass through the NOx catalyst 4, many opportunities for the reducing agent to react in the NOx catalyst 4 can be obtained, and the NOx reduction efficiency can be improved. During this time, the drivability can be prevented from deteriorating by running the vehicle using the internal combustion engine 1 and the electric motor 32 as drive sources.

  In the present embodiment, the exhaust throttle valve 10 is closed when the reducing agent is added, but this is not always necessary. That is, it takes time until the internal combustion engine 1 is completely stopped after the signal for stopping the internal combustion engine 1 is transmitted, but the flow rate of the exhaust gas passing through the NOx catalyst 4 also decreases during that time, so that the above effect can be obtained. it can.

Further, in this embodiment, the reducing agent may be added from the reducing agent addition valve 9 and the internal combustion engine 1 may be stopped and the exhaust throttle valve 10 may be closed after a predetermined time has passed. That is, the longer the distance from the reducing agent addition valve 9 to the NOx catalyst 4, the longer the time from when the reducing agent is added into the exhaust gas from the reducing agent addition valve 9 until the reducing agent reaches the NOx catalyst 4. It also takes time for the reducing agent to pass from the upstream side to the downstream side of the NOx catalyst 4. Furthermore, the time until the reducing agent reaches the NOx catalyst 4 also varies depending on the flow rate of the exhaust gas. For this reason, if the internal combustion engine 1 is stopped immediately after the addition of the reducing agent, the flow of exhaust gas is stopped before the reducing agent is supplied to the NOx stored in the NOx catalyst 4. On the other hand, if the internal combustion engine 1 is stopped and the exhaust throttle valve 10 is closed after a lapse of a predetermined time from the supply of the reducing agent, sufficient reducing agent can be supplied to the NOx catalyst 4. This predetermined time may be changed in accordance with the operating state of the internal combustion engine, for example, the intake air amount and the engine speed related to the exhaust gas flow rate. Further, the predetermined time may be obtained by experiments or the like so that the optimal time for reducing the NOx stored in the NOx catalyst 4 is reached.

  In this embodiment, the internal combustion engine is stopped and the exhaust throttle valve 10 is closed after a predetermined time has elapsed since the addition of the reducing agent. Instead, the exhaust gas obtained from the air-fuel ratio sensor 11 after the addition of the reducing agent is replaced. When the air-fuel ratio changes from lean to stoichiometric or rich, the internal combustion engine may be stopped and the exhaust throttle valve 10 may be closed. That is, when the output signal of the air-fuel ratio sensor 11 changes to stoichiometric or rich, the reducing agent has actually reached the downstream side of the NOx catalyst 4, so at this time the internal combustion engine is stopped and the exhaust throttle valve By closing 10, it becomes possible to stop the flow of exhaust gas when a large amount of reducing agent is present in the NOx catalyst 4.

It is a figure which shows schematic structure of the hybrid system by an Example, and the exhaust system of an internal combustion engine. It is the flowchart which showed the flow of the reducing agent supply control by an Example.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 4 NOx storage reduction catalyst 5 Fuel injection valve 6 ECU
7 Accelerator opening sensor 8 Crank position sensor 9 Reducing agent addition valve 10 Exhaust throttle valve 11 Air-fuel ratio sensor 31 Power split mechanism 32 Electric motor 33 Generator 34 Battery 35 Inverter 36 Axle 37 Reducer 38 Wheel

Claims (3)

An internal combustion engine and / or an electric motor comprising: a NOx occlusion reduction catalyst that occludes NOx in an oxidizing atmosphere and reduces NOx in a reducing atmosphere; and a reducing agent addition means that adds a reducing agent to the NOx occlusion reduction catalyst. In an exhaust emission control device for a hybrid vehicle provided in a hybrid vehicle capable of traveling as a power source,
After adding a reducing agent to the NOx occlusion reduction catalyst, the electric motor is used as a power source when the rotational speed of the internal combustion engine is made lower than before addition of the reducing agent or the internal combustion engine is stopped and the hybrid vehicle is run. By doing so, the amount of exhaust gas passing through the NOx occlusion reduction catalyst is reduced as compared with that before the addition of the reducing agent.   The exhaust throttle valve for adjusting the flow rate of exhaust gas in the exhaust passage of the internal combustion engine is further provided, and the exhaust throttle valve is closed after the reducing agent is added by the reducing agent adding means. Hybrid vehicle exhaust purification system.   When a predetermined time after the reducing agent is added by the reducing agent addition means, when the rotational speed of the internal combustion engine is reduced from that before addition of the reducing agent or the internal combustion engine is stopped and the hybrid vehicle is run, The exhaust purification device for a hybrid vehicle according to claim 1 or 2, wherein an electric motor is used as a power source.

Images