JP2025009480A - Vehicle exhaust system - Google Patents

Abstract

To suppress lowering of a catalyst temperature due to a driving state of a vehicle.SOLUTION: An exhaust system for a vehicle includes: an exhaust passage (4) for discharging exhaust gas generated in an internal combustion engine (1) mounted to the vehicle; and a catalyst (5) provided in the exhaust passage (4) and purifying exhaust gas. The exhaust system for the vehicle also includes: a first valve (6) provided upstream of the catalyst (5) in the exhaust passage (4) and regulating an amount of exhaust gas flowing into the catalyst (5) side; and a control device (100) that controls an opening of the first valve (6) according to an operating state of the vehicle.SELECTED DRAWING: Figure 1

Description

The present invention relates to a vehicle exhaust system.

In vehicles such as automobiles, a catalyst for purifying exhaust gas may be provided in an exhaust path for exhausting exhaust gas generated by an internal combustion engine. In order to maintain its purification performance, the catalyst is required to be in a high temperature state at which the catalyst is activated.
Patent Document 1 discloses a double-structure catalytic converter in which a catalyst carrier is inserted and housed in a metal inner tube, an outer tube is fitted to the outside of the inner tube, and an insulating member is interposed between the inner tube and the outer tube.

Patent No. 2957163

Depending on the vehicle's operating conditions, for example when the engine is running during fuel cut, unburned intake air (low temperature air) may flow to the catalyst side, causing the temperature of the catalyst to drop. As a result, there is a risk that the purification performance will decrease until the catalyst is heated to an activation temperature.
In Patent Document 1, it is possible to improve the warm-up characteristics of the catalyst by using an insulating effect, thereby improving exhaust purification performance, but it does not take into consideration the fact that low-temperature air flows toward the catalyst depending on the driving conditions of the vehicle, causing a drop in the catalyst temperature.

The present invention was made in consideration of this situation, and aims to suppress the drop in catalyst temperature caused by the vehicle's driving conditions.

The exhaust system of the present invention is a vehicle exhaust system that includes an exhaust path that exhausts exhaust gas generated by an internal combustion engine mounted on the vehicle, and a catalyst that is provided in the exhaust path and purifies the exhaust gas. It is characterized in that it also includes a first valve that is provided upstream of the catalyst in the exhaust path and adjusts the amount of exhaust gas that flows into the catalyst, and a control device that controls the opening degree of the first valve depending on the driving conditions of the vehicle.

The present invention makes it possible to suppress the drop in catalyst temperature caused by the vehicle's driving conditions.

1 is a diagram showing a schematic configuration of an exhaust system of a vehicle according to an embodiment; 4 is a flowchart showing a process executed by an ECU of the exhaust system of the vehicle according to the embodiment. FIG. 4 is a diagram for explaining a first valve and a second valve.

An exhaust system for a vehicle according to one embodiment of the present invention is an exhaust system for a vehicle comprising an exhaust path (4) for exhausting exhaust gas generated by an internal combustion engine (1) mounted on a vehicle, and a catalyst (5) provided in the exhaust path (4) for purifying the exhaust gas, a first valve (6) provided upstream of the catalyst (5) in the exhaust path (4) for adjusting the amount of exhaust gas flowing into the catalyst (5), and a control device (100) for controlling the opening degree of the first valve (6) in accordance with the driving conditions of the vehicle.
As a result, in a situation where low-temperature air flows toward the catalyst (5) due to the driving conditions of the vehicle, the opening of the first valve (6) is narrowed to limit the amount of low-temperature air flowing into the catalyst (5), thereby suppressing a drop in the temperature of the catalyst (5). Since the first valve (6) is located upstream of the catalyst (5), it is possible to prevent the low-temperature air from flowing into the catalyst (5), and the low-temperature air does not stagnate within the catalyst (5).

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
1 shows a schematic configuration of an exhaust system for a vehicle according to an embodiment of the present invention. The vehicle is an automobile equipped with an engine 1, which is an internal combustion engine.
Although a detailed description of the engine 1 is omitted, the engine 1 burns fuel in cylinders and obtains driving force for the automobile using the combustion gas generated by the combustion. An intake path 2 that introduces intake air is connected to the engine 1. The intake path 2 includes an intake pipe 2a that is connected to the engine 1. An injector 3 that injects fuel is installed in each cylinder on the intake side. An exhaust path 4 that exhausts exhaust gas generated by the engine 1 is also connected to the engine 1. The exhaust path 4 includes an exhaust pipe 4a that is connected to the engine 1, and a catalytic converter (hereinafter simply referred to as a catalyst) 5. The catalyst 5 is a three-way catalyst or the like that purifies harmful substances in the exhaust gas by oxidation and reduction.

A first valve 6 is installed upstream of the catalyst 5 in the exhaust path 4 to adjust the amount of exhaust gas flowing into the catalyst 5. A second valve 7 is installed downstream of the catalyst 5 in the exhaust path 4 to adjust the amount of exhaust gas flowing out from the catalyst 5. A temperature sensor 8 is installed in the exhaust path 4 to detect the temperature T of the catalyst 5.

The automobile is also equipped with an ECU (Electronic Control Unit) 100. The ECU 100 is responsible for engine control, and controls fuel injection by the injector 3, the opening and closing timing of the intake valve and exhaust valve, the ignition timing of the spark plug, and the like.
In this embodiment, the ECU 100 functions as a control device for the exhaust system. Fig. 1 shows a functional configuration for the ECU 100 to function as a control device for the exhaust system. The ECU 100 includes an acquisition unit 101 that acquires information necessary for controlling the exhaust system, a determination unit 102 that makes a determination necessary for controlling the exhaust system, and an output unit 103 that outputs commands to the first valve 6 and the second valve 7.
The ECU 100 receives the detection results of an accelerator pedal sensor 9 that detects the operation of an accelerator pedal 9a and a brake pedal sensor 10 that detects the operation of a brake pedal 10a. The ECU 100 also receives a vehicle speed V. The ECU 100 also receives a temperature T of the catalyst 5 detected by a temperature sensor 8.

In the ECU 100, the acquisition unit 101 acquires the detection results input from the accelerator pedal sensor 9 and the brake pedal sensor 10. The acquisition unit 101 also acquires the vehicle speed V. The acquisition unit 101 also acquires the temperature T of the catalyst 5 input from the temperature sensor 8. Note that while the example in which the temperature sensor 8 directly detects the temperature T of the catalyst 5 has been given, for example, the acquisition unit 101 may estimate and calculate the temperature T of the catalyst 5 based on the driving conditions (load) and the outside air temperature.

The determination unit 102 determines the driving status of the vehicle based on the detection results of the accelerator pedal sensor 9, the detection results of the brake pedal sensor 10, and the vehicle speed V acquired by the acquisition unit 101. In this embodiment, the driving status of the vehicle is determined to be whether or not fuel is being cut and whether or not the vehicle is stopped. The determination unit 102 also determines the relationship between the temperature T of the catalyst 5 acquired by the acquisition unit 101 and preset threshold values 1 and 2. Threshold value 1 is assumed to be a temperature slightly lower than the upper limit of the temperature at which the catalyst 5 deteriorates (upper deterioration temperature limit). Threshold value 2 is assumed to be a temperature slightly higher than the temperature at which the catalyst 5 becomes active (activation temperature), and is a value smaller than threshold value 1 (a temperature lower than threshold value 1).

Based on the result of the judgment by the judgment unit 102, i.e., in response to the driving conditions of the vehicle and the temperature T of the catalyst 5, the output unit 103 outputs commands to the first valve 6 and the second valve 7 to control the opening degree of each. FIG. 3(a) shows a schematic diagram of the first valve 6 and the second valve 7 being fully closed. FIG. 3(b) shows a schematic diagram of the first valve 6 being limited in opening degree and the second valve 7 being fully open. FIG. 3(c) shows a schematic diagram of the first valve 6 and the second valve 7 being fully open. Note that the illustration of the state in which the opening degree of the second valve 7 is limited is omitted, but it is the same as the state in which the opening degree of the first valve 6 is limited.

Fig. 2 is a flowchart showing an example of a control process for the exhaust system executed by the ECU 100. The flowchart in Fig. 2 is executed repeatedly.
In step S1, the determination unit 102 determines whether or not fuel is being cut based on the detection result of the accelerator pedal sensor 9 and/or the detection result of the brake pedal sensor 10 acquired by the acquisition unit 101. If fuel is being cut, it can be said that the vehicle is coasting, decelerating, or idling stop. If fuel is being cut, the process proceeds to step S2, and if fuel is not being cut, the process proceeds to step S10.

In step S2, the determination unit 102 determines whether the vehicle speed V exceeds 0 based on the vehicle speed V acquired by the acquisition unit 101. In this embodiment, the automobile has an engine stop function when the automobile is stopped (a so-called idling stop function) that detects a decrease in vehicle speed and stops the engine 1. If the vehicle speed V exceeds 0, the process proceeds to step S3, and if the vehicle speed V does not exceed 0, i.e., if the engine 1 is stopped, the process proceeds to step S6.

In step S3, the determination unit 102 determines whether the temperature T of the catalyst 5 acquired by the acquisition unit 101 is less than threshold value 1. Threshold value 1 is assumed to be a temperature slightly lower than the upper degradation temperature limit of the catalyst 5, and corresponds to the first threshold value in the present invention. If the temperature T of the catalyst 5 is less than threshold value 1, the process proceeds to step S4, and if the temperature T of the catalyst 5 is not less than threshold value 1, the process proceeds to step S5.

In step S4, the output unit 103 outputs a command to the first valve (referred to as valve 1 in FIG. 2) 6 to limit its opening. Limiting the opening means narrowing the opening compared to full opening. During fuel cut, the rotation of the engine 1 causes unburned intake air (low-temperature air) to flow to the catalyst 5, lowering the temperature of the catalyst 5. Therefore, by limiting the opening of the first valve 6, the amount of low-temperature air flowing into the catalyst 5 is restricted, and the drop in the temperature of the catalyst 5 is suppressed in order to maintain the purification performance of the catalyst 5.
On the other hand, in step S5, the output unit 103 outputs a command to fully open the first valve 6. When the temperature T of the catalyst 5 exceeds the threshold value 1 (a temperature slightly lower than the upper degradation temperature limit of the catalyst 5), the first valve 6 is fully opened, and the amount of low-temperature air flowing into the catalyst 5 side is not restricted, thereby preventing thermal degradation of the catalyst 5.

In step S6, the determination unit 102 determines whether the temperature T of the catalyst 5 acquired by the acquisition unit 101 is less than threshold value 1. Threshold value 1 corresponds to the second threshold value in the present invention. If the temperature T of the catalyst 5 is less than threshold value 1, the process proceeds to step S7, and if the temperature T of the catalyst 5 is not less than threshold value 1, the process proceeds to step S9. Note that, since a threshold value that is assumed to be slightly lower than the upper degradation temperature limit is used in step S6 as well, the same threshold value 1 as in step S3 is used, but a value other than threshold value 1 may be used.

In step S7, the output unit 103 outputs a command to fully close the first valve 6. Then, in step S8, the output unit 103 outputs a command to fully close the second valve (referred to as valve 2 in FIG. 2) 7. Since the engine 1 is stopped and there is no intake or exhaust, the first valve 6 and the second valve 7 can be fully closed. As shown in FIG. 3A, by fully closing the first valve 6 and the second valve 7, an enclosed space is formed that blocks the upstream and downstream of the catalyst 5, and the heat retention effect suppresses a drop in the temperature of the catalyst 5 in order to maintain the purification performance of the catalyst 5.
On the other hand, in step S9, the output unit 103 outputs a command to fully open the first valve 6. When the temperature T of the catalyst 5 exceeds the threshold value 1 (a temperature slightly lower than the upper degradation temperature limit of the catalyst 5), the first valve 6 is fully opened so as not to impede heat dissipation, thereby preventing thermal degradation of the catalyst 5.

In step S10, the output unit 103 outputs a command to the first valve 6 to fully open it.
In step S11, the determination unit 102 determines whether the temperature T of the catalyst 5 acquired by the acquisition unit 101 is less than threshold value 2. Threshold value 2 is assumed to be a temperature slightly higher than the activation temperature of the catalyst 5, and is a value smaller than threshold value 1 (a temperature lower than threshold value 1). Threshold value 2 corresponds to the third threshold value referred to in the present invention. If the temperature T of the catalyst 5 is less than threshold value 2, the process proceeds to step S12, and if the temperature T of the catalyst 5 is not less than threshold value 2, the process proceeds to step S13.

In step S12, the output unit 103 outputs a command to limit the opening degree to the second valve 7. When the temperature T of the catalyst 5 is below the threshold value 2 (activation temperature of the catalyst 5) during normal driving (driving with the accelerator pedal 9a depressed and not during fuel cut), the opening degree of the second valve 7 is limited to limit the amount of exhaust gas flowing out from the catalyst 5 side, and the high-temperature exhaust gas is retained near the catalyst 5, thereby raising the temperature of the catalyst 5 in order to maintain the purification performance of the catalyst 5.
On the other hand, in step S13, the output unit 103 outputs a command to fully open the second valve 7. During normal driving (driving with the accelerator pedal 9a depressed and not during fuel cut), the first valve 6 and the second valve 7 are fully opened through steps S10 and S13, as shown in Fig. 3(c) , except when it is necessary to raise the temperature of the catalyst 5 (step S12).

As described above, when the vehicle's operating conditions cause cold air to flow toward the catalyst (5), the opening of the first valve 6 can be narrowed to limit the amount of cold air flowing into the catalyst 5, thereby suppressing a drop in the temperature of the catalyst 5. Since the first valve 6 is located upstream of the catalyst 5, it is possible to prevent cold air from flowing into the catalyst 5, and cold air does not stagnate within the catalyst 5.

Although the embodiments of the present invention have been described in detail above with reference to the drawings, each embodiment merely shows a specific example of the implementation of the present invention. The technical scope of the present invention is not limited to each embodiment. Various modifications of the present invention are possible without departing from the spirit of the present invention, and these modifications are also included in the technical scope of the present invention.
In this embodiment, the first valve 6 and the second valve 7 are provided on the upstream and downstream sides of the catalyst 5, respectively, but simply providing the first valve 6 on the upstream side of the catalyst 5 can suppress the decrease in temperature of the catalyst 5 caused by the driving conditions of the vehicle. In this case, the processes of steps S8 and S11 to S13 in the flowchart of FIG. 2 can be omitted.

1: engine, 2: intake path, 3: injector, 4: exhaust path, 5: catalyst, 6: first valve, 7: second valve, 8: temperature sensor, 9: accelerator pedal sensor, 10: brake pedal sensor, 100: ECU, 101: acquisition unit, 102: judgment unit, 103: output unit

Claims (6)

An exhaust path for discharging exhaust gas generated by an internal combustion engine mounted on a vehicle;
A catalyst provided in the exhaust path for purifying exhaust gas,
a first valve provided in the exhaust path upstream of the catalyst and configured to adjust an amount of exhaust gas flowing into the catalyst;
a control device that controls an opening degree of the first valve in accordance with a driving condition of the vehicle. The vehicle exhaust system according to claim 1, characterized in that the control device limits the opening degree of the first valve when fuel is being cut and the temperature of the catalyst is below a first threshold value. The vehicle exhaust system according to claim 1 or 2, characterized in that the control device fully closes the first valve when the internal combustion engine is stopped and the temperature of the catalyst is less than a second threshold value. a second valve provided in the exhaust path downstream of the catalyst and configured to adjust an amount of exhaust gas flowing out from the catalyst side;
2. The vehicle exhaust system of claim 1, wherein the controller controls the second valve. a second valve provided in the exhaust path downstream of the catalyst and configured to adjust an amount of exhaust gas flowing out from the catalyst side;
3. The exhaust system of claim 2, wherein the control device limits the opening degree of the second valve when a fuel cut is not being performed and the temperature of the catalyst is lower than a third threshold value that is lower than the first threshold value. a second valve provided in the exhaust path downstream of the catalyst and configured to adjust an amount of exhaust gas flowing out from the catalyst side;
4. The exhaust system for a vehicle according to claim 3, wherein the control device fully closes the first valve and also fully closes the second valve.

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