JP2006112300A - Secondary air introduction device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration and failure of a three-way conversion catalyst without deteriorating drivability in a small displacement engine system provided with the three-way conversion catalyst in an exhaust system. <P>SOLUTION: A secondary air supply path providing secondary air to an exhaust system of an engine purifying exhaust gas with using the three-way conversion catalyst is provided. An air introducing valve is provided in a middle of the secondary air supply path. Quantity of secondary air supplied to the exhaust system is controlled by using the air introducing valve. Supply control of secondary air is periodically performed according to cycle of a crankshaft. Duty ratio of valve open period t2 during which supply of secondary air is performed is controlled in a range of supply quantity for keeping catalyst temperature L2 of the three-way conversion catalyst at a predetermined value or less and in a range of supply quantity preventing carbon deposition deterioration L3 of the three-way conversion catalyst while air-fuel ratio is rich. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a secondary air introduction device that supplies secondary air to an exhaust system of an engine.

In a four-wheeled vehicle, a three-way catalyst is generally provided in the exhaust system in order to purify the exhaust gas. The air-fuel ratio of the exhaust gas supplied to the three-way catalyst is preferably maintained at the stoichiometric air-fuel ratio. However, since the air-fuel ratio changes according to the operating state of the engine, the stoichiometric air-fuel ratio is not always maintained. In order to solve such a problem, a secondary air introduction device for supplying secondary air to the exhaust system and maintaining the air-fuel ratio of the exhaust gas supplied to the three-way catalyst at the stoichiometric air-fuel ratio is known (patent) Reference 1).
Japanese Utility Model Publication No. 62-67915

  In a small displacement engine used for a small motorcycle or the like, the exhaust gas purification has not been considered so far, and a three-way catalyst has not been provided in the exhaust system. Therefore, for example, when a three-way catalyst is used in a small motorcycle, there is no consideration as to whether a specific problem may occur or what would be a problem if a specific problem exists.

  The inventor of the present application has considered a problem that occurs when a three-way catalyst is used in a small displacement engine (particularly, a small motorcycle) and has come to recognize a unique problem. In other words, in a small motorcycle using a small displacement engine, the engine output is small and the torque is likely to be insufficient at the time of acceleration. Due to the deterioration, the rich state often needs to be maintained for a long time. In such a case, if the secondary air is supplied and controlled in consideration of only the theoretical air-fuel ratio as in the case of a conventional secondary air introduction device used in a four-wheeled vehicle or the like, the temperature in the catalyst rises rapidly, and three-way Causes deterioration and damage of the catalyst. Further, if the supply amount of the secondary air is significantly reduced when the rich state continues for a long time, not only the exhaust gas purification becomes insufficient, but also the carbon deposition deterioration of the three-way catalyst occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to prevent deterioration and breakage of a three-way catalyst in a small displacement engine system in which a three-way catalyst is provided in an exhaust system.

  The secondary air introduction device of the present invention is supplied to the exhaust system through a secondary air supply path for supplying secondary air to the engine exhaust system provided with the three-way catalyst, and the secondary air supply path. A secondary air supply amount control device for controlling the supply amount of the secondary air, and the supply amount is within a range in which the catalyst temperature of the three-way catalyst is kept below a predetermined value while the air-fuel ratio is rich, and the supply amount is three. It is characterized in that it is controlled within a range that suppresses carbon deposition deterioration of the original catalyst.

  The supply of the secondary air is periodically performed with a duty ratio of less than 50%, for example. Preferably, the supply of secondary air is further performed in a duty ratio range of 30% to 5%. More preferably, the supply of secondary air is performed in a duty ratio range of 20% to 10%.

  Moreover, it is preferable to provide the temperature sensor which detects the temperature in a three-way catalyst, and it is preferable that a secondary air supply amount control apparatus controls supply amount based on this temperature. It is preferable that an oxygen concentration sensor for detecting the oxygen concentration in the exhaust system is provided, and the secondary air supply amount control device controls the supply amount based on the detected oxygen concentration. Further, for example, the secondary air introduction device includes an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust system, and the secondary air supply amount control device controls the supply amount based on the air-fuel ratio. The secondary air introduction device is mounted on, for example, a small motorcycle.

  As described above, according to the present invention, deterioration and breakage of a three-way catalyst can be prevented in a small displacement engine system in which a three-way catalyst is provided in an exhaust system.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an outline of an engine system according to an embodiment of the present invention. For example, the engine system is employed in a motorcycle equipped with a small displacement engine.

  An intake system duct 12 including an intake manifold and the like is attached to the intake port of the cylinder head 11 of the engine 10. An air cleaner 13, a throttle body 14, and the like are connected to the intake system duct 12, and outside air is guided to the intake port through these. Fuel is supplied from the fuel injection device 15 to the intake air (outside air) before the intake port. That is, the sucked air is made into an air-fuel mixture with a predetermined air-fuel ratio and then supplied into the engine 10. On the other hand, an exhaust system duct 16 including an exhaust manifold and the like is attached to the exhaust port of the cylinder head 11. The combustion gas in the engine cylinder is sent to the exhaust system duct 16 through the exhaust port, and then through a catalytic converter 17 and a muffler (not shown) made of a three-way catalyst imaged on the exhaust system duct 16. It is discharged outside.

  In the intake system duct 12, one end of the secondary air supply pipe 18 is connected to the downstream side of the air cleaner 13, and the other end of the secondary air supply pipe 18 is connected to the exhaust port of the cylinder head 11. An air introduction valve 19 is provided in the middle of the secondary air supply pipe 18. That is, the secondary air supply pipe 18 communicates the intake system and the exhaust system via the air introduction valve 19, and the amount of secondary air supplied to the exhaust system is controlled by driving the air introduction valve 19. Note that the air introduction valve 19 includes, for example, one using negative pressure and one using an air pump.

  The engine 10 is provided with an engine temperature sensor 20 for monitoring the engine temperature and a crank angle sensor 21 for detecting the rotation angle of the crank. The exhaust system duct 16 is provided with an oxygen concentration sensor 22 for monitoring the oxygen concentration. The catalytic converter 17 is provided with a catalyst temperature sensor 23 for monitoring the temperature of the three-way catalyst, and the throttle body 14 is provided with a throttle position sensor (TPS) 24 and the like. Each of the sensors 20 to 24 is connected to and monitored by an electronic control unit (ECU) 25.

  The ECU 25 is connected to the fuel injection device 15, the air introduction valve 19, and the ignition device 26. For example, based on a signal from the sensor, the fuel injection amount, the secondary air supply amount, and the ignition of the ignition plug 27. Control timing.

  FIG. 2 is a graph schematically showing the relationship between the supply timing of secondary air when the air-fuel ratio is rich, the catalyst temperature, and the carbon deposition deterioration. The principle of the secondary air supply amount control in this embodiment will be described with reference to FIG. In FIG. 2, the horizontal axis t is time.

  As described above, the supply amount of the secondary air is controlled by the opening / closing operation of the air introduction valve 19, and the air introduction valve 19 is driven at a substantially cycle Ts. The cycle Ts includes a valve closing period t1 in which the valve is closed and the supply of secondary air is shut off, and a valve opening period t2 in which the valve is opened and secondary air is supplied. The period Ts corresponds to, for example, one cycle of the crankshaft. In FIG. 2, a rectangular pulse L <b> 1 represents a driving pulse for the air introduction valve 19, and curves L <b> 2 and L <b> 3 schematically indicate the catalyst temperature in the catalytic converter 17 and the degree of carbon deposition deterioration.

  As indicated by the curve L3, since the air-fuel ratio is rich, the carbon remaining in the exhaust gas is combined with the precious metal in the catalyst during the valve closing period t1 in which the supply of secondary air is not performed, and the carbon deposition deterioration is increased. To do. This continues until the valve opening period t2 during which secondary air (secondary air) is supplied starts. When the supply of secondary air is started and the exhaust gas is in an oxygen-excess atmosphere, the three-way catalyst begins to recover gradually, and the carbon deposition deterioration decreases. For comparison, FIG. 2 shows, as a broken line, an increase in carbon deposition deterioration when the valve opening period t2 is not provided and the secondary air is not supplied.

  On the other hand, as shown by the curve L2, when the supply of the secondary air is started, the fuel remaining in the exhaust gas is combusted by the supplied secondary air, and the catalyst temperature in the catalytic converter 17 rises rapidly. This continues until the supply of secondary air is cut off during the valve opening period t2, that is, in the valve closing period t1 of the next cycle. When the supply of the secondary air is cut off, the combustion of the fuel remaining in the exhaust gas is also terminated, so that the catalyst temperature gradually decreases.

When paying attention to the catalyst temperature, the relationship between the valve opening period t2 in which the secondary air is supplied and the valve closing period t1 in which the secondary air is shut off is such that the catalyst temperature is a predetermined temperature (for example, in a period in which the rich state is continuously maintained) The allowable maximum temperature of the catalytic converter) is determined within a range not exceeding θc. For example, the average temperature increase rate per unit time in the valve closing period t1 is α (<0), the average temperature increase rate per unit time in the valve opening period t2 is β (> 0), and the rich predicted in the small motorcycle When the state upper limit duration is T _R and the initial catalyst temperature is θ ₀ , t1 and t2 are set to satisfy at least the relationship of θc−θ ₀ > (α · t1 + β · t2) × T _R / Ts. . That is, substituting the relationship of t1 = Ts−t2 into the above equation and obtaining the condition regarding the duty ratio R (= t2 / Ts) of the valve opening period, R <(θc−θ ₀ −αT _R ) / [(β −α) T _R ], and the duty ratio R is determined in a range that satisfies this equation.

  Generally, since the absolute value of α is larger than the absolute value of β, the duty ratio in the valve opening period in which the secondary air is supplied is less than 50%. In this embodiment, for example, it is set to less than 30% or less than 20%.

On the other hand, when attention is paid to carbon deposition deterioration, the relationship between the valve opening period t2 in which the secondary air is supplied and the valve closing period t1 in which the secondary air is shut off is such that the carbon deposition deterioration does not occur in the period in which the rich state is continuously maintained. The predetermined deterioration degree (for example, the allowable maximum carbon deposition deterioration degree of the three-way catalyst) Qc is determined in a range not exceeding. For example, the average carbon deposition deterioration increase rate per unit time in the valve closing period t1 is γ (> 0), the average carbon deposition deterioration increase rate per unit time in the valve opening period t2 is δ (<0), and the initial deterioration degree is When Q ₀ , t 1 and t 2 are set so as to satisfy at least the relationship of Qc−Q ₀ > (γ · t 1 + δ · t 2) × T _R / Ts. That is, the duty ratio R in the valve opening period is determined in a range satisfying R> (Qc−Q ₀ −γT _R ) / [(δ−γ) T _R ].

  In the present embodiment, considering the catalyst temperature and carbon deposition deterioration, for example, the duty ratio R is set to 30% to 5%, or 20% to 10%. These values are set in advance under the above conditions using the rotation speed, throttle valve opening, and the like as parameters, and are stored, for example, in a memory connected to the ECU 25. The duty ratio R may be set to a predetermined fixed value (predetermined time) that satisfies the above conditions.

  As described above, according to the present embodiment, even when the rich state continues for a long time as in a small motorcycle equipped with a small displacement engine, the increase in the catalyst temperature is suppressed and carbon deposition is suppressed. Since deterioration can be prevented, exhaust gas can be purified without impairing drivability.

  For example, it is possible to feedback control the duty ratio of the valve opening period based on the catalyst temperature detected by the catalyst temperature sensor. It is also possible to add the exhaust system oxygen concentration detected by the oxygen concentration sensor to the feedback.

  An air-fuel ratio sensor that detects the air-fuel ratio may be provided in the exhaust system. For example, the catalyst temperature sensor 23 in FIG. 1 may be replaced with an air-fuel ratio sensor, or an air-fuel ratio sensor may be provided in the catalytic converter 17 to control the supply amount of secondary air based on the air-fuel ratio in the catalytic converter 17. Good. For example, the secondary air can be supplied when the detected air-fuel ratio is equal to or higher than a predetermined value, and not supplied when the detected air-fuel ratio is equal to or lower than the predetermined value. These predetermined values are, for example, 14.7 ± 3. Set to a range value. For example, the threshold (predetermined value) when turning on the supply of secondary air is set to about 11, and the threshold (predetermined value) when turning off is set to about 17.

  The position where the secondary air introduction pipe supplies the secondary air is not limited to the exhaust port as long as it is upstream of the exhaust system catalyst. The intake port of the secondary air is not limited to the downstream side of the air cleaner of the intake system duct, and may be configured to take in outside air independently.

1 is a block diagram showing an outline of an engine system according to an embodiment of the present invention. It is a graph which shows typically the supply timing of secondary air when an air fuel ratio is a rich state, catalyst temperature, and carbon deposition degradation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 11 Cylinder head 12 Intake system duct 13 Air cleaner 14 Throttle body 15 Fuel injection device 16 Exhaust system duct 17 Catalytic converter 18 Secondary air supply pipe 19 Air introduction valve 20 Engine temperature sensor 21 Crank angle sensor 22 Oxygen concentration sensor 23 Catalyst temperature Sensor 24 Throttle position sensor (TPS)
25 Electronic control unit (ECU)

Claims (8)

A secondary air supply passage for supplying secondary air to an exhaust system of an engine provided with a three-way catalyst;
A secondary air supply amount control device for controlling a supply amount of secondary air supplied to the exhaust system via the secondary air supply path;
While the air-fuel ratio is in a rich state, the supply amount is controlled in a range in which the catalyst temperature of the three-way catalyst is maintained below a predetermined value, and the supply amount is controlled in a range in which the carbon deposition deterioration of the three-way catalyst is suppressed. A secondary air introduction device characterized by the above.   The secondary air introduction device according to claim 1, wherein the supply of the secondary air is periodically performed, and the supply of the secondary air is performed with a duty ratio of less than 50%.   The secondary air introduction apparatus according to claim 2, wherein the supply of the secondary air is performed at a duty ratio of 30% to 5%.   The secondary air introduction apparatus according to claim 3, wherein the supply of the secondary air is performed at a duty ratio of 20% to 10%.   The secondary air according to claim 1, further comprising a temperature sensor that detects a temperature in the three-way catalyst, wherein the secondary air supply amount control device controls the supply amount based on the temperature. Introduction device.   2. The secondary according to claim 1, further comprising an oxygen concentration sensor that detects an oxygen concentration of the exhaust system, wherein the secondary air supply amount control device controls the supply amount based on the oxygen concentration. Air introduction device.   2. The secondary according to claim 1, further comprising an air-fuel ratio sensor that detects an air-fuel ratio of the exhaust system, wherein the secondary air supply amount control device controls the supply amount based on the air-fuel ratio. Air introduction device. The secondary air introduction device according to claim 1, wherein the secondary air introduction device is mounted on a small motorcycle.

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