JP4332102B2 - Engine air-fuel ratio control device - Google Patents

Description

  In the present invention, an exhaust system including a three-way catalyst is connected to an exhaust port provided in an engine cylinder head, and detects whether the air-fuel ratio is rich or lean according to the oxygen concentration in the exhaust gas. The present invention relates to an air-fuel ratio control device for an engine that is attached to the exhaust system upstream of the three-way catalyst so that an oxygen sensor reflects the detected value in the air-fuel ratio control.

For example, Patent Document 1 and Patent Document 2 have already been known in which the air-fuel ratio is controlled by an oxygen sensor attached to the exhaust pipe upstream of the three-way catalyst.
JP 59-74360 A JP 2000-335467 A

  In the multi-cylinder engine disclosed in Patent Document 1, an oxygen sensor is attached to an exhaust collecting pipe portion separated from the engine in the exhaust system. In the single-cylinder engine disclosed in Patent Document 2, maintenance performance and sensor protection are provided. From this point of view, it is attached to the exhaust pipe in an empty space that does not interfere with the engine body. In any case, the oxygen sensor is disposed at a position away from the exhaust port of the engine body.

  Incidentally, the oxygen sensor detects whether the air-fuel ratio is rich or lean according to the oxygen concentration in the exhaust gas, and the voltage output from the oxygen sensor is shown in FIG. It changes depending on whether the fuel ratio is rich or lean. In the air-fuel ratio control using the output voltage of the oxygen sensor, as shown in FIG. 8, the correction term of the fuel supply control amount is changed to the opposite side to the output of the oxygen sensor, and the air-fuel ratio is calculated theoretically. It converges near the air-fuel ratio.

On the other hand, NO _X purification rate of the exhaust gas by the three-way catalyst, which is higher in richer, particularly, in a high load region of the engine, a region where the purification rate is higher is shifted more to the rich side Therefore, the conventional air-fuel ratio control using the oxygen sensor that detects whether the air-fuel ratio is rich or lean cannot increase the NO _x purification rate in the exhaust gas. Such a problem can be solved by using a linear air-fuel ratio sensor, but the linear air-fuel ratio sensor is expensive, leading to an increase in cost.

The present invention has been made in view of such circumstances, and an object thereof is to provide an air-fuel ratio control device for an engine that can effectively remove NO _x in exhaust gas using an inexpensive oxygen sensor. To do.

In order to achieve the above object, the invention according to claim 1 is that an exhaust system including a three-way catalyst is connected to an exhaust port provided in an engine cylinder head, and the air-fuel ratio is rich according to the oxygen concentration in the exhaust gas. In an air-fuel ratio control device for an engine, an oxygen sensor for detecting whether the engine is in a lean state or lean is attached to the exhaust system upstream of the three-way catalyst so that the detected value is reflected in the air-fuel ratio control. ,-out based on that amount of oxygen remaining in exhaust gas discharged from the pre-Symbol exhaust port becomes constant in subsequent distance of more than 10 times the diameter of the exhaust port, said oxygen sensor, the distance from the exhaust port wherein as the remaining oxygen amount by 10 times within the diameter of the exhaust port is disposed in the region before the constant, connected to the exhaust port to form part of the exhaust system Characterized in that it is attached to the exhaust pipe.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the body frame of the motorcycle mounted with the engine includes a head pipe that supports a front fork that pivotally supports a front wheel so as to be steerable. A down tube extending downwardly from the head pipe, the oxygen sensor being attached to the exhaust pipe in the vicinity of the down tube, and a sensor cord connected to the oxygen sensor partially extending along the down tube It arrange | positions so that it may cause.

  According to a third aspect of the invention, in addition to the configuration of the first or second aspect of the invention, the exhaust gas from the exhaust pipe is first introduced into the silencer casing to which the downstream end of the exhaust pipe is connected. A catalyst case connected to the exhaust pipe is disposed, and an expansion chamber for introducing exhaust gas immediately after passing through the three-way catalyst accommodated in the catalyst case is formed in the casing. Features.

  According to a fourth aspect of the invention, in addition to the configuration of the third aspect of the invention, the catalyst case is disposed at a front portion in the casing extending in the front-rear direction, and the front end portion is connected to the catalyst case in the front-rear direction. A rear end portion of the conduit extending in the direction is inserted into the expansion chamber formed in the rear portion of the casing.

  Further, the invention according to claim 5 is characterized in that, in addition to the configuration of the invention according to claim 2, the oxygen sensor is disposed between the exhaust port and the down tube in a side view of the motorcycle. .

According to the first to fifth aspects of the present invention, the oxygen sensor is attached to the exhaust pipe so that a distance within 10 times the diameter of the exhaust port is provided between the exhaust port and the oxygen sensor is close to the exhaust port. Will be placed in position. Thus, the amount of residual oxygen in the exhaust gas flowing through the exhaust system gradually decreases as the distance from the exhaust port increases, and the residual oxygen from the vicinity of the position where the distance from the exhaust port becomes 10 times the diameter of the exhaust port. The inventors of the present application have confirmed that the amount is almost constant, and the output of the oxygen sensor is shifted to the lean side by setting the attachment position of the oxygen sensor to the exhaust pipe in accordance with the present invention as described above. will be, by the air-fuel ratio control using the output of the oxygen sensor, since the exhaust gas burned at an air-fuel ratio shifted to a rich side is to flow through the three-way catalyst effectively removing NO _X in the exhaust gas Moreover, the responsiveness of the air-fuel ratio control can be improved by providing the oxygen sensor near the exhaust port.

  In particular, according to the second aspect of the present invention, it is possible to lay out the sensor cord connected to the oxygen sensor along the down tube, so that the sensor cord can be easily protected and wired.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below based on one embodiment of the present invention shown in the accompanying drawings.

FIG. 1 is a side view of a motorcycle to which the present invention is applied, FIG. 2 is a side view of an engine, FIG. 3 is a longitudinal side view of a silencer, and FIG. 4 is a view after a three-way catalyst is passed through in a low load region of the engine. CO in the exhaust gas, graph according to the concentration of HC and NO _X to changes in air-fuel ratio, FIG. 5 in the exhaust gas after flowed through the three-way catalyst in the high load region of the engine CO, HC and NO _X FIG. 6 is a graph showing the change in the amount of residual oxygen in the exhaust gas flowing through the exhaust system, FIG. 7 is a graph showing the output characteristics of the oxygen sensor, and FIG. It is a figure which shows the change of the correction | amendment term of the fuel supply control amount by an output.

  Referring to FIG. 1, a motorcycle body frame F includes a head pipe 7 that supports a front wheel WF and a front fork 5 to which a steering handle 6 is coupled, and a rear pipe from the head pipe 7. A main frame 8 that extends downward, and a down tube 9 that is steeper than the main frame 8 and extends rearward and downward from the head pipe 7 and extends substantially horizontally at the rear, and between the main frame 8 and the rear portion of the down tube 9 The front portion of the rear fork 15 is supported on the pivot plate 10 via the support shaft 14 so as to be able to swing up and down, and the rear wheel WR is supported on the rear portion of the rear fork 15.

  The upper part of the rear cushion unit 16 is connected to the upper part of the vehicle body frame F, and the lower part of the rear cushion unit 16 is connected to the intermediate part of the rear fork 15 via the link mechanism 17.

  A power unit P composed of a single cylinder engine E and a transmission M is mounted on the body frame F, and the power output from the power unit P, that is, the power output from the output shaft 18 of the transmission M is a chain type. It is transmitted to the rear wheel WR via the transmission means 19.

  Referring also to FIG. 2, the intake system 22 connected to the intake port 21 provided on the rear side surface of the cylinder head 20 provided in the engine E includes a throttle body 24 to which a fuel injection valve 23 is attached. The exhaust system 26 connected to the exhaust port 25 provided on the front side surface of the cylinder head 20 includes an exhaust pipe 27 connected to the exhaust port 25 at the upstream end, and a three-way catalyst 28. A muffler 30 disposed on the right side, and a connecting pipe 29 connecting the downstream end of the exhaust pipe 27 and the upstream end of the muffler 30 are provided.

  The exhaust pipe 27 is bent so as to extend rearward from the exhaust port 25 provided on the front side surface of the cylinder head 20 through the lower part of the power unit P, and is arranged on the right side of the rear wheel WR. A bracket 31 provided at 30 is supported by the vehicle body frame F via a support member 32.

  In FIG. 3, the casing 34 of the silencer 30 is formed in a cylindrical casing main body 35 that extends rearward on the right side of the rear wheel WR, and is formed in a tapered shape having a diameter that decreases toward the front. A cone member 36 to be joined and a lid member 37 to be joined to the rear end of the casing main body 35 are provided. The bracket 31 is provided on the upper outer surface of the casing main body 35.

  A cylindrical catalyst case 38 containing the three-way catalyst 28 is disposed in the cone member 36, and the front end portion of the catalyst case 38 is fitted to the front end portion of the cone member 36. The intermediate portion of the catalyst case 38 is slidably supported by a support cylinder 39. The support cylinder 39 includes a tapered support stay 40 fixed to the inner surface of the intermediate portion of the cone member 36, and the cone member 36. It is fixedly supported by a disk-shaped support plate 41 whose outer periphery is fixed to the rear inner surface. Moreover, the downstream end of the connection pipe 29 is fitted to the front end of the catalyst case 38, and the exhaust gas flowing downstream from the exhaust pipe 27 through the connection pipe 29 flows through the three-way catalyst 28 so as to pass through the catalyst. Introduced in case 38.

  The rear end portion of the catalyst case 38 is joined to the front end portion of a conduit 42 that passes through the support plate 41 and extends back and forth in the casing 34, and the rear end of the conduit 42 is in the vicinity of the lid member 37. Placed in. In addition, a bottomed cylindrical cap 44 provided with a plurality of through holes 43, 43... Is fitted and fixed to the rear end portion of the conduit 40.

  First, second, and third partition plates 45, 46, and 47 are fixed to the inner surface of the casing main body 35 in order from the front with an interval in the front-rear direction, and these partition plates 45, 46, and 47 are fixed. The conduit 42 penetrating through the wall is slidably supported by the partition plates 45 to 47. Thus, in the casing 34, the first, second, third and fourth are sequentially arranged from the front side by the support plate 41, the first, second and third partition plates 45 to 47 and the lid member 37. It is divided into expansion chambers 48, 49, 50, 51.

  The rear end portion of the conduit 42 is disposed in the fourth expansion chamber 51, and exhaust gas that flows through the three-way catalyst 28 and flows backward in the conduit 42 passes through the plurality of through holes 43, 43. It flows into the expansion chamber 51. In addition, the third partition plate 47 is provided with a large number of small-diameter communication holes 52, 52... And the exhaust gas flowing into the fourth expansion chamber 51 passes through the small-diameter communication holes 52, 52. Guided to the expansion chamber 50.

  The first and second partition plates 45 and 46 are provided with a first connecting pipe 53 having both ends opened to the first and third expansion chambers 48 and 50. The first partition plate 45 has both ends connected to the first and second partition plates 45 and 46. A second communication pipe 54 that opens to the second expansion chambers 48 and 49 is provided. Therefore, the exhaust gas introduced into the third expansion chamber 50 is guided to the first expansion chamber 48 via the first communication pipe 53 and further to the second expansion chamber 49 via the second communication pipe 54.

  The second partition plate 46 has a front end opened to the second expansion chamber 48 and a front end portion of a discharge pipe 55 passing through the third partition plate 47 is fixed. The rear end portion of the discharge pipe 55 is a casing. 34 is supported by the rear end lid member 37 and opens rearward. In addition, a part of the discharge pipe 55 is covered with the outer pipe member 56 in the fourth expansion chamber 51, and the annular portion between the outer pipe member 56 and the discharge pipe 55 is filled with a sound absorbing material 57, and the outer pipe member 56. A number of small holes (not shown) are provided in the pipe wall of the discharge pipe 55 at a portion corresponding to the above.

  Referring again to FIGS. 1 and 2, the air-fuel ratio is rich and lean in the exhaust system 26 upstream of the three-way catalyst 28, that is, the silencer 30, according to the oxygen concentration in the exhaust gas as shown in FIG. The oxygen sensor 33 that changes the output voltage in accordance with which state is present is attached to reflect the detected value in the air-fuel ratio control, and is located upstream of the three-way catalyst 28 in the exhaust system 26. The oxygen sensor 33 is attached to the exhaust pipe 27 so as to be positioned in the vicinity of the down tube 9 in the vehicle body frame F. In addition, the sensor cord 59 connected to the oxygen sensor 33 extends below the riding seat 60 so that a part of the sensor cord 59 extends along the down tube 9, and is disposed in a space formed below the riding seat 60. Connected to a control unit (not shown).

By the way, as shown in FIGS. 4 and 5, the purification rate of CO and HC in the exhaust gas by the three-way catalyst 28 increases as the air-fuel ratio (A / F) becomes leaner, whereas in the exhaust gas, NO _X purification rate are those air-fuel ratio (a / F) becomes higher as becomes richer, especially as shown in Figure 5, in a high load region of the engine E, more area where NO _X purification rate is higher Shift to the rich side.

Here, as shown in FIG. 4, the amount of residual oxygen in the exhaust gas flowing through the exhaust system 26 gradually decreases as the distance from the exhaust port 25 increases, and the distance from the exhaust port 25 is 10 times the diameter D of the exhaust port 25. The amount of residual oxygen is substantially constant from the vicinity of the double position to the downstream side, and the oxygen sensor 33 for detecting whether the air-fuel ratio is in a rich state or a lean state is used. When the air-fuel ratio control using the output voltage of the oxygen sensor 33 is arranged in the region, the correction of the fuel injection control amount from the fuel injection valve 23 on the side opposite to the output of the oxygen sensor 33 as shown in FIG. The term is changed and the air-fuel ratio is converged to the vicinity of the theoretical air-fuel ratio, so the NO _x purification rate in the exhaust gas cannot be increased.

  Therefore, according to the present invention, the oxygen sensor 33 is attached to the exhaust pipe 27 so that a distance L within 10 times the diameter D of the exhaust port 25 is provided between the exhaust sensor 25 and the oxygen sensor 33. The voltage on the side having a large amount of residual oxygen, that is, the lean side is output.

  Next, the operation of this embodiment will be described. The oxygen sensor 33 is connected to the exhaust pipe 27 so that a distance L within 10 times the diameter D of the exhaust port 25 in the cylinder head 20 of the engine E is opened between the exhaust port 25 and the engine. Therefore, the oxygen sensor 33 is disposed at a position close to the exhaust port 25.

  Thus, the amount of residual oxygen in the exhaust gas flowing through the exhaust system 25 gradually decreases as the distance from the exhaust port 25 increases, and the distance from the exhaust port 25 reaches the downstream from the position where the distance D becomes 10 times the diameter D of the exhaust port 25. Since the amount of residual oxygen is substantially constant on the side, the output of the oxygen sensor 33 is shifted to the lean side when the position of the oxygen sensor 33 attached to the exhaust pipe 27 is set as described above. By the air-fuel ratio control using the output of 33, the exhaust gas burned with the air-fuel ratio shifted to the rich side as shown by the arrow in FIG.

Therefore, without using an expensive linear air-fuel ratio sensor, a conventional inexpensive oxygen sensor 33 that detects whether the air-fuel ratio is rich or lean according to the oxygen concentration in the exhaust gas can be used. The NO _x can be effectively removed by the three-way catalyst 28, and the oxygen sensor 33 is disposed near the exhaust port 25, whereby the responsiveness of the air-fuel ratio control can be improved.

  Further, since the oxygen sensor 33 is attached to the exhaust pipe 27 so as to be positioned in the vicinity of the down tube 9 in the body frame F, the sensor cord 59 connected to the oxygen sensor 33 is laid out along the down tube 9. As a result, the sensor cord 59 can be easily protected and wired.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. It is.

  For example, although the case where the present invention is applied to the single-cylinder engine E has been described in the above embodiment, the present invention is also applicable to a multi-cylinder engine.

1 is a side view of a motorcycle. It is a side view of an engine. It is a vertical side view of a silencer. 3 is a graph showing the concentrations of CO, HC, and NO _{x in} exhaust gas after flowing through a three-way catalyst in a low load region of the engine according to changes in the air-fuel ratio. 3 is a graph showing the concentrations of CO, HC and NO _{x in} exhaust gas after flowing through a three-way catalyst in a high load region of the engine according to changes in the air-fuel ratio. It is a figure which shows the change of the residual oxygen amount in the waste gas which distribute | circulates an exhaust system. It is a figure which shows the output characteristic of an oxygen sensor. It is a figure which shows the change of the correction | amendment term of the fuel supply control amount by the output of an oxygen sensor.

5 ... front fork 7 ... head pipe 9 ... down tube 20 ... cylinder head 25 ... exhaust port 26 ... exhaust system 27 ... exhaust pipe 28 ... three-way catalyst 30 ... Silencer 33 ... Oxygen sensor 34 ... Casing 38 ... Catalyst case 42 ... Conduit 51 ... Expansion chamber 59 ... Sensor code E ... Engine F ... Body frame WF ... front wheel

Claims (5)

An exhaust system (26) including a three-way catalyst (28) is connected to an exhaust port (25) provided in the cylinder head (20) of the engine (E), and the air-fuel ratio is rich according to the oxygen concentration in the exhaust gas. An oxygen sensor (33) for detecting which state is lean is attached to the exhaust system (26) upstream of the three-way catalyst (28) so that the detected value is reflected in the air-fuel ratio control. the air-fuel ratio control apparatus for an engine that is, based on that amount of oxygen remaining in exhaust gas discharged from the pre-Symbol exhaust port (25) to be constant in the subsequent distance of more than 10 times the diameter of the exhaust port (25) The oxygen sensor (33) is disposed in a region before the residual oxygen amount becomes constant by setting the distance from the exhaust port (25) to be within 10 times the diameter of the exhaust port (25). Like To the exhaust system (26) air-fuel ratio control system for an engine, characterized in that attached to the exhaust pipe which constitutes a part connected to the exhaust port (25) (27) of.   A body frame (F) of a motorcycle on which the engine (E) is mounted includes a head pipe (7) that supports a front fork (5) that pivotally supports a front wheel (WF), and a head pipe (7) 7), and the oxygen sensor (33) is attached to the exhaust pipe (27) in the vicinity of the down tube (9) and continues to the oxygen sensor (33). The air-fuel ratio control apparatus for an engine according to claim 1, characterized in that the sensor cord (59) is arranged so that a part thereof is along the down tube (9).   The exhaust pipe (27) is configured such that the exhaust gas from the exhaust pipe (27) is first introduced into the casing (34) of the silencer (30) to which the downstream end of the exhaust pipe (27) is connected. An expansion chamber (51) for introducing exhaust gas immediately after passing through the three-way catalyst (28) accommodated in the catalyst case (38) is disposed in the casing (34). The air-fuel ratio control apparatus for an engine according to claim 1 or 2, wherein   The catalyst case (38) is disposed in the front portion of the casing (34) extending in the front-rear direction, and the rear end portion of the conduit (42) extending in the front-rear direction is connected to the catalyst case (38). 4. The engine air-fuel ratio control device according to claim 3, wherein the engine air-fuel ratio control device is inserted into the expansion chamber (51) formed in a rear portion of the casing (34).   The engine air-fuel ratio control apparatus according to claim 2, wherein the oxygen sensor (33) is disposed between the exhaust port (25) and the down tube (9) in a side view of the motorcycle.

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