Exhaust system of internal combustion engine

Abstract: An exhaust system of an internal combustion engine is described, which has an exhaust gas inlet tube (4) extending from the engine. A muffler (1) connected is at its inlet side to the exhaust gas inlet tube (4). The muffler (1) includes first and second exhaust gas flowing passages. First and second exhaust gas outlet tubes (5,8) are respectively connected to the first and second exhaust gas flowing passages and extend from the muffler (1) independently. A flow controller (12) is arranged which steplessly varies the flow passage area of the second exhaust gas outlet tube (8) in accordance with the pressure of the exhaust gas discharged from the engine. The flow controller (12) continuously increases the flow passage area with increase of the magnitude of the exhaust gas pressure.

Description: The present invention is directed to an exhaust system of an internal combustion engine according to the precharacterizing portion of claim 1. A corresponding exhaust system is known from US-A-4 665 692. According to this conventional exhaust system, there is provided a control valve which is operated by a negative pressure applied to a diaphragm type actuator. Said negative pressure is generated by a vacuum pump. The negative pressure level acting on said diaphragm type actuator is controlled via a solenoid valve. From DE-B-2 110 000 there is known an exhaust system including a valve structure provided within an outlet section of a muffler. This valve structure is operated by a diaphragm type actuator which is controlled via a control unit. Hitherto, for muffling the exhaust gas emitted from an automotive internal combustion engine, various types of exhaust systems have been proposed and put into practical use. Some of them are of a controllable type which comprises a muffler for muffling the exhaust gas and a muffler controller for controlling the performance of the muffler. Some of the muffler controllers are of a type which includes a valve for opening and closing a certain exhaust passage of the muffler and an actuator for actuating the valve. These muffler controllers are shown in Japanese Patent First Provisional Publications Nos. 3-185209, 4-124418 and 2-259217. However, due to inherent construction, the conventional exhaust systems of the above-mentioned controllable type have failed to exhibit a satisfied performance in optimally muffling the exhaust gas. Furthermore, some are highly costed due to their complicated construction and costly parts inevitably used therein. In consideration of the above-given explanations, it is an object of the present invention to provide an exhaust system for an internal combustion engine which provides an improved, fast response of operation characteristic and which requires minimum space in the under body structure of a vehicle. According to the present invention this object has been performed by an exhaust system for an internal combustion engine as specified in claim 1. Further details of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic view of a controllable exhaust system of an internal combustion engine, according to the present invention; Fig. 2 is a partially sectioned plan view of the controllable exhaust system of the invention; Fig. 3 is an enlarged view of an essential portion of the controllable exhaust system of the invention; Fig. 4 is a partially sectioned view of a cylinder type actuator employed in the present invention; Fig. 5 is a graph showing the characteristic of the cylinder type actuator in terms of the relationship between a pressure applied to the actuator and a piston stroke of the actuator; Fig. 6 is a graph showing both an exhaust pressure control performance exhibited by the exhaust system of the invention and that exhibited by a conventional exhaust system, the performance being depicted in terms of the relationship between a static pressure of the exhaust gas and an engine speed; and Fig. 7 is a graph showing both an exhaust sound controlling performance exhibited by the exhaust system of the invention and that exhibited by the conventional exhaust system, the performance being depicted in terms of the relationship between an exhaust sound and the engine speed. DETAILED DESCRIPTION OF THE INVENTION Referring to Figs. 1 to 4, particularly Figs. 2 and 3, there is shown a controllable exhaust system according the present invention. In Figs. 2 and 3, denoted by numeral 1 is an exhaust muffler. Three partition walls 2, 3 and 9 are arranged in the muffler 1 to divide the interior of the same into four chambers "A", "B", "C" and "D". Denoted by numeral 4 is an exhaust gas inlet tube having a rear end portion projected into the muffler 1. First and second exhaust gas outlet tubes 5 and 8 extend from the interior of the muffler 1. Denoted by numerals 6 and 7 are longer and shorter intermediate tubes installed in the muffler 1. Denoted by numeral 10 is a pressure induction pipe, 11 is a cylinder type actuator and 12 is a control valve, which constitute a muffler controller as will be described in detail hereinafter. The chamber "A" is defined between a rear wall 1b of the muffler 1 and the partition wall 2, the chamber "B" is defined between the partition wall 2 and the partition wall 3, the chamber "C" is defined between the partition wall 3 and the partition wall 9, and the chamber "D" is defined between a front wall 1a of the muffler 1 and the partition wall 9, as shown. As will become apparent as the description proceeds, the three chambers "A", "B" and "D" are expansion chambers, and the chamber "C" is a resonance chamber. The exhaust gas inlet tube 4 has a front open end connected to an exhaust manifold (not shown) of an internal combustion engine or a catalytic converter (not shown). The rear end portion of the tube 4 passes through the chambers "D" and "C" having a rear open end thereof exposed to the chamber "B". The rear end portion of the tube 4 is formed, at a part exposed to the chamber "D", with four small openings 4a. Each opening 4a is about 10 mm in diameter. Thus, the exhaust gas flowing in the exhaust gas inlet tube 4 can flow into the chamber "B" through the rear open end and into the chamber "D" through the four small openings 4a. The first exhaust gas outlet tube 5 has a front end portion projected into the muffler 1 from the front wall 1a of the muffler 1. That is, the front end portion of the tube 5 passes through the chamber "D" having a front open end thereof exposed to the chamber "C". The front end portion is formed, at a part exposed to the chamber "D", with a plurality of small openings 5a. Each opening 5a is about 4 mm in diameter. Thus, the exhaust gas in the chamber "D" can flow into the first exhaust gas outlet tube 5 through the small openings 5a. The second exhaust gas outlet tube 8 has a front half portion projected into the muffler 1 from the rear wall 1b of the muffler 1. That is, the front half portion of the tube 8 passes through the chambers "A", "B" and "C" having a front open end thereof exposed to the chamber "D". A rear half portion 8c of the tube 8, which is exposed to the open air, is provided with the above-mentioned control valve 12. The front half portion of the tube 8 is formed, at parts exposed to the chambers "B" and "D", with a plurality of small openings 8a' and 8a". Each opening 8a' or 8a'' is about 3 mm in diameter. Thus, the exhaust gas in the chamber "B" can flow into the tube 8 through the small openings 8a' and the exhaust gas in the chamber "D" can flow into the tube 8 through both the front open end and the small openings 8a". The front half portion of the tube 8 is formed, at a part exposed to the chamber "A", with a plurality of small openings 8a. This perforated part of the tube 8 is wrapped with an outer cover 8b. A glass wool is packed in a cylindrical space defined between the perforated part and the outer cover 8b. Due to provision of the outer cover 8b, there is no direct communication between the chamber "A" and the tube 8. The longer intermediate tube 6 passes through the chambers "B" and "C" to communicate the chambers "A" and "D". The longer intermediate tube 6 is formed, at a part exposed to the chamber "B", with a plurality of small openings 6a. Each opening 6a is about 4 mm in diameter. Thus, the chambers "A", "B" and "D" are communicated by the longer intermediate tube 6. Due to provision of the openings 6a, the exhaust gas led into the chamber "B" can flow into the longer intermediate tube 6. The shorter intermediate tube 7 passes through the partition wall 2 to communicate the chambers "A" and "B". It is to be noted that the shorter intermediate tube 7 is aligned with the rear end portion of the exhaust gas inlet tube 4 which is projected into the muffler 1, as shown. As is best shown in Fig. 3, the pressure induction pipe 10 has a tapered open end 13 led into the chamber "A". As shown, the tapered open end 13 of the pipe 10 faces the rear end of the shorter intermediate tube 7. That is, the rear end portion of the exhaust gas inlet tube 4, the shorter intermediate tube 7 and the tapered open end 13 are coaxially aligned, in the illustrated manner. The other open end of the pipe 10 is connected to the cylinder type actuator 11. Thus, the positive pressure consisting of static and dynamic pressures created in the chamber "A" of the muffler 1 is led into the actuator 11. As is seen from Fig. 4, the actuator 11 comprises a cylindrical casing 11f, an annular piston 11b slidably received in the casing 11f to define a work chamber 11a, a coil spring 11c installed in the casing 11f to bias the annular piston 11b rightward in the drawing, a piston rod 11d extending from the annular piston 11b and projected to the outside of the casing 11f, and a stopper 11e installed in the casing 11f to stop excessive displacement of the piston 11b. The work chamber 11a is connected to the other open end of the pressure induction pipe 10. Thus, when the positive pressure is led into the work chamber 11a through the pipe 10, the piston 11b is slid leftward in Fig. 4 against the biasing force of the spring 11c thereby pushing out the piston rod 11d. Referring back to Fig. 3, the cylinder type actuator 11 is mounted on a bracket 14 which is secured to the rear wall 1b of the muffler 1. The piston rod 11d of the actuator 11 is operatively connected to the control valve 12. The control valve 12 comprises a butterfly plate 12a pivotally installed through a pivot shaft 15 in the exposed rear half portion 8c of the second exhaust gas outlet tube 8. The pivot shaft 15 is connected through a link 16 to the piston rod 11d of the actuator 11. Thus, when, due to application of positive pressure to the actuator 11, the piston rod 11d is pushed out, the butterfly plate 12a is pivoted in a direction to open and increase the flow passage area of the second exhaust gas outlet tube 8. It is to be noted that the open degree of the butterfly plate 12a (viz., the flow passage area of the tube 8) is continuously varied in accordance with the magnitude of the positive pressure fed to the actuator 11. Thus, it will be appreciated that when the engine is under a low load condition, such as idling or the like, the butterfly plate 12a keeps its closed position due to the work of the biasing coil spring 11c of the actuator 11. In fact, the coil spring 11c is so set as to permit the rod-pushing movement of the piston 11b when the engine runs at a speed higher than 1500 rpm. In the following, operation of the controllable exhaust system of the invention will be described. For ease of understanding, the description will be commenced with respect to a standstill condition of the engine. Under this rest condition, the butterfly plate 12a of the control valve 12 assumes its closed position thereby fully closing the flow passage of the second exhaust gas outlet tube 8. When now the engine is started, the exhaust gas from the engine is fed into the muffler 1 through the exhaust gas inlet tube 4. The exhaust gas in the muffler 1 travels in order the chamber "B", the shorter intermediate tube 7, the chamber "A", the longer intermediate tube 6 and the chamber "D" and travels the first exhaust gas outlet tube 5 before being discharged to the open air. During traveling in the muffler 1, the exhaust gas looses its energy due to the above-mentioned unique arrangement of the chambers "A", "B", "C" and "D" and the shorter and longer intermediate tubes 7 and 6. When the engine speed is increased by depressing an accelerator pedal, the pressure of the exhaust gas is increased accordingly. When the engine speed is further increased and comes to a certain level, for example, about 1500 rpm, the butterfly plate 12a of the control valve 12 starts to open for the reason as has been mentioned hereinabove. Upon this, the second exhaust gas outlet tube 8 becomes operative but partially. That is, in addition to the exhaust gas flow directed toward the first exhaust gas outlet tube 5, the muffler 1 produces another exhaust gas flow directed toward the second exhaust gas outlet tube 8, which comprises a gas flow from the chamber "B" to the tube 8 through the small openings 8a' and a gas flow from the chamber "D" to the tube 8 through both the front open end of the tube 8 and the small openings 8a". When the engine speed is further increased, the butterfly plate 12a increases its open degree. Thus, the resistance of the muffler 1 against the flow of the exhaust gas flowing therein is reduced. Advantages of the present invention will become apparent from the following description. OPEN/CLOSE OPERATION OF CONTROL VALVE 12 Under operation of the engine, a certain positive pressure is created in the chamber "A" of the muffler 1 and the pressure is thus fed to the work chamber 11a of the actuator 11. In accordance with the magnitude of the pressure fed to the actuator 11, the butterfly plate 12a of the control valve 12 is continuously pivoted varying the flow passage area of the second exhaust gas outlet tube 8. The stroke characteristic of the piston rod 11d of the actuator 11 with respect the magnitude of the positive pressure fed to the actuator 11 is shown in the graph of Fig. 5. As is seen from this graph, the stroke characteristic of the piston rod 11d obtained when the pressure in the work chamber 11a is increasing is different from that of the piston rod 11d obtained when the pressure in the work chamber 11a is decreasing. That is, the stroke of the piston rod 11d has a hysteresis between the pressure increasing mode and the pressure decreasing mode of the actuator 11. This is because of an inevitable friction of the piston 11b against the inner wall of the casing 11f of the actuator 11. Accordingly, when the pressure in the work chamber 11a varies within a small range, the hysteretic pressure range can serve as a non-working zone and thus the undesired hunting of the control valve 12, which would occur when the butterfly plate 12a makes the opening and closing movement, can be eliminated. Since the tapered open end 13 of the pressure induction pipe 10 is arranged to face the rear end of the shorter intermediate tube 7, the pipe 10 can catch the dynamic pressure of the exhaust gas as well as the static pressure of the same. This means a certain increase in pressure level of the positive pressure fed to the actuator 11, and thus the valve actuating operation of the actuator 11 is assured. PRESSURE REGULATING FUNCTION Under operation of the engine, the exhaust gas is discharged from the engine with a certain pressure fluctuation varied in accordance with the speed of the engine. Thus, if such exhaust gas is directly fed to the actuator 11, the movement of the piston rod 11d would be severely affected by the pressure fluctuation. In fact, the opening and closing movement of the butterfly plate 12a of the control valve 12 would be fluctuated in such case. However, in the invention, such apprehension is eliminated by positioning the tapered open end 13 of the pipe 10 at the chamber "A" which is an expansion chamber. As is known, when the exhaust gas is led into such expansion chamber, the pressure fluctuation of the same is reduced and thus the pressure in the chamber "A" is regulated. This pressure regulating function becomes most effective when the engine is under a low speed operation. If a thinner pressure induction pipe 10 is employed, much regulated positive pressure can be obtained from the exhaust gas. OPERATION OF CONTROL VALVE 12 UNDER ACCELERATION OF ENGINE When, for accelerating the vehicle, the accelerator pedal is depressed and thus the speed of the engine increases, the pressure of the exhaust gas is increased. With this, the positive pressure in the chamber "A" of the muffler 1 and thus the pressure in the work chamber 11a of the actuator 11 is increased. With this, the butterfly plate 12a of the control valve 12 is turned from the closed position toward the full open position. Since the turning of the butterfly plate 12a is continuously and steplessly effected, smoothed acceleration of the vehicle as well as ear-agreeable exhaust sound are obtained. These advantageous phenomena will be readily understood from the graphs of Fig. 6 and Fig. 7. Fig. 6 shows both an exhaust pressure control performance exhibited by the exhaust system of the invention and that exhibited by a conventional exhaust system. In the conventional exhaust system, an ON/OFF type control valve is employed, which controls a valve proper in ON/OFF manner, so that the valve proper takes only a fully closed position and a fully open position. As is seen from this graph, in the conventional exhaust system (whose characteristic is depicted by the curve of dotted line), the exhaust static pressure is suddenly but temporarily dropped at a certain engine speed (viz., about 2400 rpm) during the time when the engine speed is increasing. The sudden drop is produced when the valve proper changes its position from the fully closed position to the fully open position. Of course, in this case, smoothed acceleration of a vehicle is not expected. However, in the exhaust system of the present invention (whose characteristic is depicted by the curve of solid line), such undesired pressure drop does not appear. This is because of usage of the steplessly openable butterfly plate 12a of the control valve 12. As has been described hereinabove, in the present invention, the butterfly plate 12a can vary the open degree in the second exhaust gas outlet tube 8. That is, with increase of engine speed, the exhaust static pressure increases substantially linearly, and due to the gradual opening of the butterfly plate 12, the exhaust resistance is gradually decreased, which provides the vehicle with a smoothed acceleration. The curve illustrated by a phantom line shows a case wherein the butterfly valve 12a (or valve proper) is kept closed throughout the increase in engine speed. Fig. 7 shows both an exhaust sound controlling performance exhibited by the exhaust system of the invention and that exhibited by the conventional exhaust system. As is seen from this graph, in the conventional exhaust system (whose characteristic is depicted by the curve of dotted line), the exhaust sound is suddenly but temporarily dropped at the certain engine speed (viz., about 2400 rpm) during increase in engine speed. This sound drop is not agreeable to the ear. However, in the exhaust system of the present invention (whose characteristic is depicted by the curve of solid line), such undesired sound drop does not appear. Thus, in the invention, ear-agreeable exhaust sound is obtained. The curve illustrated by a phantom line shows a case wherein the butterfly valve 12a (or valve proper) is kept closed throughout the increase in engine speed. APPLICATION TO MOTOR VEHICLE In the invention, the exhaust gas from the engine is used as a power for driving the control valve 12. Thus, the exhaust system of the invention can be manufactured at low cost as compared with other exhaust systems in which electric actuators are used for actuating the control valve. In the following, modifications of the present invention will be described. If desired, for feeding the actuator 11 with a positive pressure, the pressure induction pipe 10 may be connected to the exhaust gas inlet tube 4, as is shown in Fig. 1 by a dotted line. However, in this case, the above-mentioned pressure regulating function exclusively possessed by the expansion chamber in the muffler 1 is not expected. If desired, a shutter type valve plate may be used in place of the butterfly plate 12a, so long as it can vary the open degree continuously. If desired, a negative pressure created by using the exhaust pressure from the engine may be used for driving the actuator 11.

Claims: An exhaust system of an internal combustion engine comprising: an exhaust gas inlet tube (4) extending from said engine; a muffler (1) connected at an inlet side thereof to said exhaust gas inlet tube, said muffler including first and second exhaust gas flowing passages; first and second exhaust gas outlet tubes (5,8) respectively connected to said first and second exhaust gas flowing passages and extending from said muffler respectively; a control valve (12) disposed in said second exhaust gas outlet tube (8) in a manner to vary a flow passage area defined in said second exhaust gas outlet tube; and an actuator (11) for actuating said control valve in a manner to increase said flow passage area, characterized by a pressure induction pipe (10) which feeds a pressurized gas to said actuator to increase said flow passage area, said pressure induction pipe having a pressure inlet end (13) exposed to an expansion chamber defined in said muffler, said pressure inlet end (13) being arranged to face against the flow of the exhaust gas in the expansion chamber: An exhaust system as claimed in claim 1, in which said pressure inlet end (13) is tapered to have an enlarged open end. An exhaust system as claimed in claim 2, in which the tapered pressure inlet end (13) of said pressure induction pipe (10) is positioned just behind a leading end of said exhaust gas inlet tube (4), said leading end being projected into the muffler (1). An exhaust system as claimed in claim 1, in which said cylinder type actuator (11) is connected to a rear wall of said muffler (1) through a bracket (14). An exhaust system as claimed in claim 1, in which said control valve (12) comprises: a butterfly plate (12a); a pivot shaft (15) through which said butterfly plate (12a) is pivotally installed in said second exhaust gas outlet tube (6); and a link (16) pivotally connecting said pivot shaft (15) to said piston rod (11d) of said actuator. An exhaust system as claimed in claim 1, characterized in that said actuator (11) is formed as a cylinder type actuator which includes a cylindrical casing (11f), a piston (11 b) slidably received in said cylindrical casing (11f) to define therein a work chamber (11a), a seal member for sealing said work chamber, a spring (11c) installed in said cylindrical casing (11f) to bias said piston (11b) toward said work chamber (11a), and a piston rod (11 d) extending from said piston (11b) to the outside of said cylindrical casing (11f).

Inventors: NAKANISHI YUKIO, NORIKAWA TANOMO, SEKI KOJI, NAKANISHI,YUKIO, NORIKAWA, TANOMO, SEKI, KOJI, Nakanishi,Yukio, c/o Calsonic Corp., Norikawa, Tanomo, c/o Calsonic Corp., Seki, Koji, c/o Calsonic Corp.
Applicants: CALSONIC CORP, CALSONIC CORPORATION
Application year: 1995
Main classification: F01N1
IPC codes: F01N1, F02D9, F01N13