Secondary air supply system for engine unit

Abstract: A secondary air supply system of a vehicle, including an engine unit (7) having a crank chamber (8) and being operatively connected to an air cleaner (11) and an exhaust system including an exhaust pipe (14), comprises a diaphragm pump device (1) provided with an inner chamber (4a,4b,4c) and having an air inlet port (9) and an air outlet port (12) both being communicated with the inner chamber, a diaphragm (2) disposed in the inner chamber to divide it into a diaphragm chamber (3) and a pump chamber (4a,4b,4c), a first hose (10) connecting the air inlet port (9) and the air cleaner (11) to introduce a secondary air from the air cleaner (11) into the pump chamber (4a), a second hose (13) connecting the air outlet port (12) and the exhaust pipe (14) to supply the secondary air into the exhaust pipe (14) through the outlet port (12), and a third hose (6) connecting the diaphragm chamber (3) of the diaphragm pump device (1) and the crank chamber (8) of the engine unit (7). The secondary air is supplied into the exhaust pipe (14) through the diaphragm pump (1) by an amount in proportion to a magnitude of an oscillation of the diaphragm (2) caused in accordance with a pressure variation in the crank chamber (8) caused in proportion to an engine revolution speed. A valve assembly (5a,5b) is further disposed in the pump chamber (4a,4b,4c) for allowing the secondary air introduced into the pump chamber (4a,4b,4c) to flow uni-directionaly from the inlet port (9) to the outlet port (12).

Description: The present invention relates to a secondary air supply system for an engine unit, according to the pre-characterizing part of claim 1. A system this type is shown in GB-A 1 555 497. In a known four- or two-stroke cycle engine unit of a vehicle such as an automobile or motorcycle in which a piston of a piston-cylinder assembly performs a reciprocal motion in a cylinder an exhaust gas exhausted from an engine is fed into an exhaust pipe to which a catalyst is provided for the purification of the exhaust gas through an oxidation reaction. This oxidation reaction is carried out by supplying air into the exhaust pipe and this air is called secondary air for the engine unit in comparison with an air to be mixed with a fuel as a primary air. The secondary air is generally fed into the exhaust pipe through a one-way valve by the utilization of a pressure variation, i.e. pulsation, of the exhaust gas in the exhaust pipe to thereby suck the secondary air thereinto, or the secondary air is supplied by the actuation of a pump means attached to the engine unit. The secondary air supply system shown in GB-A-1 555 497 has the first hose connected between the air inlet port of the pump chamber and an air intake port. The location at which the other end of the third hose is connected to the crank chamber is not indicated in the document. Accordingly, the object of the present invention is to provide a secondary air supply system for a vehicle capable of supplying the secondary air into an exhaust pipe by an amount in proportion to an exhaust gas from the engine unit, particularly for a two-stroke cycle engine unit of a vehicle. This object can be achieved according to the present invention by the features of claim 1. In a preferred embodiment, a valve assembly is further disposed in the pump chamber for allowing the secondary air introduced into the pump chamber to flow uni-directionaly from the inlet port to the outlet port. The pump chamber is composed of a first pump chamber communicationed with the inlet port, a second pump chamber communicated with the outlet port and a common passage chamber connecting the first and second pump chambers and wherein the valve assembly comprises a first one-way valve disposed in the first pump chamber and a second one-way valve disposed in the second pump chamber, the first one-way valve being operated to introduce the secondary air into the first pump chamber when the diaphragm is displaced so as to increase an inner volume of the pump chamber and the second one-way valve being operated to discharge the secondary air from the second pump chamber when the diaphragm is displaced so as to decrease the inner volume of the pump chamber. The secondary air supply system is preferably functioned when used for the two-stroke cycle engine unit. According to the secondary air supply system for the engine unit of the characters described above, the pressure variation caused in the crank chamber of the engine unit by the reciprocation of the piston. This pressure variation is transferred to the diaphragm pump device through the connection hose and the diaphragm disposed in the diaphragm chamber of the pump device is oscillated. In proportion to the magnitude of the pressure variation, the diaphragm is oscillated thereby to vary the inner volume of the pump chamber of the pump device. Accordingly, in proportion to the magnitude and the frequency of the pressure variation, the secondary air is supplied in a regulated manner into the exhaust pipe through the diaphragm pump device of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention and to show how the same is carried out, reference will be first made, by way of a preferred embodiment, to the accompanying drawings, in which: Fig. 1 is a schematic side view of an exhaust system in association with a two-stroke cycle engine unit to whcih a secondary air supply system according to the present invention is applied; Fig. 2 is a schematic view, partially in section, of the exhaust system of Fig. 1; Fig. 3 is a side view, in an enlarged scale, of the secondary air supply system shown in Fig. 1 according to one embodiment of the present invention; and Fig. 4 is a sectional view of a diaphragm pump incorporated in the secondary air supply system shown in Fig. 3. DESCRIPTION OF THE PREFERRED EMBODIMENT First, referring to Fig. 1, a two-stroke cycle engine unit 7 is provided with a combustion chamber, not shown, into which an air is supplied from an air cleaner 11. The engine unit 7 is provided with an exhaust gas port, not shown, through which an exhaust pipe 14 is connected. As shown in Fig. 2, the exhaust pipe 14 is communicated with an expansion chamber 15, which is then communicated with a muffler 17. The exhaust pipe 14 has a portion, located in the expansion chamber 15, to which a catalyst 16 is disposed for performing an oxidation reaction for the purification of the exhaust gas. The air introduced from the air cleaner 11 into the combustion chamber of the engine unit, so-called primary air, is mixed with a fuel therein and the mixture is then exploded by the actuation of piston-cylinder assembly incorporated in the engine unit. The exhaust gas caused by the explosion is exhausted into the exhaust pipe 14 through the engine exhaust port, and the exhaust gas is then discharged externally through the muffler 17 after the silencing operation. In the above structure, the air cleaner 11 is communicated with the exhaust pipe 14 through connection means having suitable flexibility and rigidity such as hose means 10 and 13, and a diaphragm pump 1 is incorporated to this connection means. Namely, as shown in Fig. 1, one hose 10 extending from the air cleaner 11 is connected to an inlet port 9 of the diaphragm pump 1 at one end thereof and the other hose 13 has one end connected to an outlet port 12 of the diaphragm pump 1 and the other end connected to the exhaust pipe 14. The diaphragm pump 1 is further connected to a crank chamber 8 of the two-stroke cycle engine 7 through a hose 6 as best shown in Fig. 1. The connection of the hose 6 to the engine unit 7 can be easily made by preliminarily forming a connection hole to the engine crank chamber 8 and, in actual, the connection is carried out by fixing one end of the hose 6 to the hole of the engine unit by a proper fastening means 19 of known structure. As described above, since the diaphragm pump 1 is supported by the air cleaner 11 and the exhaust pipe through the hoses 10 and 13 having proper flexibility and rigidity, the diaphragm pump 1 can be itself easily secured to a body of an automobile such as frame member 18 thereof (Fig. 3). In preferred modifications, these hoses 10 and 13 may be connected to the inlet and outlet ports 9 and 12 through connection fittings, or nozzle members for the connection of these hoses 10 and 13 may be formed to the inlet and outlet ports 9 and 12. The structure of the diaphragm pump 1 has a structure as shown in Fig. 4 as a longitudinal section thereof. Referring to Fig. 4, the diaphragm pump 1 comprises a pump housing 20 in which an inner chamber means is defined. The inner chamber means is composed of a first pump chamber 4a, a second pump chamber 4b and a common chamber which communicates the first and second pump chambers 4a and 4b, and the common chamber is divided into a diaphragm chamber 3 and a passage chamber 4c as a portion of the pump chamber, which communicates the first and second pump chambers 4a and 4b, by means of a diaphragm 2 which is made of a thin metal film, for example. One-way valves 5a and 5b are incorporated in the inner chamber means at portions communicating the first and second pump chambers 4a and 4b with the passage chamber 4c. The first pump chamber 4a is communicated with the inlet port 9 to which the hose 10 is connected and the second pump chamber 4b is also communicated with the outlet port 12 to which the hose 13 is connected. The diaphragm chamber 3 is communicated with the crank chamber 8 through the hose 6. Reference numeral 21 denotes a gasket. According to the structure of the diaphragm pump 1 described above, the air, i.e. secondary air form the air cleaner 11 is introduced into the first pump chamber 4a through the hose 10 and the inlet port 9 and is discharged towards the exhaust pipe 14 through, in order, the first one-way valve 5a, the passage chamber 4c, the second one-way valve 5b, the second pump chamber 4b, the outlet port 12 and the hose 13. In this air flow, when the pressure variation is caused in the engine crank chamber 8 due to the explosion of the air-fuel mixture, the diaphragm 2 is oscillated because this pressure variation is transferred to the diaphragm chamber 3 through the hose 6. According to this oscillation of the diaphragm 2, the volume of the passage chamber 4c, i.e. the pump chamber, varies. When the volume of the pump chamber is increased, that is, with reference to Fig. 4, the diaphragm 2 is displaced downwardly, the secondary air is sucked into the diaphragm pump 1 through the inlet port 9 and then flows therein through the first one-way valve 5a, and when the volume of the pump chamber is then decreased, that is, the diaphragm 2 is displaced upwardly, the secondary air is exhausted into the hose 13, connected to the exhaust pipe 14, through the second one-way valve 5b and the outlet port 12. As described above, the oscillation of the diaphragm 2 becomes violent in proportion to the increasing of the engine revolution speed and, hence, the amount of the exhaust gas. Accordingly, the air supply amount from the air cleaner 11 into the exhaust pipe 14 can be precisely regulated in proportion to the engine revolution speed, that is, in accordance with the amount of the exhaust gas.

Claims: A secondary air supply system of a vehicle equipped with an engine unit (7) having a crank chamber (8) which engine also has an exhaust system including an exhaust pipe (14), comprising a diaphragm pump means (1) provided with an inner chamber means (3, 4a, 4b, 4c) and having an air inlet port (9) and an air outlet port (12) both being communicated with said inner chamber means (3, 4a, 4b, 4c), a diaphragm (2) disposed in said inner chamber means (3, 4a, 4b,4c); to divide said inner chamber means (3, 4a, 4b, 4c) into a diaphragma chamber (3) and a pump chamber (4a, 4b, 4c), a first hose means (10) connected to said air inlet port (9) to introduce secondary air into said pump chamber (4a, 4b, 4c); second hose means (13) connecting said air outlet port (12) and said exhaust pipe (14) to supply said secondary air from said diaphragm pump means (1) into said exhaust pipe (14) through said air outlet port (12; and third hose means (6), connecting said diaphragm chamber (3) and said crank chamber (8), having one open end opening into said diaphragm chamber (3) of said diaphragm pump means (1) and another open end opening into said crank chamber (8) characterized in that the engine unit is a two-stroke-cycle engine unit, that said first hose means (10) connects said air inlet port (9) and an air cleaner (11) to introduce secondary air from said air cleaner (11) into said pump chamber (4a, 4b, 4c) of said diaphragm pump means (1) through said air inlet port (9); and that said another open end of said third hose means (6) opens into said crank chamber at a location near a reed valve in a direction normal to air/fuel mixture flow at that location, which flow is controlled by said reed valve; wherein the secondary air is supplied into said exhaust pipe (14) through said diaphragm pump means (1) by an amount in proportion to an oscillation of said diaphragm (2) caused in accordance with a pressure variation in said crank chamber (8) caused in proportion to an engine revolution speed. The secondary air supply system of claim 1, wherein said diaphragm pump means (1), comprises a valve means (5a, 5b) disposed in said pump chamber (4a, 4b, 4c) for allowing the secondary air introduced into said pump chamber (4a, 4b, 4c) to flow uni-directionaly from said air inlet port (9) to said air outlet port (12). The secondary air supply system according to claim 1 or 2, wherein said pump chamber (4a, 4b, 4c) comprises a first pump chamber (4a) communicated with said air inlet port (9), a second pump chamber (4b) communicated with said air outlet port (12) and a common passage chamber (4c) connecting said first and second pump chambers (4a, 4b) and wherein said valve means (5a, 5b) comprises a first one-way valve (5a) disposed in said first pump chamber (4a) and a second one-way valve (5b) disposed in said second pump chamber (4b), said first one-way valve (5a) being operated to introduce the secondary air into said first pump chamber (4a) when said diaphragm (2) is displaced so as to increase an inner volume of said pump chamber (4a, 4b, 4c) and said second one-way valve (5b) being operated to discharge the secondary air from said second pump chamber (4b) when said diaphragm (2) is displaced so as to decrease the inner volume of said pump chamber (4a, 4b, 4c).

Inventors: KUME TAKETSUGU, KUME, TAKETSUGU
Applicants: SUZUKI CO LTD, SUZUKI KABUSHIKI KAISHA
Application year: 1991
Main classification: F01N3
IPC codes: F02B75, F01N3