Title of Invention

A THROTTLE UNIT FOR A MULTIPLE-CYLINDER ENGINE

Abstract

A bypass passage includes an inlet in communication with the upstream sides of first and second throttle valves of first and second suction passages. one valve body receiving chamber is coaxial with the inlet. First and second upstream side branch passage extend from the valve body receiving chamber. Downstream side branch passage extend from the end portions of the upstream side branch passages and are in communication with the downstream sides of the first and second throttle valve of the first and second suction passages.

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See Section 10; rule 13] "A THROTTLE UNIT FOR A MULTIPLE-CYLINDER ENGINE" HONDA GIKEN KOGYO KABUSHIKI KAISHA, a corporation of Japan, having a place of business at 1-1, Minamiaoyama 2-chome, Minato-ku, Tokyo, Japan The following specification particularly describes the invention and the manner in which it is to be performed: [Detailed Description of the Invention] [0001] [Technical Field to which the Invention Pertains] The present invention relates to a throttle unit for reducing manufacturing cost and assembling man hours and suitable for equalizing the amount of air passing through the bypass passages of throttle valves, wherein the bypass passage is provided for each throttle valve. ^[0002] [Description of the Related Art] As a throttle unit of an engine, in particular, a throttle unit provided with a fast idling mechanism in which a valve for opening or closing a bypass passage for bypassing a throttle valve is provided in the bypass passage and in which, when the engine is started, the valve is opened to supply air to the combustion chamber of the engine via the bypass passage to increase the number of revolution of the engine in idling to prevent the engine from unstably rotating during idling or from stopping, for example, the throttle unit disclosed in Japanese Patent No. 2723990 entitled "THROTTLE BODY FOR MULTIPLE-CYLINDER COMBUSTION ENGINE" is well known. FIG. 5 of the above official gazette will be shown as FIG. 7 in the following and FIG. 6 of the above official gazette will be shown as FIG. 8 in the following. In this connection, for the salce of convenience, in FIG. 7 will be shown the constitution in which a part of the constitution in FIG. 4 of the official gazette is added to FIG. 5 of the official gazette, and in FIG. 8 will be shown the main portion of FIG. 6 of the official gazette. Further, reference numerals are newly assigned. [0003], FIG. 7 is the first cross-sectional view of a conventional throttle unit and shows a state in which a throttle body 100 is provided with suction passages 101, 102, and in which the respective suction passages 101, 102 are provided with throttle valves 103, 104 (reference numeral 104 is not shown) , and in which the upstream side of the throttle valve 103 of one suction passage 101 is made to communicate with the downstream side of the throttle valve 103 of the suction passage 101 by a common bypass suction passage hole 105 and a bypass suction passage hole 106 for controlling an idling speed, which is connected to the common bypass suction passage 105, and in which an idling speed control valve 107 for opening or closing the bypass suction passage hole 106 for controlling an idling speed is disposed at the inlet of the bypass suction passage hole 106 for controlling an idling speed. 4-9004] FIG. 8 is the second cross-sectional view of the conventional throttle unit and shows a state in which a bypass suction passage hole 108 for controlling an idling speed is branched from the common bypass suction passage hole 105 (see FIG. 7) and is made to communicate with the downstream side of the throttle valve 104 of the suction passage 102, and in which an idling speed control valve 111 for opening or closing the bypass suction passage hole 108 for controlling an idling speed is disposed at the inlet of the bypass suction passage hole 108 for controlling an idling speed, and in which operating levers 112, 112 are secured to the end portions of the idling speed control valves 107, 111, and in which a link shaft 113 for opening or closing the idling speed control valves 107, 111 by one operation is mounted on the operating levers 112, 112. [PROBLEM TO BE SOLVED BY THE INVENTION] However, according to the above-mentioned technology, idling speed control valves 107, 111 are provided for each of the bypass suction passage holes 106, 108. Therefore, in addition to the idling speed control valves 107, 111, operating levers 112, 112 and parts relating to these valves are required." This increases the number of parts and manufacturing costs of the throttle unit and man hours required for assembling the throttle unit. [0006] Further, since the plurality of idling speed control valves 107, 111 are opened or closed by one link shaft 113 via the operating levers 112, 112, depending on variations in sizes the idling speed control valves 107, 111, the operating levers 112, and the link shaft 113, there is the possibility that a difference may be produced in the opening between the idling speed control valves 107, 111 to make the amount of air passing through the respective bypass suction passage holes 106 for controlling an idling speed different from the amount of air passing through the respective bypass suction passage holes 108 for controlling an idling speed, whereby the number of revolution of the engine in idling might be unstable. For this reason, the object of the present invention is to reduce the manufacturing costs and the assembling man hours of the throttle unit of an engine and to equalize the amount of air passing through the bypass passages made for each of the throttle valves. [Means for Solving the Problem] In order to accomplish the object described above, the first claim is characterized in that, in a throttle unit of an engine including suction passages from an air cleaner to the respective combustion chambers of a multiple-cylinder engine, throttle valves disposed in the respective suction passages, and bypass passages bypassing the throttle valves, the bypass passage includes an inlet of the bypass passage communicating with the upstream side of the throttle valve of the suction passage, one valve body receiving chamber coaxial with the inlet of the bypass passage, a plurality of upstream side branch passages extending from the valve body receiving chamber, downstream side branch passages extending from the end portions of the upstream side branch passages and communicating with the downstream sides of the throttle valve of the suction passage, one valve body which is movably received in the valve body receiving chamber and is moved in the valve body receiving chamber in the direction away from the inlet of the bypass passage to open the plurality of upstream side branch passages at the same opening when opening the bypass passage. In a conventional throttle unit, a bypass passage for bypassing a throttle valve is disposed in each suction passage sending air into the combustion chamber of each cylinder and a valve for opening or closing the bypass passage is disposed at each bypass passage and a link mechanism is disposed at each valve to activate the valve. For this reason, in the conventional throttle unit, parts increase in number and the manufacturing costs of the throttle unit increase and man hours required for assembling the unit increase. However, according to the present invention, a mechanism for activating the bypass valve can be simplified by reducing the number of the bypass valves of the multiple-cylinder engine to one, which can reduce the manufacturing costs and the assembling man hours of the throttle unit. Further, in the control of opening or closing the bypass passage by one valve body in the conventional throttle unit, suction air tends to be sucked into one cylinder from the other cylinder by a difference in negative pressure between the respective cylinders. However, by controlling the openings of the plurality of upstream side branch passages at the same opening, it is possible to make the total sum of the opening areas of the upstream side branch passages smaller than the passage area of the inlet side of the bypass passage at a time where the number of revolution of the engine is not more than 2000 rpm and tends to vary widely, so that it is possible to prevent the suction air from being sucked into one cylinder from the other cylinder and to reduce the effects that sucking the suction air into one cylinder from the other cylinder makes on variations in the number of revolution. Therefore, it is possible to control the number of revolution of the engine in idling with high accuracy. The second claim is characterized in that the plurality of upstream side branch passages are formed on a line crossing at right angles and passing through the valve body receiving chamber. The plurality of upstream side branch passages can be easily formed by one machining to reduce machining time and machining cost. The third claim is characterized- in that the valve body receiving chamber has a diameter larger than the inlet of the bypass passage and wherein the valve body is butted against the step-wise portion between the valve body receiving chamber and the inlet of the bypass passage to completely close the bypass passage. The above-mentioned constitution can minimize the amount of air leak when all the bypass passages are closed and can more correctly conduct a suction control except when the engine is started. The present invention relates to a throttle unit for a multiple-cylinder engine, comprising: a pluraHty of suction passages, said plurality of suction passages being extendable from an air cleaner to respective combustion chambers of the multiple-cylinder engine; a plurality of throttle valves, each of said plurality of throttle valves being disposed in said plurality of suction passages, respectively; and a bypass passage for bypassing said plurality of throttle valves, said bypass passage comprising: an inlet, said inlet being in communication with an upstream side of said plurality of throttle valves; a valve body receiving chamber, said valve body receiving chamber being coaxial with said inlet; a plurality of upstream side branch passages, each of said plurality of upstream side branch passages extending from said valve body receiving chamber; a plurality of downstream side branch passages, each of said downstream side branch passages extending from end portions of said plurality of upstream side branch passages, respectively, each of said downstream side branch passages being in communication with a downstream side of said plurality of throttle valves; and a valve body movably received in said valve body receiving chamber for opening and closing said bypass passage, said valve body being movable in a direction away from said inlet to open said plurality of upstream side branch passages at the same opening quantity when said bj^pass passage is in an open condition. [Preferred Embodiments] Preferred embodiments in accordance with the present invention will hereinafter be described in detail based on the accompanying drawings. In this connection, assume that the drawings are seen in the direction shown by reference numerals. [BRIEF DESCRIPTION OF THE DRAWINGS] [FIG. 1] FIG. 1 is a side view of an engine provided with a throttle unit in accordance with the present invention is applied. [FIG. 2] FIG. 2 is a front view of a throttle unit in accordance with the present invention. [FIG. 3] FIG. 3 is a cross-sectional view taken on a line 3 - 3 in FIG. 2. [FIG. 4] FIG. 4 is a rear view of a throttle unit in accordance with the present invention. [FIG. 5] FIG. 5 is a perspective view to show a bypass passage of a throttle unit in accordance with the present invention. [FIG, 6] FIG. 6 is a view to show the action of a bypass passage of a throttle unit in accordance with the present invention. [FIG. 7] FIG. 7 is the first cross-sectional view of a conventional throttle unit. [FIG. 8] FIG. 8 is the second cross-sectional view of a conventional thrsttle unit, FIG. 1 is a side view of an engine provided with a throttle unit in accordance with the present invention. An engine 10 is a V-type two-cylinder engine having a first cylinder block 12 and a second cylinder block 13 which are mounted on the top of a crank case 11, a first cylinder head 14 and a second cylinder head 15 which are mounted on the respective first and second cylinder blocks 12, 13, a throttle unit 18 interposed between the first and second cylinder heads 14, 15 via a first suction manifold 16 and a second suction manifold 17, and an air cleaner 21 mounted on the throttle unit 18. The first cylinder block 12 and the first cylinder head 14 are O^ the first cylinder side and the second cylinder block 13 and the second cylinder head 15 are the second cylinder side. FIG. 2 is a front view of the throttle unit in accordance with the present invention. In the throttle body 23 of the throttle unit 18 are made a first suction passage 24 communicating with the combustion chamber of the first cylinder head 14 (see FIG. 1) and a second suction passage 25 communicating with the combustion chamber of the second cylinder head 15 (see FIG. 1) . A first throttle valve 26 for controlling the rate of air passing through the first suction passage 24 is mounted in the first suction passage 24 and a second throttle valve 27 for controlling the rate of air passing through the second suction passage 25 is mounted in the second suction passage 25. A depressed portion 28 is formed in the front of the throttle body 23 (at the side of the air cleaner 21 (see FIG. 1)). In the depressed portion 28 is made an inlet 31 of a bypass passage 30 (to be described in detail below) for air bypassing the first and second throttle valves 26, 27. FIG. 3 is a cross-sectional view taken on a line 3 - 3 in FIG. 2. A valve body receiving chamber 32 continued to the inlet 31 of the bypass passage 30 is made in the throttle body 23 and receives a bypass valve 33 as a valve body for opening or closing the bypass passage 30 such that the bypass valve 33 can move, and a valve body driving mechanism 34 utilizing the expansion or contraction of wax caused by a change in the temperature of the cooling water of the engine is fixed to the bypass valve 33. Here, a reference numeral 35 designates a valve adjusting mechanism for manually adjusting the opening of the bypass valve 33 and a reference numeral 36 designates a first upstream side branch passage communicating with the valve body receiving chamber 32. In FIG. 2, a first upstream side branch passage 36 is disposed at the right side of the valve body receiving chamber 32 and a second upstream side branch passage 37 communicating with the valve body receiving chamber 32 is disposed at the left side of the valve body receiving chamber 32. In FIG. 3, the inlets of the first and second upstream side branch passages 36, 37 (reference numeral 37 is not shown) are closed by the first bypass valve 33. The valve body receiving chamber 32 is coaxial with the inlet 31 and has a diameter larger than the inlet 31 and the bypass valve 33 is pressed on the end portion 32a of the inlet 32 side of the valve body receiving chamber 32 (that is, an annular step-wise portion 32a formed by the inlet 31 and the valve body receiving chamber 32) by a spring 38 to completely close the bypass passage 30. The valve body driving mechanism 34 includes a wax-filled portion 45 which is filled with wax, a cylinder portion 46 for receiving a piston (not shown) moved by the expansion or contraction of the wax such that the piston can move, a rod 48 fixed to the piston and having the bypass valve 33 mounted at the tip by a nut 47, a case 51 mounted on a throttle body 23 so as to receive the wax-filled portion 45 and the cylinder portion 46, a sub-case 52 interposed between the case 51 and the cylinder portion 46, and the spring 38 interposed between the sub-case 52 and the bypass valve 33. In this connection, a reference numeral 54 designates a cooling water passage for flowing engine cooling water, a reference numeral 55 designates a stop ring, and a reference numeral 56 designates a spring for preventing the sub-case 52 from withdrawing. FIG. 4 is a rear view of the throttle unit in accordance with the present invention. Depressed portions 61, 62 are made at the back (at the side of the first and second suction manifolds 16, 17 (see FIG. 1) of the throttle body 23. The outlet of a first downstream side branch passage 63 communicating with the first upstream side branch passage 36 (see FIG. 2) is made in the depressed portion 61 to make the depressed portion 61 communicate with the first suction passage 24 by a groove 64, and the outlet of a second downstream side branch passage 65 communicating with the second upstream side branch passage 37 (see FIG. 2) is made in the depressed portion 62 to make the depressed portion 62 communicate with the second suction passage 25 by a groove 66. In this connection, the first suction manifold 16 is connected to the first suction passage 24 and the second suction manifold 17 is connected to the second suction passage 25. FIG. 5 is a perspective view to show the bypass passage of the throttle unit in accordance with the present invention. The bypass passage 30 includes the inlet 31 communicating with the upstream sides of the first and second throttle valves 26, 27 (see FIG. 4), for example, the inside of the first and second suction passages 24, 25 (see FIG. 4) or the inside of the air cleaner 21 (see FIG. 1); one valve body receiving chamber 32 which is coaxial with the inlet 31 and has a diameter larger than the inlet 31; the first and second upstream side branch passages 36, 37 extending from the valve receiving chamber 32; the first and second downstream side branch passages 63, 65 extending from the end portions of the first and second upstream side branch passages 35, 37 and communicating with the downstream sides of the first and second throttle valves 26, 27 of the first and second suction passages 24, 25; and one bypass valve 33 which is movably received in the valve body receiving chamber 32 and can be pressed on the end portion of the inlet 31 side of the valve receiving chamber 32 when closing the bypass passage 30 and can be moved in the valve body receiving chamber 32 in the direction thatis away from the inlet 31 when opening the bypass passage 30. In this connection, reference numerals 68, 68 designate plugs for closing the first and ,second upstream side branch passages 36, 37. According to the above constitution, it is possible to form the plurality of -first and second upstream side branch passages 36, 37 by one machining with,ease and hence to reduce machining time and machining cost. Further, since the valve body receiving chamber 32 is formed coaxially with the inlet 31, it is possible to machine the inlet 31 and the valve body receiving chamber 32 without changing the position where the throttle unit 18 (see FIG. 1) is mounted on a machine tool and hence to" reduce machining time and machining cost. The action of the bypass passage 30 described above will be described in the following. FIG. 6 (a) , (b) are views to show the action of the bypass passage of the throttle unit in accordance with the present invention. In FIG. 6(a) , when the engine is started, engine cooling water having a low temperature flows in a cooling water passage 54 as shown by an arrow This contracts the wax in the valve body driving mechanism 34 and hence pulls the bypass valve 33 in the direction shown by an arrow (2) against the elastic force of the spring 38 via the piston (not shown) and the rod 48 . As a result, the inlets of the first and second upstream side branch passages 36, 37 (reference numeral 37 is not shown) are opened. In FIG. 6(b) , when the inlets of the first and second upstream side branch passages 36, 37 are opened, the suction air flows from the upstream sides of the first and second throttle valves 26, 27 through the inlet 31 into the valve body receiving chamber 32, as shown by arrows, and branches from the valve body receiving chamber 32 into the first upstream side branch passages 36 and the second upstream side branch passages 37. Further, the suction air 37 flows from the first upstream side branch passages 36 into the first downstream side branch passages 63 and from the second upstream side branch passages 37 into the second downstream side branch passages 65 and flows from the first and second downstream side branch passages 63, 65 into the downstream sides of the first and second throttle valves 26, 27 to bypass the first and second throttle valves 26, 27. Therefore, the amount of air supplied to the respective combustion chambers of the first and second cylinders in a state where the first and the second throttle valves 26, 27 are closed is increased, whereby the number of revolution of the engine in idling can be increased. Further, in FIG. 6, when the temperature of the engine cooling water passing through a cooling water passage 54 increases, the wax in the valve body driving mechanism 34 is expanded and the elastic force of the spring 38 is added thereto to push the bypass valve 33 in the direction opposite to an arrow (D via the piston and the rod 48 to decrease the opening of the inlets of the first and the second upstream side branch passages 36, 37, whereby the rate of flow of air passing through the bypass passage 30 is gradually decreased. Further, when the temperature of the engine cooling water exceeds a predetermined value, the bypass valve 33 completely closes the inlets of the first and second upstream side branch passages 36, 37. As shown in FIG. 1, FIG. 2, and FIG. 5, the present invention is the throttle unit 18 of the multiple-cylinder engine 10 including the first and second suction passages 24, 25 extending from the air cleaner 21 to the respective combustion chambers of the engine 10, the first and second throttle valves 26, 27 disposed in the respective first and second suction passages 24, 25, and the bypass passage 30 for bypassing the first and second throttle valves 26, 27, wherein the bypass passage 30 is constituted by the inlet 31 communicating with the upstream sides of the first and second throttle valves 26, 27 of the first and second suction passages 24, 25, one valve body receiving chamber 32 coaxial with the inlet 31, the first and second upstream side branch passages 36, 37 extending from the valve body receiving chamber 32, the first and second downstream side branch passages 63, 65 extending from the end portions of the first and second upstream side branch passages 36, 37 and communicating with the downstream sides of the first and second throttle valves 26, 27 of the first and second suction passages 24, 25, and one bypass valve 33 which is movably received in the valve body receiving chamber 32 and is moved in the valve body receiving chamber 32 in the direction away from the inlet 31 to open the first and second upstream side branch passages 36, 37 at the same opening when opening the bypass passage 30. In a conventional throttle unit, a bypass passage for bypassing a throttle valve is disposed in each suction passage sending air into the combustion chamber of each cylinder and a valve for opening or closing the bypass passage is disposed at each bypass passage and a link mechanism is disposed at each valve to activate the valve. For this reason, in the conventional throttle unit, parts increase in number and man hours required for assembling the unit increase and hence manufacturing costs of the throttle unit increases. However, according to the present invention, a mechanism for activating the bypass valve 33 can be simplified by reducing the number of the bypass valves 33 of the multiple-cylinder engine 10 to one, which can reduce the manufacturing cost and the assembling man hours of the throttle unit 18. Further, in the control of opening or closing the bypass passage by one valve body in the conventional throttle unit, suction air tends to be sucked into one cylinder from the other cylinder by a difference in negative pressure between the cylinders, that is, aside from the flow of air from the upstream side of the valve body to the respective branch passages, air tends to flow from one branch passage into the other branch passage. However, according to the present invention, it is possible to control the openings of the first and second upstream side branch passages 36, 37 at the same opening by one bypass valve 33. Therefore, it is possible to make the total sum of the opening areas of the first and second upstream side branch passages 36, 37 smaller than the passage area of the inlet 31 side of the bypass passage at a time where the number of revolution of the engine is nor more than 2000 rpm and tends to vary widely, whereby air can easily flow from the inlet 31 side of the bypass passage to the first and second upstream side branch passages 36, 37 and air resists flowing from the first upstream side branch passage 36 to the second upstream side branch passage 37 or from the second upstream side branch passage 37 to the first upstream side branch passage 36. In this manner, it is possible to prevent the suction air from being sucked into one cylinder from the other cylinder, and to reduce the effects that sucking the suction air into one cylinder from the other cylinder makes on variations in the number of revolution, and to equalize the air flow between the side of the first upstream side branch passage 36 and the first downstream side branch passage 63 and the side of the second upstream side branch passage 37 and the second downstream branch passage 65. Therefore, it is possible to control the number of revolution of the engine in idling with high accuracy. Further, the present invention is characterized in that the valve body receiving chamber 32 has a diameter larger than the inlet 31 of the bypass passage and that the bypass valve 33 is butted against the step-wise portion 32a (see FIG. 3) between the valve body receiving chamber 32 and the inlet 31 of the bypass passage to completely close the bypass passage 30. The above constitution can minimize the amount of air leak from the step-wise portion 32a and the bypass valve 33 when the bypass passage 3 0 is completely closed and can more correctly conduct a suction air control except when the engine is started. In this connection, while the throttle unit in accordance with the present invention has been applied to the V-type two-cylinder engine, it is not intended to limit the present invention to this preferred embodiment, but the present invention can be applied to a V-type engine having four or more cylinders and a straight type engine or horizontal opposed-cylinder engine having two or more cylinders. In this case, inlets of the upstream side branch passages corresponding to the number of cylinders (number of bypass passages) are made in the valve body receiving chamber of the present invention. Further, while the valve body driving mechanism 34 utilizing the expansion or contraction of the wax caused by a change in the temperature of the engine cooling water is provided at the bypass valve 33 in the preferred embodiment in accordance with the present invention, it is also possible to adopt a valve body control using a step motor or the like instead of the wax or a manual operation of the valve body by the use of a wire or the like. [Effect of the Invention] The present invention can produce the following effects by the constitution described above. The throttle unit of the engine as claimed in claim 1 is a throttle unit of an engine including suction passages from an air cleaner to the respective combustion chambers of a multiple-cylinder engine, throttle valves disposed in the respective suction passages, and bypass passages bypassing the throttle valves, wherein the bypass passage includes an inlet of the bypass passage communicating with the upstream side of the throttle valve of the suction passage, one valve body receiving chamber coaxial with the inlet of the bypass passage, a plurality of upstream side branch passages extending from the valve body receiving chamber, downstream side branch passages extending from the end portions of the upstream side branch passages and communicating with the downstream sides of the throttle valve of the suction passage, one valve body which is movably received in the valve body receiving chamber and is moved in the valve body receiving chamber in the direction away from the inlet of the bypass passage to open the plurality of upstream side branch passages at the same opening when opening the bypass passage. Therefore, by reducing the number of the valve bodies of the multiple-cylinder engine to one, it is possible to simplify a mechanism for activating the valve body and hence to reduce the manufacturing cost and assembling man hours of the throttle unit. Further, in the control by one valve body, suction air tends to be sucked into one cylinder from the other cylinder by a difference in negative pressure between the respective cylinders. However, by controlling the openings of the plurality of branch passages at the same opening, it is possible to make the total sum of the opening areas of the branch passages smaller than the passage area of the inlet side of the bypass passage at a time where the number of revolution of the engine is not more than 2000 rpm and tends to vary widely, so that it is possible to prevent the suction air from being sucked into one cylinder from the other cylinder and to reduce the effects that sucking the suction air into the one cylinder from the other cylinder makes on variations in the number of revolution. Therefore, it is possible to control the number of revolution of the engine in idling with high accuracy In the throttle unit of an engine as claimed in claim 2, the plurality of upstream side branch passages are formed on a line crossing at right angles and passing through the valve body receiving chamber. Therefore, it is possible to easily form the plurality of upstream side branch passages by one machining and hence to reduce the manufacturing time and manufacturing cost. In the throttle unit of an engine as claimed in claim 3, the valve body receiving chamber has a diameter larger than the inlet of the bypass passage and the valve body is butted against the step-wise portion between the valve body receiving chamber and the inlet of the bypass passage to completely close the bypass passage. Therefore, it is possible to minimize the amount of air leak when the bypass passages are completely closed and hence to more correctly conduct the suction control except when the engine is started. [DESCRIPTION OF REFERENCE NUMERALS] 10 ... engine, 18 ... throttle unit, 21 ... air cleaner, 24, 25 ... suction passage (first suction passage, second suction passage), 26, 27 ... throttle valve (first throttle valve, second throttle valve), 30 . . . bypass passage, 31 . . . inlet of a bypass passage, 32 . . . valve body receiving chamber, 32a ... step-wise portion (end potion), 33 . . . valve body (bypass valve), 34 ... valve body driving mechanism, 36, 37 . . . upstream side branch passage (first upstream side branch passage, second upstream side branch passage) , 63, 65 ... downstream side branch passage (first downstream side branch passage, second downstream side branch passage) WE CLAIM; 1. A throttle unit (18) for a multiple-cylinder engine (10), comprising: a plurality of suction passages (24, 25), said plurality of suction passages being extendable from an air cleaner (21) to respective combustion chambers of the multiple-cylinder engine; a plurality of throttle valves (26, 27), each of said plurality of throttle valves being disposed in said plurality of suction passages, respectively; and a bypass passage (30) for bypassing said plurality of throttle valves, said bypass passage comprising: an inlet (31), said inlet being in communication with an upstream side of said plurality of throttle valves; a valve body (33) receiving chamber (32), said valve body receiving chamber being coaxial with said inlet; a plurality of upstream side branch passages(36, 37), each of said plurality of upstream side branch passages extending from said valve body receiving chamber; a plurality of downstream side branch passages(63, 65), each of said downstream side branch passages extending from end portions (32a) of said plurality of upstream side branch passages, respectively, each of said downstream side branch passages being in communication with a downstream side of said plurality of throttle valves; and a valve body movably received in said valve body receiving chamber for opening and closing said bypass passage, said valve body being movable in a direction away from said inlet to open said plurality of upstream side branch passages at the same opening quantity when said bjrpass passage is in an open condition. 2. The throttle unit(18) for a multiple-cylinder engine (10) as claimed in claim 1, wherein each of said plurality of upstream side branch passages (36, 37) have an axis crossing an axis of said valve body (33) receiving chamber(32) at generally a right angle. 3. The throttle unit (18) for a multiple-cylinder engine (10) as claimed in claim 1, wherein said valve body (33) receiving chamber (32) has a diameter larger than said inlet (31) and wherein said valve body is abutted against a stepped portion between said valve body receiving chamber and said inlet to completely close the bypass passage (30) when said valve body is in a closed position. 4. The throttle unit (18) for a multiple-cylinder engine (10) as claimed in claim 2, wherein said valve body (33) receiving chamber (32) has a diameter larger than said inlet (31) and wherein said valve body is abutted against a stepped portion between said valve body receiving chamber and said inlet to completely close the bypass passage (30) when said valve body is in a closed position. 5. The throttle unit (18) for a multiple-cylinder engine (10), substantially as hereinbefore described and illustrated with reference to the accompanjdng drawings. Dated this 27th day of August, 2001

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