An intake system for a multi-cylinder engine

Abstract

 An intake manifold with its-trunk portion (9a) connected to a carburretor (10) and with its branch portions (9b) connected to the cylinder heads (5) of the multi-cylinder engine.
In order to achieve increased output power of the engine at all levels of operation at minimized reduction of acceleration responsiveness in a low output range as well as low cost production of lightweight and simple construction, each branch portion (9b) of the intake manifold (9) is partitioned into a first (8a) and a second (8b) intake passage by a partition (9c) and control valves (12) adapted to be opened during light output operation of the engine only, are arranged in the second intake passages (8b) of all branch portions.

Description

[0001] The invention relates to an intake system for a multi-cylinder engine and contemplates to provide an engine which has such a low weight and a high output power that it is suitable for use with an automobile, and relates specifically to such an intake system for a multi-cylinder engine as can feed an air-fuel mixture from a single carburettor to a plurality of cylinders.

[0002] In most of small-sized engines for automobiles according to the prior art, both three or four cylinders arranged in straight and a downdraft type dual carburettor shared among the cylinders are connected through a banana or tournament-shaped intake manifold. In order to increase the output power of that engine to a high level or to prevent the acceleration responsiveness of the same from being deteriorated while ensuring the high output power, it is known in the art to provide each combustion chamber with two intake valves, to provide the respective intake valves with independent intake passages and to provide the respective intake passages with carburettors.

[0003] Nevertheless, such structure has its construction complicated and its weight increased, although it is excellent in performance, so that it cannot avoid industrial disadvantages such as rise in the production cost and deterioration in the fuel economy of the engine.

[0004] The present invention as claimed has been conceived in view of the background thus far described and has an object to raise the output power of the engine while minimizing the complexness in the construction and the increase in the weight.

[0005] The advantages offered by the invention are mainly that with a simple, reliable and lightweight design of a manifold system of the kind in question with branch portions partitioned into first and second intake passages and with control valves in the second intake passages an increase in the engine output power at all operational levels can be effected and the reduction in acceleration responsiveness of the engine at a low output range is minimized. Production of the intake system can be effected at low cost.

[0006] One specific embodiment of the invention will now be described with reference to the accompanying drawings in which:-

Fig. 1 is a sectional view showing the essential portion of a multi-cylinder engine with an intake system according to the invention and;

Fig. 2 is a broken top plan view showing the same portion.

[0007] Reference numeral 1 appearing in the drawings indicates a multi-cylinder engine such as a four- cylinder engine which has four combustion chambers 2. Each of the combustion chambers 2 is defined by a cylinder 3, a piston 4 and a cylinder head 5 and is connected to an intake passage 8 and an exhaust passage 13 through intake and exhaust valves 6 and 7 which are disposed in the cylinder head 5. The intake passage 8 is formed in series to lead from the cylinder heads 5 through an intake manifold 9 and a carburet cor.10. The intake manifold 9 is composed of a trunk portion 9a and four branch portions 9b branched from the trunk portion 9a. Each of the branch portions 9b is composed of first and second intake passages 8a and 8b which are partitioned at the right and left sides by a partition 9c Characters 9d indicate a hot water riser which forms the bottom of the trunk portion 9a so that it is heated to about 80°C by the cooling water of the engine to abruptly gasify the fuel droplets contained in the air-fuel mixture, when it is wetted with the latter, thereby to make uniform the air-fuel ratio of the mixture to be distributed into the respective branch portions 9b.

[0008] The carburettor 10 is of such a well known dual type as is formed with both a primary passage P having a manual throttle valve 10a and a secondary passage S having an automatic throttle valve 10b which is to be opened during a high output operation of the engine. Characters 10c indicate a main fuel injection port which is opened into a venturi portion 10e through a small venturi 10d. Numeral 11 indicates a valve drum which is sandwiched between the intake manifold and the cylinder heads 5 such that it supports butterfly type control valves 12 in openable and closable manners within the second intake passages 8b therein. The control valves 12 are connected to the actuating rod 15a of a diaphragm device 15 through an arm 14, which is fixed to the common valve stem thereof, so that they are opened and closed by the operation of the diaphragm device 15. More specifically, the diaphragm device 15 has its inside chamber defined by a casing 15b and partitioned by an elastic diaphragm 15c into two compartments, one of which provides an atmospheric compartment 15d leading to the atmosphere and the other of which provides a vacuum compartment communicating with the aforementioned venturi portion 10e through a duct 16. Characters 15f indicate a return spring which is made operative to urge said elastic diaphragm 15c toward the atmospheric compartment 15d at all times.

[0009] If the multi-cylinder engine 1 having the construction thus far described is run at a state with the manual throttle valve 10a having its idling opening or its small opening in the neighbourhood of the idling opening, the intake air is sucked from the primary passage P, because the automatic throttle valve 10 is closed in such low load range, and is admixed at the venturi portion 10e with the fuel into an air-fuel mixture, which is metered by the manual throttle valve 10a to flow into the intake manifold 9 until it is distributed into the respective branch portions 9b. Since, at this running state, the flow rate of the intake air is so small that the venturi vacuum is low (namely, the absolute pressure is high), the diaphragm device 15 has its elastic diaphragm 15c warped toward the atmospheric compartment 15d by the elastic force of the return spring 15f thereby to close the control valves 12 connected thereto. As a result, the mixture wholly reaches the intake valves 6 at a high speed through the first intake passages 3a forming a part of the intake passage 8 until it flows into the combustion chambers 2 when the intake valves 6 are opened. As a result, the mixture having its gasification promoted by the riser 9d is sucked into the combustion chambers 2 without inviting a disadvantage that the fuel is condensed again in the first intake passages 8a having a high flow speed until it wets the inner wall thereof. As a result, fluctuations in the air-fuel ratio of the mixture to be fed to the respective combustion chambers 2 are so reduced and the stability of the combustions is so excellent that a keen acceleration responsiveness can be attained.

[0010] If the manual throttle valve 10a is so widely opened as to augment the engine output power, the flow rate of the intake air to be introduced from the primary passage P is increased so that the venturi vacuum to be established in the venturi portion 10e is raised (in other words, the absolute pressure is lowered). As a result, that high venturi vacuum pressure is exerted through the duct 16 upon the vacuum compartment 15e to pull the elastic diaphragm 15d toward the vacuum compartment 15e against the elastic force of the return spring 15f so that the actuating rod 15a pulls the arm 14 thereby to open the control valves 12 to have an opening corresponding to the magnitude of the venturi vacuum.

[0011] If the manual throttle valve 10a is opened to the neighbourhood of its full opening, the automatic throttle valve 10b is also opened so that the intake air flows into not only the first intake passage 8a but also the second intake passage 8b . Since, at this time, the flow rate of the intake air is remarkably increased, the flow speeds of the intake air streams in both the intake passages 8a and 8b are so sufficiently high that the fluctuations in the air-fuel ratio in the mixture can be reduced and that a high output power can be achieved.

[0012] As has been described hereinbefore, according to the present invention, there are disposed at each of the branch portions of the intake manifold said first and second intake passages which are partitioned by the partition and the second intake passages are equipped with the control valves which are adapted to be opened only during the high output operation of the engine. As a result, during a low output operation of the engine having a low flow rate of the mixture, the control valves are closed to reduce the effective areas of the intake passages at the branch portions thereby to prevent the intake flow speed from being lowered. Thus, without changing so much the conventional construction using the dual carburettor and the intake manifold, an increase in the engine output power can be effected,, and the reduction in the acceleration responsiveness in a low output range at that time can be minimized. Moreover, since the partitions are disposed at the branch portions, there can be attained advantages that the intake manifold can be produced relatively easily and that the distribution of the mixture among the respective branch portions is made less non-uniform than in the case in which the partitions are disposed to protrude into the trunk portion of the intake manifold.

Claims

1. An intake system for a multi-cylinder engine., characterized in that an intake passage communicating with combustion chambers (2) through intake valves (6) is formed in series to lead from cylinder heads (5) through an intake manifold (9) and a carburettor (10); in that said intake passage is constructed such that in at least each branch portion (9b) of said intake manifold (9) first and second intake passages (8a, 8b) are provided for, which are partitioned by a partition (9c) and in that said second intake passage (8b) is equipped with a control valve (12) which is adapted to be opened only during a high output power operation of said engine.

2. Intake system according to claim 1, characterized in that a valve drum (11) with passages being flush with the passages (8a, 8b) in the branches (9b) of the intake manifold (9)' - is sandwiched between the intake manifold (9) and the cylinder heads (5) and in that said control valves (12) are arranged in said passages being flush with the second intake passages (8b) of all branches (9b) of the intake manifold (9).

3. Intake system according to claim 1 or 2, characterized in that a trunk portion (9a) of the intake manifold (9) is connected to a dual type carburettor (10) with a primary passage P with manual throttle valve (10a) and a secondary passage S with an automatic throttle valve (10b) arranged therein, respectively.

4. Intake system according to at least one of claims 1 to 3, characterized in that the control valves (12) are being actuated by actuation means (15, 15a) controlled by the pressure in a venturi portion (10e) of the main fuel injection part of the carburettor (10).

Drawing