EP0092595B1

EP0092595B1 - An intake system for a multi-cylinder engine

Info

Publication number: EP0092595B1
Application number: EP82103523A
Authority: EP
Inventors: Keiichi Sugiyama
Original assignee: Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd
Priority date: 1982-04-26
Filing date: 1982-04-26
Publication date: 1987-11-04
Also published as: EP0092595A1

Description

The invention relates to an intake system for a multi-cylinder engine of the type as indicated in the precharacterizing clause of claim 1.
A multi-cylinder engine of this type is known from GB-A-20 11 537. Said prior art multi-cylinder internal combustion engine has a main intake passage communicating through an intake valve with a combustion chamber and an auxiliary intake passage opening to the main intake passage in the vicinity of the intake port through a nozzle which is of smaller cross-sectional area than the main intake passage and is directed toward the combustion chamber.
This conventional design improves fuel economy under idling and part-load engine operation. Under wide open throttle conditions, however, this prior art design exhibits some demerits, one of which being a remarkable loss of power at maximum rate of intake airflow. This power loss is effected since both airflows interfere with each other having different velocity, different mass rate or flow etc.
From US-A-4174 686, an internal combustion is known having a primary and a secondary intake passage for each cylinder, the passages opening to the combustion chamber through a common intake port. A substantially radially extending partition plate is disposed at the intake port so as to separate the two passages, one from the other, when the intake valve is closed.
It is the object of the present invention to overcome the demerits of the prior art and in particular, to provide an intake system for a multi-cylinder engine which makes it possible to increase the output power of the engine at all levels of operation, including the output power of the engine whilst minimizing the complexity of the construction and the increase in weight.
In accordance with the invention, the first and second intake passages are formed by means of a partition wall which, beginning at the trunk portion of the manifold, ends at the valve stem guide portion of the cylinder head, dividing said first and second intake passages along their whole length.
The inventive design results in that each pressure differential of the two induction passages are identical. Therefore, the two intake airflows have the same velocity and have the same rate of flow, resulting in the desired increased output power. Moreover, the intersection angle of the two intake passages is practically zero.
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.

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 carburettor 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. As shown in Figs. 1 and 2, the partition wall 9c ends at the valve stem guide portion of the cylinder head.
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 15e 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.
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 10b is closed in such a 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 8a 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 the 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.
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.
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 not only into 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 sufficiently high that the fluctuations in the air-fuel ratio in the mixture can be reduced and a high output can be achieved.
As has been described hereinbefore, according to the present invention, the first and second intake passages are formed by means of a partition wall which, beginning at the trunk portion of the manifold, ends at the valve stem guide portion of the cylinder head, dividing said first and second intake passages along their whole length. The second intake passages are equipped with the respective 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 preventing the intake flow speed from being lowered. Thus, without changing the conventional construction so much 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 can be minimized at that time. Since the partitions are disposed at the branch portions, the advantages can be attained that the intake manifold can be produced relatively easily and that the distribution of the mixture along the respective branch portions is made less non-uniform in the case where the partitions are disposed to protrude into the trunk portion of the intake manifold.

Claims

1. An intake system for a multi-cylinder engine with intake passages each of which communicates with a respective combustion chamber (2), through a respective intake valve in the cylinder head and is connected by branch portions (9b) of a manifold (9) to a common trunk portion (9a) of said manifold (9) to which fuel air mixture from a carburettor (10) is supplied, each of the intake passages comprising a first intake passage (8a) and a second intake passage (8b); each of the second intake passages (8b) being equipped with a control valve (12) which is adapted to be opened only during a high output power operation of said engine, and the intake valves (6) being mounted in valve stem guide portions of the cylinder head (5), characterized in that said first and second intake passages (8a, 8b) are formed by means of a partition wall (9c) which, beginning at the trunk portion (9a) of the manifold, ends at the valve stem guide portion of the cylinder head, dividing said first and second intake passages (8a, 8b) along their whole length.

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 the 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 one of claims 1 to 3, characterized in that the control valves (12) are 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).