Multiple throttle mechanism for internal combustion engines
Background of the Invention 
     This invention relates to a throttle mechanism in a multiple cylinder engine and, more particularly, to a multiple throttle mechanism which has air control throttle valves provided in intake manifold passages that introduces air into respective cylinders. 
     In a multiple throttle mechanism for internal combustion engines as disclosed in the Japanese Patent Laid-Open No. 28038/1984, a shaft on which throttle valves are mounted passes through the intake manifold passages and is supported by two bearings for each the intake manifold passage, so that eight bearings are required for a four-cylinder engine and twelve for a six-cylinder engine. 
     In this conventional multiple throttle mechanism with the above structure, a large frictional resistance is caused on the bearing, so that the multiple throttle mechanism requires large throttle valve drive force and cannot be put to practical use. 
     Further in this multiple throttle valve mechanism, variations in a flow rate of air flowing in each the manifold passage take place. 
     The throttle valves each are provided with an air bleed hole or notch to obtain a certain amount of initial air flow and thereby minimize variations in the air flow rate during idling. 
     The throttle valve requires a special machining to provide the initial air flow rate and this deteriorates the manufacturing efficiency. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to reduce the bearing friction acting upon a throttle shaft thereby to minimize the force required for driving throttle valves, and reduce variation in flow rate of air flowing respective engine cylinders during idling of the engine. 
     Another object of this invention is to provide a multiple throttle mechanism which can drive a plurality of throttle valves with minimized driving force and provide respective manifold passages with an initial air flow rate without performing an additional special machining on the throttle mechanism. 
     The present invention is characterized by providing a plurality of manifold blocks each of which has two or more intake manifold passages that go through one block to reduce the number of walls between the adjacent intake manifold passages and therefore the number of bearings, providing supporting throttle valves bearings only in the intake manifold block walls situated at both ends of the shaft, loosely inserting the shaft through holes in the walls that separate the adjacent intake manifold passages. 
     Further, the present invention is characterized by providing two or more intake manifold passages that go through one block to reduce the number of walls between the adjacent intake manifold passages and therefore the number of bearings, providing supporting throttle valves bearings only in the intake manifold block walls situated at both ends of the shaft, loosely inserting the shaft through holes in the walls that separate the adjacent intake manifold passages and providing air gaps between the shaft and the inner circumference of the holes to obtain the initial air flow rate thereby obtaining desired fuel air ratio during idling of the engine. The initial air flow rate is an air flow rate necessary to attain the revolution number of the engine for idling. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a multiple throttle mechanism for a four-cylinder internal combustion engine which represents one embodiment of this invention; 
     FIG. 2 is a sectional view taken along line II--II of FIG. 3; 
     FIG. 3 is a partial enlarged cross-sectional view of FIG. 1; 
     FIG. 4 is a partial vertical cross-sectional view of a multiple throttle mechanism for a six-cylinder internal combustion engine to which the invention applies; 
     FIGS. 5 and 6 are diagrams showing the measured deflection of throttle shaft; 
     FIG. 7 is a diagram showing the comparison of required shaft driving torque between a conventional multiple throttle mechanism and the mechanism of this invention; and 
     FIG. 8 is a sectional view showing a gap between a throttle shaft and a through hole. 
    
    
     Description of the Invention 
     One embodiment of this invention will now be described by referring to FIGS. 1 through 3. 
     FIG. 1 shows the structure of a fuel injection type multiple cylinder engine. Reference numeral 101 designates an air cleaner and sucked air is cleaned by a cleaner element 102. A main air intake passage 103 has a hot wire type air flow meter 104 installed in a bypass passage ina venturi portion. The main air intake passage 103 is connected to a distribution chamber 105 at a downstream end thereof. The distribution chamber 105 is connected to the upstream ends of the intake manifold passages 106a to 106d whose downstream ends communicate with the cylinders 108a to 108d of an engine block 107 through bent passages 109a to 109d. The intake manifold passages 106a to 106d are composed of straight passages 116a to 116d formed in intake manifold blocks 106A, 106B, and the bent passages 109a to 109d formed in connecting blocks 109A, 109B. 
     The straight portions 116a to 116d of the intake manifold passages 106a to 106d are provided with throttle valves 100a to 100d, respectively. The throttle valves 100a and 100b are mounted on a throttle shaft lllA that is supported on the intake manifold block 106A through bearing 123a, 123b and traverses the passages 106a and 106b at right angles. The throttle valves 100c and 100d are mounted on a throttle shaft lllB that is supported on the intake manifold block 106B through bearing 123c, 123d and traverses the straight passages 116c and 116d at right angles. These throttle valves 100a to 100d are securely fastened to the shafts lllA, lllB by set screws 120. The throttle shafts lllA and lllB are interconnected by a link mechanism 115, so that as the shaft lllB is turned by a throttle actuating member 112, the shaft lllA is also turned with the shaft lllB, causing the throttle valves 100a  to 100d to turn in the direction of an arrow A in FIG. 2. 
     Injectors 113a to 113d are provided downstream of the throttle valves 100a to 100d in the straight portions 116a to 116d of the intake manifold passages 106a to 106d. The injectors 113a to 113d are of a known electronic control type and controlled by an electronic control device such as a microcomputer 114 to control the amount of fuel to be injected. As the air flow meter 104 measures the volume of air that flows through the main air intake passage 103, it supplies the computer 114 with an electric signal representing the measured air flow rate Based on the signal from the air flow meter 104, the-number-of-revolution signal N, A/F signal from an air-fuel ratio sensor not shown, throttle valve opening signal θ, cooling water temperature signal Tw, and so on, the computer 114 calculates the amount of fuel to be injected and, according to the result of calculation, supplies control signals to each injector 113a to 113d. The injectors 113a to 113d then inject fuel into the intake manifold passages 106a to 106d according to the control signals from the computer 114. 
     A wall of the intake manifold block separating the straight passages 116a and 116b and a wall separating the straight passages 116c and 116d each are formed with a through-hole 118a, 118b through which the throttle shaft lllA lllB is loosely inserted. The same cross sectional area of a gap between the inner circumference of the through-hole and the outer circumference of the throttle shaft is formed for both shafts. As shown in FIG. 8, the gap G on the downstream side is made larger than the maximum deflection (described later) of the throttle shaft lllA lllB. 
     Now, the operation of the embodiment with the above structure will be explained in the following: 
     During engine operation, the air sucked through the air cleaner 101 into the main air intake passage 103 is distributed by the distribution chamber 105 to the intake manifold passages 106a to 106d, from which it is further led into the cylinders 108a to 108d. 
     The fuel is injected from the injectors 113a to 113d into the intake manifold passages 106a to 106d downstream of the throttle valves 100a to 100d according to the amount of air flowing through the main air intake passage 103. Thus, in the intake manifold passages 106a to 106d, the fuel is mixed with air downstream of the throttle valves 100a to 100d and the air-fuel mixture is introduced into the cylinders 108a to 108d. 
     The fuel amount variation among the intake manifold passages 106a to 106d is small because the amount of fuel injected into the intake manifold passages 106a to 106d is controlled by the computer 114 according to the amount of air sucked in through the main air intake passage 103. On the other hand, there are variations among the intake manifold passages 106a to 106d in the amount of air flowing through these passages. These are caused by variations in air distribution caused by the distribution chamber 105, variations in the opening degree of the throttle valves 100a to 100d, etc. 
     With this embodiment, however, since the air gaps 118a and 118b of the same sectional area are provided at the through-holes in the intake manifold block walls through which the throttle shafts are inserted, the amounts of air passing through the air gaps 118a and 118b are substantially equal among the intake manifold passages 106a to 106d. 
     In this type of engine, the amount of fuel injected into each of the intake manifold passages is controlled according to the total amount of air flowing through the main air intake passage. So, the variation in the amount of fuel injected into each of the intake manifold passages is small among these passages. However, the amount of air supplied into the intake manifold passages varies from one passage to another because of the air distribution variations, opening degree variations of the throttle valves, and assembly errors of the throttle valves to the throttle shaft. 
     This results in variations among the cylinders in the air-fuel ratio, which are significantly large especially when the throttle valves are closed as during idling. 
     However, with this embodiment the amount of air that flows through the air gaps 118a and 118b is substantially equal for all of the passages 106a to 106d and can be used at least as the initial air flow. This alleviates the adverse effects of the air distribution variations and of the throttle opening degree variations. As a result, the air amount variation among the passages and therefore the air-fuel ratio variation is reduced. 
     The air gaps 118a and 118b work effectively particularly when the throttle valves 100a to 100d are closed or when they are opened only to small degrees. Under such condition of the throttle valves a ratio of air flow rate from the air gap to air flow rate from the closed throttle valve is relatively large. This ratio decreases as the revolution number of the engine increases with the throttle valves being opened. 
     In the conventional multiple throttle mechanism the intake manifold passages are formed independently of each other, so that each passage requires a pair of bearings. And this means that a four-cylinder engine requires eight bearings and a six-cylinder engine twelve bearings. 
     FIG. 7 shows the relationship between the number of bearings and the torque required to rotate the throttle shaft. It is noted that the rotating torque of the throttle shaft increases with the number of bearings. In an idling condition where the throttle valves are nearly closed, suction vacuum pressure acts upon the throttle valve pressing the shaft against the bearing, so that the torque required to turn the throttle shaft increases further. 
     According to this embodiment, two or more intake manifold passages as one set are formed in the intake manifold block in such a way that their straight portions are parallel. The block wall between the adjacent intake manifold passages is a common wall for the passages. Thus, as shown in FIGS. 1 and 3, with the four-cylinder engine which has two intake manifold blocks 106A and 106B each with two intake manifold passages, the number of bearings decreases to six. Furthermore, in this embodiment, the block wall that separates the adjacent passages in the same block is formed with the throughhole through which the shaft is loosely inserted, so as to keep the shaft out of contact with the wall. This further reduces the number of bearings to two, which are installed on both sides of each block, that is, there is only four in all on the engine. This in turn results in a significant reduction in the rotation torque of the shaft. 
     To keep the throttle shaft lllA, lllB from contacting the block wall when the throttle valves are subjected to suction vacuum pressure, the air gaps 118a and 118b at the through-holes through which the shafts are loosely inserted must be determined considering the diameter of the shaft, shaft length between the bearings, and the maximum suction vacuum pressure. 
     FIG. 5 shows the deflections of the shafts at various points measured when the throttle valves are fully closed at the revolution of 800 rpm during idling with the shaft diameter of 10 mm, the throttle valve diameter of 45 mm, and the shaft length (between a and f) of 97 mm. 
     The maximum deflection of about 0.06 mm occurred at the center wall. 
     Therefore, in FIG. 8 the air gap G downstream of the shaft, that is, between the lower end of the shaft (with respect to the air flow) and the through-hole circumference needs to be made greater than 0.06 mm. As explained earlier, when this air gap is used also as a gap to provide the initial air flow amount, the air gap downstream of the shaft should be set to more than 0.06 mm and the air gaps upstream of and at each side of the shaft should be set to magnitudes necessary to obtain the initial air flow amount. Maximum air gap is 0.12 mm for an engine of displacement of 2000 cc, for example. One of the methods to attain this purpose involves making the through-hole 118 eccentric with respect to the center axis of the shaft 111. 
     Although in this embodiment the block formed with the straight passages is directly secured to the distribution chamber 105 through a gasket 105a, it is possible to interpose a connecting pipe means between the block and the distribution chamber when bent passages are required between them. 
     Furthermore, it is possible to form the connecting blocks 109A and 109B of FIG. 1 integral with the intake manifold blocks 106A and 106B. 
     FIGS. 4 and 6 show a case where the straight portions of three intake manifold passages 106a to 106f are formed as one set in each intake manifold block for the six-cylinder engine. A pair of throttle shafts lllA, lllB each are provided with throttle valves 100a to 100f and supported by the intake manifold block through bearings 123a to 123d. The shafts, lllA, lllB are interlocked by a link mechanism 115 and driven by a throttle actuating member 112. The shafts lllA, 111B turns to an initial position by spring 116A, 116B. 
     In this case, for the shaft length (between a and e) of 150 mm, the maximum deflection of 0.09 mm occurred at the central point C. But since the maximum deflection at each intermediate wall is about 0.08 mm, the gap G may be set to 0.08 mm. In this example, the number of bearings is reduced from the ordinary 12 to four with a significant desirable effect on the shaft rotation torque. 
     While in the above embodiment the intake manifold passages 106a to 106f are formed in two blocks, it is possible to form four straight passages in one block for the four-cylinder engine or six straight passages in one block for the six-cylinder engine, provided the problems with the shaft and bearing strength have been resolved. 
     As explained above, this embodiment supports the throttle shaft on four bearings and therefore can keep the shaft torque constant regardless of the number of the cylinders as shown in FIG. 7. 
     If all the intake manifold passages are formed in one block and structured in a manner similar to this embodiment, the bearing is needed at only two locations with further reduction in the shaft torque. 
     In the above embodiments, an air gap is provided around the shaft extending through the block walls to secure the initial air flow and to allow for the shaft deflection. If, however, a separate means for securing the initial air flow is provided, the bearing may be installed in the block walls where the air gap is formed. In this case also, the number of bearings is smaller than that in the conventional structure and the effect of this invention can be had. 
     According to the invention as explained in the foregoing, the number of bearings mounted in the multiple throttle mechanism can be reduced, with the resultant reduction in the shaft torque. Further, since the openings in the block walls through which the throttle shaft of the multiple throttle mechanism is inserted are made larger than the shaft diameter, it is possible to provide the initial air flow rate without any additional special machining process and to provide fuel air mixture of a desirable fuel air ratio during idling of the engine.