INTAKE SYSTEM FOR MULTIPLE-CYLINDER ENGINE

Abstract: An intake system for a multiple-cylinder engine has first and second branch passages (7a, 7b), a plurality of discrete intake passages (5) for connecting the cylinders (2a-2f) to one of the first and second branch passages (7a, 7b), an intake air supply passage (10), an upstream side communicating passage (8) for communicating the first and second branch passages with each other and with the downstream end of the intake air supply passage (10), and a downstream side communicating passage (9) for communicating the downstream side ends of the first and second branch passages (7a, 7b) with each other. The firing order is set so that the cylinders (2a-2f) connected to each of the branch passages (5) do not fire one after another. The first and second branch passages (7a-7b) and the upstream side and downstream side communicating passages (8, 9) forming a circular passage (6) for supercharging the engine by resonance tuning effect of intake air. The downstream side communicating passage (9) is provided with a cross-sectional area changing means (14) for changing the effective cross-sectional area of the downstream side communicating passage (9) according to the engine speed to increase the effective cross-sectional area of the downstream side communicating passage (9) with increase in the engine speed.

Description: Intake system for a multiple-cylinder engine This invention relates to an intake system for a multiple-cylinder engine, and more particularly to an intake system for a multiple-cylinder engine which is arranged to be supercharged by a resonance tuning effect of intake air. There are known various multiple-cylinder engines having intake systems which are designed in such a way that the volumetric efficiency of the engine is increased by a kinetic effect of the intake air. For example, the intake system according to JP-A 60(1985)-14169 utilizes an inertia supercharging effect for this purpose. Another known multiple-cylinder engine (JP-A 59(1984)-565) has an intake system including a plenum type intake manifold and a plurality of ram type intake pipes. Further, supercharging can be effected by a resonance tuning effect by connecting the cylinders in each cylinder group (whereby the cylinders fire alternately in the groups) to an intake passage having no enlarged volume chamber like a surge tank and by selecting the length of the intake passage so that the resonant frequency of intake air in the intake passage conforms to a particular engine speed range. When supercharging an engine utilizing the resonance of the intake air in the resonance intake passage, the resonance frequency of intake air is determined mainly depending upon the effective length of the resonance intake passage. Accordingly, in order to obtain an excellent supercharging by a resonance tuning effect of the intake air in a low engine speed range, the intake passage must be long. This is undesirable from the standpoint of designing the engine as compact as possible. JP-A 61-138824 discloses an intake system for a multiple-cylinder engine wherein, in order to increase an inertial suction effect, a surge tank is divided by a partition so as to provide two branch passages wherefrom a plurality of discrete intake passages extend for connecting the cylinders to one of the first and second branch passages. At the downstream end of the branch passages there is provided, within the surge tank, a butterfly valve which is actuatable by a mechanism controlled by low pressure in a vacuum chamber. The vacuum obtaining in the vacuum chamber is controlled in such a way that it is substantially in reverse proportion to the rotational speed of the engine so that the butterfly valve is opened at high engine speed and is closed at low engine speed, whereby intermediate positions of the butterfly valve may be achieved by controlling the low pressure in the vacuum chamber to a corresponding intermediate low pressure. In another known intake system (US-A 4527392) there are provided two manifold passages which are interconnected by a bypass passage for changing the tuning point for inertia supercharging. The bypass passage has a bypass valve disposed therein which is actuatable by an actuator operable in response to the depression of an accelerator pedal. Thus the bypass valve is open when the engine speed is high, while the bypass valve is closed at increased engine load. There is known a further intake system for a multiple-cylinder engine (JP-A 61-155618) which includes a surge tank and a resonant box for each of two cylinder groups. Each of the resonant boxes is communicated with the surge tank by means of a plurality of resonant tubes which are disposed in parallel to each other. The number of the tubes in communication between the resonant box and the surge tank is selected in response to the operational conditions of the engine, whereby valves controlling the opening and closing of the resonant tubes are opened when the engine speed increases. In view of the foregoing observations and description, the primary object of the present invention is to provide an intake system for a multiple-cylinder engine which can smoothly increase the engine output torque from the low engine speed range to the high engine speed range by a resonance tuning effect of intake air and, at the same time, allows for a sufficiently compact arrangement of the engine. This object is achieved by the intake system defined in patent claim 1. The present invention is based on the fact that the resonance frequency of the intake air can be changed by changing the length of the resonance passage. That is, as the cross-sectional area of the resonance passage reduces, the resistance to the pressure wave increases and the velocity of propagation thereof is lowered, whereby the resonance frequency is shifted toward the low engine speed range. Accordingly, by changing the cross-sectional area of the resonance passage according to the engine speed, the peak of the engine output torque can be shifted according to the engine speed, thereby obtaining smooth torque characteristics. Further, in order to obtain high engine output by the resonance tuning effect at the maximum engine speed, the intake system is designed in such a way that the shorter passage resonance tuning engine speed at full opening of the butterfly valves is lower than 1,2 times the maximum engine speed and higher than 0,7 times the maximum engine speed. Thereby the shorter passage resonance tuning engine speed is defined as the resonance tuning engine speed of the shorter one of the passage between the junction of the upstream-most discrete intake passage in one of the cylinder banks to the corresponding branch passage and the junction of the ring passage to the intake air supply passage, and the passage between the junction of the downstream-most discrete intake passage in the cylinder bank to the same branch passage and the middle of the downstream side communicating passage. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view showing a V-6 engine provided with an intake system in accordance with an embodiment of the present invention, Figure 2 shows a relation between the opening of the butterfly valves and the engine speed, and a relation between the mean effective pressure and the engine speed in the engine shown in Figure 1, Figure 3A and 3B are schematic views for illustrating an example of valve means which can be employed in the present invention, Figure 4A and 4B are schematic views for illustrating an example of valve means which can be employed in the present invention, Figure 5 is a view similar to Figure 2 but for the intake system provided with the valve shown in Figures 3A and 3B or Figures 4A and 4B, Figure 6 is a schematic view showing a modification of the intake system shown in Figure 1, Figure 7 is a schematic view showing another modification of the intake system shown in Figure 1, and Figure 8 shows engine output torque-engine speed characteristics for various values of the shorter passage resonance tuning engine speed N R . DESCRIPTION OF THE PREFERRED EMBODIMENTS In Figure 1, a V-6 engine having a fuel injection system (not shown) is provided with No. 1 to No. 6 cylinders 2a to 2f which fire in this order. No. 1, No. 3 and No. 5 cylinders 2a, 2c and 2e are formed in a first cylinder bank 1a and No. 2, No. 4 and No. 6 cylinders 2b, 2d and 2f are formed in a second cylinder bank 1b. That is, the cylinders in each cylinder bank do not fire one after another. Each of the cylinders 2a to 2f is provided with an intake port 3 and an exhaust port (not shown), and the intake ports 3 of the respective cylinders 2a to 2f are connected to an intake passage 4. The intake passage 4 has no enlarged volume chamber such as a surge tank and comprises an intake air supply passage 10 for introducing intake air by way of an air cleaner 11, an airflow meter 12 and a throttle valve 13, a ring passage 6 connected to the downstream end of the intake air supply passage 10, and discrete intake passages 5 for communicating the respective cylinders 2a to 2f with the ring passage 6. The ring passage 6 comprises a first branch passage 7a to which the discrete intake passages 5 for the cylinders in the first cylinder bank 1a are connected, a second branch passage 7b to which the discrete intake passages 5 for the cylinders in the second cylinder bank 1b are connected, an upstream side communicating passage 8 which connects the upstream side ends of the first and second branch passages 7a and 7b and is connected to the downstream end of the intake air supply passage 10 at the middle between the upstream side ends of the first and second branch passages 7a and 7b, and a downstream side communicating passage 9'which connects the downstream side ends of the first and second branch passages 7a and 7b. Both the upstream side communicating passage 8 and the downstream side communicating passage 9′ are longer than the passage length between junctions of adjacent discrete intake passages 5 for the cylinders in each cylinder bank to the corresponding branch passage 7a or 7b, e.g., the passage length between No. 1 cylinder 2a and No. 3 cylinder 2c. A positive pressure wave generated near the intake port 3 for each cylinder in the each cylinder bank at the end of the intake stroke is propagated along the circular passage 6 in opposite directions and acts on the intake ports for the other cylinders in the same cylinder bank, thereby supercharging the cylinders by resonance tuning effect of intake air. The downstream side communicating passage 9′ comprises first and second communicating passages 9′a and 9′b extending in parallel to each other between the downstream side ends of the first and second branch passages 7a and 7b, the second communicating passage 9′b being larger than the first communicating passage 9′a in cross-sectional area. A pair of first butterfly valves 14′a are provided in the first communicating passage 9′a to be opened and closed in synchronization with each other, one near the junction of the downstream side communicating passage 9′ to the first branch passage 7a and the other near the junction of the same to the second branch passage 7b. Further, a pair of second butterfly valves 14′b are provided in the second communicating passage 9′b to be opened and closed in synchronization with each other in positions-corresponding to the first butterfly valves 14′a. As shown in Figure 2, the first butterfly valves 14′a are closed by the control unit 31, in the low engine speed range lower than a first preset speed N1 and are fully opened when the engine speed exceeds the first preset speed N1. The second butterfly valves 14′b are closed when the engine speed is lower than a second preset speed which is higher than the first preset speed and are fully opened in the high engine speed range higher than the second preset speed. In the low engine speed range lower than the first preset speed N1, both the first and second butterfly valves 14′a and 14′b are closed and accordingly, the downstream side communicating passage 9′ is completely closed. In this state, negative pressure wave generated near the intake port 3 for each cylinders in each cylinder bank at the beginning of the intake stroke of the corresponding cylinder propagates upstream through the upstream side communicating passage 8 and is reflected into positive pressure wave at the junction of the ring passage 6 to the intake air supply passage 10, and the positive pressure wave acts on the same cylinder at the end of the intake stroke to supercharge the cylinder by inertia effect of intake air. The intake system of this embodiment is arranged so that the mean effective pressure in each cylinder (corresponding to the engine output torque) reaches a peak in the low engine speed range lower than the first preset speed N1 in such an inertia tuning supercharging state as shown by the solid line in Figure 2. When the engine speed exceeds the first preset speed N1, the ring passage 6 is opened and a positive pressure wave generated near the intake port 3 for each cylinder in the each cylinder bank is propagated along the ring passage 6 through the upstream side communicating passage 8 and the downstream side communicating passage 9′ in opposite directions and acts on the intake ports for the other cylinders in the same cylinder bank, thereby supercharging the cylinders by resonance tuning effect of intake air. However, in the intermediate speed range between the first and second preset speeds N1 and N2, the downstream side communicating passage 9′ opens only through the first communicating passage 9′a and the resistance to the pressure wave is relatively high, and accordingly, the resonance tuning supercharging effect becomes maximum in the intermediate speed range as shown by the broken line in Figure 2. On the other hand, in the high engine speed range higher than the second preset speed, both the first and second communicating passages 9′a and 9′b are opened and the resistance to the pressure wave is relatively low, and accordingly, the resonance tuning supercharging effect becomes maximum in the high engine speed range as shown by the chain line in Figure 2. Thus the output torque characteristic is switched among three characteristics according to the engine speed range, and by the combination of the three characteristics, smooth torque characteristic can be obtained in totality. Though, in the embodiment described above, each of the first and second communicating passages 9′a and 9′b is provided with a pair of butterfly valves at the junctions of the communicating passage to the first and second branch passages 7a and 7b, each communicating passage may be provided with only one butterfly valve at the middle between the junctions as shown by the chain line in Figure 1. Further, though, in the embodiment described above, butterfly valves are used as the means for opening and closing the ring passage 6, other various valve means can be used. For example, honeycomb type shutter valves such as shown in Figures 3A and 3B, and 4A and 4B may be used. The shutter valve shown in Figures 3A and 3B comprises a disk-like valve body 40 which is mounted on the downstream side communicating passage 9″ by way of a housing 41 to be slidable into and away from the downstream side communicating passage 9″. The downstream side communicating passage 9″ is divided into three sections 9″a, 9″b and 9″c. The valve body 40 is moved into the downstream side communicating passage 9″ pushed by an actuator rod 42 to close the passage 9″ and is moved in the reverse direction under the force of a return spring 43. The shutter valve shown in Figures 4A and 4B comprises a disk-like valve body 50 to be pivoted about a shaft 51 into and away from the downstream side communicating passage 9″ to close and open the communicating passage 9″. The position of the valve body 50 is controlled by stepping motor 52 which connected to the shaft 51 by way of gears 53. The opening of the shutter valve shown in Figures 3A and 3B or 4A and 4B is changed according to the engine speed as shown in Figure 5, and the peak of the mean effective pressure in each cylinder is shifted with the change of the opening of the shutter valve as shown in Figure 5. Thus an effect similar to the embodiment shown in Figure 1 can be obtained. In the modification shown in Figure 6, the downstream side communicating passage 9″′ comprises first to third sub-passages 9″′a, 9″′b and 9″′c, and a sector valve body 61 is mounted for rotation in the downstream side communicating passage 9″′. The sector valve body 61 is driven by a stepping motor 62 by way of gears 63 among a first position in which it closes all the sub-passages 9″′a, 9″′b and 9″′c of the downstream side communicating passage 9″′, i.e., completely closes the downstream side communicating passage 9″′, a second position in which it opens only the first sub-passage 9″′a, a third position in which it opens both the first and second sub-passages 9″′a and 9″′b, and fourth position in which it opens all the sub-passages 9″′a, 9″′b and 9″′c. In the fourth position, the sector valve body 61 is accomodated in a recess 64 formed on a side of the passage 9″′ not to interfere with propagation of the pressure wave. In the modification shown in Figure 7, a plate-like valve body 71 is used in lieu of the sector valve body 61 in the modification shown in Figure 6. The plate-like valve body 71 is pivoted about a shaft 72 among a first position in which it closes all the sub-passages 9″′a, 9″′b and 9″″c of the downstream side communicating passage 9″′, i.e., completely closes the downstream side communicating passage 9″′, a second position in which it opens only the first sub-passage 9″′a, a third position in which it opens both the first and second sub-passages 9″′a and 9″′b, and fourth position in which it opens all the sub-passages 9″′a and 9″′b and 9″′c. In the fourth position, the sector valve body 71 is accomodated in a recess 65 formed on a side of the passage 9″′ not to interfere with propagation of the pressure wave. In order to compactly arrange the engine, it is important to size each discrete intake passage 5 not to produce an inertia tuning effect in the working engine speed range. For this purpose, the inertia tuning engine speed N I of each discrete intake passage is set to be higher than the maximum engine speed Nmax. The inertia tuning engine speed N I of each discrete intake passage 5 is represented by the following formula: represents the intake valve opening time, ν represents the natural frequency, a represents the sonic speed, f represents the mean cross-sectional area of the discrete intake passage, ℓ represents the mean length of the discrete intake passage, and Vn represents the mean volume of the combustion chamber during the intake stroke. Further, in order to obtain high engine output by resonance tuning effect at the maximum engine speed Nmax, it is preferred that the shorter passage resonance tuning engine speed N R , when the butterfly valves 14′a, 14′b are fully opened, be lower than 1.2 × Nmax and higher than 0.7 × Nmax, the shorter passage resonance tuning engine speed N R being defined in this specification as the resonance tuning engine speed of the shorter one of the passage between the junction of the upstream-most discrete passage in one of the cylinder banks to the corresponding branch passage (7a or 7b) and the junction Y of the ring passage 6 to the intake air supply passage 10 and the passage between the junction of the downstream-most discrete passage in the cylinder bank to the same branch passage and the middle X of the downstream side communicating passage 9, the former being indicated at L1 and the latter being indicated at L2 in Figure 1. The shorter passage resonance tuning engine speed N R is represented by the following formula: N R = 120 × ν R /m, wherein ν R represents the resonance natural frequency and is equal to a/4 × [1/(V R /F + L + D)], L, F and D respectively represent the length, the mean cross-sectional area and the mean diameter of the shorter one of said passages, m represents the number of the cylinders in each cylinder bank, and V R represents the volume of the dotted portion in Figure 1, i.e.,the volume of the intake passage between the junction of the upstream-most discrete intake passage to the branch passage and the junction of the downstream-most discrete intake passage to the branch passage including the volume of all the discrete intake passages connected to the branch passage. Engine output torque-engine speed characteristics were detected for various values of V R , i.e., the shorter passage resonance tuning engine speed N R . Figure 8 shows the result. As can be understood from Figure 8, when the shorter passage resonance-tuning engine speed N R is not higher than 0.7 Nmax or not lower than 1.2 Nmax, engine output torque cannot be sufficiently high as compared with the case of common intake systems with neither inertia tuning effect nor resonance tuning effect represented by curve A in Figure 8. In this embodiment, the resonance tuning frequency is changed according to the engine speed by changing the cross-sectional area of the ring passage 6. This is advantageous in compactly arranging the engine over an intake system in which the resonance tuning frequency is changed by changing the length of the intake system. Further, the valves for changing the cross-sectional area of the ring passage 6 (the butterfly valves 14′a, 14′b) are disposed in the downstream side communicating passage 9′ in this embodiment. This is advantageous over the case where the valves are disposed in the upstream side communicating passage 8 in that flow of intake air introduced through the intake supply passage 10 and the upstream side communicating passage 8 is not affected by opening and closure of the valves. Though, in the embodiments described above, the intake system of the present invention is applied to a V-6 engine, the intake system of the present invention may also be applied to other multiple-cylinder engines.

Claims: 1. An intake system for a multiple-cylinder engine having a plurality of cylinders (2a..2f) comprising first and second branch passages (7a, 7b), a plurality of discrete intake passages (5) for connecting the cylinders to one of the first and second branch passages, an intake air supply passage (10), an upstream side communicating passage (8) for communicating the first and second branch passages with each other and with the downstream end of the intake air supply passage, and a downstream side communicating passage (9′,9″,9″′) for communicating the downstream side ends of the first and second branch passages with each other, the firing order being set so that the respective cylinders connected to the first branch passage (7a) fire alternately with the cylinders connected to the second branch passage (7b), and the first and second branch passages and the upstream side and downstream side communicating passages (8; 9′,9″, 9″′) forming a ring passage for supercharging the engine by resonance tuning effect of intake air, whereby said downstream side communicating passage is provided with a cross-sectional area changing means (14a, 14b; 61, 71) for switching the effective cross-sectional area of the downstream side communicating passage among at least a full closed state, a part opening state and a full opening state according to the engine speed to increase the effective cross-sectional area of the downstream side communicating passage with increase in the engine speed, characterized in that said downstream side communicating passage (9′,9″, 9″′) comprises a plurality of sub-passages (9′a, 9′b; 9″a, 9″b...;9″′a, 9″′b...) separated by partition walls,whereby said cross-sectional area changing mean's includes a valve means (14′a, 14′b; 61, 71) which selectively opens and closes the sub-passages so that the number of the opened sub-passages increases with increase in the engine speed and in that the tuning engine speed N I of each discrete intake passage (5), the maximum engine speed N max and the shorter passage resonance tuning engine speed N R , which is the resonance tuning engine speed of the shorter one of the passage portion (L1) between the junction of the upstream-most discrete intake passage in one of the cylinder banks to the corresponding branch passage (7a, 7b) and the junction (Y) of the ring passage to the intake air supply passage (10) and the passage portion (L2) between the junction of the downstream-most discrete intake passage in the cylinder bank to the same branch passage (7a, 7b) and the middle (X) of the downstream side communicating passage, satisfy the relations N I > N max and 0,7 N max < N R < 1,2 N max . 2. An intake system as defined in claim 1 in which said multiple-cylinder engine is a V-type engine having first and second cylinder banks (1a, 1b), the cylinders in the first cylinder bank being connected to the first branch passage by way of the discrete intake passages and the cylinders in the second cylinder bank being connected to the second branch passage by way of the discrete intake passages. 3. An intake system as defined in claim 1 in which said valve means is a rotary valve (61) positioned at the one ends of the partition walls. 4. An intake system as defined in claim 1 in which each of said sub-passages is provided with a shutter valve (14′a, 14′b).

Inventors: HATTORI, TOSHIHIKO MAZDA MOTOR CORP., HITOMI, MITSUO MAZDA MOTOR CORP., YAMASHITA, AKINORI MAZDA MOTOR CORP., YUZURIHA, YASUHIRO MAZDA MOTOR CORP.
Applicants: MAZDA MOTOR CORPORATION
Application year: 1988
Main classification: F02B27
IPC codes: F02B75, F02B27