Intake system for internal combustion engine

Abstract: An intake system for a V-type engine having a plurality of cylinders disposed in each of left and right cylinder banks (L, R) has a central surge tank (11) which is disposed above the space between the left and right cylinder banks and communicates with the atmosphere through a common intake passage, and left and right surge tanks (12, 13) which are respectively disposed above the left and right cylinder banks. Communicating passages (31) connect the central surge tank (11) with the left and right surge tanks (12, 13), and discrete intake passages (15) communicate the left and right surge tanks (12, 13) with the cylinders. At least one of the communicating passages on each side of the central surge tank (11) is disposed between the discrete intake passages (15) on the side of the central surge tank.

Description: This invention relates to an intake system for a V-type engine, the intake system having the features stated in the preamble of claim 1. In a known intake system of this type (JP-A 60-156 926) three surge tanks are respectively provided above the respective cylinder banks and above the space between the cylinder banks. The central surge tank above the space between the cylinder banks communicates with the atmosphere by way of a common intake passage the downstream end portion of which is connected to one end of the central surge tank. The central surge tank further communicates with the lateral surge tanks above the cylinder banks via a respective communicating passage extending right from that end of the central surge tank which forms the junction with the common intake passage. The lateral surge tanks above the cylinder banks communicate with the cylinders in the respective opposite cylinder bank through discrete intake passages which are relatively long to form low engine speed intake passages. The central surge tank communicates with the cylinders in the respective cylinder banks through discrete intake passages which are relatively short to form high engine speed intake passages and which are provided with control valves. In the low engine speed range the control valves are closed, and intake air introduced into the lateral surge tanks above the cylinder banks via the respective communicating passage flows into the cylinders through the low engine speed intake passages. In the low engine speed range an inertia effect of the intake air corresponding to the equivalent length of each of the low engine speed intake passages is obtained. In the high engine speed range the control valves are opened and intake air is partly introduced into the cylinders through the central surge tank and the high engine speed intake passages and partly introduced into the cylinders through the lateral surge tanks and the low engine speed intake passages. In the high engine speed range an inertia effect of intake air corresponding to the equivalent length of each of the high engine speed intake passages is obtained. In the low engine speed range, when the control valves are closed, substantially only the surge tanks above the cylinder banks function as such, while the central surge tank is substantially out of function because it is connected with the two lateral surge tanks by said communicating passages only at its end forming the junction with the common intake passage. In order to avoid any undue increase of the overall size of the engine, particularly of the engine height, the surge tanks above the cylinder banks must he kept fairly small in volume. This might induce the risk of intake air interference. The greater the volume of the surge tank is, the better it is in order to suppress such intake air interference. GB-A 21 21 473 discloses an intake system for a V-type engine having a first surge tank located above the space between the cylinder banks and feeding into a second surge tank, which is implicitly located above one of the cylinder banks, via a communicating passage. This communicating passage is located between discrete intake passages which feed the cylinders from the second surge tank. Since the discrete passages feeding one bank of cylinders are longer than those feeding the other bank, the one bank of the V-type engine will need to be tuned differently to the other so as to achieve inertia supercharging. This requires additional attention and expense in the design of the engine. SUMMARY OF THE INVENTION In view of the foregoing observations and description, the primary object of the present invention is to provide an intake system of the type stated in the first part of claim 1 in which the effective volume of the surge tank can be increased without substantially increasing the overall size, particularly the height, of the engine. This object is achieved by the structure stated in the characterizing portion of claim 1. Since the three surge tanks are operatively integrated with each other by the plurality of communicating passages and function as a single surge tank having a large volume, accordingly, the intake air interferences is effectively suppressed. Further since at least one of the communicating passages is disposed between the discrete intake passages, the overall size of the engine is not substantially increased. It is preferred that the overall cross-sectional area of the communicating passages be as large as possible since if the overall cross-sectional area of the communicating passages is small, resonance which can adversely affect the charging efficiency in the high engine speed range can be generated. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view showing an intake system in accordance with an embodiment of the present invention with the lid of the first surge tank removed, Figure 2 is a side view of the intake system, Figure 3 is a cross-sectional view taken along line III-III in Figure 1, Figure 4 is a cross-sectional view taken along line IV-IV in Figure 1, Figure 5 is a plan view showing an intake system in accordance with another embodiment of the present invention with the lid of the first surge tank removed, Figure 6 is a cross-sectional view taken along line VI-VI in Figure 5, and Figure 7 is a cross-sectional view taken along line VII-VII in Figure 5. DESCRIPTION OF THE PREFERRED EMBODIMENT In Figures 1 to 4, a V-6 engine provided with an intake system in accordance with an embodiment of the present invention has a cylinder block 1, and left and right cylinder heads 2 and 3 which respectively form left and right cylinder banks L and R. Three cylinders which form combustion chambers 6 together with pistons (not shown) are formed in each of the cylinder heads 2 and 3. Cylinder head covers 4 and 5 are mounted on the respective cylinder heads 2 and 3. Each cylinder is provided with an intake port 7 and an exhaust port 8. Each intake port 7 opens to the space between the cylinder banks L and R, and each exhaust port 8 opens in the outer side of the cylinder bank. A rectangular first surge tank 11 extends in the direction of the cylinder row above the space between the cylinder banks L and R. Second and third surge tanks 12 and which are rectangular extend in the direction of the cylinder row above the respective cylinder banks L and R. The second surge tank 12 above the left cylinder bank L communicates with the intake ports 7 in the right cylinder bank R through discrete intake passages 15, and the third surge tank 13 above the right cylinder bank R communicates with the intake ports in the left cylinder bank L through discrete intake passages 15. Each discrete intake passage 15 extends from the inner side of the corresponding surge tank in the direction perpendicular to the cylinder row and has an intermediate portion 15a which extends along the lower surface of the first surge tank 11. The discrete intake passages 15 are at substantially regular intervals in the direction of the cylinder row. Each discrete intake passage 15 is connected to the first surge tank 11 at the intermediate portion 15a through a bypass passage 16 which is provided with a butterfly on-off valve 17. Three on-off valves 17 in the three discrete intake passages 15 connected to the cylinders in each cylinder bank are connected with each other by a shaft 18. The shafts 18 are driven by an actuator 19 which operates under intake vacuum. Each discrete intake passage 15 is provided with a fuel injector 21 at the intake port side end portion thereof. A throttle body 22 provided with a throttle valve 23 is connected to one end of the first surge tank 11. The second surge tank 12 communicates with the first surge tank 11 through three communicating passages 31, and also the third surge tank 13 communicates with the first surge tank 11 through three communicating passages 31. The three discrete intake passages 15 and the three communicating passages 31 on each side of the first surge tank 11 alternate with each other as viewed from above as clearly shown in Figures 1 and 4. In a low engine speed range, the actuator 19 closes the on-off valves 17. Accordingly, intake air introduced into the first surge tank 11 through the throttle body 22 flows into the second and third surge tanks 12 and 13 and then into the respective combustion chambers 6 through the discrete intake passages 15 and the intake ports 7. In the low engine speed range, inertia effect of intake air corresponding to the sum of the equivalent lengths of each discrete intake passage 15 and each intake port 7 is obtained. In a high engine speed range, the actuator 19 closes the on-off valves 17. Accordingly, a part of intake air introduced into the first surge tank 11 through the throttle body 22 flows into the second and third surge tanks 12 and 13 and then into the respective combustion chambers 6 through the discrete intake passages 15 and the intake ports 7, and the other part of the intake air flows into the intermediate portions 15a of the discrete intake passages 15 through the bypass passages 16 and then into the respective combustion chambers 6 through the downstream side end portions of the discrete intake passages 15 and the intake ports 7. In the high engine speed range, there is obtained inertia effect of intake air corresponding to the sum of the equivalent lengths of each bypass passage 16, the end portion of each discrete intake passage 15 downstream of the intermediate portion 15a and each intake port 7 which is shorter than the sum of the equivalent lengths of each discrete intake passage 15 and each intake port 7. In this embodiment, the first surge tank 11 communicates with each of the second and third surge tanks 12 and 13 through three communicating passage 31. Accordingly, the three surge tanks 11, 12 and 13 are operatively integrated with each other to function as a single surge tank having a large volume, and the intake air interference is effectively suppressed and the inertia effect of intake air is enhanced. Further since two of the three communicating passages 31 are disposed between the discrete intake passages 15, the overall size of the engine is not substantially increased. Figures 5 to 7 show a V-6 engine provided with an intake system in accordance with another embodiment of the present invention. In Figures 5 to 7, the parts analogous to the parts shown in Figures 1 to 4 are given the same reference numerals and will not be described here. In this embodiment, the bypass passages 16 are not provided, and two of the three communicating passages 31 on each side of the first surge tank 11 are provided with butterfly on-off valves 41 at the first surge tank side end portions thereof. In this particular embodiment, the central communicating passage 31 on each side of the first surge tank 11 is not provided with the on-off valve. The on-off valves 41 which are disposed on opposite sides of the first surge tank 11 at one end of the cylinder row are connected to a first actuator 43 by way of shafts 42. The on-off valves 41 which are disposed on opposite sides of the first surge tank 11 at the other end of the cylinder row are connected to a second actuator 44 by way of shafts 42. The first and second actuators 43 and 44 operate under intake vacuum. In a low engine speed range, the first and second actuators 43 and 44 close all the on-off valves 41. Accordingly, intake air introduced into the first surge tank 11 through the throttle body 22 flows into each of the second and third surge tanks 12 and 13 only through the central communicating passage 31, and then into the combustion chambers 6 through the discrete intake passages 15 and the intake ports 7. In the low engine speed range, inertia effect of intake air corresponding to the sum of the equivalent lengths of each discrete intake passage 15 and each intake port 7 is obtained. In an intermediate engine speed range, the first actuator 43 opens the on-off valves 41 at said one end of the cylinder row and the second actuator 44 closes the on-off valves 41 at said the other end of the cylinder row. In the intermediate engine speed range, the effective volume of the surge tank is increased since the three surge tanks 11, 12 and 13 are integrated by the four communicating passages 31 (two on each side of the first surge tank 11), and accordingly the intake air interference is effectively suppressed and the inertia effect of intake air is enhanced. Further resonance effect of intake air can be obtained among the three surge tanks 11 to 13 by way of the four communicating passages 31, which further improves the charging efficiency in the intermediate engine speed range. In a high engine speed range, the first and second actuators open all the on-off valves 41. Accordingly, the effective volume of the surge tank is further increased since the three surge tanks 11, 12 and 13 are integrated by the six communicating passages 31 (three on each side of the first surge tank 11), and the intake air interference is more effectively suppressed and the inertia effect of intake air is further enhanced. Further resonance effect of intake air can be obtained among the three surge tanks 11 to 13 by way of the six communicating passages 31, which further improves the charging efficiency in the high engine speed range. Though, in the embodiments described above, the actuators operate under intake vacuum, they may be electrically driven under the control of a control unit which receives a signal from an engine speed sensor and outputs a control signal to the actuator.

Claims: An intake system for a V-type engine having a plurality of cylinders disposed in each of left and right cylinder banks (L, R), comprising a central surge tank (11) which is disposed above the space between the left and right cylinder banks and communicates with the atmosphere through a common intake passage, left and right surge tanks (12, 13) which are respectively disposed above the left and right cylinder banks, discrete intake passages (15) which communicate the left and right surge tanks with the cylinders, whereby discrete intake passages (15) extending from the left surge tank (12) communicate with cylinders in the right cylinder bank (R) and discrete intake passages (15) extending from the right surge tank (13) communicate with the cylinders in the left cylinder bank (L) and whereby the discrete intake passages (15) are connected with the respective sides of the left and right surge tanks which face the central surge tank, and communicating passages (31) which connect the central surge tank (11) with the left and right surge tanks (12, 13) thereby extending from the left and right side faces, respectively, of the central surge tank toward and connected with the respective sides of the left and right surge tanks which face the central surge tank, characterized in that a plurality of communicating passages (31) are provided for each of the left and right surge tanks (12, 13) and in that at least one of the communicating passages (31) on each side of the central surge tank is disposed between the discrete intake passages (15). An intake system as defined in claim 1, characterized in that the central surge tank (11) communicates with each of the discrete intake passages (15) through a bypass passage (16) which opens to the discrete intake passage at an intermediate portion (15a) of the discrete intake passage, and each of the bypass passages (16) is provided with an on-off valve (17) which is opened in a high engine speed range. An intake system as defined in claim 2, characterized in that the on-off valves (17) in the bypass passages (16) connected to the discrete intake passages (15) which communicate the cylinders in the same cylinder bank are arranged in a row and driven by a shaft (18). An intake system as defined in any of claims 1 to 3, characterized in that each of the left and right surge tanks is connected with the central surge tank by a number of communicating passages (31) which is equal to the number of cylinders in the cylinder bank (L, R) below the respective left and right surge tank (12, 13). An intake system as defined in claim 4, characterized in that the communicating passages (31) and the discrete intake passages (15) on each side of the central surge tank alternate with each other. An intake system as defined in claim 1 and any of claims 4 and 5, characterized in that at least one of the communicating passages (31) is provided with an on-off valve (41). An intake system as defined in claim 6, characterized in that three cylinders are provided in each of the left and right cylinder banks (L, R), and the communicating passages (31) communicating with each of the left and right surge tanks (12, 13) are three in number, two of the three communicating passages being provided with on-off valves (41) and the two on-off valves being both closed in a low engine speed range, one of the two on-off valves being opened in an intermediate engine speed range, and the two on-off valves being both opened in a high engine speed range.

Inventors: FUKADA HIROTAKA C O MAZDA MOTO, MATUBARA NOBUYUKU C O MAZDA MO, OKASAKO YASUHIRO C O MAZDA MOT, TANAKA FUSATOSHI C O MAZDA MOT, FUKADA, HIROTAKA C/O MAZDA MOTOR CORPORATION, MATUBARA, NOBUYUKU C/O MAZDA MOTOR CORPORATION, OKASAKO, YASUHIRO C/O MAZDA MOTOR CORPORATION, TANAKA, FUSATOSHI C/O MAZDA MOTOR CORPORATION
Applicants: MAZDA MOTOR, MAZDA MOTOR CORPORATION
Application year: 1990
Main classification: F02B27
IPC codes: F02B27, F02M35, F02B75