V-Type Engine

1. Field of the Invention

This invention relates to an intake system for a V-type engine, and more particularly to an intake system for a V-type engine which is arranged for supercharing by the kinetic effect of intake air.

2. Description of the Prior Art

Various multiple-cylinder engines are known which are arranged to increase the volumetric efficiency, and thereby the engine output torque, by the kinetic effect of intake air. For example, in the multiple-cylinder engine disclosed in Japanese Pat. Publication No. 60(1985)-14169, the cylinders are divided into first and second cylinder groups so that the cylinders in each cylinder group do not fire one after another, and the cylinders in the first and second cylinder groups are respectively connected to first and second intake passages, each of which comprises an enlarged volume chamber to which discrete intake passages are connected at the upstream side ends, and a resonance intake passage connected to the enlarged volume chamber. The upstream end of each resonance intake passage is communicated with an upstream side junction, and the enlarged volume chamber is provided with a switching means for selectively bringing the first and second intake passages into communication with each other or interrupting communication therebetween. When communication between the first and second intake passages is interrupted, negative pressure waves generated by the intake strokes in each cylinder are reflected at the upstream side junction as positive pressure waves, and an inertia supercharging effect is obtained by the positive pressure waves at relatively low engine speed ranges. On the other hand, when the first and second intake passages are communicated with each other, the negative pressures are reflected nearer the intake port than when communication between the intake passages is interrupted, whereby the natural frequency of the intake pressure oscillation is increased, and an inertia supercharging effect is obtained at higher engine speed ranges.

Further, supercharging can be effected by a resonance tuning effect by connecting the cylinders in each cylinder group (the cylinders which do not fire one after another) to an intake passage which has having no enlarged volume chamber, like a surge tank, and by selecting the length of the intake passage so that the resonant frequency of the intake air in the intake passage conforms to a particular engine speed range.

Based on the concepts used in such conventional intake systems, it would be expected to supercharge a V-type engine by the resonance effect of intake air by arranging the firing order so that the cylinders in each cylinder bank do not fire one after another, by communicating the cylinders in each cylinder bank by way of a resonance communicating passage and by connecting the resonance communicating passages for the respective cylinder banks to an intake air supply passage so that intake air resonates in the resonance communicating passages and the intake air supply passage.

The frequency of oscillation of the intake air depends upon the effective length of the intake passage. In order to obtain a sufficient supercharging effect by the kinetic effect of the intake air at low engine speed ranges, the intake passage must be long. However, the size of the intake system of an engine carried by a vehicle is naturally limited by the space allotted to the engine.

In view of the foregoing observations and description, the primary object of the present invention is to provide an intake system for a V-type engine in which an intake passage of a length sufficient to obtain an excellent supercharging effect by the kinetic effect of intake air at low engine speed ranges can be provided without substantially adding to the overall size of the engine.

In the intake system of the present invention, the cylinders in one of the cylinder banks are connected to a first communicating passage and the cylinders in the other cylinder bank are connected to a second communicating passage. The cylinders in each cylinder bank do not fire one after another. First and second intake air supply passages are connected to the first and second communicating passages at positions near one end of the communicating passages and extend toward the other end of the communicating passages.

With this arrangement, the overall size of the intake system can be minimized for the effective length of the intake passages for the respective cylinder banks since the first and second intake air supply passages extend in a folded fashion over the first and second communicating passages. Accordingly, the effective length of the intake passage can be made longer and the supercharging effect by the kinetic effect of intake air can be obtained at low engine speed ranges without substantially increasing the overall size of the intake system.

FIG. 1 is a schematic view showing a V-6 engine provided with an intake system in accordance with an embodiment of the present invention,

FIG. 2 is a side view of the engine,

FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1,

FIG. 4 is a schematic view showing the whole intake system of the engine, and

FIG. 5 shows a graph of the relation between the opening and closing of the butterfly valves and the engine speed, and a graph of the relation between the volumetric efficiency and the engine speed.

FIGS. 1 to 4, a V-6 engine 1 comprises a cylinder block 2 and left and right cylinder heads 3 and 4 mounted on the cylinder block 2 to form left and right cylinder banks 1a and 1b. The V-6 engine 1 is provided with a fuel injection system. The engine 1 has No.1 to No.6 cylinders 5a to 5f which respectively fire in this order. No.1, No.3 and No.5 cylinders 5a, 5c and 5e are formed in the left cylinder bank 1a from the front (the left side as seen in FIGS. 1 and 2) to the rear, and No.2, No.4 and No.6 cylinders 5b, 5d and 5f are formed in the right cylinder bank 1b from the front to the rear. That is, the cylinders in each cylinder bank do not fire one after another.

The cylinders 5a to 5f are connected to an intake passage 8 which, like a surge tank, has no enlarged volume chamber and to an exhaust passage 20 with which the cylinders 5a to 5f are communicated through respective exhaust ports 21.

The intake passage 8 includes first and second communicating passages 10 and 11. The cylinders 5a, 5c and 5e in the left cylinder banks 1a are connected to the first communicating passage 10 through respective discrete intake passages 9 which open to the cylinders through intake ports 9a, whereby the cylinders 5a, 5c and 5e are communicated with each other through the first communicating passage 10. The cylinders 5b, 5d and 5f in the right cylinder bank 1b are connected to the second communicating passage 11 through respective discrete intake passages 9 which open to the cylinders through intake ports 9a, whereby the cylinder 5b, 5d and 5f are communicated with each other through the second communicating passage 11. First and second intake air supply passages 12 and 13 are respectively connected to the first and second communicating passages 10 and 11 at the respective downstream ends. The first and second intake air supply passages 12 and 13 are merged into a common intake air supply passage 30 at the respective upstream ends. A pair of throttle valves 14 and 15 are respectively disposed in the first and second intake air supply passages 12 and 13 near the junction of the common intake air supply passage 30. An airflow meter 31 and an air cleaner 32 are disposed in the common intake air supply passage 30. The first and second communicating passages 10 and 11 are respectively defined in first and second communicating pipes 10a and 11a which are formed integrally with the cylinder heads 3 and 4, respectively, by casting, and extend in the longitudinal direction of the engine. The first and second intake air supply passages 12 and 13 are respectively defined in first and second intake air supply pipes 12a and 13a, which extend linearly in the longitudinal direction of the engine. The first and second communicating pipes 10a and 11a and the first and second intake air supply pipes 12a and 13a are accommodated in the space between the left and right cylinder banks 1a and 1b.

The first intake air supply pipe 12a linearly extends between the left and right cylinder banks 1a and 1b, curves downward at the front end portion thereof, and is connected to the first communicating pipe 10a at a position between the junction of the first communicating pipe 10a of the discrete intake passage 9 for No.1 cylinder 5a and that of the discrete intake passage 9 for No.3 cylinder 5c. Similarly, the second intake air supply pipe 13a linearly extends between the left and right cylinder banks 1a and 1b, curves downward at the front end portion thereof, and is connected to the second communicating pipe 11a at a position between the junction of the second communicating pipe 11a of the discrete intake passage 9 for No.2 cylinder 5b and that of the discrete intake passage 9 for No.4 cylinder 5d. That is, each of the intake air supply pipes 12a and 13a is connected to the corresponding communicating pipe at a location near the front end of the communicating pipe and extends rearward

The first and second communicating passages 12 and 13 are connected to each other by a third communicating passage 16 immediately downstream of the throttle valves 14 and 15. The third communicating passage 16 is defined as a u-shaped third communicating pipe 16a which is disposed below the first and second intake air supply pipes 12a and 13a and extends in a vertical plane with the right portion directed downward (FIGS. 2 and 3). A pair of first switching valves (butterfly valves in this particular embodiment) 17 are provided in the third communicating passage 16 respectively at the junctions of the third communicating passage 16 with the first and second intake air supply passages 12 and 13 to selectively communicate the first and second intake air supply passages 12 and 13 with each other or break the communication therebetween. Further, the first and second communicating passages 10 and 11 are connected with each other by a fourth communicating passage at their respective rear ends. The fourth communicating passage 18 is defined as a U-shaped fourth communicating pipe 18a which is disposed between the first and second intake air supply pipes 12a and 13a and the first and second communicating passages 10 and 11 and extends in a horizontal plane with the right portion directed forward (FIGS. 1 and 2). A pair of second switching valves (butterfly valves in this particular embodiment) 19 are provided in the fourth communicating passage 18 respectively at the junctions of the fourth communicating passage 18 with the first and second communicating passages 10 and 11 to selectively communicate the first and second communicating passages 10 and 11 with each other or break the communication therebetween.

As shown in FIG. 5, when the engine speed falls within a given low range, both the first and second switching valves 17 and 19 are closed. When the engine speed falls within an intermediate engine speed range, the first switching valves 17 are opened and the second switching valves remain closed, and when the engine speed falls within a high engine speed range, both the first and second switching valves 17 and 19 are closed.

In order to arrange the engine compactly, it is important to make each discrete intake passages 9 a size which will not produce an inertia tuning effect in the working engine speed range. For this purpose, the inertia tuning engine speed N.sub.I of each discrete intake passage 9 is set to be higher than the maximum engine speed Nmax. The inertia tuning engine speed N.sub.I of each discrete intake passage 9 is represented by the following formula:

wherein ##EQU1## , .theta. represents the intake valve opening time, .nu. 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 intake passage, and Vm represents the mean volume of the combustion chamber during the intake stroke.

When the engine speed falls within a low engine speed range, the switching valves 17 and 19 are closed to break the communication between the first and second intake air supply passages and between the first and second communicating passages 10 and 11. In this state, a negative pressure wave, which is generated near the intake port 9a for each cylinder in each cylinder bank at the beginning of the intake stroke of the cylinder, propagates upstream through the corresponding communicating passage (10 or 11) and the corresponding intake air supply passage (12 or 13) and is reflected as a positive pressure wave at the junction of the intake air supply passages 12 and 13. The positive pressure wave acts on the same cylinder at the end of the intake stroke to supercharge the cylinder by the inertia effect of the intake air.

When the engine speed becomes higher than a predetermined value and falls within an intermediate engine speed range, the first switching valves 17 are opened and the second switching valves 19 kept closed. When the first switching valves 17 are opened and the first and second intake air supply passages 12 and 13 are communicated with each other through the third communicating passage 16 downstream of the junction of the first and second intake air supply passages 12 and 13, a negative pressure wave, which is generated near the intake port 9a for each cylinder in each cylinder bank at the beginning of the intake stroke of the cylinder, propagates upstream through the corresponding communicating passage (10 or 11) and the corresponding intake air supply passage (12 or 13) and is reflected as a positive pressure wave at the junction of the corresponding intake air supply passage and the third communicating passage 16. Since the distance from the cylinders of the junction of the intake air supply passages 12 and 13 to the third communicating passage 16 is shorter than that of the junction of the intake air supply passages 12 and 13, the distance along which the pressure wave propagates is shortened which increases the resonant frequency of intake air. This permits the positive pressure wave to act on the cylinder at the end of the intake stroke to supercharge the cylinder by the inertia effect of the intake air in the intermediate engine speed range.

When the engine speed falls within the high engine speed range, both the first and second switching valves 17 and 19 are opened. When the first and second switching valves 17 and 19 are opened, the first and second intake air supply passages 12 and 13 are communicated with each other through the third communicating passage 16, and the first and second communicating passages 10 and 11 are communicated with each other through the fourth communicating passage 18. In this state, a positive pressure wave generated near the intake port 9a for each cylinder in each cylinder bank is propagated in opposite directions along the circular passage formed by the first and second communicating passages 10 and 11, the first and second intake air supply passages 12 and 13 and the third and fourth communicating passages 16 and 18, and acts on the intake ports for the other cylinders in the same cylinder bank, thereby supercharging the cylinders by the resonance tuning effect on the intake air.

Thus in this embodiment, the volumetric efficiency for each cylinder can be improved to increase the engine output power over a wide engine speed range from low engine speed ranges to high engine speed ranges as shown in FIG. 5.

In this embodiment, the downstream end of the first intake air supply passage 12 is connected to the first communicating passage 10 at a position between the junction of the first communicating passage 10 of the discrete intake passage 9 for No.1 cylinder 5a and the discrete intake passage 9 for No.3 cylinder 5c, and the downstream end of the second intake air supply passage 13 is connected to the second communicating passage 11 at a position between the junction of the second communicating passage 11 of the discrete intake passage 9 for No.2 cylinder 5b and the discrete intake passage 9 for No.4 cylinder 5d, and the intake air supply passages 12 and 13 extend rearward above the first and second communicating passages 10 and 11 and parallel thereto. This arrangement greatly contributes toward a compact arrangement for the whole intake system. Further, the effective length of the intake passage for each cylinder, i.e., the sum of the length of each of the first and second communicating passages 10 and 11 and the corresponding intake air supply passage, can be made sufficient to obtain an excellent supercharging effect at low engine speed ranges without substantially enlarging the overall size of the intake system.

Further, since the third communicating passage 16 is disposed below the intake air supply passages 12 and 13, and since the fourth communicating passage 18 is disposed between the first and second communicating passages 10 and 11 and the first and second intake air supply passages 12 and 13, the lengths of third and fourth communicating passages can be accommodated in relatively narrow spaces.

Further, since the communicating passages 10, 11, 16 and 18, and the intake air supply passages 12 and 13 are disposed between the cylinder banks la and lb, the dead space between the cylinder banks can be efficiently utilized. Further, by forming the communicating pipes 10a and 11a (which define the first and second communicating passages 10 and 11) integrally with the cylinder heads 3 and 4, the intake system can be yet more compactly arranged.

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 V-type engines.