Internal combustion engine
When viewed from the upper face of a cylinder head in which an intake port communicating with a combustion chamber of an internal combustion engine is formed, a starting point of the port is defined as a point of intersection of the streamline of the intake port and an inlet-side opening plane of the intake port as projected on a horizontal plane, and an end point is defined as a point of intersection of the streamline of the port and the center axis of an intake valve as projected on the horizontal plane. The starting point is located closer to the center of the chamber than a straight line that contains the end point and extends in a direction orthogonal to the axis of the crankshaft on the plane, and the streamline of the port projected on the horizontal plane is curved toward the center of the chamber, with respect to a straight line that contains the starting point and extends in a direction orthogonal to the axis of the crankshaft on the plane.
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1. Field of the Invention
The invention relates to an internal combustion engine, and in particular to an internal combustion engine in which a whirling airflow formed in a combustion chamber can be intensified even when a valve lift of intake valves is in a small to middle range.
2. Description of the Related Art
Various intake port designs have been proposed for the purpose of improving the manner in which intake air flows into a combustion chamber. For example, it has been proposed in Japanese Patent Application Publication No. 10-169453 (JP-A-10-169453) to provide a direct injection type internal combustion engine having intake ports that are inclined inwards, i.e., toward each other, such that the distance between two intake ports becomes gradually smaller as they get closer to the combustion chamber. In the direct injection type engine thus constructed, two tumble flows from the two intake ports join together so that strong turbulence is formed at around the ignition plug while a fuel-air mixture having a rich air-fuel ratio is formed at around the ignition plug, whereby the engine can operate in a lean-burn mode with improved reliability. It has also been proposed in Japanese Patent Application Publication No. 09-236043 (JP-A-09-236043) to provide a cylinder head of an internal combustion engine having upright ports that are curved in the axial direction of a camshaft so as to secure spacing between the upright ports and inner pivots for swing arms. In the cylinder head of the engine in which the swing arms of the inner pivot type and the upright ports are both provided, the space available for formation of the upright ports is greatly restricted. Even in this case, deterioration of the intake air efficiency or other problems due to the space restrictions can be minimized.
In the meantime, technologies for producing whirling airflows, such as tumbles or swirls, in cylinders of the engine are known in the art. By causing the engine of this type to produce a whirling airflow having an increased intensity, it may be possible to expand a lean-burn region in which the engine is operable in a lean-burn mode and improve the output performance. In this regard, the manner of introducing the intake air into the cylinder is one of the important factors in producing a high-intensity whirling airflow. With this background, technologies for improving the manner of introducing the intake air into the cylinder have been proposed in Japanese Patent Application Publication No. 07-279751 (JP-A-07-279751) and Japanese Utility Model Application Publication No. 59-135335 (JP-U-59-135335).
In order to produce a high-intensity whirling airflow in the cylinder, it is necessary to design intake ports so as to achieve the optimum intake-port shape or arrangement that satisfies this requirement. However, the whirling airflow is intensified typically when the valve lift of the intake valves is mainly in a middle to high range.
In
When the valve lift of the intake valve is in a small to middle range, in particular, a valve stem portion, for example, of the intake valve becomes a major obstacle to flow of the intake air since the mainstream of intake air normally has no particular directional characteristics, namely, the mainstream is not caused to flow in any particular direction. Thus, a whirling airflow formed in the combustion chamber, if any, is not always intensified as desired when the valve lift is in a small to middle range. Therefore, some room for improvements remains in the degree of mixing of the fuel-air mixture required for reducing emissions, such as HC and CO, and lessening deterioration of the fuel economy, frame propagation characteristics required for improvement of combustion during cold start or lean-burn operation, and the combustion speed required for preventing knocking. Nevertheless, no particular guidelines or schemes have been presented for designing the intake ports so that the whirling airflow can be favorably intensified even in the small to middle range of the valve lift.
Another problem encountered when intake air flows into the cylinder is that the intake air interferes with the stem of the intake valve and is thus split into streams, whereby an intended flow of intake air cannot be formed in the combustion chamber. In this respect, when the intake valve is lifted largely, a large amount of intake air is intensely introduced into the cylinder, and therefore, a high-intensity whirling airflow is relatively easily produced in the cylinder even in the presence of the above problem. However, it is difficult to produce a whirling airflow having a sufficiently high intensity solely from the flow of intake air at the time when the intake valve is lifted high. It is thus necessary to improve the manner of introducing the intake air into the cylinder when the valve lift of the intake valve is in a small to middle range, so as to produce a whirling airflow having a sufficiently high intensity.
With the background as described above, it has been proposed in JP-A-07-279751 as identified above to offset the opening of the intake port, along with the intake valve, to the outer side of the combustion chamber, thereby to form a large quantity of intake airflow directed to the middle of the combustion chamber and draw the intake air toward the middle of the combustion chamber. According to the technology proposed in the above-identified publication, therefore, it may possible to improve the manner of introducing the intake air into the cylinder when the valve lift of the intake valve is in a small to middle range. With this technology, however, the intake air is split into branch streams by the stem of the intake valve, thus still leaving a large amount of intake air that does not flow toward the middle of the combustion chamber, which makes it difficult to provide a whirling airflow having a sufficiently high strength. Also, with the proposed technology, the intake air may be concentrated too much at around the middle of the combustion chamber when the intake valve is in a middle- to high-lift region, and the intake air flowing into the cylinder may hit against the wall of the cylinder at an excessively high velocity, which may result in a reduction of the intensity of the whirling airflow produced in the cylinder.
SUMMARY OF THE INVENTIONThe present invention was developed in view of the above-described problems. Thus, it is an object of the invention to provide an internal combustion engine wherein intake ports are designed so that a whirling airflow produced in a combustion chamber can be intensified even when the valve lift of intake valves is in a small to middle range, and wherein the intake air can be introduced into the cylinder in a favorable manner so as to produce a whirling airflow in the cylinder, from the time when the valve lift of the intake valves is in a small to middle range.
According to one aspect of the invention, there is provided an internal combustion engine including an intake port that communicates with a combustion chamber, and an intake valve having an umbrella portion and a stem connected at one end thereof to the umbrella portion, wherein the intake port has a starting point that is a first point of intersection of a streamline of the intake port and an inlet-side opening plane of the intake port, and an end point that is a second point of intersection of the streamline of the intake port and a center axis of the intake valve, as viewed from an upper face of a cylinder head in which the intake port is formed, the first and second points of intersection being projected on a horizontal plane. In this internal combustion engine, the streamline of the intake port projected on the horizontal plane is curved toward a center of the combustion chamber so as to be at least partially located closer to the center of the combustion chamber than a first straight line that contains the starting point and extends in a direction orthogonal to an axis of a crankshaft on the horizontal plane, and a second straight line that contains the end point and extends in a direction orthogonal to the axis of the crankshaft on the horizontal plane.
While the positional relationship between the starting point and the end point may vary widely in designing the intake port, the intake air drawn into the combustion chamber through the intake port flows outwards, or straight, or inwards, depending upon the design of the intake port. In the internal combustion engine having the above-described intake port design, the intake air flowing into the combustion chamber is given an increased directional characteristic due to the curved shape, so that the intake air is more likely to flow in a particular direction. Thus, even when the valve lift of the intake valve is in a small to middle range, a whirling airflow produced in the combustion chamber can be intensified.
In the internal combustion engine as described above, the starting point may be located closer to the center of the combustion chamber than the second straight line.
When the intake port is designed so that the starting point and the end point are positioned as described above, the intake air that flows through the intake port normally tends to be directed outwards as a whole when flowing into the combustion chamber, as shown in
In the engine as described above, the starting point may lie on the second straight line.
When the intake port is designed so that the starting point and the end point are positioned as described above, the intake air that flows through the intake port normally tends to flow straight into the combustion chamber. In the internal combustion engine having the curved intake-port design as described above, on the other hand, the mainstream of intake air can be directed in the manner as described above, and therefore, a whirling airflow produced in the combustion chamber can be intensified even when the valve lift of the intake valve is in a small to middle range.
In the engine as described above, the starting point may not be located closer to the center of the combustion chamber than the second straight line.
When the intake port is designed so that the starting point and the end point are positioned as described above, the intake air that flows through the intake port normally tends to be directed inwards as a whole when flowing into the combustion chamber. In the internal combustion engine having the curved intake-port deign as described above, the directional characteristic of the intake air can be enhanced (i.e., the intake air is further likely to be directed inwards), and therefore, a whirling airflow produced in the combustion chamber can be intensified even when the valve lift of the intake valve is in a small to middle range.
Thus, in the internal combustion engine as described above, the whirling airflow produced in the combustion chamber can be intensified even when the valve lift of the intake valve is in a small to middle range.
In a preferred embodiment of the invention, the intake valve is a specific intake valve in which the stem is offset such that an inner passage region located closer to the center of the combustion chamber, out of two intake-air passage regions on the opposite sides of a plane that contains a center axis of the stem, becomes larger, and such that the center axis of the stem does not contain a center of a bottom face of the umbrella portion.
In the engine according to the preferred embodiment as described above, the intake air that is about to flow into the combustion chamber toward the middle thereof is more likely to be prevented from interfering with the stem of the intake valve, thereby to form an increased quantity of intake-air flow toward the middle of the combustion chamber when the valve lift of the intake valve is in a small to middle range. Thus, the intake air can be introduced into the cylinder in a favorable manner so as to form a whirling airflow in the cylinder, from the time when the valve lift of the intake valve is in a small to middle range.
The preferred embodiment as described above is different from the technologies proposed in JP-A-07-279751 and JP-U-59-135335 as identified above, in that the stem is offset in the manner as described above, in view of the object of the invention to improve the manner of flowing of intake air from the time when the valve lift of the intake valve is in a small to middle range, and the level of the necessity to accomplish the object. In this respect, the stem of the intake valve is conventionally formed, in view of the strength and the ease in machining, such that the center axis of the stem contains the center of the bottom face of the umbrella portion, and the stem extends in a direction perpendicular to the bottom face. As compared with the case where the location of the intake valve is changed along with the position of the opening of the intake port so as to improve the manner of flowing of intake air without offsetting the stem, for example, it is advantageous or preferable to offset the stem in terms of the increased freedom in changes. In this respect, too, the manner in which the intake air flows into the cylinder can be more favorably improved in the engine as described above.
While the plane that contains the center axis of the stem is not necessarily limited to a single plane provided that the plane can divide the intake-air passage region into the inner side and outer side of the stem with respect to the combustion chamber, this plane is specified as a plane that divides the intake-air passage region into the inner side and the outer side with respect to the combustion chamber so that the mainstream of intake air that flows into the cylinder so as to produce a whirling airflow in the cylinder is mainly contained in the inner passage region. In this respect, in the engine in which the intake port is formed so as to produce a tumble flow as a whirling airflow in the cylinder, if the plane that contains the center axis of the stem is further made parallel to the axis of the cylinder, the mainstream of intake air is mainly contained in the inner passage region, and therefore, the intake air that is about to flow into the cylinder toward the middle of the combustion chamber is more likely to be prevented, with higher reliability, from interfering with the stem.
The above statement that “the inner passage region becomes larger” means that the inner passage region becomes larger as compared with the case where a conventional intake valve is provided in which the stem is not offset as in the preferred embodiment. In this respect, where the conventional intake valve in which the stem is not offset is provided in the engine in which the intake port is formed so as to produce a tumble flow in the cylinder, the intake-air passage region is usually supposed to be substantially equally divided into an inner passage region and an outer passage region by a plane parallel to the axis of the cylinder. In the preferred embodiment, therefore, the stem of the specific intake valve is offset such that, more specifically, the inner passage region becomes larger than the other region, i.e., the outer passage region.
The stem of the specific intake valve as indicated above may be offset to an upstream side with respect to the center of the specific intake valve, in a direction of flow of intake air.
As a specific method for offsetting the stem of the specific intake valve so as to improve the manner in which the intake air flows into the cylinder, the stem may be offset in a direction perpendicular to the direction of flow of intake air as viewed in a horizontal projection plane, and may be further offset to the downstream side with respect to the center of the specific intake valve in the direction of flow of intake air, or may be further offset to the upstream side with respect to the center of the specific intake valve in the direction of flow of intake air. Namely, the stem of the specific intake valve may be offset away from the plane that contains the center axis of the cylinder and is parallel to the flow of intake air. If the stem of the specific intake valve is further offset to the downstream side with respect to the center of the specific intake valve in the direction of flow of intake air, the flow of intake air may not be smoothly formed right above and downstream of the umbrella portion of the specific intake valve. It is, therefore, preferable that the stem is offset in the manner as described above, namely, is offset to the upstream side with respect to the center of the specific valve, in the direction of flow of intake air.
The specific intake valve may be formed such that a portion of the umbrella portion of the specific intake valve, which corresponds to the inner passage region, has a smaller volume than a portion of the umbrella portion which corresponds to the outer passage region.
In the engine as described just above, the inner passage region of intake air located close to the center of the combustion chamber can be made larger than the outer passage region, and therefore, an increased amount of intake air can be caused to flow toward the middle of the combustion chamber when the valve lift of the intake valve is in a small to middle range. Thus, the intake air can be introduced into the cylinder in a favorable manner so as to produce a whirling airflow in the cylinder, from the time when the valve lift of the intake valve is in a small to middle range. Also, even where the degree of offsetting of the stem, i.e., the offset amount of the stem, is reduced to be smaller than that of the intake valve in which the stem is offset without making the volume of the inner passage region larger, an equivalent effect can be provided, and therefore, the strength of the intake valve can be favorably maintained.
It is preferable that the umbrella portion of the specific intake valve is smoothly formed over the entire circumference thereof so as not to impede flow of intake air. To smoothly form the umbrella portion of the specific intake valve, at least a part of the umbrella portion of the specific intake valve may be formed in the shape of an arc in cross section. In this regard, a portion of the umbrella portion of the specific intake valve corresponding to the inner passage region and a portion corresponding to the outer passage region may be both formed in the shape of arcs in cross section, and the radius of curvature of the portion corresponding to the inner passage region may be made smaller than that of the portion corresponding to the outer passage region, so that the volume of the portion corresponding to the inner passage region can be easily made smaller than the portion corresponding to the outer passage region, as described above.
The specific intake valve may further include a rotation preventing device that prevents the specific intake valve from rotating about the center axis of the stem of the specific intake valve.
When the specific intake valve rotates about the stem, the intake port may not be properly closed. This problem can be eliminated by providing the specific intake valve with the above-mentioned rotation preventing device.
In the engine as described above, the intake air can be introduced into the cylinder in a favorable manner so as to produce a whirling airflow in the cylinder, from the time when the valve lift of the intake valve is in a small to middle range.
In another preferred embodiment of the invention, the intake valve is a specific intake valve in which the stem is inclined, when the intake valve is in a closed state, such that a distal end of the stem is located closer to a plane that contains a center axis of a cylinder and is substantially orthogonal to the axis of the crankshaft, than a center of a bottom face of the umbrella portion, in a direction substantially parallel to the axis of the crankshaft.
In the engine in which the stem of the specific intake valve is inclined in the manner as described above, an increased flow of intake air is drawn toward the middle of the combustion chamber, so that the mainstream of intake air that flows into the cylinder toward the middle of the combustion chamber can be increased or intensified. Thus, according to the preferred embodiment, the intensity of a whirling airflow produced in the cylinder can be enhanced even when the valve lift of the intake valve is in a small to middle range, and the intake air can be introduced into the cylinder in a favorable manner so as to produce such a whirling airflow in the cylinder, from the time when the valve lift of the intake valve is in a small to middle range.
In the above-described engine in which the stem of the specific intake valve is inclined, the umbrella portion of the intake valve is also inclined so that the intake air that flows along a portion of the umbrella portion of the specific intake valve which is closer to the center of the combustion chamber than the stem is particularly directed so as to be dispersed toward the periphery of the combustion chamber. Generally, the mainstream of intake air is more likely to be concentrated at around the middle of the combustion chamber as the lift of the intake valve becomes higher, resulting in an increased velocity of flow of intake air that flows toward the middle of the combustion chamber. In the engine according to the preferred embodiment as described above, on the other hand, the intake air that flows into the cylinder when the lift of the intake valve is in a middle to high range is favorably prevented from hitting against the wall of the cylinder at an excessively high velocity, and the intensity of a whirling airflow produced in the cylinder will not be reduced or less likely to be reduced. In the above description of the preferred embodiment, the phrase that “the specific intake valve is in a closed state” is used for defining the specific intake valve as that being in a certain state (i.e., closed state) by way of example. The same phrase will be used in the description of the following embodiment.
The stem of the specific intake valve may be inclined, when the specific intake valve is in a closed state, such that the distal end of the stem is located closer to an exhaust port than the center in a direction of flow of intake air.
With the above arrangement, the intake air that flows into the cylinder along the umbrella portion can be further dispersed toward the bottom dead center of the cylinder. Thus, the intake air flowing into the cylinder is favorably prevented from hitting against the wall of the cylinder at an excessively high flow velocity, which would result in a reduction of the intensity of a whirling airflow produced in the cylinder. Furthermore, in the engine as described above, it may be possible to prevent the mainstream of intake air from being concentrated too much at around the middle of the combustion chamber, and further improve the intensity of the whirling airflow, depending upon the degree by which the stem of the specific intake valve is inclined in the direction of flow of intake air.
Thus, in the engine as described above, the intake air can be introduced into the cylinder in a favorable manner so as to produce a whirling flow in the cylinder from the time when the valve lift of the intake valve is in a small to middle range, and at the same time the intake air is prevented from hitting against the wall of the cylinder at an excessively high velocity, which would result in a reduction of the intensity of the whirling airflow produced in the cylinder.
The features, advantages, and technical and industrial significance of this invention will be better understood by reading the following detailed description of preferred embodiments of the invention, when considered in connection with the accompanying drawings in which:
In the following description and the accompanying drawings, the present invention will be described in more detail with reference to exemplary embodiments.
Initially, a first embodiment of the invention will be described.
The engine 50A includes a cylinder block 51, a cylinder head 52A, a piston 53, and other components. The cylinder 51a having a generally cylindrical shape is formed in the cylinder block 51. The piston 53 is received in the cylinder 51a. A cavity 53a that serves to guide tumble flow T is formed in the top face of the piston 53. The cylinder head 52A is fixed to the upper face of the cylinder block 51. A combustion chamber 54 is formed as a space surrounded by the cylinder block 51, cylinder head 52A and the piston 63. The cylinder head 52A is formed with intake ports 10A (10Aa and 10Ab) through which intake air is drawn to the combustion chamber 54, and exhaust ports 20 (20a and 20b) through which combustion gas is discharged from the combustion chamber 54. Also, an intake valve 55 for opening and closing a channel of each intake port 10A and an exhaust valve 56 for opening and closing a channel of each exhaust port 20 are mounted in the cylinder head 52A. In addition, an ignition plug and a fuel injection valve (not shown), for example, are mounted in the cylinder head 52A.
The intake air flows into the combustion chamber 54 through the intake port 10A after being deflected by an airflow control valve (not shown), so as to create a high-intensity tumble flow T in the combustion chamber 54. While an inlet-side opening of the intake port 10A is formed in a side face of the cylinder head 52A in this embodiment, the intake port 10A may be an upright port whose inlet-side opening is formed in the upper face of the cylinder head 52A. Also, a whirling airflow produced in the combustion chamber 54 is not limited to the tumble flow T, but may be, for example, a reverse tumble flow that circulates in the direction opposite to that of the tumble flow T as shown in
Next, an intake port 10B having an intake port design according to a second embodiment of the invention will be described. The intake port 10B is different from the intake port 10A having the intake port design according to the first embodiment, in that the starting point P1 is located to be contained on a straight line L3 that contains the end point P2 and extends in a direction orthogonal to the axis of the crankshaft on the horizontal plane S, and that the projected streamline F of the intake port 10B as projected on the horizontal plane S is curved inwardly of the straight line L3.
With the above arrangement, the mainstream of the intake air is directed mainly before passing the curved portion so as to be introduced into the combustion chamber 54 from between the valve stem portion of the intake valve 55 and the inner wall of the intake port 10B. Namely, even if the positions of the starting point P1 and end point P2 have the relationship as shown in
Next, an intake port 10C having an intake port design according to a third embodiment of the invention will be described. The intake port 10C is different from the intake port 10A having the intake port design according to the first embodiment, in that the starting point P1 is not located on the inner side of the straight line L2 (namely, is located on the outer side), and the projected streamline F of the intake port 10C as projected on the horizontal plane S is curved inwardly of the straight line L2.
With the above arrangement, the mainstream of the intake air is directed mainly before passing the curved portion so as to be introduced into the combustion chamber 54 from between the valve stem portion of the intake valve 55 and the inner wall of the intake port 10C. Namely, even if the positions of the starting point P1 and end point P2 have the relationship as shown in
The illustrated embodiments are preferred embodiments of the invention. It is, however, to be understood that the invention is not limited to these embodiments, but may be otherwise embodied with various modifications without departing from the principle of the invention. For example, while the intake ports 10A, 10B and 10C are independent ports in the illustrated embodiments, the intake port is not limited to this type, but may be a Siamese port in which the intake passage is divided into two branch passages at the downstream side, which join into a single passage at the upstream side.
Next, a fourth embodiment of the invention will be described.
The internal combustion engine 100A has a cylinder block 151, a cylinder head 152, a piston 153, and other components. A cylinder 151a having a generally cylindrical shape is formed in the cylinder block 151, and the piston 153 is received in the cylinder 151a. The cylinder head 152 is fixed to the cylinder block 151. A combustion chamber 154 is formed as a space surrounded by the cylinder block 151, cylinder head 152 and the piston 153. The cylinder head 152 is formed with intake ports 110Aa and 110Ab (which will be simply and generically called “intake port 110A”, this way of calling being applied to other components) through which the intake air is introduced into the combustion chamber 154 (or into the cylinder), and exhaust ports 120 (120a and 120b) through which combustion gas is discharged from the combustion chamber 154. Furthermore, an intake valve 155A for opening and closing each intake port 110A and an exhaust valve 156 for opening and closing each exhaust port 120 are respectively mounted in the cylinder head 152. The engine 100A is provided with a rotation preventing means (not shown). The rotation preventing means may be implemented by, for example, forming a slit that extends in a direction in which a stem stm of the intake valve 155A extends, in the stem stm, and providing the cylinder head 152 with a stem holding part that engages with the slit. In this embodiment, the intake valves 155A (155Aa, 155Ab) are regarded as specific intake valves.
An ignition plug 157 is mounted in the cylinder head 152 such that its electrode protrudes from above into the combustion chamber 154. A fuel injection valve (not shown) is mounted in the cylinder head 152 such that its injection hole protrudes into the intake port 110A. The fuel injection valve is adapted to inject fuel directly into the cylinder 151a on the intake stroke. The fuel injection valve is not limited to this type or position, but may be mounted in the cylinder head 152 at a position closer to the cylinder block 151 than the intake port 110A such that its injection hole protrudes into the combustion chamber 154, or at a position above the combustion chamber 154. The intake air flowing from the intake port 110A into the cylinder 151a creates a whirling airflow in the cylinder. In this embodiment, the whirling airflow is, specifically, in the form of a tumble flow T as shown in
As shown in
In
In this respect, it is preferable that a portion corresponding to the inner passage region inr is larger than a portion corresponding to the outer passage region otr in all of the sections of the intake port 110A, but this is not always true, depending upon the design of the intake port 110A. As described above, the inner and outer passage regions inr, otr are intake-air passage regions taken at the position where the stem stm is disposed in the intake port 110A. Thus, the inner and outer passage regions inr, otr do not include intake-air passage regions partitioned by the plane S1 at the location where the stem stm is not disposed in the intake port 110A.
Next, the offset amount L of the stem stm will be described in detail.
As shown in
0<L (1)
If the offset amount L further increases to be around D/4, on the other hand, the valve strength of the intake valve 155A starts being largely reduced. If the offset amount L further increases to be larger than D/4, the valve strength is largely reduced, and the flow rate of air starts being largely reduced. The reduction in the flow rate of air is considered as being caused by an extreme reduction in the amount of intake air passing the outer passage region otr. It is thus preferable that the offset amount L is within a permissible range as indicated by the following expression (2).
0 <L≦D/4 (2)
Since the tumble intensity is in the middle of largely increasing when the offset amount L is in the range of 0 to D/12, as shown in
D/12≦L≦D/4 (3)
0<L<D/12 (4)
If the offset amount L is within the recommended range as indicated by the above expression (3), on the other hand, the flow velocity becomes equal to or larger than the predetermined value α. As is understood from this result, it is further preferable that the offset amount L is within the recommended range as indicated by the expression (3). The range as indicated by the above expression (3) or (4) is considered as a range that can provide a reasonable effect even in the case where the position of the stem stm as viewed in the direction F of flow of intake air is changed. In
Next, a fifth embodiment of the invention will be described. An internal combustion engine 100B according to the fifth embodiment is basically identical with the engine 100A of the fourth embodiment, except that an intake valve 155B (which represents intake valve 155Ba and intake valve 155Bb) of the engine 100B replaces the intake valve 155A of the engine 100A. The intake valve 155B is different from the intake valve 155A in that a stem stm of the intake valve 155B is further offset to the upstream side of the center P2 as viewed in the direction F of flow of intake air. In this embodiment, the intake valve 155B is considered as a specific intake valve.
As described above with regard to the fourth embodiment, it is preferable that the offset amount L is within the recommended range as indicated by the above expression (3). If the installation angle θ is further set to be larger than about 70 degrees or smaller than about −70 degrees, the stem stm will be contained in the area AR1. Thus, it is preferable that the installation angle θ is within a permissible range as indicated by the following expression (5).
−70°≦θ≦70° (5)
- It is, however, to be noted that the tumble intensity is more or less improved if the stem stm is located in the area AR1, and therefore, a reasonable effect can be provided if the installation angle θ is equal to or larger than −90° and is equal to or smaller than 90°.
If the stem stm is offset to the upstream side with the installation angle θ set to 90°, the tumble intensity increases at a low rate as the offset amount L increases, and then largely increases, as shown in
0°≦θ≦70° (6)
Even in the case where the installation angle θ is set to within the above-described range, the valve strength is reduced as shown in
When the stem stm is offset by an appropriate degree, a high-intensity tumble flow T can be formed in the cylinder and strong turbulence can be produced from the time when the valve lift of the intake valve is in a small to middle range. Therefore, the combustion characteristics are improved during lean-burn operation, resulting in a reduction of the fuel consumption rate, and the output performance can be improved during high-load operation. As shown in
If the offset amount L is set to within the ranges of the expression (2) and the expression (3), the fuel consumption reduction rate and output performance improvement rate as quantitatively indicated in
Next, a sixth embodiment of the invention will be described. An internal combustion engine 100C according to the sixth embodiment is substantially identical with the engine 100B according to the fifth embodiment, except that an intake valve 155C (which represents intake valve 155Ca and intake valve 155Cb) of the engine 100C replaces the intake valve 155B of the engine 100B. The intake valve 155C is different from the intake valve 155B in that the volume of a portion of the umbrella portion ub corresponding to the inner passage region inr is made smaller than that of a portion of the umbrella portion ub corresponding to the outer passage region otr. More specifically, when the portion corresponding to the outer passage region otr is rotated about the center axis C1 of the stem stm, to be superimposed on the portion corresponding to the inner passage region inr, these portions do not coincide with each other, and the portion corresponding to the inner passage region inr is at least partially contained in the portion corresponding to the outer passage region otr. In this embodiment, the intake valve 155C is considered as a specific intake valve.
In the sixth embodiment in which the umbrella portion ub is formed in the manner as described above, the portion of the umbrella portion ub corresponding to the inner passage region inr has a smaller volume than the portion corresponding to the outer passage region otr. Thus, the inner passage region inr can be made larger, and therefore, further increased flow of intake air toward the middle of the combustion chamber 154 can be formed when the valve lift of the intake valve is in a small to middle range. The umbrella portion ub of the intake valve 155C is smoothly formed over the entire circumference so as not to impede flow of intake air. In this respect, the umbrella portions ub of the intake valves 155A and 115B are formed in a similar manner.
D/24≦L≦D/4 (7)
- In
FIG. 20 , area AR4 represents an area corresponding to the recommended range as indicated by the above expression (7), in which a reasonable effect is supposed to be provided.
In the case where the installation angle θ is established, if the installation angle θ is larger than about 80 degrees or smaller than about −80 degrees when the offset amount L is D/4, the stem stm is contained in the above-mentioned area AR4. Thus, in the case of the engine 100C, the permissible range of the installation angle θ can be expanded as indicated by the following expression (8), as compared with the permissible range as indicated by the above expression (5).
−80°≦θ≦80° (8)
As in the case of the engine 100B, it is preferable in the engine 100C that the stem stm is offset to the upstream side relative to the center P2, in the direction F of flow of intake air. Thus, in the case of the engine 100C, the recommended range of the installation angle θ can be expanded as indicated by the following expression (9), as compared with the recommended range as indicated by the above expression (6).
0°≦θ≦80° (9)
As the ranges of the offset amount L and the installation angle θ are expanded as described above, the strength of the intake valve 155C can be more favorably maintained. Also, in the case of the engine 100C, the stem stm is preferably formed so as to satisfy both of the ranges indicated by the above expressions (7) and (9). In
Next, a seventh embodiment of the invention will be described. An internal combustion engine 100D according to the seventh embodiment is different from the engines 100A, 100B and 100C of the fourth through sixth embodiments as described above, in that the engine 100D has a three-intake-valve structure, namely, each cylinder is provided with three intake valves.
In the engine 100D as shown in
Next, an eighth embodiment of the invention will be described. An internal combustion engine 100E according to the eighth embodiment is substantially identical with the engine 100A according to the fourth embodiment, except that intake ports 110E (which represent intake port 110Ea and intake port 110Eb) are further provided with an airflow control valve 160 that deflects intake air in the intake ports 110E so as to create a high-intensity tumble flow T in the cylinder. Namely, the engine 100E is equivalent to the engine 100A that is further equipped with the airflow control valve 160. The engines 100B, 100C and 100D according to the fifth through seventh embodiments may also be provided with airflow control valves that operate in substantially the same manner and provide substantially the same effect as the airflow control valve 160.
Next, a ninth embodiment of the invention will be described.
The internal combustion engine 200A has a cylinder block 251, a cylinder head 252, a piston 253, and other components. A cylinder 251a having a generally cylindrical shape is formed in the cylinder block 251, and the piston 253 is received in the cylinder 251a. The cylinder head 252 is fixed to the cylinder block 251. A combustion chamber 254 is formed as a space surrounded by the cylinder block 251, cylinder head 252 and the piston 253. The cylinder head 252 is formed with intake ports 210Aa and 210Ab (which will be simply and generically called “intake port 210A”, this way of calling being applied to other components) through which the intake air is introduced into the combustion chamber 254 (or into the cylinder), and exhaust ports 220 (220a and 220b) through which combustion gas is discharged from the combustion chamber 254. Furthermore, an intake valve 255A for opening and closing each intake port 210A and an exhaust valve 256 for opening and closing each exhaust port 220 are respectively mounted in the cylinder head 252. In this embodiment the intake valves 255A (255Aa, 255Ab) are regarded as specific intake valves.
An ignition plug 257 is mounted in the cylinder head 252 such that its electrode protrudes from above into the combustion chamber 254. A fuel injection valve (not shown) is mounted in the cylinder head 252 such that its injection hole protrudes into the intake port 210A. The fuel injection valve is adapted to inject fuel directly into the cylinder 251a on the intake stroke. The fuel injection valve is not limited to this type or position, but may be mounted in the cylinder head 252 at a position closer to the cylinder block 251 than the intake port 210A such that its injection hole protrudes into the combustion chamber 254, or at a position above the combustion chamber 254. The intake air flowing from the intake port 210A into the cylinder 251a creates a whirling airflow in the cylinder. In this embodiment, the whirling airflow is, specifically, in the form of a tumble flow T as shown in
In
In the engine 200A in which the stems stem of the intake valves 255A are inclined, the umbrella portions ub of the intake valves 255A are also inclined as shown in
In the engine 200A in which the mainstream of intake air is drawn toward the middle of the combustion chamber 254, the distance Lv between the valve seats on which the intake valves 255Aa, 255Ab rest as shown in
Next, the inter-stem angle θ2 will be explained in detail. In a common internal combustion engine, the inter-stem angle θ2 is set to 0°. If the angle θ2 is within a range as indicated by the following expression (10), on the other hand, the tumble intensity can be improved.
0°<θ2 (10)
As the inter-stem angle θ2 increases, however, it becomes physically difficult to appropriately place cams (not shown) for opening and closing the intake valves 255A. Accordingly, it is preferable in view of the placement of the cams that the angle θ2 is within a permissible range as indicated by the following expression (11).
0°<θ2≦10° (11)
When the angle θ2 is set to be larger than 0°, the intake air flowing into the cylinder is dispersed toward the periphery of the combustion chamber 254. If the dispersion occurs excessively, however, the tumble intensity may be reduced, rather than improved.
If the inter-stem angle θ2 is set to be larger than 6° and equal to or smaller than 10°, there may arise a situation where the intake air flowing into the cylinder is excessively dispersed, as shown in
1°≦θ2≦6° (12)
Next, a tenth embodiment of the invention will be described. An internal combustion engine according to the tenth embodiment is substantially identical with the engine 200A of the ninth embodiment, except that when the intake valve 255A is in the closed state, the stem stm of the intake valve 255A is inclined such that the distal point P11 of the stem stm is located closer to the exhaust port 220 than the center P2 as viewed in the direction F of flow of intake air. The intake valve 255A inclined in this manner will be hereinafter referred to as intake valve 255B (which represents intake valve 255Ba and intake valve 255Bb) In this embodiment, the intake valve 255B is regarded as a specific intake valve.
In
When the stem stm of the intake valve 255B is inclined with the installation angle θ3 being set to 90°, it is difficult to draw the intake air toward the middle of the combustion chamber 254. Where the installation angle θ3 is reduced from 90°, too, a significant effect cannot be expected if the degree of the reduction is small. If the installation angle θ3 is smaller than 0°, on the other hand, it may be difficult to smoothly form flow of intake air to the downstream side, right. above the umbrella portion ub. Thus, it is preferable that the installation angle θ3 is within in a permissible range as indicated by the following expression (13).
0°≦θ3≦70° (13)
If the installation angle θ is set to within the range of the above expression (13), the umbrella portion ub is further inclined, and the intake air flowing along the umbrella portion ub on one side of the stem stm closer to the center of the combustion chamber 254 is also dispersed toward the bottom dead center of the cylinder 251a. As a result, the intake air flowing into the cylinder is more favorably prevented from hitting against the wall of the cylinder 251a, which would result in noticeable occurrence of flow Fs along the wall of the cylinder 251a. Depending upon the installation angle θ3, which is in the range of the expression (13), the dispersion of the intake air may contribute to production of the tumble flow T, or the intake air may be introduced into the cylinder in a manner suitable for production of the tumble flow T. In this respect, where the tumble intensity is to be further improved, it is further preferable that the installation angle θ3 is within a recommended range as indicated by the following expression (14).
10°≦θ3≦60° (14)
When the stem stm is inclined by an appropriate degree, through setting of the inter-stem angle θ2 and the installation angle θ3, a high-intensity tumble flow T can be formed in the cylinder and strong turbulence can be produced from the time when the valve lift of the intake valve is in a small to middle range. Therefore, the combustion characteristics are improved during lean-burn operation, resulting in a reduction of the fuel consumption rate, and the output performance can be improved during high-load operation. As shown in
If the inter-stem angle θ2 is set to within the ranges of the expression (11) and the expression (12), the fuel consumption reduction rate and output performance improvement rate as quantitatively indicated in
Next, an eleventh embodiment of the invention will be described. An internal combustion engine 200C according to the eleventh embodiment is different from the engines 200A and 200B according to; the ninth and tenth embodiments in that the engine 200C has a three-intake-valve structure, namely, each cylinder is provided with three intake valves.
In the engine 200C, the intake valves 255Ca, 255Cb located at the opposite ends with respect to one cylinder are regarded as specific intake valves. With the specific intake valves thus provided, the mainstream of intake air flowing toward the middle of the combustion chamber 254 can be increased or intensified when the valve lift of the intake valves is in a small to middle range, and occurrence of flow Fs along the wall of the cylinder 251a can be suppressed when the valve lift of the intake valves is in a middle to high range, even where the engine 200C has the three-intake-valve structure. In the engine 200C constructed as described above, the intake air can be introduced into the cylinder in a favorable manner so as to form a tumble flow T in the cylinder from the time when the valve lift of the intake valve is in a small to middle range, and the intake air flowing into the cylinder is prevented from hitting against the wall of the cylinder 251a at an excessively high velocity, which would result in a reduction in the intensity of the tumble flow T formed in the cylinder.
Next, a twelfth embodiment of the invention will be described. An internal combustion engine 200D according to the twelfth embodiment is substantially identical with the engine 200A according to the ninth embodiment, except that intake ports 210D (which represent intake port 210Da and intake port 210Db) are further provided with an airflow control valve 260 that deflects intake air in the intake ports 210D so as to create a high-intensity tumble flow T in the cylinder. Namely, the engine 200D is equivalent to the engine 200A that is further equipped with the airflow control valve 260. The engines 200B and 200C according to the tenth and eleventh embodiments may also be provided with airflow control valves that operate in substantially the same manner and provide substantially the same effect as the airflow control valve 260.
The illustrated embodiments are preferable embodiments of the invention. It is, however, to be understood that the invention is not limited to these embodiments, but may be embodied with various modifications or improvements, without departing from the principle of the invention.
Claims
1. An internal combustion engine comprising:
- an intake port that communicates with a combustion chamber, and
- an intake valve that has an umbrella portion and a stem connected at one end thereof to the umbrella portion, wherein
- said intake port having a starting point that is a first point of intersection of a streamline of the intake port and an inlet-side opening plane of the intake port, and an end point that is a second point of intersection of the streamline of the intake port and a center axis of the intake valve, as viewed from an upper face of a cylinder head in which the intake port is formed, said first and second points of intersection being projected on a horizontal plane, wherein
- the streamline of the intake port projected on the horizontal plane is curved toward a center of the combustion chamber so as to be at least partially located closer to the center of the combustion chamber than a first straight line that contains the starting point and extends in a direction orthogonal to an axis of a crankshaft on the horizontal plane, and a second straight line that contains the end point and extends in a direction orthogonal to the axis of the crankshaft on the horizontal plane, wherein:
- the intake valve comprises a specific intake valve in which the stem is offset such that an inner passage region located closer to the center of the combustion chamber, out of two intake-air passage regions on the opposite sides of a plane that contains a center axis of the stem, becomes larger, and such that the center axis of the stem does not contain a center of a bottom face of the umbrella portion.
2. The internal combustion engine according to claim 1, wherein
- the stem of the specific intake valve is offset to an upstream side with respect to the center of the specific intake valve, in a direction of flow of intake air.
3. The intake combustion engine according to claim 1, wherein
- a portion of the umbrella portion of the specific intake valve, which corresponds to the inner passage region, has a smaller volume than a portion of the umbrella portion which corresponds to the outer passage region.
4. The internal combustion engine according to claim 1, wherein
- the specific intake valve further includes a rotation preventing device that prevents the specific intake valve from rotating about the center axis of the stem of the specific intake valve.
5. An internal combustion engine comprising:
- an intake port that communicates with a combustion chamber, and
- an intake valve that has an umbrella portion and a stem connected at one end thereof to the umbrella portion, wherein
- said intake port having a starting point that is a first point of intersection of a streamline of the intake port and an inlet-side opening plane of the intake port, and an end point that is a second point of intersection of the streamline of the intake port and a center axis of the intake valve, as viewed from an upper face of a cylinder head in which the intake port is formed, said first and second points of intersection being projected on a horizontal plane, wherein
- the streamline of the intake port projected on the horizontal plane is curved toward a center of the combustion chamber so as to be at least partially located closer to the center of the combustion chamber than a first straight line that contains the starting point and extends in a direction orthogonal to an axis of a crankshaft on the horizontal plane, and a second straight line that contains the end point and extends in a direction orthogonal to the axis of the crankshaft on the horizontal plane, and wherein
- the intake valve comprises a specific intake valve in which the stem is inclined, when the intake valve is in a closed state, such that a distal end of the stem is located closer to a plane that contains a center axis of a cylinder and is substantially orthogonal to the axis of the crankshaft, than a center of a bottom face of the umbrella portion, in a direction substantially parallel to the axis of the crankshaft.
6. The internal combustion engine according to claim 5, wherein
- the stem of the specific intake valve is inclined, when the specific intake valve is in a closed state, such that the distal end of the stem is located closer to an exhaust port than the center in a direction of flow of intake air.
7. The intake combustion engine according to claim 2, wherein
- a portion of the umbrella portion of the specific intake valve, which corresponds to the inner passage region, has a smaller volume than a portion of the umbrella portion which corresponds to the outer passage region.
8. The internal combustion engine according to claim 2, wherein the specific intake valve further includes a rotation preventing device that prevents the specific intake valve from rotating about the center axis of the stem of the specific intake valve.
9. The internal combustion engine according to claim 3, wherein the specific intake valve further includes a rotation preventing device that prevents the specific intake valve from rotating about the center axis of the stem of the specific intake valve.
Type: Application
Filed: Oct 1, 2007
Publication Date: Feb 18, 2010
Applicant: Toyota Jidosha Kabushiki Kaisha (Toyota-shi)
Inventor: Takashi Amano (Susono-shi)
Application Number: 12/310,797
International Classification: F01L 1/14 (20060101);