The present invention refers to an air inlet manifold for an internal combustion engine, which air inlet manifold has pipes for distribution of air to cylinders of the engine.
A combustion engine comprises combustion chambers, cylinders, a fuel supply, and an air inlet manifold to supply and distribute air to the combustion chambers of the engine. The air is supplied to the air inlet manifold via a throttle, which controls the amount of air. The manifold comprises at least one distribution chamber and a number of pipes mounted to the combustion chambers, normally one pipe per combustion chamber.
The features of the distribution chamber and the pipes are important for many reasons. When a driver increases or decreases pressure on the gas pedal, thereby demanding a change in throttle and airflow, it is desirable to have the engine respond as quickly as possible. One way to achieve this is to have a small volume in the air inlet manifold, since such a small volume gives a smaller air volume within the air inlet manifold, and the smaller air volume responds more quickly to changes of airflow/pressure dependent on the changes of the throttle. To get a small volume, it is desirable to place the pipes as close together as possible.
The features of the pipes are important for providing the best air supply to the combustion chambers. Between the combustion chambers and the pipes there are valves that open and close, typically, synchronized with the movement of the pistons in the combustion chambers. The valves are mounted in the cylinder head, which cylinder head is mounted to the pipe. Each valve opens with a movement away from the cylinder head, i.e., in the direction of the airflow, and closes with a movement in the opposite direction. When the valve opens, a pressure pulse propagates in the pipe into the distribution chamber of the air inlet manifold, where the pulse changes direction and returns back into the pipe. This phenomena is well known, and it is desirable to design the pipes in such a way that when the engine rotates with a predetermined rotation per minute, rpm, the pulse returns to the valve when the valve opens, thereby pushing en extra amount of air into the combustion chamber. When designing a combustion engine, this phenomenon is normally designed to occur when the torque curve is reaching its maximum, giving an extra amount of air into the cylinder. In fact, the design of the pipes normally decides the torque maximum.
A typical air inlet manifold extends in a longitudinal direction from a first end to a second end, and the air inlet manifold has an air inlet at the first end, a distribution chamber for air extending in the longitudinal direction restricted by at least a first internal wall, and an end wall at the second end. At least one air pipe for each cylinder is distributed along the longitudinal direction and protrudes essentially perpendicular to the first wall. The pipes each have an pipe inlet, a pipe channel restricted by at least a second internal wall, and a pipe outlet. The upper part of the pipes, the part of the pipe closest to the distribution chamber, extends essentially perpendicular to the first internal wall of the distribution chamber, with the pipe inlet towards the distribution chamber. The pipe inlet of each pipe has a phased edge that is rounded by a convex radius from the second internal wall to first internal wall, which edge is uniform around the pipe inlet.
In view of the above, it is important that the volume in the distribution chamber is small enough to give good engine response, and the features of the pipes are important to gain a good pressure pulse charging. One important feature for gaining good pressure pulse charging is that the edges in the pipes are phased with a small convex radius. However, when the engine is running at high engine speed, the airflow is high. If the edges are phased with too small a radius, undesirable turbulent phenomena can occur which limits the air flow in the pipe channels. Thus, to supply maximum air to the combustion chambers at high engine speeds, it is important that the edges have a radius large enough to avoid turbulent phenomena around the pipe inlet. Thus, there is a problem in designing the air inlet manifold since the design of the edge at the pipe inlet has to be a trade off between good pressure pulse charging and avoiding turbulent phenomena to supply enough air to the combustion chambers at high engine speed.
Pipes with different geometric features are known, for example, circular cross-sections, oval cross-sections, rectangular cross-sections, and D-shaped pipes. However, the trade off problem mentioned above applies to all.
In a multi-cylinder engine, it is desirable to have similar conditions in each combustion chamber. This implies that the air for the different combustion chambers shall be as similar as possible, i.e., the air inlet manifold must distribute the air equally over the pipes. This in turn implies that each pipe in the air inlet manifold have similar properties regarding the shape of the pipe inlet, pipe channel, and a pipe outlet. In the case where the pipes are mounted to the distribution chamber in a row, the shape of the pipe farthest from the air inlet of the air inlet manifold differs from the other pipes.
The second internal wall of the last pipe differs from the corresponding parts in the other pipes in that the second internal wall of the last pipe transitions into the end wall of the distribution chamber, i.e., the second internal wall of the last pipe does not have a phased edge on this part, but the second internal wall continues in a straight line and then follows the curvature of the end wall. Thus, the last pipe does not have the same geometry around the pipe inlet as the other pipes, thereby supplying air to the corresponding combustion chamber differently than the other pipes supplying air to their corresponding combustion chambers, thereby giving rise to different conditions for the different combustion chambers. As mentioned before, it is desirable to have as similar conditions as possible in the respective combustion chambers. The different features of the last pipe give rise to the problem of non-similar properties in the different combustion chambers. It is important to have similar properties regarding the air supply to the combustion chamber for good emissions.
The present invention aims to solve the above-mentioned problems by introducing a new shape of the edges of the pipe inlets in the air inlet manifold. The pipes can be fitted closer to each other, giving a smaller volume and thereby an engine with quick response. The invention also solves the problem of good pressure pulse charging. The invention also solves the problem with an air inlet manifold distributing the air equally over the pipes.
The identified problems are solved, according to the invention, by using an air inlet manifold for a multi-cylinder internal combustion engine. The air inlet manifold has a first end, an opposing second end with an end wall, and at least a first internal wall, if the body of the air inlet manifold has a circular cross-section. Alternatively, the air inlet manifold body has a rectangular cross-section, with several internal walls.
The air inlet manifold extends in a longitudinal direction from the first end to the second end. The air inlet manifold has an air inlet at the first end and at least one distribution chamber for air extending along the longitudinal direction and restricted by at least the first internal wall. The air inlet manifold also has at least one air pipe for each cylinder. The pipes are distributed along the longitudinal direction. The pipes each have an inlet towards the distribution chamber, and an opposing outlet, an upper part defined by a first length, L1 from the inlet to a first point. The upper part protrudes essentially perpendicular to the first internal wall.
Each pipe has a pipe channel between the inlet and the outlet, which is restricted by at least a second internal wall, i.e., if the pipe channel has a circular cross-section. Alternatively, the pipe channel has a rectangular cross-section with several internal walls. Further alternatives are a D-shape and an oval shape. The pipe outlet has an edge between the first internal wall and the second internal wall. The pipe inlet is described by a first surface with a first area restricted by a first line in the boundary between the first internal wall and the edge.
Each pipe channel, in a first cross-section, is described by a second surface with a second area restricted by a second line along the perimeter of the second internal wall. The first cross-section is taken in the first point perpendicular to the extension direction of the upper part of the pipe channel. The first and second area also comprise a first center point and a second center point, respectively, which center points represents the center of gravity of the area, e.g., the origin for a circle and the origin of an ellipse.
The invention is characterized in that for at least one of said pipes, a profile between the first line and the second line located proximate to the air inlet has different curvature than a profile between the first line and the second line located distant from the air inlet. The profiles may advantageously be in the form of curvatures and the first area is preferably greater than the second area. Preferably, the profile between the first line and the second line located proximate to the air inlet has a greater curvature than the profile between the first line and the second line located distant from the air inlet, and preferably the first area is greater than the second area.
According to the invention, the edges of each of the pipe inlets are phased with a surface described by a convex curvature, which convex curvature extends from the second internal wall to the first internal wall, with the convex part towards the pipe channel and distribution chamber. The convex curvature can be in the form of different radii, with different radii around the edge, preferably with the greater radii in the direction towards the air inlet. Here, radii mean convex curvatures with circular properties, i.e., one radius describes a part of a circle and the size of the radius (convex curvature) is dependent on the length of the radius. However, the convex curvature can according to the invention advantageously be in a parabolic shape or any other suitable shape.
Accordingly, if the edges are described by convex curvatures of different length and with the greater convex curvature in the direction towards the air inlet, then the pipe inlet, as seen from above, gets a different geometrical shape than the pipe channel. According to the invention, this gives rise to a pipe inlet and an upper part of the pipe channel with an edge phased with large convex curvatures towards the air inlet and small convex curvatures away from the air inlet. This difference in the phasing of the edge results in a preserved pulse loading (compared to prior art with small radii edges uniform around the pipe inlet), and also results in an enhanced air supply to the cylinders when the engine is running on high number of revolutions. The air supply is enhanced since the turbulence problem in the upper part of the pipe channel due to the xe2x80x9csharpxe2x80x9d edges, mentioned in prior art, is reduced or even eliminated.
A part of or all of the upper part of the pipes may also be funnel-shaped, i.e., a part of the upper part of the pipe can be described as a cone-shape that transitions into the convex curvature of the edge.
According to one embodiment of the invention, the second area has a circular shape. But, as mentioned above, the second area can have a rectangular cross-section, a D-shape, or an oval shape, or any other shape suitable for the purpose.
In one embodiment of the invention, the first area has an elliptical shape with the two end points in a direction perpendicular to the longitudinal direction and with the first center point displaced along the longitudinal direction towards the air inlet, compared to the second center point.
In another embodiment of the invention, the first area has a rectangular shape with rounded corners, and with the first center point displaced along the longitudinal direction towards the air inlet compared to the second center point.
In yet another embodiment of the invention, the first area has a circular shape with the first center point displaced along the longitudinal direction towards the air inlet compared to the second center point.
In a further embodiment of the invention, the first area has a shape described by a first circular line, a second circular line, and a first and a second connecting curvature adapted to connect the first circular line with the second circular line. The first circular line is described by a first variable radius, r1, greater than or equal to a second variable radius, r2, describing the second circular line. The first and a second connecting curvature do not cross the second line in any point. The first and second radii have their starting point in the second center point, and which first variable radius describes the first circular line depending on a first angle, "PHgr"1, and which second radius describes the second circular line dependent on a second angle, "PHgr"2. The first and second angles relate to an imaginary centerline running through the second point in the longitudinal direction, and the length of the first and second radii varies dependent on the angles. The first angle is in the range between 0xe2x89xa6"PHgr"1xe2x89xa620xc2x0 and 340xc2x0xe2x89xa6"PHgr"1xe2x89xa6360xc2x0, and the second angle is in the range between 160xe2x89xa6"PHgr"2xe2x89xa6340xc2x0. The first area is oriented in such way that when the first angle is 0xc2x0, the first radius points towards the air inlet. Preferably, the first radius may be constant during one segment within the range of the first angle, and the second radius may be constant during one segment within the range of the second angle.
Another way to describe the invention is to use the following wording in conjunction with the air inlet manifold described above. The pipe channel is defined by an interior periphery of said pipe, which pipe inlet is defined by a surface extending between said first internal wall and said interior periphery. The invention is then characterized in that for at least one of said pipes, a profile of said surface located proximate to the air inlet has a different curvature than a profile of said surface located distant from the air inlet.
In yet a further embodiment of the invention, the end wall is placed at a predetermined first distance from the closest pipe, which predetermined first distance is greater than 0.2 times the pipe channel diameter and less than the pipe channel diameter, preferably half the pipe channel diameter. If the pipe channel has a non-circular cross-section, said diameter may, for example, equal the hydraulic diameter dh=4A/U, where A=cross-section area of the channel and U=the xe2x80x9cwettedxe2x80x9d perimeter of the channel.
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