A PISTON FOR AN INTERNAL COMBUSTION ENGINE

Abstract

Method, control unit, and target arrangement of a leading vehicle for triggering a follower vehicle, which is situated at a lateral distance from the leading vehicle, to coordinate its movements with the leading vehicle. The target arrangement comprises a target configured to be placed at a lateral distance from to the leading vehicle. The target is also configured to be recognized by at least one forwardly directed sensor of the follower vehicle.

Claims

1. A piston for an internal combustion engine, wherein the piston has an upper end and a lower end between which a central axis and a peripheral envelope surface extend, wherein the upper end comprises an annular top surface defining a plane; and a piston bowl configured to form part of a combustion chamber, wherein the piston bowl is recessed with respect to the annular top surface, and wherein the piston bowl comprises: an annular bottom portion defining a lowest level of the piston bowl; a central bottom portion which is located radially inside of the annular bottom portion and which is elevated with respect to the lowest level; an annular upper side wall portion extending downward and radially inward from the top surface; an annular lower side wall portion extending upward from the annular bottom portion toward the annular upper side wall portion; an annular ridge formed in a transition between the annular upper side wall portion and the annular lower side wall portion, projecting toward the central axis; and, a plurality of angularly spaced protrusions, protruding toward the central axis from the annular upper side wall portion, each protrusion having a respective concave surface portion, wherein the piston bowl is configured so that a fluid spray injected toward a target position located below one of said angularly spaced protrusions is split by the annular ridge into an upper flow portion and a lower flow portion, wherein the upper flow portion is deflected by the concave surface portion of the protrusion located above the target position so that it contributes to creation of a swirl motion in the combustion chamber.

2. The piston according to claim 1, wherein the concave surface portion of each of the angularly spaced protrusions is configured to face radially inward.

3. The piston according to claim 1, wherein the concave surface portion of each of the angularly spaced protrusions is configured so that at least a part of the upper flow portion is redirected toward a position above the annular ridge.

4. The piston according to claim 1, wherein each of the angularly spaced protrusions has an innermost point located at a radial distance from the central where such radial distance is within a range of 10% of a radial distance between an innermost point of the annular ridge to the central axis.

5. The piston according to claim 1, wherein the annular lower side wall portion is in the form of a concave surface free from protrusions.

6. The piston according to claim 1, wherein each of the angularly spaced protrusions further comprises a convex surface portion located opposite the concave surface portion.

7. The piston according to claim 1, wherein the central bottom portion has a highest point located on the central axis, from which highest point the central bottom portion slopes downward toward the annular bottom portion.

8. An internal combustion engine comprising at least one cylinder with a piston comprising: an upper end and a lower end between which a central axis and a peripheral envelope surface extend, wherein the upper end comprises an annular top surface defining a plane; and a piston bowl configured to form part of a combustion chamber, wherein the piston bowl is recessed with respect to the annular top surface, and wherein the piston bowl comprises: an annular bottom portion defining a lowest level of the piston bowl; a central bottom portion which is located radially inside of the annular bottom portion and which is elevated with respect to the lowest level; an annular upper side wall portion extending downward and radially inward from the top surface; an annular lower side wall portion extending upward from the annular bottom portion toward the annular upper side wall portion; an annular ridge formed in a transition between the annular upper side wall portion and the annular lower side wall portion, projecting toward the central axis; and a plurality of angularly spaced protrusions protruding toward the central axis from the annular upper side wall portion, each protrusion having a respective concave surface portion, wherein the piston bowl is configured so that a fluid spray injected toward a target position located below one of said angularly spaced protrusions is split by the annular ridge into an upper flow portion and a lower flow portion, wherein the upper flow portion is deflected by the concave surface portion of the protrusion located above the target position so that it contributes to creation of a swirl motion in the combustion chamber.

9. The internal combustion engine according to claim 8, further comprising an injector configured to inject and direct a fluid spray toward a plurality of target positions, wherein each target position is located below one of said angularly spaced protrusions.

10. The internal combustion engine according to claim 9, wherein the internal combustion engine is a diesel engine and wherein the injector is a fuel injector.

11. A motor vehicle comprising an internal combustion engine according to claim 8 comprising at least one cylinder with a piston comprising: an upper end and a lower end between which a central axis and a peripheral envelope surface extend, wherein the upper end comprises an annular top surface defining a plane; and a piston bowl configured to form part of a combustion chamber, wherein the piston bowl is recessed with respect to the annular top surface, and wherein the piston bowl comprises: an annular bottom portion defining a lowest level of the piston bowl; a central bottom portion which is located radially inside of the annular bottom portion and which is elevated with respect to the lowest level; an annular upper side wall portion extending downward and radially inward from the top surface; an annular lower side wall portion extending upward from the annular bottom portion toward the annular upper side wall portion; an annular ridge formed in a transition between the annular upper side wall portion and the annular lower side wall portion, projecting toward the central axis; and a plurality of angularly spaced protrusions protruding toward the central axis from the annular upper side wall portion, each protrusion having a respective concave surface portion, wherein the piston bowl is configured so that a fluid spray injected toward a target position located below one of said angularly spaced protrusions is split by the annular ridge into an upper flow portion and a lower flow portion, wherein the upper flow portion is deflected by the concave surface portion of the protrusion located above the target position so that it contributes to creation of a swirl motion in the combustion chamber.

12. The motor vehicle according to claim 11, wherein the motor vehicle is a heavy motor vehicle.

13. A method for creating a swirl motion in a combustion chamber of a cylinder in an internal combustion engine, wherein the combustion engine comprises at least one cylinder with a piston comprising: an upper end and a lower end between which a central axis and a peripheral envelope surface extend, wherein the upper end comprises an annular top surface defining a plane; and a piston bowl configured to form part of a combustion chamber, wherein the piston bowl is recessed with respect to the annular top surface, and wherein the piston bowl comprises: an annular bottom portion defining a lowest level of the piston bowl; a central bottom portion which is located radially inside of the annular bottom portion and which is elevated with respect to the lowest level; an annular upper side wall portion extending downward and radially inward from the top surface; an annular lower side wall portion extending upward from the annular bottom portion toward the annular upper side wall portion; an annular ridge formed in a transition between the annular upper side wall portion and the annular lower side wall portion, projecting toward the central axis; and a plurality of angularly spaced protrusions protruding toward the central axis from the annular upper side wall portion, each protrusion having a respective concave surface portion, wherein the piston bowl is configured so that a fluid spray injected toward a target position located below one of said angularly spaced protrusions is split by the annular ridge into an upper flow portion and a lower flow portion, wherein the upper flow portion is deflected by the concave surface portion of the protrusion located above the target position so that it contributes to creation of a swirl motion in the combustion chamber, wherein said method comprises: providing a flow of air into the combustion chamber during an intake stroke of the piston; and, during or after a compression stroke of the piston, injecting a fluid spray toward the plurality of target positions, so that the fluid spray is at each one of the target positions split by the annular ridge into an upper flow portion and a lower flow portion, wherein the upper flow portion is deflected by the concave surface portion of the protrusion located above the target position so that a swirl motion is created in the combustion chamber.

14. The method according to claim 13, wherein the internal combustion engine is a diesel engine and wherein the injector is a fuel injector, wherein injecting a fluid spray comprises, following a compression stroke of the piston, injecting a fuel spray so that when the fuel spray is ignited and a flame is formed, at least an upper flow portion of the flame is deflected by the concave surface portion so that a swirl motion is created in the combustion chamber.

15. The method according to claim 13, wherein the flow of air into the combustion chamber is provided independent of creating a swirl motion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Embodiments of the invention will in the following be described with reference to the appended drawings, in which:

[0037] FIG. 1 schematically shows an axial section of a cylinder of an internal combustion engine according to an embodiment,

[0038] FIG. 2 is a perspective view of a piston according to a first embodiment,

[0039] FIG. 3 is an upper end view of the piston in FIG. 2,

[0040] FIG. 4 is a section taken along the line IV-IV in FIG. 2,

[0041] FIG. 5 is a section taken along the line V-V in FIG. 2,

[0042] FIG. 6 is a perspective view of a piston according to a second embodiment,

[0043] FIG. 7 is an upper end view of the piston in FIG. 6,

[0044] FIG. 8 is a section taken along the line VIII-VIII in FIG. 6,

[0045] FIG. 9 is a section taken along the line IX-IX in FIG. 6, and

[0046] FIG. 10 is a cross section taken along the line X-X in FIG. 9 shown together with a diagram showing rotational speed within a combustion chamber as a function of distance from a central axis.

DETAILED DESCRIPTION OF THE INVENTION

[0047] FIG. 1 shows a section taken along a central axis C of a cylinder 1 of an internal combustion engine in the form of a diesel engine according to an embodiment of the invention. In the cylinder 1, a piston 2 configured to reciprocate within the cylinder along the common central axis C is provided. A piston bowl 3 is formed in the piston 2, which together with internal walls of the cylinder 1 and an internal surface of a cylinder head 4 creates a combustion chamber 5. A fuel injector 6 is positioned on the central axis C above the piston bowl 3. An intake port 7 is provided in the cylinder head 4 for supply of air into the combustion chamber 5 via an intake valve 8. Furthermore, an exhaust port 9 is provided in the cylinder head 4 for evacuation of exhaust gases via an exhaust valve 10.

[0048] The piston 2 according to the embodiment shown in FIG. 1 is shown in closer detail in FIGS. 2-5. A piston 2 according to a second embodiment is shown in FIGS. 6-10. Common elements of the piston 2 according to the first and the second embodiment will in the following be described using common reference numerals.

[0049] The piston 2 according to both embodiments has the basic shape of a right circular cylinder with an upper end 11 and a lower end 12, between which a central axis C and a peripheral envelope surface 13 extend. The upper end 11 comprises an annular top surface 14 defining an upper plane P.sub.u. The piston bowl 3 is recessed with respect to the upper plane P.sub.u defined by the top surface 14. An annular bottom portion 15 defines a lowest level of the piston bowl 3. Radially inside of the annular bottom portion 15, a central bottom portion 16 which is elevated with respect to the lowest level is provided. The central bottom portion 16 is cone shaped with a rounded top 17, which top 17 is recessed with respect to the upper plane P.sub.u. An annular upper side wall portion 18 extends downward and radially inward from the top surface 11. An annular lower side wall portion 19 extends upward from the annular bottom portion 15 toward the upper side wall portion 18. Between the upper side wall portion 18 and the lower side wall portion 19, an annular ridge 20 is formed, projecting toward the central axis C. Together, the annular bottom portion 15 and the lower side wall portion 19 delimit an annular channel 26 surrounding the central bottom portion 16.

[0050] The fuel injector 6 is configured for injecting fuel into the cylinder 1 as a fuel spray 25 so that the fuel is mixed with air compressed in the cylinder 1 to form a fuel/air mixture. The fuel/air mixture is after an ignition delay ignited by compression heat generated in the cylinder 1. The ignited part of the fuel spray 25 forms a flame. The fuel can be injected with different injection pressures, from low to very high pressures. The fuel injector 6 includes a plurality of small injection orifices (not shown), formed in the lower end of a nozzle assembly of the fuel injector 6 for permitting the high pressure fuel to flow from a nozzle cavity of the fuel injector 6 into the combustion chamber 5 with high pressure to induce thorough mixing of the fuel with the hot compressed air within the combustion chamber 5. It should be understood that the fuel injector 6 may be any type of fuel injector capable of injecting high pressure fuel through a plurality of injector orifices into the combustion chamber 5. Also, the fuel injector need not necessarily be positioned on the central axis C.

[0051] In other embodiments, in which the internal combustion engine is e.g. an Otto engine, the fuel injector may be configured to inject a mixture of fuel and air into the combustion chamber. The injector may also be configured to inject other fluids such as gases or liquids, e.g. water, which are not combusted but are primarily used to induce a swirl motion.

[0052] In the first embodiment shown in FIGS. 2-5, a plurality of identical and angularly spaced protrusions 21 protrude toward the central axis C from the upper side wall portion 18 above target positions located on the ridge 20. Each protrusion 21 is wedge shaped with a first concave surface portion 22, which in the radial direction extends from the upper side wall portion 18 to a curved innermost edge 23 of the protrusion 21, whose innermost point is located closest to the central axis C at approximately the same distance from the central axis C as the annular ridge 20. In the axial direction, the protrusion extends from the top surface 14 to the ridge 20. The first concave surface portion 22 is directed so that no part of the concave surface portion 22 is hidden behind any part of the protrusion 21 as seen from the central axis C. The first concave surface portion 22 has a curvature both as seen in an upper end view such as in FIG. 3 and in a sectional view across the protrusion 21, such as shown in FIG. 5. Each protrusion 21 further has a smaller second concave surface portion 24 located opposite the first concave surface portion 22 and a planar upper surface portion 27 at the level of the upper plane P.sub.u.

[0053] The injection orifices of the fuel injector 6 are arranged so that the fuel spray 25 is injected toward target positions on, above or below the annular ridge 20, which target positions are located below the first concave surface portions 22 of the protrusions 21. It should be noted that the piston 2 is moving along the central axis C as the fuel spray 25 is injected, and therefore the exact target positions in the axial direction will vary. The target position aimed for in the axial direction also depends on e.g. load and injection timing. As the ignited fuel spray 25, i.e. the flame, strikes the target positions, the flame is split on the annular ridge 20 into an upper flow portion 25a and a lower flow portion 25b. The upper flow portion 25a of the flame is deflected upward, toward the concave surface portion 22. The lower flow portion 25b of the flame is deflected downward, into the annular channel 26 and toward the central bottom portion 16. As the upper flow portion 25a impinges on the concave surface portion 22, it is deflected toward a position in an upper part of the combustion chamber 5, above the annular ridge 20, which position is angularly spaced from the concave surface portion 22 by which the flame was deflected. The deflected upper flow portions 25a of the flames thereby together induce a swirl motion in the upper part of the combustion chamber 5, i.e. a large scale rotation in the direction of rotation R around the central axis C. Between a lower part of the combustion chamber 5, below the annular ridge 20, and the upper part of the combustion chamber 5, turbulence may be created as the rotating flow of fuel/air mixture in the upper part of the combustion chamber 5 interacts with the fuel/air mixture in the lower part of the combustion chamber 5, which rotates with an axis of rotation perpendicular to or essentially perpendicular to the central axis C.

[0054] In the second embodiment shown in FIGS. 6-10, a plurality of mutually identical and angularly spaced protrusions 31 protrude toward the central axis C from the upper side wall portion 18 above target positions located on the ridge 20. The protrusions 31 are in the form of fins having a concave surface portion 32, which in the radial direction extends from the upper side wall portion 18 to a curved innermost edge 33 of the protrusion 31, whose innermost point is located at the level of the upper plane P.sub.u, closest to the central axis C at approximately the same distance from the central axis C as the annular ridge 20. In the axial direction, the protrusion extends from the top surface 14 to the ridge 20. The concave surface portion 32 is directed so that no part of the concave surface portion 32 is hidden behind any part of the protrusion 31 as seen from the central axis C. The concave surface portion 32 has a curvature both as seen in a transverse cross sectional view such as in FIG. 10 and in an axial sectional view across the protrusion 31, such as shown in FIG. 9. Each protrusion 31 further has a convex surface portion 34 located opposite the first concave surface portion 32, extending from the upper side wall portion 18 to the innermost edge 33. The protrusion 31 has an upper edge 35 extending in the upper plane P.sub.u. An inclined surface 36 extends from the upper edge 35 to a curved edge 37 defining a transition between the inclined surface 36 and the concave surface portion 32.

[0055] The injection orifices of the fuel injector 6 are in the second embodiment arranged so that fuel spray 25 is injected toward target positions on, below or above the annular ridge 20, which target positions are located below the protrusions 31, in the shown embodiment below the innermost edge 33. As the ignited fuel spray 25, i.e. the flame, strikes the target positions, the flame is split on the annular ridge 20 into an upper flow portion 25a and a lower flow portion 25b. The upper flow portion 25a of the flame is deflected upward, toward the concave surface portion 32. The lower flow portion 25b of the flame is deflected downward, into the annular channel 26 and toward the central bottom portion 16. As the upper flow portion 25a of the flame impinges on the innermost edge 33 of the protrusion 31, it is split into a first portion 25a following the convex surface portion 34 and a second portion 25 following the concave surface portion 32. Both portions 25a, 25a are deflected toward a position within the upper part of the combustion chamber 5 above the annular ridge 20, which position is angularly spaced from protrusion 31 on which the flame was deflected. The deflected upper flow portions of the flames thereby together induce a swirl motion in the direction of rotation R in the upper part of the combustion chamber 5. Between the lower part of the combustion chamber 5, below the annular ridge 20, and the upper part of the combustion chamber 5, turbulence may be created as the rotating flow of fuel/air mixture in the upper part of the combustion chamber 5 interacts with the fuel/air mixture in the lower part of the combustion chamber 5, which rotates with an axis of rotation perpendicular to or essentially perpendicular to the central axis C.

[0056] In the embodiment shown in FIGS. 6-10, the ignition delay may be expected to be relatively short due to the relatively narrow protrusions 21. The relatively short ignition delay is expected to result in a reduced amount of NOx gases created during combustion, but instead the soot emissions may be somewhat increased in comparison with longer ignition delays.

[0057] In a method according to an embodiment of the present invention, carried out in the internal combustion engine described with reference to FIG. 1, a flow of air is provided into the combustion chamber 5 during an intake stroke of the piston 2 via the intake port 7 and the intake valve 8. During a subsequent compression stroke of the piston 2, a fuel spray 25 is injected by the fuel injector 6 toward the plurality of target positions, so that the fuel spray 25 is at each one of the target positions split by the annular ridge 20 into an upper flow portion 25a and a lower flow portion 25b. The upper flow portion 25a is deflected by at least the concave surface portion 22, 32 of the protrusion 21, 31 located above the target position, so that a swirl motion is created in the combustion chamber 5.

[0058] FIG. 10 shows rotational velocity w as a function of distance r from the central axis C of the piston 2 at the end of injection. As can be seen, the large scale swirl motion created during fuel injection leads to large variations in the rotational velocity w depending on the distance r from the central axis. During the post oxidation phase, the large scale swirl motion created in the combustion chamber 5 may be fractured into small scale turbulence leading to accelerated soot oxidation and thereby lower soot emissions.

[0059] The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.