Air intake port for a lean-burn gasoline engine

Abstract

An air intake port (10) for a lean-burn gasoline engine (110) comprises an air inlet (14), two air outlets (15a, 15b), and an air channel connecting the air inlet (14) to the two air outlets (15a, 15b) and comprising an upstream common duct (11) and two downstream port legs (12a, 12b), the two downstream port legs (12a, 12b) branching off from the common duct (11) at a bifurcation point (13). A total cross section of the air intake port (10) gradually decreases between the air inlet (14) and the two air outlets (15a, 15b). A gradient of decrease of the total cross section is locally reduced in a region adjacent the bifurcation point (13).

Claims

1. An air intake port for a lean-burn gasoline engine, the air intake port comprising: an air inlet, two air outlets, and an air channel connecting the air inlet to the two air outlets and comprising an upstream common duct and two downstream port legs, the two downstream port legs branching off from the common duct at a bifurcation point, wherein a total cross section of the air intake port gradually decreases between the air inlet and the two air outlets, and wherein a gradient of decrease of the total cross section is locally reduced in a region adjacent the bifurcation point.

2. An air intake port according to claim 1, wherein the air channel has an average gradient of decrease of the total cross section and wherein the gradient of decrease of the total cross section is locally at least 20% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point.

3. An air intake port according to claim 2, wherein the air channel has an average gradient of decrease of the total cross section and wherein the gradient of decrease of the total cross section is locally at least 40% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point.

4. An air intake port according to claim 1, wherein the gradient of decrease of the total cross section is approximately zero in at least a portion of the region adjacent the bifurcation point.

5. An air intake port according to claim 4, wherein the gradient of decrease of the total cross section is below zero in at least a portion of the region adjacent the bifurcation point.

6. An air intake port according to claim 1, wherein the gradient of decrease of the total cross section increases downstream of the region adjacent the bifurcation point.

7. An air intake port according to claim 1, wherein the gradient of decrease of the total cross section is locally reduced in the region immediately upstream of the two air outlets.

8. An air intake port according to claim 1, wherein the air channel has an average gradient of decrease of the total cross section and wherein the gradient of decrease of the total cross section is locally at least 20% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point, and wherein the gradient of decrease of the total cross section is approximately zero in at least a portion of the region adjacent the bifurcation point.

9. An air intake port according to claim 1, wherein the air channel has an average gradient of decrease of the total cross section and wherein the gradient of decrease of the total cross section is locally at least 40% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point, and wherein the gradient of decrease of the total cross section is approximately zero in at least a portion of the region adjacent the bifurcation point.

10. An air intake port according to claim 1, wherein the air channel has an average gradient of decrease of the total cross section and wherein the gradient of decrease of the total cross section is locally at least 20% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point, and wherein the gradient of decrease of the total cross section increases downstream of the region adjacent the bifurcation point.

11. An air intake port according to claim 1, wherein the air channel has an average gradient of decrease of the total cross section and wherein the gradient of decrease of the total cross section is locally at least 20% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point, and wherein the gradient of decrease of the total cross section is locally reduced in the region immediately upstream of the two air outlets.

12. An air intake port according to claim 1, wherein the gradient of decrease of the total cross section is approximately zero in at least a portion of the region adjacent the bifurcation point, and wherein the gradient of decrease of the total cross section increases downstream of the region adjacent the bifurcation point.

13. An air intake port according to claim 1, wherein the gradient of decrease of the total cross section is approximately zero in at least a portion of the region adjacent the bifurcation point, and wherein the gradient of decrease of the total cross section is locally reduced in the region immediately upstream of the two air outlets.

14. A lean-burn gasoline engine comprising at least one air intake port according to claim 1.

15. A vehicle comprising a lean-burn gasoline engine according to claim 14.

16. A lean-burn engine comprising at least one air intake port according to claim 1.

17. An air intake port for a lean-burn engine, the air intake port comprising: an air inlet, two air outlets, and an air channel connecting the air inlet to the two air outlets and comprising an upstream common duct and two downstream port legs, the two downstream port legs branching off from the common duct at a bifurcation point, wherein a total cross section of the air intake port remains substantially constant in a region adjacent the bifurcation point.

18. An air intake port according to claim 17, wherein the total cross section of the air intake port gradually decreases between the air inlet and the two air outlets, and wherein the gradient of decrease of the total cross section increases downstream of the region adjacent the bifurcation point.

19. An air intake port according to claim 17, wherein the total cross section of the air intake port gradually decreases between the air inlet and the two air outlets, and wherein the gradient of decrease of the total cross section is locally reduced in the region immediately upstream of the two air outlets.

20. A lean-burn engine comprising at least one air intake port according to claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a vehicle in which the invention may be used;

(3) FIG. 2 shows an air intake port according to an embodiment of the invention; and

(4) FIG. 3 schematically shows a bottom view of the air intake port of FIG. 2, together with a diagram indicating the cross section at different positions along its length.

DETAILED DESCRIPTION

(5) FIG. 1 shows a vehicle 100 in which the invention may be used. In this example, the vehicle 100 is a car, but the invention is equally applicable to other vehicles driven by a lean-burn gasoline engine 110. As mentioned above, it is to be noted that air intake port according to the invention and as described herein can be advantageously used in engines burning other fuels or fuel mixtures than gasoline. For example, the air intake port would be useful in a hydrogen burning internal combustion engine. In this vehicle 100, the lean-burn gasoline engine 110 is positioned in the front and coupled to a drivetrain to drive the front and/or rear wheels of the vehicle 100. The energy needed for driving the vehicle 100 is provided by burning fuel in the engine's cylinders causing the cylinder pistons to drive a crankshaft that is mechanically connected to the vehicle's drivetrain.

(6) Compared to classic internal combustion engines, the lean-burn engine 110 of this vehicle 100 burns the fuel with an excess of air in the air-fuel mixture. Lean-burn engines may mix air and fuel in proportions of, for example, 20:1 (lambda>1.3) or even 30:1 (lambda>2). Advantages of lean-burn engines include more efficient fuel use and lower exhaust hydrocarbon emissions than conventional gasoline engines.

(7) In order to enable the lean burning of fuel over a large portion of the engine map, i.e. in a large range of different engine speeds as well as engine output power or torque, the engine 110 is designed in such a way to enable a large air flow into the combustion chamber and a good mixing with the relatively small amount of fuel that is to be burnt to ensure a reliable combustion process that will effectively burn all fuel, despite the oxygen rich conditions.

(8) FIG. 2 shows an air intake port 10 according to an embodiment of the invention. The air intake port 10 has an air inlet 14 and two air outlets 15a, 15b. An air channel connects the air inlet 14 to the two air outlets 15a, 15b. The first, upstream portion of the air channel, starting at the air inlet 14 forms a common duct 11. Ata bifurcation point 13, at a downstream end of the common duct 11, the common duct 11 branches off in two port legs 12a, 12b that provide the two respective air outlets 15a, 15b. The terms upstream and downstream are used to refer to parts of the air intake port 10 relative to flow of air through the air intake port 10 in its normal use with a lean-burn gasoline engine 110. The predominant air flow direction is from an upstream position to a downstream position. It follows that in normal use the engine 110 is downstream of the air intake port 10. The air outlets 15a, 15b are configured to connect to two respective inlets of the combustion chamber. Near the downstream ends of the port legs 12a, 12b, two valve guides 16a, 16 are provided, each being configured to receive a valve stem that is used for controlling the valve that selectively opens and closes the combustion chamber inlets.

(9) FIG. 3 schematically shows a bottom view of the air intake port 10 of FIG. 2 together with a diagram indicating the cross section at different positions along its length. In addition to what has already been shown in and described with reference to FIG. 2, the bottom view also shows the air outlets 15a, 15b. As can be seen in the diagram, the total cross section of the air intake port 10 gradually decreases from A.sub.in at the air inlet to A.sub.out at the two air outlets. A.sub.in therein is the cross section at the start of the common duct and A.sub.out is the sum of the cross sections at the end of the two port legs 12a.12b. The decrease of the cross section does not follow a simple continuous and linear profile but is specifically designed to provide optimal air flow conditions with an aim to provide an undisturbed, high speed and high-volume flow of air at the outlets 15a, 15b of the air intake port 10. It is noted that, if the common duct 11 and the leg ports 12a, 12b are tubular or have a constant height-width ratio, the change in cross-section size may alternatively be visualised by showing the development of the radius, height, or width between the air inlet 14 and the air outlets 15a, 15b. Even though the overall profile of the cross section does not follow a linear pattern, the cross section may decrease linearly over parts of the common duct 11 and or the port legs 12a, 12b. This may particularly happen in sections where, e.g., the width of the common duct 11 or leg ports 12a, 12b is kept constant while the height decreases linearly (or vice versa).

(10) As can be seen in the diagram, the gradient of decrease of the total cross section is locally reduced in a region 31 adjacent the bifurcation point 13. The inventors have found that by introducing this local reduction of the gradient of decrease of the total cross section in the region 31 around the bifurcation point 13, any possible disturbance of the air flow caused by the splitting and deflecting of the air flow is minimised. Preferably, the local reduction of the gradient of decrease of the total cross section is realised in the region immediately upstream and downstream of the bifurcation point 13, but the desired flow enhancing effect is at least partly achieved when reducing the gradient of decrease at only one side of the bifurcation point 13.

(11) The air channel has an average gradient of decrease of the total cross section. The optimal average gradient will usually be a compromise between different design considerations. One possible constraint is the desired maximum speed of the air flow at the entrance of the combustion chamber. Too high speeds may lead to excessive NVH (noise, vibration, and harshness) problems and to choking of the port flow. Cylinder size and space constraints may define the maximum cross section of the air outlets of the air intake port. Given a maximum cross section and air flow speed at the outlet, an optimum average gradient of decrease of the total cross section can be established. Further constraints on the length and width of the air intake port may also play a role when determining the optimum. In preferred embodiments, the gradient of decrease of the total cross section may, for example, be locally at least 20% below the average gradient of decrease in at least a portion of the region adjacent the bifurcation point. In other embodiments, the gradient of decrease at that position may even be more than 25%, 30%, 35%, 40%, 45%, or 50% below the average gradient of decrease of the total cross section.

(12) Optionally, like in the embodiment shown in FIG. 3, the gradient of decrease of the total cross section is locally about zero in at least a portion of the region 31 adjacent the bifurcation point 13. In this embodiment, the cross section of the air intake port 10 remains substantially constant in the region around the bifurcation point, thereby allowing the air flow to move through undisturbed. In some embodiments, the gradient of decrease of the total cross section may even be locally below zero in at least a portion of the region 31 adjacent the bifurcation point 13, which means that the cross section locally increases in the region 31 around the bifurcation point 13.

(13) Preferably, the gradient of decrease of the total cross section increases downstream of the region adjacent the bifurcation point 13. As soon as the air flow is properly split in two branches 12a, 12b, the cross section can be decreased again in order to further increase the air flow.

(14) In the embodiment shown in FIG. 3, the gradient of decrease of the total cross section is locally reduced in the region 32 immediately upstream of the two air outlets too. The air outlets 15a, 15b of the air intake port 10 connect to the air inlets of the combustion chamber. Like near the bifurcation point 13 of the air intake port 10, there may be a risk of undesired flow disturbances when the air flow reaches the intake valves and the transition point between the air intake port 10 and the combustion chamber. To minimise such disturbances, it may be preferred to bring the gradient of decrease of the total cross section down to or below zero in the region 32 immediately upstream of the air outlets 15a, 15b.

(15) It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.