Exhaust turbocharger

Abstract

An internal combustion engine (20) has two exhaust valves (24, 25) for each combustion chamber, to permit separation of blow-down and expulsion phases of an exhaust stroke. The separate exhaust streams are directed to different geometries of an exhaust turbocharger (30), so as to make best use thereof. Variable exhaust valve timing, and bypass passage for the exhaust streams are disclosed.

Claims

1. A method of operating an internal combustion engine and exhaust turbocharger in combination, said engine having a combustion chamber with first and second exhaust orts, the first exhaust port having a first exhaust valve for controlling flow of exhaust gas through the first exhaust port and the second exhaust port having a second exhaust valve for controlling flow of exhaust gas through the second exhaust port, wherein the first and second exhaust ports are coupled via respective first and second exhaust tracts to respective first and second turbine inlets of said exhaust turbocharger, wherein turbine geometries associated with said first and second exhaust tracts are distinct, the method comprising: controlling at least one of a cam shaft and a variable valve timing system to separate exhaust blow-down and exhaust expulsion phases of an exhaust stroke of the engine; directing gas exhausted from the combustion chamber during said blow-down chase of said exhaust stroke to a first of the distinct turbine geometries via the first turbine inlet and the first exhaust port; and directing gas exhausted from the combustion chamber during said expulsion phase of said exhaust stroke to a second of the distinct turbine geometries via the second turbine inlet and the second exhaust port.

2. The method of claim 1, including varying the timing of the exhaust valves according to engine speed and load, to vary a proportion of exhaust gas directed to said different geometries.

3. The method of claim 2, including diverting to a downstream exhaust side of a turbine wheel of said turbocharger a proportion of exhaust gas from one or both said phases.

4. A system, comprising; an internal combustion engine and an exhaust-driven turbine, said engine having a combustion chamber with first and second exhaust ports, the first exhaust port having a first exhaust valve for controlling flow of exhaust gas through the first exhaust port and the second exhaust port having a second exhaust valve for controlling flow of exhaust gas through the second exhaust port, wherein the first and second exhaust ports are coupled via respective first and second exhaust tracts to respective first and second turbine inlets of said exhaust-driven turbine, wherein turbine geometries associated with said first and second exhaust tracts are distinct, wherein an electronic control unit (ECU) is configured to control at least one of a cam shaft and a variable valve timing system to separate exhaust blow-down and exhaust expulsion phases of an exhaust stroke by: directing gas exhausted from the combustion chamber during said exhaust blow-down phase of said exhaust stroke to a first turbine geometry of the distinct turbine geometries via the first turbine inlet and the first exhaust port, and directing gas exhausted from the combustion chamber during said expulsion phase of said exhaust stroke to a second turbine geometry of the distinct turbine geometries via the second turbine inlet and the second exhaust port.

5. A system, comprising: an internal combustion engine; an exhaust turbocharger, said engine having a combustion chamber with first and second exhaust ports, the first exhaust port having a first exhaust valve for controlling flow of exhaust gas through the first exhaust port and the second exhaust port having a second exhaust valve for controlling flow of exhaust gas through the second exhaust port, wherein the first and second exhaust ports are coupled via respective first and second exhaust tracts to respective first and second turbine inlets of said exhaust turbocharger, wherein turbine geometries associated with said first and second exhaust tracts are distinct; and an electronic control unit (ECU) configured to control at least one of a cam shaft and a variable valve timing system to separate exhaust blow-down and exhaust expulsion phases of an exhaust stroke by: directing gas exhausted from the combustion chamber during said exhaust blow-down phase of said exhaust stroke to a first turbine geometry of the distinct turbine geometries via the first turbine inlet and the first exhaust port, and directing gas exhausted from the combustion chamber during said expulsion phase of said exhaust stroke to a second turbine geometry of the distinct turbine geometries via the second turbine inlet and the second exhaust port.

6. The system as claimed in claim 5, wherein vanes of the turbine wheel are arcuate.

7. The system as claimed in claim 5, wherein one of said first and second turbine inlets comprises a nozzle.

8. The system as claimed in claim 7, wherein the first and second turbine inlets comprise respective nozzles.

9. The system as claimed in claim 8, wherein an outlet direction of the nozzle associated with the first turbine inlet is non-parallel to an outlet direction of the nozzle associated with the second turbine inlet.

10. The system as claimed in claim 7, wherein one of said nozzles comprises an actuator controllable to vary the outlet direction of the one of said nozzles.

11. The system as claimed in claim 5, wherein one of said first and second turbine inlets includes a stator having one or more vanes to direct an exhaust stream.

12. The system as claimed in claim 11, wherein the first and second turbine inlets each comprise a respective stator.

13. The system as claimed in claim 11, wherein the stator is movable to change a direction of an exhaust stream.

14. The system as claimed in claim 5, wherein the ECU is configured to change an opening duration of at least one of said first and second exhaust valves.

15. The system as claimed in claim 5, wherein the ECU is configured to change an opening area of at least one of said first and second exhaust valves.

16. The system as claimed in claim 5, wherein the ECU is configured to vary a timing of opening and/or closing of one or more of said first and second exhaust valves with respect to the rotation of an output member of said engine.

17. The system as claimed in claim 5, wherein one of said exhaust tracts includes a diverter valve having an inlet from said engine and an outlet for connection to a downstream exhaust side of a turbine wheel of said turbocharger.

18. The system as claimed in claim 17, wherein said diverter valve has an inlet from said engine, a first outlet to said turbocharger, and a second outlet for connection to a bypass of a turbine wheel of said turbocharger.

19. The system as claimed in claim 5, wherein both said exhaust tracts includes a diverter valve, each diverter valve having an inlet from said engine and an outlet for connection to a downstream exhaust side of a turbine wheel of said turbocharger.

20. The system as claimed in claim 5, wherein said engine has multiple cylinders.

21. The system as claimed in claim 20, wherein said engine has four cylinders in line.

22. A vehicle incorporating the system of claim 5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features of the invention will be apparent from the following description of several embodiments shown by way of example only in the accompanying drawings in which:—

(2) FIG. 1 is a schematic illustration of a first embodiment of the invention;

(3) FIG. 2 is a schematic illustration of a second embodiment of the invention; and

(4) FIG. 3 is a schematic illustration of a third embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

(5) A first embodiment of the invention is illustrated in FIG. 1, and comprises a four cylinder, in-line, reciprocating piston, internal combustion engine 20 having four identical cylinders 21 each with an inlet valve 22 coupled to an inlet manifold 23, and two exhaust valves 24, 25 coupled to respective exhaust manifolds 26, 27. The number of inlet valves 22 is not important in this invention, and for simplicity only one per cylinder is shown; more could be provided if desirable. The exhaust manifolds 26, 27 define independent exhaust tracts, so that the exhaust stream is divided immediately downstream of each cylinder. The valves are typically conventional spring loaded poppet valves, opened and closed by a suitable camshaft arrangement.

(6) In this embodiment, the operation of one or both sets of exhaust valves is controlled by one or more variable devices of known kind which may vary the timing of valve opening and closing with respect to an engine output member (typically crank angle), and/or may vary the duration of opening, and/or may vary the size of the aperture defined by a valve during the period for which it is open. Thus for a poppet valve, the valve lift may be adjusted to more or less throttle the flow of exhaust gas therethrough, and accordingly to permit flow of exhaust gas from the cylinder more or less quickly.

(7) Valves may be operated in unison by, for example, a camshaft. Valves may also be operated by individual actuators, in which case each set of individual actuators may be operated in unison. This invention is not concerned with variable valve timing as such.

(8) In an embodiment, the exhaust valves associated with each exhaust manifold are operated in common, thus with the same characteristics of timing, duration and aperture. However the two sets of exhaust valves will typically have different operating characteristics. For example the set of exhaust valves associated with the blow-down phase will open earlier and close earlier than the set of exhaust valves associated with the expulsion phase; there may be a period of overlap where both valves of each combustion chamber are open.

(9) An exhaust turbocharger 30 is provided downstream of the exhaust manifolds 26,27, and within a common housing 31 the usual exhaust turbine wheel 32 connected to the usual inlet tract compressor wheel 33 by a shaft 34. This invention is not concerned with exhaust turbochargers as such, and further details of the general design thereof are omitted.

(10) The outlet of the turbine is directed to an exhaust tailpipe 35. The compressor wheel 33 has an inlet 36 for receiving fresh air, and an outlet 37 connected to the inlet manifold via a conventional intercooler (charge air cooler) 38. The compressor wheel 33 includes a bypass passage 39 which is opened and closed by actuation of a bypass valve 40. The passage 39 is conventional, and allows inlet air to bypass the compressor wheel when stationary to improve natural (unassisted) aspiration. the bypass valve 40 may also provide a conventional blow-off or surge valve whereby excess inlet pressure downstream of the compressor wheel may be vented to the inlet side, or to atmosphere (not shown).

(11) On the exhaust side, each exhaust manifold 26,27 is coupled to a respective exhaust valve 41,42 whereby the exhaust gas stream may be directed either to the turbine 32 through a nozzle 102, 104 associated with respective inlets to the turbine 32, or via a respective bypass passage 43,44 to the exhaust tail pipe 35. The exhaust bypass passages 43,44 allow the respective exhaust gas streams to have a greater or lesser effect on the turbine 32, as will be explained.

(12) Typically the operation of the bypass valves 40, 41, 42, and the variable valve timing arrangement 61,62 are under the control of a device such as a camshaft or an electronic control unit (ECU) (either schematically represented at) 60 according to conventional systems of engine management, whereby an operating map determines operational parameters according to e.g. engine speed and load.

(13) Thus, in use the engine 20 is typically capable of operation over an operating range, from tickover at minimum speed to maximum power at maximum speed. Various operating parameters of the engine are typically adjusted, in particular valve timing, ignition timing and fuelling, to provide an appropriate operating characteristic, with minimum fuel consumption and minimum undesirable emissions. Such adjustments are generally not apparent to the driver of the vehicle.

(14) Operation of this embodiment of the invention is as follows:

(15) At lower engine speed/low load, it is desirable to extract as much energy from the exhaust gas stream as possible, so as to provide the highest possible inlet charge pressure via the compressor wheel 33. With two exhaust gas streams, via the manifolds 26,27 the possibilities for energy extraction are increased.

(16) In the blow-down phase, a high pressure pulse of short duration is available, and can be directed to an aggressive turbine geometry best able to take advantage thereof. This pulse may for example be directed via exhaust valves 24, manifold 26 and valve 41. At the conclusion of the blow-down phase, the exhaust valves 24 will close, and accordingly the aggressive turbine geometry is no longer supplied with an exhaust gas stream.

(17) However, as the exhaust valve 24 closes, the exhaust valves 25 are opened to permit the longer expulsion phase to provide a comparatively steady flow of exhaust gas via the manifold 27 and valve 42 to a less aggressive turbine geometry.

(18) By this means energy extraction is maximised whilst avoiding excessive back pressure on the combustion chamber. In contrast, use of an aggressive turbine geometry would allow effective energy conversion in the blow-down phase but impose excessive back pressure in the expulsion phase. On the other hand, a benign turbine geometry would be effective in the expulsion phase, but cause excess pressure to be vented (for example) via a conventional wastegate) in the blow-down phase. In the latter case energy is lost to the exhaust tailpipe, and moreover back pressure on the combustion chamber is high due to the large pressure drop across the wastegate valve.

(19) The variable valve timing modules 61,62 ensure that parameters of valve timing and overlap are in accordance with a pre-determined operating regime, which may be determined empirically on, for example, an engine test bed and retained in an engine management system according to conventional practices. Thus the closing of one set of exhaust valves may overlap the opening of another set of exhaust valves to provide for maximum extraction of energy from the exhaust gas stream.

(20) In certain instances it may be desirable to wholly or partially bypass the turbine wheel, for example to reduce back pressure on the combustion chamber, or to ensure rapid “light-off” of the usual catalytic converter upon cold engine start.

(21) At higher engine speeds and loads, the proportion of exhaust gas directed to the respective turbine geometries may change, according to exhaust valve timing, and operation of the exhaust bypass valves 41,42, so as to optimise the extraction of energy from the exhaust gas stream.

(22) In the embodiment of FIG. 1, a single turbine housing and a single turbine wheel is envisaged. The turbine housing is divided to separate the exhaust gas streams up to the entrance to the turbine wheel.

(23) As compared with a pulse divided manifold and twin scroll turbine, which is used to avoid exhaust events in one cylinder affecting an exhaust event in another cylinder, the present invention obviates such interference by providing separate paths for the blow-down and expulsion phases of an exhaust stroke. As a result exhaust valve pulsation events are able to overlap because cross-communication between cylinders can be avoided.

(24) As noted above, the different turbine geometries may vary by changing one or more parameters, such as aspect ratio, nozzle outlet size and direction etc.

(25) In an enhanced embodiment one or both of the turbine geometries may itself be variable, by using an actuator under control of the ECU 60 to change one or more parameters such as aspect ratio, nozzle outlet size and direction etc.

(26) It will be appreciated that for any group of cylinders, the allowable length of blow-down and expulsion phases is determined by: maximum length of blow-down (in arc degrees of crank rotation)=720/no. of cylinders feeding the exhaust manifold maximum length of expulsion (in arc degrees of crank rotation)=720/no. of cylinders feeding the exhaust manifold.

(27) FIG. 2 illustrates an alternative embodiment in which the bypass valve 42 is omitted, along with the corresponding bypass passage 44. This simplified arrangement may be appropriate where, for example bypass in the expulsion phase is not required. Such a construction may be less expensive, and less consuming of space in the engine compartment.

(28) FIG. 3 shows another embodiment, similar to FIG. 2, but in which the single bypass valve 41a is located downstream of the branch to the turbine. By this means all of the flow from manifold may be directed to the turbine wheel 32, or most thereof via the bypass passage to the exhaust tailpipe.

(29) The valves 41,42 are typically proportional valves allowing flow to be divided in any proportion between the two outlets. Such valves are well known, and may be controlled by, for example, a vacuum or an electrical actuator. The valve 41a is similar, save that it controls the proportion flowing through the single outlet thereof, and the proportion directed to the turbocharger is an inevitable consequence.

(30) Certain aspects of the invention are stated in the numbered paragraphs which follow:—

(31) 1. An internal combustion engine and exhaust turbocharger in combination, said engine having a combustion chamber with two exhaust ports, each exhaust port having a respective exhaust valve for controlling the flow therethrough, wherein respective exhaust ports are coupled via respective exhaust tracts to respective turbine inlets of said exhaust turbocharger, whereby the turbine geometries associated with each exhaust tract are distinct.

(32) 2. The combination of aspect 1 wherein said turbocharger has a single turbine wheel.

(33) 3. The combination of aspects 1 or 2 wherein the vanes 100 of the turbine wheel 32 are arcuate.

(34) 4. The combination of aspect 1 wherein a turbine inlet 102, 104 comprises a nozzle 106, 108.

(35) 5. The combination of aspect 4 wherein the turbine inlets comprise respective nozzles.

(36) 6. The combination of aspect 5 wherein the outlet direction of said nozzle is non-parallel.

(37) 7. The combination of aspect 4 wherein a nozzle comprises means to vary the outlet direction thereof.

(38) 8. The combination of aspect 1 wherein a turbine inlet 102, 104 includes a stator 110, 112 having one or more vanes 114 to direct an exhaust stream.

(39) 9. The combination of aspect 8 wherein the turbine inlets comprise a respective stator.

(40) 10. The combination of aspect 8 wherein a stator is movable to change the direction of an exhaust stream.

(41) 11. The combination of aspect 1 wherein said engine comprises a variable exhaust valve timing system whereby the opening duration of one or more exhaust valves may be changed.

(42) 12. The combination of aspect 1 wherein said engine comprises a variable exhaust valve timing system whereby the opening area of one or more exhaust valves may be changed.

(43) 13. The combination of aspect 1 wherein said engine comprises a variable exhaust valve timing system whereby the timing of opening and/or closing of one or more exhaust valves may be vaned with respect to the rotation of an output member of said engine.

(44) 14. The combination of aspect 1 wherein one of said exhaust tracts includes a diverter valve having an inlet from said engine and an outlet for connection to the downstream exhaust side of said turbocharger.

(45) 15. The combination of aspect 14 wherein said diverter valve has an inlet from said engine, a first outlet to said turbocharger, and a second outlet for connection to a bypass of said turbocharger.

(46) 16. The combination of aspect 15 wherein both said exhaust tracts include a said diverter valve.

(47) 17. A combination according to aspect 1 wherein said engine has multiple cylinders.

(48) 18. A combination according to aspect 17 wherein said engine has four cylinders in line.

(49) 19. A vehicle incorporating an engine and turbocharger in combination, according to aspect 1.

(50) 20. A method of operating an internal combustion engine and exhaust turbocharger in combination and according to any preceding claim, the method comprising substantially separating the exhaust blow-down and exhaust expulsion phases of an exhaust stroke, and directing said phases to different geometries of a turbine wheel of said turbocharger.

(51) 21. The method of aspect 20 including the step of varying the timing of exhaust valves according to engine speed and load, to vary the proportion of exhaust gas directed to said different geometries.

(52) 22. The method of aspect 21 including the step of diverting to the downstream exhaust side of said turbocharger a proportion of exhaust gas from one or both said phases.