WO2001051786B1

WO2001051786B1 - Method and device for improving the operation of supercharged internal combustion engines at low engine revs

Info

Publication number: WO2001051786B1
Application number: PCT/FR2001/000053
Authority: WO
Inventors: Daniel Drecq
Original assignee: Daniel Drecq
Priority date: 2000-01-11
Filing date: 2001-01-09
Publication date: 2001-11-22
Also published as: AR026829A1; WO2001051786A1; FR2803628A1

Abstract

The supercharged 4-stroke internal combustion engine (M) comprises: a first cylinder (1) provided with an intake valve and an exhaust valve; means for controlling the opening of said exhaust valve after the opening of the intake valve during part of the intake phase of the above-mentioned cylinder; supercharging means generating boost pressure in an intake manifold (56, 1a) so that the boost pressure is greater than the pressure inside the first cylinder and the pressure inside the first cylinder is greater than the pressure in an exhaust manifold (57, 1e), said supercharging means including a main turbocharger (5); in addition to at least one second cylinder (4) connected to the same exhaust manifold (57) as the first cylinder, whereby the supercharging means include an auxiliary turbocompressor (15) and the inertia thereof is considerably lower than the inertia of the main turbocompressor (5).

Claims

MODIFIED CLAIMS [received by the International Bureau on August 6, 2001 (06.08.01); original claims 1 and 2 amended; other claims unchanged (5 pages)]

1. Method for improving the low-speed operation of a four-stroke thermal engine (M), supercharged by means of at least one main turbocharger (5) or another main compression means, said method comprising the steps consists in :

- open an exhaust valve (32) at the same time as an intake valve (31) of a first cylinder (1) of the engine during at least part of an intake phase of said first cylinder, so transferring intake air (40) from an intake manifold (56, la) through said first cylinder to an exhaust manifold (le, 57), a boost pressure (PI) being generated in said intake manifold so that, during said transfer, said boost pressure is greater than the pressure (P2) in said first cylinder and the pressure in said first cylinder is greater than the pressure (P3) in said manifold exhaust, said boost pressure being generated essentially using said main turbocharger (5) when the engine (M) is running at medium or high speed (Ω),

- temporarily store in said exhaust manifold (le, 57) said transferred intake air (41),

- generate an overpressure (49) in said exhaust manifold after closing (B) of the intake valve and before closing (B ') of the exhaust valve of the first cylinder by means of a puff of exhaust (42) of a second cylinder (4) connected to the same exhaust manifold (57) as the first cylinder, in order to post-fill said first cylinder with said intake air (43) previously stored in said manifold d exhaust, possibly mixed with exhaust gases, characterized in that it consists, at low speed and / or during at least one acceleration phase from substantially an engine idling speed (M), in generating said boost pressure (PI) in the intake manifold (56, la) essentially using an auxiliary turbocharger (15) of inertia significantly lower than the inertia of the main turbocharger (5), the compressor (17 ) and the turbine (16) of the auxiliary turbocharger being mounted in bypass on the intake and exhaust circuits of the engine respectively.

2. Supercharged four-stroke engine (M) comprising:

- a first cylinder (1) provided with an intake valve (31) for alternately opening or closing a communication between said first cylinder and an intake manifold (56, la) and with an exhaust valve (32 ) alternatively to open or close a communication between said first cylinder and an exhaust manifold (le, 57),

- valve control means (45,47,48) for controlling an opening of said exhaust valve after an opening of said intake valve during part of an intake phase (37) of said first cylinder, in order to transfer intake air (40, 41) from said intake manifold through said first cylinder to said exhaust manifold and to temporarily store said transferred intake air in said exhaust manifold, - boost means for generating a boost pressure (PI) in said intake manifold (56) so that, during said transfer, said boost pressure is greater than a pressure (P2) in said first cylinder and that the pressure in said first cylinder is greater than a pressure (P3) in said exhaust manifold, said supercharging means comprising a main turbocharger (5) or other main means of compression to essentially contribute to generating said boost pressure when the engine (M) is operating at medium or high speed (Ω), - at least one second cylinder (4) connected to the same exhaust manifold (57) as the first cylinder, the opening of an exhaust valve (35) of said second cylinder being controlled so as to generate an overpressure (49) in said exhaust manifold (57) after closing (B) of said intake valve (31 ) of said first cylinder and before closing of said exhaust valve (32) of said first cylinder, said 27

exhaust valve of the first cylinder remaining open only during the start of an exhaust phase (38 ') of the second cylinder, characterized in that said supercharging means comprise an auxiliary turbocharger (15) of inertia significantly less than the inertia of the main turbocharger (5), the compressor (17) and the turbine (16) of said auxiliary turbocharger being bypassed on respectively the intake and exhaust circuits of the engine, the compressor (17) of said auxiliary turbocharger being connected to said intake manifold (56) to essentially contribute to generating said boost pressure (PI) in the intake manifold at least when the engine (M) is running at low speed and / or during an acceleration phase from substantially an engine idling speed (M).

3. A heat engine (M) according to claim 2, characterized in that said exhaust manifold (57) is connected to a branch (10) between an inlet (1 1) of a turbine (6) of the main turbocharger and an inlet (21) of a turbine (16) of the auxiliary turbocharger, a means of distribution (22, 33) or of calibration (34) of flow being provided at said branch to direct a part of the exhaust gases towards the input of the turbine (16) of the auxiliary turbocharger (15) at least when the engine (M) is running at low speed and / or during said acceleration phase.

4. A heat engine (M) according to claim 3, characterized in that said exhaust manifold (57) has substantially the same length and substantially the same volume between said branch (10) on the one hand, and respectively the first (1) and second (4) cylinders on the other hand.

5. Heat engine (M) according to claim 4, characterized in that said exhaust manifold (57) has two openings opening respectively into said first and second cylinders, the section (19) of said openings being substantially greater than a section efficiency of the main turbine (6).

6. Heat engine (M) according to one of claims 3 to 5, characterized in that a first bypass line (68) provided with a first bypass valve (67) is provided between the inlet (1 1) of the turbine (6) of the main turbocharger and an exhaust pipe (12, 13), to limit an exhaust gas flow in said main turbine.

7. Heat engine (M) according to claim 6, characterized in that a second bypass line (65) provided with a second bypass valve (64) is provided between the inlet (21) of the auxiliary turbine (16) and the exhaust pipe, to limit the load of said auxiliary turbine to a predetermined maximum value.

8. Heat engine (M) according to claim 7, characterized in that said first and second bypass valves are servo-controlled as a function of the boost pressure (PI) so as to maintain the pressures at the outlet of the main compressor (7) and the auxiliary compressor (17) at substantially equal values.

9. Heat engine (M) according to one of claims 6 to 8, characterized in that it comprises an air intake manifold (18) connecting the compressor (17) of the auxiliary turbocharger (15) to said manifold intake (56), said intake manifold being optionally provided with a coolant (9).

10. Heat engine (M) according to claim 9, characterized in that a means of orientation (23, 24) of an air flow sucked by the compressor (17) of the auxiliary turbocharger (15) in the direction of the exhaust (13) is provided to reduce pollution of the exhaust (14).

11. Heat engine (M) according to claim 10, characterized in that said orientation means is a conduit (24) provided with a first servo-controlled valve (23), said intake manifold (18) being provided with a second servo-controlled valve (71), said first and second valves being servo-controlled as a function of the boost pressure (PI) so as to close the first valve (23) and to open the second valve (71) when said pressure at the outlet compressor main (7) is below a predetermined threshold, and to open the first valve and to close the second valve when said pressure at the outlet of the main compressor (7) exceeds said predetermined threshold.

12. A heat engine (M) according to any one of claims 2 to 1 1, characterized in that the main turbocharger (5) and the auxiliary turbocharger (15) suck the supply air through a common inlet (66 ), preferably through a filter (55).

13. A heat engine (M) according to any one of claims 2 to 12, characterized in that it comprises an even number of cylinders, preferably 4, 6 or 8 cylinders, said cylinders (1 -4) being matched by common exhaust manifolds (57,59), the respective operating cycles of the cylinders of each pair being phase shifted so that one (4) of said cylinders produces a burst of exhaust gas (42) in the manifold exhaust (57) common to the pair of cylinders (1, 4) so as to generate said overpressure (49) while the other (1) of said cylinders is substantially at the end of a suction phase.

14. A heat engine (M) according to any one of claims 2 to 13, characterized in that said intake manifold (56) is common to all the cylinders (1 -4).

15. Heat engine (M) according to any one of claims 2 to 14, characterized in that said low operating speed is less than 1300 rpm, preferably less than 1200 rpm, and for example l '' order of 1000 rpm or less.

16. A heat engine (M) according to any one of claims 2 to 15, characterized in that it is a diesel engine with direct or indirect injection or gasoline with direct injection.