EP2670957A1

EP2670957A1 - Gas exchange valve arrangement and cylinder head

Info

Publication number: EP2670957A1
Application number: EP12706626.4A
Authority: EP
Inventors: Sören HÖSTMAN; Håkan NYNÄS; Magnus Sundsten
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2011-02-02
Filing date: 2012-01-30
Publication date: 2013-12-11
Anticipated expiration: 2032-01-30
Also published as: CN103429857B; KR20140007886A; FI20115102A; WO2012104482A1; KR101681363B1; FI20115102A0; FI123409B; EP2670957B1; CN103429857A

Abstract

A gas exchange valve arrangement for a supercharged internal combustion engine, which arrangement comprises a gas exchange valve (1) having a valve head (2) and a valve stem (3) connected to the valve head (2), the arrangement further comprising a valve spring (4) being arranged around the valve stem (3) for creating a force for closing the valve (1), a chamber (5) being arranged around the valve stem (3), and thrust means (6, 19) being attached to the valve stem (3) and being movable in the direction of the longitudinal axis of the valve stem (3) together with the gas exchange valve (1). The arrangement comprises means (7, 14) for introducing pressurized charge from an air intake duct (10) of the engine air into the chamber (5) between the thrust means (6, 19) and the inner end of the chamber (5) for assisting in keeping the valve (1) closed. The invention also concerns a cylinder head (9).

Description

Gas exchange valve arrangement and cylinder head

Technical field of the invention

The present invention relates to a gas exchange valve arrangement for a supercharged internal combustion engine, as defined in the preamble of claim 1. The invention also concerns a cylinder head in accordance with the preamble of claim 14.

Background of the invention

Very high charge pressures are used in state-of-the-art compression ignition internal combustion engines to achieve better fuel efficiency. A practical method for achieving high charge pressures is to use two-stage turbocharging, where two turbochargers are connected in series. With two-stage turbocharging charge pressures of over ten bar can be achieved. High charge pressures are advantageously accompanied with Miller timing, where intake valves are closed well before bottom dead center during the intake stroke. Miller timing reduces cylinder temperature during combustion and helps to achieve lower NOx emissions. Since all the gas exchange valves are closed when the piston is still moving downwards, the cylinder pressure at the end of the intake phase might be significantly lower than the pressure in the air intake duct. A problem with large pressure differences over the intake valves is that standard valve springs have been designed for smaller pressure differences and the intake valves tend to open. A similar problem is encountered with the exhaust valves. Since a high charge pressure increases also the pressure in the exhaust manifold, greater force is needed for keeping the exhaust valves closed at the end of the intake phase and at the beginning of the compression phase. An obvious solution for solving this problem would naturally be the use of stiffer valve springs. However, this is often not possible without significant modifica- tions to the cylinder head. In many cases it would be very difficult or even impossible to redesign the cylinder head so that it could accommodate the larger springs needed to withstand the large pressure differences over the gas exchange valves.

One option for reducing the force the valve springs need to carry is to use air springs to assist conventional mechanical springs. Patent document US 6745738 Bl discloses a valve spring device using pressurized gas for biasing a gas exchange valve. The device comprises a dynamic housing having a chamber into which pressurized gas can be communicated so that the dynamic housing moves away from a static housing moving the attached valve. The device uses a sepa- rate pressure source and control means for controlling the flow of the pressurized gas into the dynamic chamber and out of the chamber.

Patent document US 5988124 A discloses an electromagnetically actuated cylinder valve having pneumatic resetting springs. The valve is opened and closed by means of electromagnetic actuators. Control means are needed for operating the gas springs. The arrangement also comprises a mechanical spring for closing the valve when the gas springs are in a depressurized state.

Patent application GB 2326444 A discloses another electro-pneumatically actuated gas exchange valve. The system may also employ a mechanical spring for closing the valve when the electro-pneumatic means are not activated. Also this system needs control means and a separate compressor for regulating the pressure in the gas springs.

In none of the above mentioned documents the air springs are meant for assisting the mechanical springs, but they are rather used for valve timing. The mechanical springs are provided for closing the valves when the air springs are depressurized. All of the disclosed systems use an external source of pressurized gas and control means for regulating gas flow into the gas springs. This makes the systems complicated and susceptible to malfunction.

Summary of the invention

The object of the present invention is to provide an improved gas exchange valve arrangement for a supercharged internal combustion engine. Another object of the invention is to provide an improved cylinder head. The characterizing features of the ar- rangement according to the present invention are given in the characterizing part of claim 1. The characterizing features of the cylinder head according to the present invention are given in the characterizing part of claim 14. According to the present invention, a gas exchange valve arrangement for a supercharged internal combustion engine comprises a gas exchange valve having a valve head and a valve stem connected to the valve head, and a valve spring arranged around the valve stem for creating a force for closing the valve. The arrangement further comprises a chamber being arranged around the valve stem, and thrust means being attached to the valve stem and being movable in the direction of the longitudinal axis of the valve stem together with the gas exchange valve. The arrangement comprises means for introducing pressurized charge air from an air intake duct of the engine into the chamber between the thrust means and the inner end of the chamber for assisting in keeping the gas exchange valve closed.

According to the present invention, a cylinder head for an internal combustion engine, which comprises a gas exchange valve having a valve head and a valve stem connected to the valve head, a valve spring being arranged around the valve stem for creating a force for closing the valve, a chamber being arranged around the valve stem, and thrust means being attached to the valve stem and being movable in the direction of the longitudinal axis of the valve stem together with the gas exchange valve, comprises a boring for introducing pressurized charge air from an air intake duct of the engine into the chamber between the thrust means and the inner end of the chamber for assisting in keeping the gas exchange valve closed.

The invention has many advantages. Because pressurized charge air from the air intake duct is used to assist in keeping the valves closed, leakage from the air intake duct and the exhaust gas duct into the cylinder can be prevented even with very high charge air pressures. The arrangement is very compact and is suitable even for existing cylinder heads with only minor modifications. Since charge air from the air intake duct is used for keeping the valves closed, an auxiliary system for pressurized air is not needed. Neither is there a need for more robust steel springs, but normal springs can be used. The arrangement is also self-adjusting. Larger force is needed to keep the gas exchange valves closed when higher charge air pressures are used, and in the arrangement according to the present invention this larger force is automatically created. Similarly, when the engine is operated at low load, the force resisting opening of the valves is lower and friction in cam shaft and rocker arm bearings is minimized. Since the arrangement is provided also with normal springs, starting of the engine is not problematic.

According to an embodiment of the invention, the means for introducing charge air into the chamber comprise an aperture in the chamber and a boring in a cylinder head. If the charge air is introduced into the chamber through a boring in the cylinder head, no extra piping is needed above the cylinder head. According to an embodiment of the invention the boring is arranged in the cylinder head between the chamber and the air intake duct. This is the simplest route for introducing the charge air into the chamber. The boring can also be provided with a check valve. The cylinder head can also be provided with a second boring for letting the charge air out of the chamber.

According to an embodiment of the invention, the thrust means is a thrust plate arranged inside the chamber. This kind of arrangement is relatively easy to provide with good sealing performance and the thrust plate can also work as a valve rotator. Another alternative is that the thrust means is a cap forming part of the chamber.

Other features of the embodiments of the present invention are given in the dependent claims.

Brief description of the drawings

Fig. 1 shows a cross-sectional view of a cylinder head of an internal combustion engine with a gas exchange valve arrangement according to an embodiment of the present invention.

Fig. 2 shows a cross-sectional view of a cylinder head according to another embodiment of the invention.

Fig. 3 shows a cross-sectional view of a cylinder head according to a third embodiment of the invention.

Fig. 4 shows a cross-sectional view of a cylinder head according to a fourth embodi- ment of the invention. Detailed description of the invention

Embodiments of the invention are now described in more detail with reference to the accompanying drawings. In Fig. 1 is shown a simplified cross-sectional view of a cylinder head 9 of a large compression ignition internal combustion engine that could, for instance, be a main or auxiliary engine of a ship or which could be used in a power plant. The invention is not, however, limited to compression ignition engines, but could also be used in spark ignition engines. The engine is supercharged for achieving high intake air pressure. For in- stance two turbochargers that are connected in series can be used, each of the turbo- chargers comprising a turbine and a compressor. Only one cylinder 12 is shown, but the engine can comprise a plurality of cylinders 12 and each of the cylinders is equipped with its own cylinder head 9. The cylinders 12 can be arranged for instance in-line or in a V-configuration. Through the cylinder head 9 goes an air intake duct 10 for introduc- ing pressurized charge air into the cylinder 12 and an exhaust duct 11 for guiding exhaust gas out of the cylinder 12. Only those parts of the air intake duct 10 and the exhaust duct 1 1 that are inside the cylinder head 9 are shown in figure 1. However, the air intake duct 10 and the exhaust duct 1 1 continue outside the cylinder head 9 and are connected to the compressors and turbines of the turbochargers, respectively. The air intake duct 10 is equipped with intake valves la and the exhaust duct 11 is equipped with exhaust valves lb. Together the intake valves la and the exhaust valves lb are referred to as gas exchange valves 1. Parts related to the intake valves la are denoted in the figures by reference numbers ending with 'a' and parts related to the exhaust valves lb are denoted by reference numbers ending with 'b'. In the description and claims, identical or similar parts may be referred to collectively by reference numbers without either of the letters at the end.

The engine comprises two intake valves la and two exhaust valves lb, but only one of both valve types can be seen in figure 1. Of course, the number of gas exchange valves 1 could also be different. The gas exchange valve 1 comprises a valve head 2 and a valve stem 3. When the gas exchange valve 1 is closed, it forms a tight connection with a valve seat 13. The valve stem 3 is connected to the valve head 2 and is needed for moving the gas exchange valve 1 in a reciprocating manner for opening and closing the flow connection between the cylinder 12 and the air intake duct 10 or the exhaust gas duct 11. The cylinder head 9 is provided with valve guides 15 for aligning the gas exchange valves 1. A conventional cam mechanism with push rods and rocker arms (not shown in the figures) is used for opening the gas exchange valves 1.

Each gas exchange valve 1 is provided with a spring 4 that creates a force with a direction away from the cylinder 12. This force tends to close the valve 1 and keep it closed. In the embodiment of figure 1 , also a second spring 8 is provided for each gas exchange valve 1 for increasing the closing force.

A chamber 5 is arranged around the stem 3 of each gas exchange valve 1. In the embodiment of figure 1 , the chamber 5 is partly inside the cylinder head 9 and partly above it. The springs 4, 8 are arranged inside the chamber 5. Inside the chamber 5 there is also a thrust plate 6 that is attached to the valve stem 3. The chamber 5 is provided with an aperture 7 for introducing pressurized charge air from the air intake duct 10 into the chamber 5. The aperture 7 is at the inner end of the chamber 5, i.e. at that end of the chamber 5 that is closer to the cylinder 12. The charge air can thus be introduced into the chamber 5 between the inner end of the chamber 5 and the thrust plate 6. The thrust plate 6 can move in the longitudinal direction of the valve stem 3 together with the whole gas exchange valve 1. The thrust plate 6 is in close contact with the wall of the chamber 5 so that a significant gas flow past the thrust plate 6 cannot occur. When the gas exchange valve 1 is closed, the thrust plate 6 is at the outer end of the chamber 5. Since the pressure in the air intake duct 10 is high due to the supercharging of the intake air, the charge air introduced into the chamber 5 pushes the thrust plate 6 upwards and assists in keeping the gas exchange valve 1 closed. The thrust plate 6 also works as a valve rotator and turns the gas exchange valve 1 slightly each time the valve 1 closes. In the embodiment of figure 1, there is provided a boring 14a in the cylinder head 9 between the air intake duct 10 and the chamber 5 a that is in connection with the intake valve la. Through the boring 14a the charge air is introduced into the chamber 5a. When the intake valve la is closed, the same pressure is applied to the top surface of the valve head 2a of the intake valve la as to the thrust plate 6a. The force created by the pressure applied to the valve head 2a pushes the intake valve la towards the cylinder 12. Since the area of the valve head 2a is close to the area of the thrust plate 6a, the forces in opposite directions compensate each other to a large extent and the force created by the springs 4a, 8a is sufficient for keeping the intake valve la closed.

To the chamber 5b that is in connection with the exhaust valve lb, the charge air is introduced through a boring in the cylinder head 9. In figure 1 this boring is not shown. Exhaust gas from the exhaust gas duct 11 cannot be used because of the high tempera- ture and soot. The same working principle of the arrangement applies to the exhaust valve lb as to the intake valve la. The pressure in the exhaust duct 11 is lower than in the air intake duct 10, but it is in the same order of magnitude. Therefore, the forces applied to the top surface of the valve head 2b of the exhaust valve lb and to the thrust plate 6b or compensate each other to a large extent and the force created by the springs 4b, 8b is sufficient for keeping the exhaust valve lb closed.

The arrangement is self-adjusting - at the intake side the same pressure is applied to two surfaces of almost equal size but in opposite directions. Therefore, the forces created by the pressure compensate each other to a large extent. At the exhaust side the opposite forces are caused by different pressures, but even there they correlate with each other. As the pressure in the air intake duct 10 increases, also the pressure in the exhaust gas duct 11 increases, and the forces caused by these pressures compensate each other at least partly. Figure 2 shows another embodiment of the invention. Only the intake valves la, la' are shown in the figure. The main difference between the embodiments of figure 1 and figure 2 is that in the embodiment of figure 2, the springs 4a, 4a' are arranged outside the chambers 5a, 5a'. Separate borings 14a, 14a' are arranged between the air intake duct 10 and the chambers 5a, 5a' for introducing charge air into the chambers 5a, 5a'. An advantage of this embodiment is that the spring force is not directed to the thrust plates 6a, 6a' and the valve rotation works better. Another advantage is that the springs 4a, 4a' can be arranged in oil bath. In the embodiment of figure 3, charge air is introduced into the chamber 5a' that is in connection with the second intake valve la' from the chamber 5a that is connection with the first intake valve la through a boring 14a' that is between the chambers 5a, 5a'. In this embodiment, the valve springs 4a, 4a' are inside the chamber 5a, 5a'. However, the springs 4a, 4a' are not supported against the thrust plates 6a, 6a' that work as the valve rotators. Instead, the springs 4a, 4a' are supported against collars 16a, 16a'. Smaller force is thus exerted towards the valve rotators 6a, 6a', and better functioning is ensured. In the embodiment of figure 4, there are no thrust plate 6a, 6b inside the chambers 5a, 5b. Instead, the outer ends of the chambers 5a, 5b, i.e. those ends of the chambers 5a, 5b that are farther from the cylinder 12, are formed of caps 19a, 19b that work as the thrust means 6, 19. The caps 19a, 19b are attached to the valve stems 3a, 3b of the gas exchange valves la, lb and sealed against the walls of the inner parts of the chambers 5a, 5b. The caps 19 thus form part of the chambers 5a, 5b. The inner ends of the chambers 5 a, 5b are formed inside the cylinder head 9. The borings 14a, 14b for introducing charge air into the chambers 5 a, 5b are provided with check valves 17a, 17b that prevent the charge air from flowing back into the air intake duct 10. Second borings 18a, 18b are arranged in the cylinder head 9 between the chambers 5 a, 5b and the exhaust gas duct 11 for letting the charge air out of the chambers 5a, 5b when the gas exchange valves la, lb are opened. The embodiment of figure 4 works according to the same principle as the previous embodiments.

Many modifications of the present invention are possible within the scope of the ap- pended claims. For instance, it is possible to arrange the chamber completely above the cylinder head. It is not necessary to introduce the charge air into the chamber through a boring in the cylinder head, but separate piping could be arranged for this purpose. In that case, the arrangement could also comprise means for controlling the pressure in the chamber, and/or a receiver for storing the charge air before introducing it into the chambers. It would also be possible to introduce the charge air into a chamber that is in connection with an exhaust valve from a chamber that is in connection with an intake valve trough an external pipe or hose.

Claims

1. A gas exchange valve arrangement for a supercharged internal combustion engine, which arrangement comprises an exhaust valve (lb) having a valve head (2) and a valve stem (3) connected to the valve head (2), the arrangement further comprising a valve spring (4) being arranged around the valve stem (3) for creating a force for closing the valve (lb), a chamber (5) being arranged around the valve stem (3), and thrust means (6, 19) being attached to the valve stem (3) and being movable in the direction of the longitudinal axis of the valve stem (3) together with the exhaust valve (lb), characterized in that the arrangement comprises means (7, 14) for introducing pressurized charge air from an air intake duct (10) of the engine into the chamber (5) between the thrust means (6, 19) and the inner end of the chamber (5) for assisting in keeping the exhaust valve (lb) closed.

2. An arrangement according to claim 1, characterized in that the means for introducing charge air into the chamber (5) comprise an aperture (7) in the chamber (5) and a boring (14) in a cylinder head (9).

3. An arrangement according to claim 2, characterized in that the boring (14) is arranged in the cylinder head (9) between the chamber (5) and the air intake duct (10).

4. An arrangement according to claim 2 or 3, characterized in that the boring (14) is provided with a check valve (17).

5. An arrangement according to any of claims 2-4, characterized in that the cylinder head (9) is provided with a second boring (18) for letting the charge air out of the chamber (5).

6. An arrangement according to claim 5, characterized in that the second boring (18) is arranged between the chamber (5) and an exhaust gas duct (11).

7. An arrangement according to any of the preceding claims, characterized in that the thrust means (6, 19) is a thrust plate (6) arranged inside the chamber (5).

8. An arrangement according to claim 7, characterized in that the thrust plate (6) works as a valve rotator.

9. An arrangement according to any of claims 1-6, characterized in that the thrust means (6, 19) is a cap (19) forming part of the chamber (5).

10. An arrangement according to any of the preceding claims, characterized in that the chamber (5) is arranged at least partly inside a cylinder head (9).

11. An arrangement according to any of the preceding claims, characterized in that the valve spring (4) is arranged inside the chamber (5).

12. An arrangement according to any of the preceding claims, characterized in that the charge air is introduced from a chamber (5 a) that is in connection with an intake valve (la) into a chamber (5b) that is in connection with an exhaust valve (lb).

13. An arrangement according to claim 12, characterized in that the charge air is introduced into the chamber (5b) that is in connection with an exhaust valve (lb) through a boring in a cylinder head (9).

14. A cylinder head (9) for an internal combustion engine, the engine comprising an exhaust valve (lb) having a valve head (2) and a valve stem (3) connected to the valve head (2), a valve spring (4) being arranged around the valve stem (3) for creating a force for closing the valve (lb), a chamber (5) being arranged around the valve stem (3), and thrust means (6, 19) being attached to the valve stem (3) and being movable in the direction of the longitudinal axis of the valve stem (3) together with the exhaust valve (lb), characterized in that the cylinder head (9) comprises a boring (14) for introducing pressurized charge air from an air intake duct (10) of the engine into the chamber (5) between the thrust means (6, 6') and the inner end of the chamber (5) for assisting in keeping the exhaust valve (lb) closed.

15. A cylinder head according to claim 14, characterized in that the cylinder head (9) comprises a second boring (18) for letting the charge air out of the chamber (5).