EP2941545B1

EP2941545B1 - Exhaust valve arrangement and method for controlling closing of an exhaust valve

Info

Publication number: EP2941545B1
Application number: EP13818759.6A
Authority: EP
Inventors: Magnus Sundsten; Saku Niinikangas
Original assignee: Wartsila Finland Oy
Current assignee: Wartsila Finland Oy
Priority date: 2013-01-03
Filing date: 2013-12-27
Publication date: 2016-11-23
Anticipated expiration: 2033-12-27
Also published as: KR20150102118A; FI20135003L; CN104903552B; EP2941545A1; WO2014106681A1; KR102192961B1; CN104903552A

Description

Technical field of the invention

The present invention relates to an exhaust valve arrangement for a piston engine in accordance with the preamble of claim 1. The invention also concerns a method for controlling closing of an exhaust valve of a piston engine, as defined in the preamble of the other independent claim.

Background of the invention

Many internal combustion engines are provided with means for variable intake valve closing (VIC), which allows different intake valve closing timings for optimizing the performance of the engine. Recently, also arrangements for variable exhaust valve closing (VEC) have become more common. VEC arrangements are beneficial especially in engines utilizing two-stage turbocharging. When the charge pressures can be high, different scavenging is needed at different loads. When the engine is operated at a high load, long scavenging time is needed for cooling down components of the engine. The exhaust valves are thus kept open for a long time during the exhaust stroke. On the other hand, when the engine is operated at a low load, the pressure of the intake air is lower than the pressure of the exhaust gases. In order to prevent flow from the exhaust duct into the intake duct, the exhaust valves need to be closed at the same time or slightly after the intake valves have been opened. Variable exhaust valve closing timing is useful also in engines comprising means for cooling recirculated exhaust gases with water injection. When the water injection is in use, overlap of the intake and exhaust valves is not needed, but if the water injection needs to be shut down, longer scavenging is needed for allowing operation of the engine at the full load. VEC arrangements are often implemented by utilizing a chamber that is arranged between the exhaust valves and the cam operating the exhaust valves. The exhaust valves are opened in a conventional manner by the cam. During the opening movement of the exhaust valves, hydraulic fluid is introduced into the chamber. The closing moment and closing speed of the exhaust valves depends on the outflow from the chamber. For instance, a closing delay can be provided by preventing the outflow by a valve. A problem with this kind of solutions is that in case of malfunction of the system, closing of the exhaust valve can be prevented and the piston may hit the exhaust valve causing extensive damage.

Summary of the invention

An object of the present invention is to provide an improved exhaust valve arrangement for a piston engine, which arrangement allows a delay in the closing of the exhaust valve, but prevents the pistons of the engine from hitting the exhaust valves. The characterizing features of the arrangement according to the invention are given in the characterizing part of claim 1. Another object of the invention is to provide an improved method for controlling closing of an exhaust valve of a piston engine. Characterizing features of the method are given in the characterizing part of the other independent claim.
The arrangement according to the invention comprises at least one exhaust valve, a rotatable cam, force transmission means for transforming the rotating motion of the cam into linear motion and transmitting it to the exhaust valve at least in the opening direction of the exhaust valve, a fluid chamber, into which fluid chamber hydraulic fluid can be introduced during the opening movement of the exhaust valve, a piston that is arranged in the fluid chamber and connected to the force transmission means or to the exhaust valve, at least one outlet port for discharging the hydraulic fluid from the fluid chamber for allowing closing of the exhaust valve, and flow control means for controlling outflow from the fluid chamber and allowing slowing or delaying of the closing movement of the exhaust valve. The outlet ports and the flow control means are configured to allow outflow from the fluid chamber at a rate that allows the closing curve of the exhaust valve to follow the cam curve at least until the exhaust valve has moved a certain predetermined distance in the closing direction.
In the method according to the invention, hydraulic fluid is introduced into a fluid chamber during the cam-controlled opening movement of the exhaust valve, and outflow from the fluid chamber is controlled for affecting the movement of a piston that is arranged in the fluid chamber and connected to the exhaust valve or to force transmission means between a cam and the exhaust valve and for allowing slowing or delaying of the closing movement of the exhaust valve. Outflow from the fluid chamber is allowed at a rate that allows the closing curve of the exhaust valve to follow the cam curve at least until the exhaust valve has moved a certain predetermined distance in the closing direction.
The expression "closing curve" means the lift of the exhaust valve as a function of crank angle. The expression "cam curve" means the movement of a cam follower as a function of the crank angle. When a delay function is not in use and the lift of the exhaust valve is determined by the shape of the cam, the closing curve of the exhaust valve thus corresponds the cam curve. With the arrangement and method according to the invention, the closing of an exhaust valve can be delayed or slowed down without the risk of a piston of the engine hitting the exhaust valve. When the closing movement of the exhaust valve starts, the outflow from the fluid chamber is not restricted. Only after the valve has moved a certain distance, throttling of the outflow takes place. The distance is determined so that the valve lift at the moment when the throttling starts is smaller than the distance between a closed exhaust valve and the piston of the engine in the respective cylinder at top dead center. The closing curve of the exhaust valve corresponds thus first the cam curve, but after the throttling starts, the slope of the closing curve can be less steep than the slope of the cam curve.
There are many alternative ways to control the outflow from the fluid chamber. For instance, the piston in the fluid chamber can be arranged to throttle the flow. The end part of the piston can have smaller diameter than the rest of the piston. When the exhaust valve is fully open, also the outlet ports of the fluid chamber are fully open. When the piston has moved the predetermined distance, it covers one or more outlet ports, and outflow from the fluid chamber is allowed through a small gap that is formed between the piston and the wall of the fluid chamber.
Another option is to provide the fluid chamber with two or more outlet ports, which are at different heights, i.e. at different distances from the end of the fluid chamber. When the exhaust valve is fully open, also all the outlet ports are fully open. When the piston has moved the predetermined distance, it blocks at least one of the outlet ports and the outflow is thus restricted. Some of the outlet ports or outlet ducts in connection with the outlet ports can be provided with throttles. The throttles can be adjustable. It is also possible to provide some of the outlet ports or ducts with a valve, which allows adjustment of the outflow.

Brief description of the drawings

Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which

Fig. 1 shows an exhaust valve opening mechanism with a VEC-function,
Fig. 2 shows an exhaust valve arrangement according to an embodiment of the invention,
Fig. 3 shows a second embodiment of the invention,
Fig. 4 shows a third embodiment of the invention,
Fig. 5 shows a fourth embodiment of the invention,
Fig. 6 shows a fifth embodiment of the invention,
Fig. 7 shows valve lifts when VEC-function is switched off, and
Fig. 8 shows valve lifts when VEC-function is switched on.

Description of embodiments of the invention

The exhaust valve arrangement according to the invention is especially suitable for large internal combustion engines, such as main or auxiliary engines of ships or engines that are used at power plants for producing electricity. The invention is particularly useful in engines with two-stage turbocharging and in engines where water cooling of recirculated exhaust gases is used. However, the arrangement can also be used in other types of engines.
In figure 1 is shown an example of a valve opening mechanism for an exhaust valve 13. In the case each cylinder of the engine is provided with more than 1 exhaust valve 13, the valve opening mechanism can be used for controlling all the exhaust valves 13 of one cylinder. The exhaust valve 13 is arranged in a cylinder head 18 for opening and closing fluid communication between a cylinder 16 of the engine and an exhaust duct 17. A spring 15 is arranged around the stem of the exhaust valve 13 to keep the exhaust valve 13 closed when it is not actuated. The valve opening mechanism is provided with a VEC-function for delaying the closing of the exhaust valve 13. The valve opening mechanism comprises a cam 1, which is part of a camshaft. The cam 1 is provided with a base circle 1 a and a lobe 1 b extending radially outwards from the base circle 1 a. A cam follower wheel 2a of a cam follower unit 2 is constantly engaged with the cam 1. The arrangement can be provided with a spring, which presses the cam follower wheel 2a against the cam 1. The opening of the exhaust valves 13 works in a conventional manner. When the cam follower wheel 2a becomes engaged with the lobe 1 a of the cam 1, the cam follower unit 2 is pushed away from the rotation axis of the cam 1, i.e. upwards in figure 1. The cam follower unit 2 forms part of force transmission means 2, 3, 14, 19, which transform the rotating motion of the cam 1 into linear motion and further transmit the movement to the exhaust valves 13. The force transmission means further comprise a first push rod 3, a second push rod 19 and a rocker arm 14. The first push rod 3 is in mechanical contact with the cam follower unit 2 at least in the opening direction of the exhaust valves 13. The second push rod 19 is connected to a rocker arm 14. The rocker arm 14 transmits the movement of the second push rod 19 to the exhaust valves 13. Also many other types of force transmission means could be used. For instance, part of the force transmission path could be hydraulic.
For slowing down or delaying the closing movement of the exhaust valves 13, the valve opening mechanism is provided with a fluid chamber 4, into which hydraulic fluid can be introduced during the opening movement of the exhaust valves 13. The fluid chamber 4 is connected to an inlet duct 5 through an inlet port 5a. Hydraulic fluid can be introduced into the fluid chamber 4 through the inlet duct 5 and the inlet port 5a. The arrangement could also be provided with two or more inlet ports 5a and/or ducts 5. The inlet duct 5 is provided with a check valve 6, which allows flow into the fluid chamber 4 but not out of the chamber 4. Instead of the check valve 6, or in addition to it, the inlet duct 5 can be provided with a closing valve for selectively allowing or preventing flow into the fluid chamber 4. The closing valve allows the VEC-function to be switched on and off. If the closing valve is closed, flow into the fluid chamber 4 is not allowed, and the VEC-function is switched off. The valve opening mechanism works then in the same way as a conventional cam-controlled exhaust valve opening mechanism. Figure 7 shows the valve lifts when the VEC is switched off. The hatched area shows the overlap of the exhaust and the intake valves.
A piston 7 is arranged in the fluid chamber 4. The piston 7 delimits the fluid chamber 4 and the hydraulic fluid is introduced between the piston 7 and the camshaft end of the fluid chamber 4. In the embodiment of figure 1, the piston 7 is connected to the first push rod 3 and the second push rod 19, i.e. the piston is between the first push rod 3 and the second push rod 19. The first push rod 3 transmits the movement of the cam follower unit 2 to the piston 7 in the opening direction of the exhaust valves 13 and the second push rod 19 transmits the movement of the piston 7 to the rocker arm 14. However, the fluid chamber 4 and the piston 7 could also be located in many other ways. In principle, the fluid chamber 4 could be arranged inside the cylinder head 18 and the piston 7 could be connected to the stem of the exhaust valve 13, but this may be impractical. However, the piston 7 can be connected to some other part of the force transmission means than the first push rod 3 and the second push rod 19. The piston 7 always moves together with the exhaust valves 13.
When the cam follower wheel 2a becomes engaged with the lobe 1a of the cam 1, the piston 7 is moved together with the first push rod 3. If the closing valve is open, the movement of the piston 7 sucks hydraulic fluid from the inlet duct 5 into the fluid chamber 4. The first push rod 3 remains engaged with the cam follower unit 2. When the cam 1 has rotated so that the cam follower wheel 2a is engaged with the tip of the lobe 1 a, the exhaust valves 13 are fully open. When the cam follower wheel 1 a enters the descending ramp of the lobe 1a, the exhaust valves 13 start closing. When the closing movement of the exhaust valves 13 starts, the exhaust valves 13 first follow the cam curve. By limiting the outflow from the fluid chamber 4, the closing speed of the exhaust valves can be slowed down. In figure 8, the lift of the exhaust valve 13 is shown with a solid line and the cam curve is shown with a broken line. The hatched area shows the overlap of the exhaust 13 and the intake valves.
In figure 2 is shown one arrangement for limiting outflow from the fluid chamber 4 of the valve opening mechanism of figure 1. In the embodiment of figure 2, the fluid chamber 4 is provided with one outlet port 8 and an outlet duct 9 that is in connection with the outlet port 8. The outlet port 8 and the outlet duct 9 are dimensioned so that maximum flow rate through the outlet port 8 is adequate for allowing the piston 7 to follow the cam curve at the beginning of the closing movement of the exhaust valves 13. When the exhaust valves 13 and the piston 7 have moved a certain predetermined distance in the closing direction of the exhaust valves 13, the piston 7 starts to throttle the flow out of the fluid chamber 4. This happens when the camshaft end of the piston 7 is at the level of the outlet port 8, i.e. in phase 3 of figure 2. The diameter of the piston 7 at the camshaft end of the piston 7 is slightly smaller than the diameter of the rest of the piston 7. The piston 7 does thus not block the outlet port 8 completely, but a small gap is formed between the piston 7 and the wall of the fluid chamber 4. The hydraulic fluid can flow through this gap to the outlet port 8. However, the flow is throttled so that the piston 7 is not able to follow the cam follower unit 2. The piston 7 thus works as a flow control means and slows down the closing speed of the exhaust valves 13 so that a gap is formed between the first push rod 3 and the cam follower unit 2, as shown in phase 4 of figure 2. As can be seen in figure 8, the slope of the closing curve of the exhaust valves 13 is less steep than the cam curve and the closing movement of the exhaust valves 13 continues when the cam follower wheel 2a has already returned to the base circle 1a of the cam 1. The duration of the scavenging time is longer than in case the VEC is switched off. When the piston 7 is close to the camshaft end of the fluid chamber 4, the thicker part of the piston 7 partly blocks the outlet port 8, as shown in phase 5 of figure 2. The closing speed of the exhaust valves 13 is thus further decreased for allowing smooth closing. Eventually the fluid chamber 4 is emptied and the first push rod 3 becomes engaged with the cam follower unit 2 again, as can be seen in phase 6 of figure 2. The piston 7 can have more than two different diameters to allow the closing speed of the exhaust valves 13 to change gradually, or the diameter of the piston 7 can decrease steplessly.
In figure 3 is shown another embodiment of the invention. The operating principle of this embodiment is the same as in the embodiment of figure 1. Also in the arrangement of figure 3, hydraulic fluid is introduced into a fluid chamber 4 during the opening movement of the exhaust valves 13 and the piston 7 works as a flow control means. When the cam follower wheel 2a enters the descending ramp of the lobe 1 a of the cam 1, the exhaust valves 13 can first move freely. The fluid chamber 4 is provided with a first outlet port 8a, a second outlet port 8b and a third outlet port 8c and with respective outlet ducts 9a, 9b, 9c. The second outlet duct 9b is provided with a valve 10, which can be used for preventing flow in the second outlet duct 9b. The valve 10 works as an additional flow control means. At the beginning of the closing movement of the exhaust valves 13, the hydraulic fluid can flow out of the fluid chamber through all the outlet ports 8a, 8b, 8c. The outlet ports 8a, 8b, 8c and ducts 9a, 9b, 9c are dimensioned so that the exhaust valves 13 are able to follow the cam curve when the first and the third outlet ports 8a, 8c are free. This ensures that an adequate closing speed is achieved even if the valve 10 of the second outlet duct 9b is closed. When the piston 7 has moved a certain distance, it blocks the first outlet port 8a and the outflow from the fluid chamber 4 is restricted. When the piston 7 moves even closer to the camshaft end of the fluid chamber 4, the piston 7 blocks also the second outlet port 8b, and the hydraulic fluid can flow out of the fluid chamber 4 only through the third outlet port 8c. This ensures that the exhaust valves 13 are closed smoothly. The valve 10 in the second outlet duct 9b can be used for preventing flow through the second outlet port 8b even earlier.
In the embodiment of figure 4, the arrangement is provided with two outlet ports 8a, 8b and outlet ducts 9a, 9b. At the beginning of the closing movement of the exhaust valves 13, the hydraulic fluid can flow out of the fluid chamber 4 through both the first outlet port 8a and duct 8b and the second outlet port 9a and duct 9b. The outlet ports 8a, 8b and ducts 9a, 9b are dimensioned so that the exhaust valves 13 can follow the cam curve when both outlet ports 8a, 8b are open. After the piston 7 has moved a certain distance, it blocks the first outlet port 8a and the outflow is restricted. The second outlet duct 9b is provided with an adjustable throttle 11, which works as an additional flow control means. With the throttle 11, different closing curves can be achieved. The throttle 11 can also be used to restrict the outflow more at the end of the closing movement of the exhaust valves 13 to ensure smooth closing.
The embodiment of figure 5 is similar to the embodiment of figure 4. In this embodiment, the second outlet duct 9b is not provided with a throttle, but the second outlet duct 9b is connected to a second chamber 12, in which the cam follower unit 2 is arranged to move. When the cam follower wheel 2a is on the lobe 1 b of the cam 1, the cam follower unit 1 blocks the other end of the second outlet duct 9b. At the beginning of the closing movement of the exhaust valves 13, the hydraulic fluid can freely flow out of the fluid chamber 4 through the first outlet port 8a. The first outlet port 8a and the first outlet duct 9a are dimensioned so that the flow rate through the first outlet port 8a is adequate to allow the exhaust valves 13 to follow the cam curve. When the exhaust valves 13 have moved a certain distance in the closing direction of the valves 13, the piston 7 blocks the first outlet port 8a. Outflow from the fluid chamber 4 is thus prevented. When the cam follower wheel 2a enters the base circle 1a of the cam 1, fluid flow through the second outlet port 8b into the second chamber 12 is allowed. However, the emptying of the fluid chamber 4 does not happen instantly, and the closing of the exhaust valves 13 is thus delayed.
Also figure 6 shows an embodiment, where the arrangement is provided with two outlet ports 8a, 8b and outlet ducts 9a, 9b. The second outlet duct 9b is provided with a quick-closing valve 10, which can be operated for example electrically or hydraulically. The first outlet port 8a and the first outlet duct 9a are dimensioned so that the flow rate through the first outlet port 8a is adequate for allowing the exhaust valves 13 to follow the cam curve. This ensures that the fluid chamber 4 is emptied quickly enough even in case the valve 10 of the second outlet duct 9b does not work. At the beginning of the closing movement of the exhaust valves 13, outflow from the fluid chamber 4 is allowed both through the first outlet port 8a and the second outlet port 8b. After the piston 7 has moved a certain distance, the piston 7 blocks the first outlet port 8a and outflow is allowed only though the second outlet port 8b. The valve 11 in the second outlet duct 9b can be used for controlling the flow through the second outlet port 8b for achieving the desired exhaust valve closing curve. As a safety arrangement, the fluid chamber 4 can be provided with a third outlet duct, in which duct flow is prevented when the cam follower wheel 2a is on the base circle 1 a or the lobe 1 b of the cam 1. For instance, the other end of the third outlet duct can be blocked by the cam follower unit 2. The profile of the cam 1 is further provided with a portion that is below the base circle 1 a of the cam 1. When the cam follower wheel 2a enters the portion below the base circle 1 a, flow through the third outlet duct is allowed. By this arrangement emptying of the fluid chamber 4 and closing of the exhaust valves 13 can be ensured even in the case of malfunction of the valve 11 in the second outlet duct 9b.
In all the described embodiments, the throttling of the outflow takes place only after the exhaust valves have 13 been closed enough for preventing the piston of the cylinder 16 from hitting the exhaust valves 13. When the throttling starts, the exhaust valve lift is thus smaller than the distance between a closed exhaust valve 13 and the piston at top dead center, as can be seen in figures 7 and 8, which show also the movement of the piston around top dead center.
In all the described embodiments of the invention, the predetermined distance, after which the throttling of the outflow from the fluid chamber 4 can start, is determined such that contact between the exhaust valve 13 and the piston in the respective cylinder of the engine is prevented. The lift of the exhaust valve 13 in the corresponding position is thus smaller than the distance between a closed exhaust valve 13 and the respective piston of the engine when the piston is at top dead center.
It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims. For instance, features from the different embodiments can be combined.

Claims

An exhaust valve arrangement for a piston engine, which exhaust valve arrangement comprises at least one exhaust valve (13), a rotatable cam (1), force transmission means (2, 3, 14, 19) for transforming the rotating motion of the cam (1) into linear motion and transmitting it to the exhaust valve (13) at least in the opening direction of the exhaust valve (13), a fluid chamber (4), into which fluid chamber (4) hydraulic fluid can be introduced during the opening movement of the exhaust valve (13), a piston (7) that is arranged in the fluid chamber (4) and connected to the force transmission means (2, 3, 14, 19) or to the exhaust valve (13), at least one outlet port (8, 8a, 8b, 8c) for discharging the hydraulic fluid from the fluid chamber (4) for allowing closing of the exhaust valve (13), and flow control means (7, 10, 11) for controlling outflow from the fluid chamber (4) and allowing slowing or delaying of the closing movement of the exhaust valve (13), which outlet ports (8, 8a, 8b, 8c) and flow control means (7, 10, 11) are configured to allow outflow from the fluid chamber (4) at a rate that allows the closing curve of the exhaust valve (13) to follow the cam curve at least until the exhaust valve (13) has moved a certain predetermined distance in the closing direction, characterized in that the outflow from the fluid chamber (4) is unthrottled until the exhaust valve (13) has moved the predetermined distance and after the exhaust valve (13) has moved the predetermined distance, throttling of the outflow takes place, and that the distance is determined so that the valve lift at the moment when the throttling starts is smaller than the distance between closed exhaust valve (13) and the piston (7) of the piston engine at top dead center.
An arrangement according to claim 1, characterized in that the predetermined distance is determined such that in the corresponding position of the exhaust valve (13) a contact between the exhaust valve (13) and the piston of the engine in the respective cylinder is prevented.
An arrangement according to claim 1 or 2, characterized in that the piston (7) in the fluid chamber (4) is arranged to throttle outflow from the fluid chamber (4) after the exhaust valve (13) has moved the predetermined distance.
An arrangement according to claim 1 or 2, characterized in that the fluid chamber (4) comprises at least two outlet ports (8, 8a, 8b, 8c) and the piston (7) is arranged to block at least one of the outlet ports (8, 8a, 8b, 8c) after the exhaust valve (13) has moved the predetermined distance.
An arrangement according to claim 4, characterized in that at least one of the outlet ports (8, 8a, 8b, 8c) or an outlet duct (9, 9a, 9b, 9c) in connection with the outlet port (8, 8a, 8b, 8c) is provided with a throttle (11).
An arrangement according to claim 5, characterized in that the throttle (11) is adjustable.
An arrangement according to claim 4, characterized in that at least one of the outlet ports (8, 8a, 8b, 8c) or an outlet duct (9, 9a, 9b, 9c) in connection with the outlet port 8, (8a, 8b, 8c) is provided with a valve (10).
A method for controlling closing of an exhaust valve (13) of a piston engine, in which method hydraulic fluid is introduced into a fluid chamber (4) during the cam-controlled opening movement of the exhaust valve (13), and outflow from the fluid chamber (4) is controlled for affecting the movement of a piston (7) that is arranged in the fluid chamber (4) and connected to the exhaust valve (13) or to force transmission means (2, 3, 14, 19) between a cam (1) and the exhaust valve (13) and for allowing slowing or delaying of the closing movement of the exhaust valve (13), in which method outflow from the fluid chamber (4) is allowed at a rate that allows the closing curve of the exhaust valve (13) to follow the cam curve at least until the exhaust valve (13) has moved a certain predetermined distance in the closing direction, characterized in that the outflow is unthrottled until the exhaust valve (13) has moved the predetermined distance and after the exhaust valve (13) has moved the predetermined distance, throttling of the outflow takes place, and that the distance is determined so that the valve lift at the moment when the throttling starts is smaller than the distance between closed exhaust valve (13) and the piston (7) of the piston engine at top dead center.
A method according to claim 8, characterized in that the outflow is restricted by blocking at least one outlet port (8, 8a, 8b, 8c) of the fluid chamber (4) by the piston (7).
A method according to claim 8, characterized in that the outflow is restricted by throttling the flow by the piston (7) after the exhaust valve (13) has moved the predetermined distance.
A method according to claim 8, characterized in that the outflow is restricted by throttling the flow by at least one throttle (11) that is arranged in connection with an outlet port (8, 8a, 8b, 8c) or an outlet duct (9, 9a, 9b, 9c) of the fluid chamber (4).
A method according to claim 8, characterized in that the outflow is restricted by at least one valve (10) that is arranged in connection with an outlet port (8, 8a, 8b, 8c) or an outlet duct (9, 9a, 9b, 9c).