CN104903552A - Exhaust valve arrangement and method for controlling closing of an exhaust valve - Google Patents

Abstract

An exhaust valve arrangement for a piston engine comprises a force transmission mechanism (2, 3, 14, 19) arranged between a cam (1) and an exhaust valve (13). Hydraulic fluid may be introduced into the fluid chamber (4) during the opening movement of the exhaust valve (13). A piston (7) is arranged in the fluid chamber (4) and connected to the force transmission mechanism (2, 3, 4, 19). By controlling the outflow from the fluid chamber (4) the closing speed of the exhaust valve (13) can be controlled. allowing the outflow from the fluid chamber (4) to be 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 been in the closing direction A certain predetermined distance is moved.

Description

Exhaust valve apparatus and method for controlling the closing of an exhaust valve

technical field

The invention relates to an exhaust valve arrangement for a piston engine according to the preamble of claim 1 . The invention also relates to a method for controlling the closing of an exhaust valve of a piston engine as defined in the preambles of the other independent claims.

Background technique

Many internal combustion engines are provided with means for variable intake valve closing (VIC), which allows different intake valve closing timings to be employed for optimum engine performance. Recently, other arrangements for variable exhaust valve closing (VEC) have become more common. The VEC arrangement is especially beneficial in engines utilizing two-stage turbocharging. When the boost pressure can be high, different scavenging is required for different loads. When the engine is running under high loads, long scavenging times are required to cool the engine's components. Therefore, the exhaust valve remains open for a long time during the exhaust stroke. On the other hand, when the engine is running under low load, the pressure of the intake air is lower than the pressure of the exhaust gas. To prevent flow from the exhaust duct into the intake duct, it is necessary to close the exhaust valve at the same time as or slightly after the opening of the intake valve. Variable exhaust valve closing timing is also useful in engines that include means for cooling recirculated exhaust gases by injecting water. When using water injection there is no need for intake and exhaust valve overlap, but if water injection needs to be turned off then longer scavenging is required to allow operation of the engine at full load. Typically, the VEC arrangement is achieved by utilizing a chamber disposed between the exhaust valve and a cam that operates the exhaust valve. The exhaust valves are opened in the traditional way by means of a cam. During the opening movement of the exhaust valve, hydraulic fluid is introduced into the chamber. The timing and speed at which the exhaust valve closes depends on the outflow from the chamber. For example, a closing delay can be provided by preventing effluent with a valve. The problem with this solution is that, in the event of a system failure, the closing of the exhaust valve may be prevented and the piston may hit the exhaust valve, causing significant damage.

Contents of the invention

It is an object of the present invention to provide an improved exhaust valve arrangement for a piston engine which allows delayed closing of the exhaust valve but prevents the engine's piston from striking the exhaust valve. The characterizing features of the device according to the invention are provided in the characterizing part of claim 1 . Another object of the invention is to provide an improved method for controlling the closing of the exhaust valves of a piston engine. The characterizing features of the method are provided in the characterizing parts of the other independent claims.

The device according to the invention comprises: at least one exhaust valve; a rotatable cam; a force transmission mechanism for converting the rotary motion of the cam into a linear motion and for converting the linear motion in at least the opening direction of the exhaust valve. motion is transmitted to the exhaust valve; a fluid chamber into which hydraulic fluid can be introduced during the opening movement of the exhaust valve; a piston arranged in the fluid chamber and connected to the force transmission mechanism or the exhaust valve; at least one discharge port for discharging the hydraulic fluid from the fluid chamber to allow closing of the exhaust valve; and a flow control mechanism for controlling the flow of the fluid chamber outflow and allow to slow or delay the closing movement of the exhaust valve. The exhaust port and the flow control mechanism are configured to allow the outflow from the fluid chamber to be at a rate that allows the closing profile of the exhaust valve to follow a cam profile at least until the exhaust valve A predetermined distance has been moved in the closing direction.

In the method according to the invention, during the cam-controlled opening movement of said exhaust valve, hydraulic fluid is introduced into a fluid chamber and the outflow from said fluid chamber is controlled to influence the movement of the piston and allow Slowing or retarding the closing movement of the exhaust valve, the piston being arranged in the fluid chamber and connected to the exhaust valve or to a force transmission mechanism between the cam and the exhaust valve. Outflow from the fluid chamber is allowed at a rate that allows the closing profile of the exhaust valve to follow the cam profile at least until the exhaust valve has moved a predetermined distance in the closing direction.

The expression "closing curve" means the lift of the exhaust valve as a function of the crank angle. The expression "cam profile" means the motion of the cam follower as a function of crank angle. When no retardation function is used and the lift of the exhaust valve is determined by the shape of the cam, the closing curve of the exhaust valve thus corresponds to the cam curve. With the device and the method according to the invention, the closing of the exhaust valves can be delayed or slowed down without the risk of the engine's pistons hitting the exhaust valves. Outflow from the fluid chamber is unrestricted as the exhaust valve begins its closing movement. The throttling of the outflow occurs only after the exhaust valve has moved a certain distance. The distance is determined such that the exhaust valve lift at the start of throttling is smaller than the distance between the piston of the engine in the corresponding cylinder and the closed exhaust valve at top dead center. The closing curve of the exhaust valve thus initially corresponds to the cam curve, but after the start of throttling, the slope of the closing curve may not be as steep as that of the cam curve.

There are many alternative ways of controlling the effluent from the fluid chamber. For example, a piston in the fluid chamber may be arranged to restrict flow. The diameter of the end of the piston may be smaller than the remainder of the piston. When the exhaust valve is fully opened, the discharge port of the fluid chamber is also fully opened. When the piston has moved a predetermined distance, it covers the discharge port(s) and allows outflow from the fluid chamber to pass through a small gap formed between the piston and the wall of the fluid chamber.

Another option is to provide the fluid chamber with two or more outlet openings at different heights, ie different distances from the ends of the fluid chamber. When the exhaust valve is fully opened, all exhaust ports are also fully opened. When the piston has moved a predetermined distance, it blocks at least one of the discharge ports and thus restricts the outflow. Some of the discharge ports or the discharge conduits connected to the discharge ports may be provided with throttle valves. These throttles may be adjustable. It is also possible to provide some of the outlets or pipes with valves which allow regulation of the outflow.

Description of drawings

Hereinafter, embodiments of the present invention are described in more detail with reference to the accompanying drawings, in which:

Figure 1 shows the exhaust valve opening mechanism with VEC function,

Figure 2 shows an exhaust valve arrangement according to an embodiment of the invention,

Figure 3 shows a second embodiment of the invention,

Figure 4 shows a third embodiment of the present invention,

Figure 5 shows a fourth embodiment of the present invention,

Figure 6 shows a fifth embodiment of the present invention,

Figure 7 shows the valve lift when the VEC function is disabled, and

Figure 8 shows the valve lift when the VEC function is enabled.

detailed description

The exhaust valve arrangement according to the invention is especially suitable for large internal combustion engines such as in main or auxiliary engines of ships or in power stations for generating electric power. The invention is particularly useful in engines with two-stage turbocharging and in engines that use recirculated exhaust gases for water cooling. However, the device can also be used with other types of engines.

An example of a valve opening mechanism of the exhaust valve 13 is shown in FIG. 1 . In the case where each cylinder of the internal combustion engine is provided with more than one exhaust valve 13, the exhaust valve opening mechanism can be used to control all exhaust valves 13 of a cylinder. An exhaust valve 13 is arranged in the cylinder head 18 for opening and closing fluid communication between the cylinders 16 of the internal combustion engine and the 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 as part of a camshaft. The cam 1 is provided with a base circle 1a and a lobe 1b extending radially outward from the base circle 1a. The cam follower wheel 2 a of the cam follower unit 2 constantly engages the cam 1 . The device may be provided with a spring which presses the cam follower 2a against the cam 1 . The opening of the exhaust valve 13 works in a conventional manner. When the cam follower 2 a comes to engage the lobe 1 a of the cam 1 , the cam follower 2 is pushed away from the rotation axis of the cam 1 , ie in the upward direction in FIG. 1 . The cam follower unit 2 forms part of force transmission mechanisms 2 , 3 , 14 , 19 which convert the rotational movement of the cam 1 into a linear movement and further transmit this movement to the exhaust valve 13 . The force transmission mechanism also includes 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 valve 13 . A second pushrod 19 is connected to the rocker arm 14 . The rocker arm 14 transmits the movement of the second pushrod 19 to the exhaust valve 13 . Additionally, many other types of force transmission mechanisms may be used. For example, parts of the force transmission path may be hydraulic.

In order to slow down or delay the closing movement of the exhaust valve 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 valve 13 . The fluid chamber 4 is connected to the inlet conduit 5 through the inlet port 5a. Hydraulic fluid can be introduced into the fluid chamber 4 through the inlet conduit 5 and the inlet port 5a. The device may also be provided with two or more inlet ports 5a and/or inlet ducts 5 . The inlet conduit 5 is provided with a non-return valve 6 which allows flow into the fluid chamber 4 but does not allow flow out of the chamber 4 . As an alternative to, or in addition to, the non-return valve 6 , the inlet conduit 5 can be provided with a closing valve for selectively allowing or preventing flow into the fluid chamber 4 . A closed valve allows the VEC function to be enabled and disabled. If the closing valve is closed, no flow is allowed into the fluid chamber 4 and the VEC function is disabled. The valve opening mechanism then works in the same manner as a conventional cam-controlled exhaust valve opening mechanism. Figure 7 shows valve lift when VEC is disabled. The shaded area indicates the overlap of the exhaust and intake valves. A piston 7 is arranged in the fluid chamber 4 . The piston 7 delimits the fluid chamber 4 and hydraulic fluid is introduced between the piston 7 and the camshaft end of the fluid chamber 4 . In the embodiment of FIG. 1 , the piston 7 is connected to the first push rod 3 and the second push rod 19 , ie the piston is located 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 valve 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 can also be arranged in many other ways. In principle, the fluid chamber 4 could be arranged in the cylinder head 18 and the piston 7 could be connected to the rod of the exhaust valve 13, but this is impractical. However, the piston 7 may be connected to some other part of the force transmission mechanism than the first push rod 3 and the second push rod 19 . Piston 7 moves with exhaust valve 13 all the time.

When the cam follower 2 a comes to engage the lobe 1 a of the cam 1 , the piston 7 moves with the first push rod 3 . If the shut-off valve is opened, hydraulic fluid is sucked from the inlet line 5 into the fluid chamber 4 by the movement of the piston 7 . The first push rod 3 remains engaged with the cam follower unit 2 . When the cam 1 is rotated such that the cam follower 2a engages the tip of the lobe 1a, the exhaust valve 13 is fully opened. When the cam follower 1a enters the down ramp of the lobe 1a, the exhaust valve 13 begins to close. When the exhaust valve 13 begins its closing movement, the exhaust valve 13 first follows the cam curve. By restricting the outflow from the fluid chamber 4, the closing speed of the exhaust valve can be slowed down. In FIG. 8 , the lift of the exhaust valve 13 is shown with a solid line and the cam curve is shown with a dashed line. The shaded area represents the overlap of the exhaust valve 13 and the intake valve.

One arrangement for restricting outflow from the fluid chamber 4 of the valve opening mechanism of FIG. 1 is shown in FIG. 2 . In the embodiment of FIG. 2 , the fluid chamber 4 is provided with an outlet opening 8 and an outlet conduit 9 connected to the outlet opening 8 . The discharge port 8 and the discharge duct 9 are dimensioned such that the maximum flow rate through the discharge port 8 is sufficient to allow the piston 7 to follow the cam curve as the exhaust valve 13 begins the closing movement. When the exhaust valve 13 and the piston 7 have moved a certain predetermined distance in the closing direction of the exhaust valve 13 , the piston 7 starts to throttle the outflow of the fluid chamber 4 . This occurs when the camshaft end of the piston 7 is at the level of the discharge port 8 (ie in stage 3 of FIG. 2 ). The diameter of the piston 7 at the cam end of the piston 7 is slightly smaller than the diameter of the rest of the piston 9 . The piston 7 thus does not completely block the outlet opening 8 , but instead forms a small gap between the piston 7 and the wall of the fluid chamber 4 . Hydraulic fluid can flow through this gap to the outlet opening 8 . However, throttling is performed such that the piston 7 cannot follow the cam follower 2 . The piston 7 can thus act like a flow control mechanism and slow down the closing speed of the exhaust valve 13 so that a gap is formed between the first pushrod 3 and the cam follower unit 2 as shown in stage 4 of FIG. 2 . As can be seen in FIG. 8 , the slope of the closing curve of the exhaust valve 13 is not as steep as the cam curve and the closing movement of the exhaust valve 13 continues when the cam follower 2 a has returned to the base circle 1 a of the cam 1 . The duration of the scavenging time is longer than with the VEC disabled. When the piston 7 approaches the camshaft end of the fluid chamber 4 , the thicker part of the piston 7 partially blocks the discharge port 8 , as shown in stage 5 of FIG. 2 . The closing speed of the exhaust valve 13 is thus further reduced, allowing smooth closing. Eventually, the fluid chamber 4 is emptied and the first pushrod 3 comes to engage the cam follower unit 2 again, as can be seen in stage 6 of FIG. 2 . The piston 7 may have more than two different diameters to allow gradual changes in the closing speed of the exhaust valve 13, or the diameter of the piston 7 may be continuously reduced.

Another embodiment of the invention is shown in FIG. 3 . The principle of operation of this embodiment is the same as in the embodiment of FIG. 1 . Furthermore, in the arrangement of FIG. 3 , during the opening movement of the exhaust valve 13 hydraulic fluid is introduced into the fluid chamber 4 and the piston 7 works like a flow control mechanism. When the cam follower 2 a enters the descending ramp of the lobe 1 a of the cam 1 , the exhaust valve 13 is first free to move. The fluid chamber 4 is provided with a first discharge port 8a, a second discharge port 8b and a third discharge port 8c and corresponding discharge conduits 9a, 9b and 9c. The second outlet conduit 9b is provided with a valve 10, which can be used to prevent flow into the second discharge conduit 9b. Valve 10 works as an additional flow control mechanism. At the beginning of the closing movement of the exhaust valve 13, hydraulic fluid can flow out of the fluid chamber through all outlet ports 8a, 8b, 8c. The discharge ports 8a, 8b, 8c and discharge ducts 9a, 9b, 9c are dimensioned such that the exhaust valve 13 can follow the cam curve when the first discharge port 8a and the third discharge port 8c are free. This ensures that a sufficient 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 discharge opening 8a and restricts the outflow from the fluid chamber 4 . When the piston 7 moves closer to the camshaft end of the fluid chamber 4, the piston 7 also blocks the second discharge port 8b, hydraulic fluid can only flow out of the fluid chamber 4 through the third discharge port 8c. This ensures that the exhaust valve 13 closes smoothly. A valve 10 in the second discharge conduit 9b can be used to prevent an earlier flow through the second discharge opening 8b.

In the embodiment of Fig. 4, the device is provided with two discharge openings 8a, 8b and discharge ducts 9a, 9b. At the beginning of the closing movement of the exhaust valve 13, hydraulic fluid can flow out of the fluid chamber 4 through the first discharge port 8a and the first discharge conduit 8b and the second discharge port 9a and the second discharge conduit 9b. The discharge ports 8a, 8b and the discharge ducts 9a, 9b are dimensioned such that the exhaust valve 13 can follow the cam curve when the discharge ports 8a, 8b are both open. After the piston 7 has moved a certain distance, it blocks the first discharge opening 8a and restricts the outflow. The second discharge conduit 9b is provided with an adjustable throttle valve 11 which works like an additional flow control mechanism. With the throttle valve 11, different closing curves can be realized. The throttle valve 11 can also be used to limit further outflow at the end of the closing movement of the exhaust valve 13 to ensure smooth closing.

The embodiment of FIG. 5 is similar to the embodiment of FIG. 4 . In this embodiment, the second outlet duct 9b is not provided with a throttle, but the second discharge duct 9b is connected to the second chamber 12 in which the cam follower unit 2 is arranged to move. When the cam follower 2a is positioned on the lobe 1b of the cam 1, the cam follower unit 1 blocks the other end of the second discharge duct 9b. At the beginning of the closing movement of the exhaust valve 13, hydraulic fluid can freely flow out of the fluid chamber 4 through the first discharge port 8a. The first discharge port 8a and the first discharge duct 9a are dimensioned such that the flow rate through the first discharge port 8a is sufficient to allow the exhaust valve 13 to follow the cam curve. When the exhaust valve 13 has moved a certain distance in the closing direction of the valve 13, the piston 7 blocks the first discharge port 8a. Thus, outflow from the fluid chamber 4 is prevented. When the cam follower 2a enters the base circle 1a of the cam 1, fluid is allowed to flow into the second chamber 12 through the second discharge port 8b. However, the emptying of the fluid chamber 4 does not take place immediately, so the closing of the exhaust valve 13 is delayed.

Furthermore, FIG. 6 shows an embodiment in which the device is provided with two outlet openings 8a, 8b and outlet ducts 9a, 9b. The second discharge conduit 9b is provided with a quick closing valve 10, which may for example be electrically or hydraulically operated. The first discharge port 8a and the first discharge duct 9a are dimensioned such that the flow rate through the first discharge port 8a is sufficient to allow the exhaust valve 13 to follow the cam curve. This ensures that the fluid chamber 4 can be emptied sufficiently quickly even if the valve 10 of the second discharge line 9b is not actuated. At the beginning of the closing movement of the exhaust valve 13, the outflow from the fluid chamber 4 is allowed to pass through both the first discharge port 8a and the second discharge port 8b. After the piston 7 has moved a certain distance, the piston 7 blocks the first discharge port 8a and only allows effluent to pass through the second discharge port 8b. A valve 11 in the second discharge conduit 9b may be used to control flow through the second discharge port 8b to achieve the desired exhaust valve closing profile. As a safety arrangement, the fluid chamber 4 may be provided with a third discharge conduit in which conduit flow is prevented when the cam follower 2a is on the base circle 1a or lobe 1b of the cam 1 . For example, the other end of the third discharge duct may be blocked by the cam follower unit 2 . The profile of the cam 1 is also provided with a portion located below the base circle 1 a of the cam 1 . When the cam follower 2a enters the portion below the base circle 1a, flow is allowed through the third discharge duct. With this arrangement, the emptying of the fluid chamber 4 and the closing of the exhaust valve 13 are ensured even in the event of a failure of the valve 11 in the second discharge line 9b.

In all embodiments described, the throttling of the effluent occurs only after the exhaust valve 13 has been closed, which is sufficient to prevent the piston of the cylinder 16 from hitting the exhaust valve 13 . When throttling begins, the exhaust valve lift is therefore less than the distance between the piston at top dead center and the closed exhaust valve 13, as seen in Figures 7 and 8, which also show the piston Movement around top dead center.

In all the embodiments of the invention described, the predetermined distance after which the outflow from the fluid chamber 4 can be throttled is determined so that the exhaust valve 13 and the piston of the internal combustion engine located in the corresponding cylinder are prevented from s contact. The lift of the correspondingly positioned exhaust valve 13 is therefore smaller than the distance between the closed exhaust valve 13 and the individual pistons of the internal combustion engine when the pistons are 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 that it may vary within the appended claims. For example, features of different implementations may be combined.

Claims (14)

1. An exhaust valve arrangement for a piston engine, wherein said exhaust valve arrangement comprises: at least one exhaust valve (13); a rotatable cam (1); a force transmission mechanism (2, 3, 14, 19) for converting the rotary motion of the rotatable cam (1) into a linear motion and transmitting the linear motion to the exhaust valve (13) at least in the opening direction of the exhaust valve (13) ); a fluid chamber (4), into which hydraulic fluid can be introduced during the opening movement of the exhaust valve (13); a piston (7), which is arranged in the fluid chamber (4 ) and connected to said force transmission mechanism (2, 3, 14, 19) or said exhaust valve (13); at least one discharge port (8, 8a, 8b, 8c) for extracting a chamber (4) to vent the hydraulic fluid to allow closure of the exhaust valve (13); and a flow control mechanism (7, 10, 11) for controlling the outflow from the fluid chamber (4) and allows slowing down or delaying the closing movement of the exhaust valve (13), characterized in that the discharge port (8, 8a, 8b, 8c) and the flow control mechanism (7, 10, 11) are configured to allow the outflow from the fluid chamber (4) to be 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 closed along the The direction moves by a predetermined distance. 2. The device according to claim 1, characterized in that the predetermined distance is determined such that at the corresponding position of the exhaust valve (13), the exhaust valve (13) is located at the same position as the engine Contact between the pistons in the respective cylinders is prevented. 3. Device according to claim 1 or 2, characterized in that the outflow from the fluid chamber (4) is not throttled until the exhaust valve (13) has moved the predetermined distance. 4. The device according to any one of claims 1 to 3, characterized in that the piston (7) in the fluid chamber (4) is arranged such that, at the exhaust valve (13) After the predetermined distance has been moved, the outflow from the fluid chamber (4) is throttled. 5. Device according to any one of claims 1 to 3, characterized in that the fluid chamber (4) comprises at least two outlet openings (8, 8a, 8b, 8c), and the piston ( 7) Arranged to block at least one of said outlet openings (8, 8a, 8b, 8c) after said exhaust valve (13) has moved said predetermined distance. 6. The device according to claim 5, characterized in that at least one of the outlets (8, 8a, 8b, 8c) is or is connected to the outlet (8, 8a, 8b, 8c) The discharge pipes (9, 9a, 9b, 9c) of are provided with throttle valves (11). 7. The device according to claim 6, characterized in that the throttle valve (11) is adjustable. 8. The device according to claim 5, characterized in that at least one of the outlets (8, 8a, 8b, 8c) or a discharge connected to the outlet (8, 8a, 8b, 8c) The pipes (9, 9a, 9b, 9c) are provided with valves (10). 9. A method for controlling the closing of an exhaust valve (13) of a piston engine, in which method hydraulic fluid is introduced into a fluid chamber during a cam-controlled opening movement of said exhaust valve (13) chamber (4), and controls the outflow from said fluid chamber (4) to affect the movement of the piston (7) and allow to slow or delay the closing movement of the exhaust valve (13), the piston ( 7) Arranged in the fluid chamber (4) and connected to the exhaust valve (13) or to the force transmission mechanism (2, 3, 14, 19), characterized in that the outflow from said fluid chamber (4) is allowed to be at a rate which allows the closing curve of said exhaust valve (13) to follow the cam curve at least until the The exhaust valve (13) has moved a certain predetermined distance along the closing direction. 10. A method according to claim 9, characterized in that the outflow is not throttled until the exhaust valve (13) has moved the predetermined distance. 11. The method according to claim 9 or 10, characterized in that limiting the effluent. 12. A method according to claim 9 or 10, characterized by restricting by throttling the flow with the piston (7) after the exhaust valve (13) has moved the predetermined distance the effluent. 13. The method according to claim 9 or 10, characterized in that the outflow is restricted by throttling the flow with at least one throttle valve (11) arranged to It is connected with the outlet (8, 8a, 8b, 8c) or the outlet pipe (9, 9a, 9b, 9c) of the fluid chamber (4). 14. The method according to claim 9 or 10, characterized in that the outflow is restricted by at least one valve (10), which is arranged in conjunction with the outlet (8, 8a, 8b, 8c) or discharge pipe (9, 9a, 9b, 9c) connection.