The present invention relates to a valve lifting arrangement for opening an exhaust valve of an internal combustion engine in accordance with the preamble of claim 1. The invention also concerns a method for operating a valve lifting arrangement.

Nitrogen oxide (NOx) emissions of internal combustion engines are subject to continuously tightening regulations. In general, NOx emissions can be reduced by reducing temperature in the combustion chamber. An effective way to reduce NOx emissions of an internal combustion engine is to use exhaust gas recirculation (EGR), where part of the exhaust gases are directed back to the cylinders of the engine. Since the heat capacity of the recirculated exhaust gas is higher than the heat capacity of air, the same amount of energy released by combustion leads to lower temperature increase in engines with EGR. Also the lower oxygen mass inside the cylinders and reduction of combustion speed help to achieve lower temperature increase. An EGR system can be either external or internal. In an external EGR system exhaust gases are recirculated from the exhaust duct into the air intake duct. In an internal EGR system part of the exhaust gas is trapped within the cylinder or back-flow from the exhaust duct into the combustion chamber is utilized. Typically, the exhaust valves of a cylinder are opened for a short period of time after closing of the intake valves. Exhaust pressure needs to be higher than the pressure in the cylinder in order to get exhaust gases to flow into the cylinder.

There are different ways for implementing the exhaust valve opening in internal EGR systems. Japanese patent application JP 2001065320 discloses a cam that comprises a second lobe that opens the exhaust valve for EGR. The second lobe is asymmetrical enabling adjustment of the valve lift by moving the cam in the camshaft direction. Patent application GB 2442813 A discloses a camshaft assembly comprising a fixed cam and a moveable cam lobe. The movable cam lobe can be used for an extra exhaust valve opening event for internal EGR. The movable cam lobe can be moved by hydraulic pressure.

An object of the present invention is to provide an improved valve lifting arrangement for opening an exhaust valve of an internal combustion engine. The characterizing features of the valve lifting arrangement according to the present invention are given in the characterizing part of claim 1. Another object of the invention is to provide a method for operating a valve lifting arrangement.

The valve lifting arrangement according to the present invention comprises a cam having a cam profile comprising a base circle and a first lobe and a second lobe extending radially outwards from the base circle, a reciprocating cam follower unit comprising a body and a cam follower wheel that is attached to the body and engaged with the cam, and force transmission means for transmitting movement of the cam follower unit to the exhaust valve. The valve lifting arrangement comprises at least one hydraulic fluid chamber, a first piston that is in mechanical connection with the cam follower unit and protrudes into the hydraulic fluid chamber for pressurizing the fluid in the chamber, a second piston that is in mechanical connection with the exhaust valve and movable by the hydraulic fluid that is pressurized by the first piston, means for introducing hydraulic fluid into the space between the first piston and the second piston, and a control valve for controlling outflow from the space between the first piston and the second piston.

A valve lifting arrangement according to the invention can be used for opening the exhaust valve for exhaust gas recirculation. The EGR function can easily be switched off and it is also possible to adjust the timing and lift of the exhaust valve opening.

According to an embodiment of the invention, the second piston is arranged in the hydraulic fluid chamber opposite to the first piston. According to another embodiment of the invention, the second piston is arranged in a second hydraulic fluid chamber that is in fluid communication with the first hydraulic fluid chamber.

According to another embodiment of the invention, the arrangement comprises a pressure accumulator for supplying the hydraulic fluid into the hydraulic fluid chamber.

According to another embodiment of the invention, the control valve is a solenoid valve.

The method for operating the valve lifting arrangement defined above comprises at least a first operating mode, in which operating mode the control valve is kept closed when the cam follower wheel is on the second lobe of the cam. In this operating mode, the second lobe opens the exhaust valve for EGR.

According to an embodiment of the invention, the method comprises a second operating mode, in which operating mode the control valve is kept open when the cam follower wheel is on the second lobe of the cam. In the second operating mode the EGR function is not in use.

According to another embodiment of the invention, the method comprises a third operating mode, in which operating mode the control valve is opened when the cam follower wheel is on the ascending ramp of the second lobe of the cam. If the control valve is opened when the cam follower wheel is on the ascending ramp of the second lobe, a smaller valve lift and shorter duration of the exhaust valve opening is achieved.

According to another embodiment of the invention, the method comprises a fourth operating mode, in which operating mode the control valve is opened when the cam follower wheel is on the descending ramp of the second lobe of the cam. In this operating mode, the duration of the exhaust valve opening is shortened.

According to another embodiment of the invention, the method comprises a fifth operating mode, in which operating mode the control valve is closed when the cam follower wheel is on the ascending ramp of the second lobe of the cam. In the fifth operating mode, the exhaust valve opening is delayed and a smaller lift is achieved.

• Fig. 1 shows a valve lifting arrangement according to an embodiment of the invention.
• Fig. 2 shows the valve lifting arrangement of Fig. 1 at different crank angles.
• Fig. 3 shows a valve lifting arrangement according to another embodiment of the invention.

Embodiments of the invention are now described in more detail with reference to the accompanying drawings.

In figure 1 is shown a valve lifting arrangement according to an embodiment of the invention. The valve lifting arrangement is used for opening an exhaust valve 1 of a large internal combustion engine. In addition to the normal opening of the exhaust valve 1, the valve lifting arrangement allows additional opening of the exhaust valve 1 for internal exhaust gas recirculation (EGR). The engine can be, for instance, a main or an auxiliary engine of a ship or an engine that is used for producing electricity at a power plant. The engine is provided with at least one camshaft for operating gas exchange valves of the engine. A V-engine can be provided with one camshaft for each bank of the engine. The camshaft is provided with one cam 2 for the exhaust valves 1 of each cylinder. Each cylinder can be provided with more than one exhaust valves 1, and the cam 2 can be used for opening all the exhaust valves 1 of the respective cylinder. The cam 2 comprises, as any conventional exhaust cam, a cam profile having a base circle 2a and a lobe 2b that extends radially outwards from the base circle 2a. In addition to the first lobe 2b, the cam 2 is provided with a second lobe 2c that is apart from the first lobe 2b. There is thus a section of the base circle 2a between the first lobe 2b and the second lobe 2c. The height of the second lobe 2c from the base circle 2a is smaller than the height of the first lobe 2b. In the embodiment of figure 1, the top of the second lobe 2c is positioned approximately 100 degrees after the top of the first lobe 2b in the rotation direction of the cam 2. The length of the second lobe 2c is approximately 30 degrees.

The valve lifting arrangement is provided with a reciprocating cam follower unit 3 that comprises a body 3a and a cam follower wheel 3b. The cam follower wheel 3b is attached to the body 3a of the cam follower unit 3 with a bearing. A spring (not shown) is arranged to keep the cam follower wheel 3b engaged with the cam 2. The valve lifting arrangement is provided with force transmission means for transmitting movement of the cam follower unit 3 to the exhaust valve 1 at least in the opening direction of the exhaust valve 1. In the embodiment of figure 1, the force transmission means comprise a push rod 4 and a rocker arm 11. The push rod 4 transmits upward movement of the cam follower unit 3, i.e. the movement away from the rotation axis of the cam, to the exhaust valve 1. The push rod 4 is engaged with one end of the rocker arm 11 that is arranged to turn around a shaft 12. The other end of the rocker arm 11 pushes the exhaust valve 1 downwards for opening it. A spring (not shown) is arranged to keep the exhaust valve 1 closed when it is not being pushed downwards by the rocker arm 11.

The valve lifting arrangement further comprises a hydraulic fluid chamber 5. The hydraulic fluid chamber 5 can be arranged for instance in a cylinder head or in the engine block. The force transmission means further comprise a first piston 6 and a second piston 7. The first piston 6 is attached to the cam follower unit 3 and protrudes into the hydraulic fluid chamber 5. The second piston 7 is attached to the push rod 4 and protrudes into the hydraulic fluid chamber 5 from the opposite direction. The hydraulic fluid chamber 5 is in fluid communication with a pressure medium source, from which hydraulic fluid can be introduced into the hydraulic fluid chamber 5. In the embodiment of the figures, the fluid source is a pressure accumulator 8 that is connected with a duct 9 to the hydraulic fluid chamber 5. The duct 9 is located so that when the cam follower wheel 3b is on the base circle 2a of the cam 2 and the exhaust valve 1 is closed, hydraulic fluid can be introduced into the hydraulic fluid chamber 5 between the first piston 6 and the second piston 7. The duct 9 is provided with a control valve 10 for opening and closing the fluid communication between the pressure medium source and the hydraulic fluid chamber 5. The control valve 10 is a quick-opening solenoid valve.

The functioning of the valve lifting arrangement is now described with reference to figure 2. Phases A-C show how the valve lifting arrangement works when the EGR function is switched off. In phase A, the piston in that cylinder of the engine of which exhaust valves 1 are operated by the valve lifting arrangement is in the middle of the power stroke. The cam follower wheel 3b of the cam follower unit 3 is on the base circle 2a of the cam 2, and the hydraulic fluid chamber 5 is filled with hydraulic fluid. The exhaust valve 1 is closed. Also the control valve 10 is closed. When the camshaft of the engine rotates, the cam follower wheel 3b enters the first lobe 2b of the cam 2. The cam follower unit 3 thus moves away from the rotation axis of the cam 2. Since the control valve 10 is closed, the hydraulic fluid cannot flow out of the hydraulic fluid chamber 5. Consequently, the second piston 7 is moved by the hydraulic fluid away from the rotation axis of the cam 2. In phase B, the cam follower wheel 3b has entered the first lobe 2b of the cam 2. Since the hydraulic fluid is in practice incompressible, the gap between the first piston 6 and the second piston 7 is as large as in phase A. The push rod 4 that is attached to the second piston 7 has turned the rocker arm 11 and the exhaust valve 1 has been opened.

After the cam follower wheel 3b has left the first lobe 2b of the cam 2, the control valve 10 has been opened. When the cam follower wheel 3b becomes engaged with the second lobe 2c of the cam 2, hydraulic fluid can flow through the duct 9 out of the hydraulic fluid chamber 5 and back into the pressure accumulator 8. In phase C, the cam follower wheel 3b has entered the second lobe 2c of the cam 2. Since the control valve 10 is open, the movement of the first piston 6 has almost emptied the hydraulic fluid chamber 5. The gap between the first piston 6 and the second piston 7 has become smaller, and the second piston 7 is at the same position as when the cam follower wheel 3b is on the base circle 2a of the cam 2. The exhaust valve 1 remains thus closed despite of the upward movement of the cam follower unit 3 and the first piston 6. When the cam follower wheel 3b leaves the second lobe 2c, the hydraulic fluid chamber 5 is filled again from the pressure accumulator 8. Before the cam follower wheel 3b enters the first lobe 2b of the cam 2, the control valve 10 needs to be closed for allowing normal exhaust valve opening.

Phase D shows how the exhaust valve 1 has been opened for the EGR. Now the control valve 10 is closed and flow of the hydraulic fluid from the hydraulic fluid chamber 5 into the pressure accumulator 8 is prevented. The first piston 6 has thus pushed the second piston 7 upwards and the exhaust valve 1 has been opened.

The valve lift and the duration of the EGR can be adjusted by the control valve 10. Consequently, the valve lifting arrangement can be operated in different operating modes. In a first operating mode, the control valve 10 is kept closed when the cam follower wheel 3b is on the second lobe 2c of the cam 2. In the first operating mode, the maximum lift of the exhaust valve 1 is in use and also the duration of the EGR is maximized. In a second operating mode, the control valve 10 is kept open when the cam follower wheel 3b is on the second lobe 2c of the cam 2. In the second operating mode, the EGR is switched off. In a third operating mode, the control valve 10 is opened when the cam follower wheel 3b is on the ascending ramp of the second lobe 2c of the cam 2. When the control valve 10 is opened before the top of the second lobe 2c, the valve lift remains smaller and the exhaust valve 1 is also closed earlier. In a fourth operating mode, the control valve 10 is opened when the cam follower wheel 3b is on the descending ramp of the second lobe 2c of the cam 2. In this operating mode, the maximum valve lift is in use, but the exhaust valve 1 is closed earlier. In a fifth operating mode, the control valve 10 is closed when the cam follower wheel 3b is on the ascending ramp of the second lobe 2c of the cam 2. When the control valve is kept open until the cam follower wheel 3b has reached a certain point on the ascending ramp of the second lobe, the opening of the exhaust valve 1 is delayed and the valve lift is also smaller.

In figure 3 is shown a valve lifting arrangement according to another embodiment of the invention. The controlling of the exhaust valve 1 works in the same manner as in the embodiment of figure 1, but the force transmission means between the cam 2 and the exhaust valve 1 are different. The force transmission means comprise a push rod 4 that is connected to the cam follower unit 3, a first piston 6 and a second piston 7. The other end of the push rod 4 is connected to the first piston 6 that protrudes into a hydraulic fluid chamber 5. The second piston 7 is not arranged in the same hydraulic fluid chamber 5, but the arrangement is provided with a second hydraulic fluid chamber 5b, which is in fluid communication with the first hydraulic fluid chamber via a connecting duct 13. The second piston 7 is connected to the exhaust valve 1. When the hydraulic fluid in the first hydraulic fluid chamber 5 is pressurized by the first piston 6, the fluid is supplied through the connecting duct 13 into the second hydraulic fluid chamber 5b, where it moves the second piston 7, which opens the exhaust valve 1. When the exhaust valve 1 is closed, the hydraulic fluid can flow from the second hydraulic fluid chamber 5b back into the first hydraulic fluid chamber 5. Also in the embodiment of figure 3, the pressure accumulator 8 is connected with a duct 9 to the first hydraulic fluid chamber 5. However, the pressure accumulator 8 could also be connected to the connecting duct 13 or to the second hydraulic fluid chamber 5b.

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, it is possible to provide the valve lifting arrangement with separate ducts for supplying the hydraulic fluid into the hydraulic fluid chamber and for emptying the chamber. In that case, the control valve is arranged in the outflow duct and the inflow duct can be provided with a check valve.