Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
  • F01L1/20—Adjusting or compensating clearance
  • F01L1/22—Adjusting or compensating clearance automatically, e.g. mechanically
  • F01L1/24—Adjusting or compensating clearance automatically, e.g. mechanically by fluid means, e.g. hydraulically
  • F01L1/245—Hydraulic tappets
  • F01L1/25—Hydraulic tappets between cam and valve stem
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
  • F01L13/0015—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque
  • F01L13/0036—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque the valves being driven by two or more cams with different shape, size or timing or a single cam profiled in axial and radial direction
  • F01L13/0047—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque the valves being driven by two or more cams with different shape, size or timing or a single cam profiled in axial and radial direction the movement of the valves resulting from the sum of the simultaneous actions of at least two cams, the cams being independently variable in phase in respect of each other
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
  • F01L13/06—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for braking
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
  • F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
  • F01L13/08—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for decompression, e.g. during starting; for changing compression ratio
  • F01L13/085—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for decompression, e.g. during starting; for changing compression ratio the valve-gear having an auxiliary cam protruding from the main cam profile
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D21/00—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas
  • F02D21/06—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air
  • F02D21/08—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air the other gas being the exhaust gas of engine
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
  • F02M26/01—Internal exhaust gas recirculation, i.e. wherein the residual exhaust gases are trapped in the cylinder or pushed back from the intake or the exhaust manifold into the combustion chamber without the use of additional passages

Definitions

• the present invention relates to a valve lifting arrangement for opening an ex- haust valve of a piston engine in accordance with the preamble of claim 1 .
• the invention also concerns a method for operating an exhaust valve of a piston engine.
• 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.
• 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.
• exhaust gas 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.
• 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.
• 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 ar- rangement for opening an exhaust valve of a piston engine.
• the characterizing features of the valve lifting arrangement according to the invention are given in the characterizing part of claim 1 .
• Another object of the invention is to provide a method for operating an exhaust valve of a piston engine, as defined in the characterizing part of the other independent claim.
• the valve lifting arrangement according to the invention comprises a first exhaust cam, which is arranged to open at least one exhaust valve for allowing outflow of exhaust gas from a cylinder of the engine during the exhaust stroke, and a second exhaust cam, which can be arranged to open the exhaust valve for allowing exhaust gas recirculation during the intake and/or compression stroke.
• the exhaust valve is opened by means of a first exhaust cam for allowing outflow of exhaust gas from a cylinder of the engine during the exhaust stroke, and a second exhaust cam is used for opening the exhaust valve for allowing exhaust gas recirculation dur- ing the intake and/or compression stroke.
• the valve lifting arrangement is thus provided with two separate exhaust cams.
• the first exhaust cam is responsible for the normal opening of the exhaust valve, and the second exhaust cam is responsible for an additional opening, which is used for the EGR.
• the normal opening can thus be partly or com- pletely mechanically implemented, which makes the system reliable. Also the additional opening is accomplished at least partly mechanically.
• the opening and closing timing and the valve lift of the exhaust valve can be controlled by the shapes of the exhaust cams, which makes the control fast, reliable and accurate.
• the valve lifting arrangement can also be used for upgrading engines already in use.
• the second exhaust cam is arranged to operate a piston device, which piston device is arranged to pressurize hydraulic fluid that is used for opening the exhaust valve for exhaust gas recirculation.
• the piston device can be arranged to protrude into a first hydrau- lie fluid chamber, which first hydraulic fluid chamber is in fluid communication with a second hydraulic fluid chamber, which second hydraulic fluid chamber is provided with a piston, which piston is in force transmission connection with the exhaust valve.
• a hydraulic force transmission from the second exhaust cam allows flexible positioning of the components of the valve lifting arrange- ment. It is also possible to easily add additional control functions to a partly hydraulic system.
• the arrangement comprises an outlet duct, which outlet duct is connected to the first hydraulic fluid chamber and provided with a valve.
• the valve can be a fast acting solenoid valve.
• the outlet duct can be connected to a pressure accumulator.
• the use of a valve allows switching the EGR function on and off. If hydraulic fluid is conducted from the first hydraulic fluid chamber into the outlet duct instead of the second hydraulic fluid chamber, the exhaust valve is not opened for the EGR. If the valve is fast enough, it can also be used for controlling the opening and closing tim- ing and lift of the exhaust valve when the exhaust valve is opened for the EGR.
• the force transmission connection can also be partly hydraulic.
• the first exhaust cam and the second exhaust cam are attached to a common camshaft.
• FIG. 1 shows schematically a valve lifting arrangement according to an embodiment of the invention
• Fig. 2 shows the embodiment of figure 1 with a VEC-function
• Fig. 3 shows a valve lifting arrangement according to another embodiment of the invention.
• valve lifting arrangement is shown for opening an exhaust valve 5 of a piston engine.
• the exhaust valve 5 opens and closes fluid communication between an exhaust port and a cylinder 1 7 of the engine.
• each cylinder 17 of the engine can be provided with more than one exhaust valves 5, and the valve lifting ar- rangement can be used for operating all the exhaust valves 5 of one cylinder 17.
• the engine is a large internal combustion engine, such as a main or an auxiliary engine of a ship or an engine that is used at a power plant for producing electricity.
• the valve lifting arrangement comprises a first exhaust cam 1 , which can be of conventional design.
• the first exhaust cam 1 comprises a base circle 1 a and a lobe 1 b extending radially away from the base circle 1 a.
• the first exhaust cam 1 is attached to a rotating camshaft.
• the valve lifting arrangement is further provided with a first cam follower 3.
• the first cam follower 3 comprises a cam follower wheel 3a, which is engaged with the cam profile of the first exhaust cam 1 .
• the first cam follower 3 forms part of force transmission means, which transform the rotating motion of the first exhaust cam 1 into a linear motion and transmit it to the exhaust valve 5 at least in the opening direction of the exhaust valve 5.
• the force transmission means further comprises a rocker arm 6, a push rod 8 and a piston 9.
• the rocker arm 6 is arranged to push the exhaust valve 5 in its opening direction when the rocker arm 6 is turned around its shaft 7.
• the push rod 8 is arranged to push the other end of the rocker arm 6 for opening the exhaust valve 5.
• the piston 9 is arranged between the first cam follower 3 and the push rod 8 and it is thus in force transmission connection with the exhaust valve 5.
• the cam follower wheel 3a is engaged with the lobe 1 b of the first exhaust cam 1
• the first cam follower 3 is forced away from the rotating axis of the first exhaust cam 1 .
• the first cam follower 3 pushes the piston 9, which in its turn moves the push rod 8.
• the push rod 8 turns the rocker arm 6 around the shaft 7 of the rocker arm 6, and the exhaust valve 5 is opened.
• the valve lifting arrangement can be provided with one or more springs for facilitating the closing of the exhaust valve 5 and for keeping the first cam follower 3 engaged with the first exhaust cam 1 .
• Part of the force transmission means between the first exhaust cam 1 and the exhaust valve 5 could also be hydraulic.
• the rocker arm 6 could be replaced by two hydraulic pistons.
• the valve lifting arrangement is provided with a second exhaust cam 2, which is separate from the first exhaust cam 1 .
• the additional opening of the exhaust valve 5 for the EGR can begin during the intake stroke, usually after the intake valves have been closed, and the exhaust valve 5 can be closed at the beginning of the compression stroke.
• exhaust pressure is higher than the pressure in the cylinder 17, exhaust gas flows from the exhaust port into the cylinder 17.
• the second exhaust cam 2 can be arranged on the same cam- shaft as the first exhaust cam 1 , or a separate camshaft can be used for rotating the second exhaust cam 2.
• the first exhaust cam 1 and the second exhaust cam 2 are arranged in a suitable angular position in relation to each other for achieving correct timing for the additional exhaust valve opening.
• the valve lifting arrangement comprises a second cam follower 4, which is provid- ed with a cam follower wheel 4a.
• the cam follower wheel 4a of the second cam follower 4 is engaged with the cam profile of the second exhaust cam 2.
• the second exhaust cam 2 comprises a base circle 2a and a lobe 2b extending radially away from the base circle 2a.
• the lobe 2b of the second exhaust cam 2 is lower than the lobe 1 b of the first exhaust cam 1 , i.e. the radius of the lobe 2b of the second exhaust cam 2 is smaller.
• the length of the lobe 2b of the second exhaust cam 2 is shorter than the length of the lobe 1 b of the first exhaust cam 1 .
• the lobe 2b of the second exhaust cam 2 thus extends over a smaller angle than the lobe 1 b of the first exhaust cam 1 .
• a hydraulic duct 1 1 connects the first hydraulic fluid chamber 13 to a second hydraulic fluid chamber 10, which is arranged around the piston 9, which forms part of the force transmission means between the first exhaust cam 1 and the exhaust valve 5.
• the piston 9 is moved.
• the piston 9 is not fixed to the first cam fol- lower 3, and the cam follower wheel 3a thus remains in contact with the base circle 1 a of the first exhaust cam 1 .
• the piston 9 moves the push rod 8, which turns the rocker arm 6 opening the exhaust valve 5.
• the valve lifting arrangement further comprises an outlet duct 18, which is connected to the first hydraulic fluid chamber 13 and to a pressure accumulator 16.
• the outlet duct 18 is branched from the hydraulic duct 1 1 .
• a valve 14 is arranged between the first hydraulic fluid chamber 13 and the pressure accumulator 16 for selectively opening and closing the fluid communication between the first hydraulic fluid chamber 13 and the pressure accumulator 16. When the valve 14 is closed, no fluid can flow from the first hydraulic fluid chamber 13 into the pressure accumulator 16. The fluid must thus flow from the first hydraulic fluid chamber 13 into the second hydraulic fluid chamber 10 when the hydraulic fluid is pressurized by the piston device 12.
• the exhaust valve 5 is thus opened every time the cam follower wheel 4a of the second cam follower 4 is engaged with the lobe 2b of the second cam 2.
• valve 14 If the valve 14 is fast enough, it can also be used for adjusting the valve lift and the duration of the time the exhaust valve 5 remains open during the EGR opening. If the valve 14 is kept open when the cam follower wheel 4a of the second cam follower 4 enters the lobe 2b of the second exhaust cam 2, the opening of the exhaust valve 5 does not start until the valve 14 is closed. The opening of the exhaust valve 5 during the EGR operation can thus be delayed and also the maximum valve lift becomes smaller. If the valve 14 is opened when the cam follower wheel 4a of the second cam follower 4 is still engaged with the lobe 2b of the second exhaust cam 2, part of the hydraulic fluid flows from the second hydraulic fluid chamber 10 into the pressure accumulator 16 and the exhaust valve 5 is closed faster.
• Figure 2 shows a valve lifting arrangement that is similar to the arrangement of figure 1 .
• the valve lifting arrangement of figure 2 is provided with an additional function for variable exhaust valve closing (VEC).
• VEC variable exhaust valve closing
• the VEC-function allows delaying or slowing of the closing movement of the exhaust valve 5 during the normal opening of the exhaust valve 5.
• the valve lifting arrangement is provided with a second piston 19, which is in force transmission connection with the exhaust valve 5.
• the second piston 19 is arranged in the second hydraulic fluid chamber 10 between the first cam follower 3 and the first piston 9.
• the arrangement could also be provided with a separate chamber for the second piston 19, and the second piston 19 could be arranged in a differ- ent place in the force transmission path between the first exhaust cam 1 and the exhaust valve 5.
• Hydraulic fluid can be introduced behind the second piston 19, i.e. into the space that grows when the second piston 19 moves in the opening direction of the exhaust valve 5.
• Hydraulic fluid can be introduced behind the second piston 19, i.e. into the space that grows when the second piston 19 moves in the opening direction of the exhaust valve 5.
• closing of the exhaust valve 5 can be delayed or slowed down.
• a throttle or a valve can be used for the flow limitation.
• the second piston 19 is not fixed to the first cam follower 3, and the cam follower wheel 3a can thus follow the cam profile of the first exhaust cam 1 even when the VEC-function is in use.
• figure 3 is shown a valve lifting arrangement according to another embodiment of the invention.
• the force transmission between the first exhaust cam 1 and the exhaust valve 5 is partly hydraulic.
• the first cam follower 3 is arranged to operate a third piston 21 , which protrudes into a third hydraulic fluid chamber 20.
• the third hydraulic fluid chamber 20 is via a second hydraulic duct 22 in fluid communication with the second hydraulic fluid chamber 10.
• the second hydraulic fluid chamber 10 is arranged in connection with the exhaust valve 5.
• the piston 9, which is used for the additional opening of the exhaust valve 5, is also used for the normal open- ing of the exhaust valve 5.
• the piston 9 is connected to the exhaust valve 5.
• the hydraulic fluid is conducted through the second hydraulic duct 22 to the second hydraulic fluid chamber 10, where the piston 9 is moved and the exhaust valve 5 opens.
• the exhaust valve 5 can be provided with a spring for closing the valve 5 when the cam follower wheel 3a of the first cam follower 3 returns to the base circle 1 a of the first exhaust cam 1 .
• the additional opening of the exhaust valve 5 for the EGR works in the same way as in the embodiment of figures 1 and 2.
• the hydraulic duct 1 1 is connected to the second hydraulic duct 22 for conducting the hydraulic fluid from the first hydraulic fluid chamber 13 into the second hydraulic fluid chamber 10 or vice versa.
• the arrangement is further provided with an inlet duct 23, which comprises a check valve 24. Via the inlet duct 23, hydraulic fluid can be supplied into the system for compensating leakages.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Valve Device For Special Equipments (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=50023593

Family Applications (1)

Country Status (3)

Cited By (1)

Citations (6)

• 2013
  • 2013-01-07 FI FI20135018A patent/FI20135018L/fi not_active Application Discontinuation
  • 2013-12-31 EP EP13824501.4A patent/EP2941548B1/de active Active
  • 2013-12-31 WO PCT/FI2013/051217 patent/WO2014106686A1/en active Application Filing

Patent Citations (6)

Also Published As

Similar Documents

Legal Events