KR100491034B1 - A hydraulic system for a two-stroke crosshead engine - Google Patents

Abstract

The two-stroke crosshead engine 1 comprises a plurality of fuel pumps 13 and exhaust valves 4, which are hydraulically driven piston pumps, the pump driving portion 14 of which is pressurized hydraulic fluid. The opening and opening of the exhaust valve are performed by hydraulic actuators 7 to which pressurized hydraulic fluid is supplied. The hydraulic system of the engine has a single high pressure supply tube 5, which is a pump drive 14 and an exhaust valve actuator (although there are two types of hydraulic devices with virtually different pressure conditions when the engine load changes). 7) Supply hydraulic fluid to them. The engine oil of the engine is used as hydraulic fluid, the hydraulic fluid is discharged from the pump drive, and the valve actuator 7 is returned to the oil tank of the engine.

Description

Hydraulic system for a two-stroke crosshead engine

The present invention includes a plurality of exhaust valves and pumps, the fuel pump is a piston pump driven by hydraulic pressure, the pump driving unit is supplied with a pressurized hydraulic fluid, the exhaust valve by a hydraulic actuator supplied with a pressurized hydraulic fluid A two-stroke crosshead engine is opened.

For a long time, it has been known to hydraulically operate the exhaust valves of large two-stroke crosshead engines widely used as propulsion engines in ships. Hydraulic fluid is supplied to the valve actuator in the form of a liquid strut formed in the conduit between the pressure chamber of the cylinder and the pressure chamber of the actuator with the piston actuated by the camshaft. In Danish Patent No. 148 664 a hydraulically driven fuel pump is proposed, the actuator of the exhaust valve being simply connected with a constant pressure hydraulic fluid source at the start of the opening operation of the exhaust valve. The duration of the connection to the high pressure hydraulic fluid source may vary depending on the engine load.

Over the years, fuel pumps of large two-stroke crosshead engines have been proposed to be operated hydraulically instead of the well known camshaft operation. Applicant's 1929 Danish Patent No. 41046 proposes a hydraulically driven fuel pump, and recent Danish Patent No. 151145 relates to a piston pump of a particular type in a hydraulically driven fuel pump.

Several known proposals for the full hydraulic operation of fuel pumps and exhaust valves of large two-stroke crosshead engines have not been applied commercially to the engines, because the hydraulic supply system with the high energy consumption associated with such hydraulic operation. Because of its complex structure.

The common high pressure pump supplies hydraulic fluid to the first supply line to the valve actuators and to the second supply line to the pump drives, and the common pump provides a constant supply of hydraulic fluid at the highest pressure required. Has been tried experimentally to supply hydraulic fluid to the supply line through a pressure regulator at lower pressure conditions. Such hydraulic supply systems have proven to be complex and involve significant energy losses.

It is an object of the present invention to provide a two-stroke crosshead engine in which the valve actuators and the pump drive are hydraulically operated, in which the hydraulic supply system is operationally reliable and simplified.

Hydraulic system according to the present invention for this purpose is to supply the hydraulic fluid to both the hydraulic actuators and the pump drive of the exhaust valves in a single high pressure supply pipe, the engine oil of the engine is used as the hydraulic fluid, the hydraulic fluid pump Discharged from the drive, the valve actuator is characterized in that returned to the engine oil tank.

By supplying hydraulic fluid to both the valve actuators and the pump drives from the common high pressure supply tube according to the invention, the piping to the engine cylinders is extremely simplified, resulting in a significant savings in the installation cost of the engine. More importantly, however, the use of a common high pressure feed tube improves the reliability of the engine, since the risk of trouble is reduced as the number of devices that are at risk of failure is reduced. Half the number of high pressure pipes into two types of devices provides a more economic advantage of producing higher strength high pressure pipes as a special safety measure against problems.

By using engine oil as the hydraulic fluid, the engine can be made more independent regardless of the external system, eliminating the need for separate tanks with pipe equipment for the storage of the hydraulic fluid and improving reliability. In addition, reliability is further increased by avoiding the use of oils for hydraulic systems that may contaminate the engine oil when leaking into the engine.

The use of engine oil as a hydraulic fluid for hydraulic systems is particularly preferred as it can simplify the hydraulic system, which in each cylinder is, as one embodiment herein, the inner space of the engine frame box and the valve actuator of the cylinder. This is because the return pipe connecting the outlet from the pump drive to the bottom of the piston rod receiving box. The oil used in the pump drives and the valve actuators can be discharged away from the air supply of the cylinder to the place of use below that position, thereby avoiding the use of a return tube in the receiving tank and the cavity. This hydraulic system allows the engine oil to be supplied and used and discharges without any problems inside the engine like engine oil in other parts of the engine. The return tube should preferably be as short as possible to open directly below the middle floor.

The pressure of the high pressure supply tube acts on the pistons of the pump drives and valve actuators, and the area of the pistons is adapted to the pump drives and the valve actuators so that the pump drives and the valve actuators at 100% engine load. It is desirable to have virtually constant hydraulic conditions. This provides an optimal use of energy consumption to supply hydraulic fluid to hydraulically driven devices at full engine load when the amount of hydraulic fluid used per engine cycle is maximum and when the greatest supply pressure is required.

At engine loads significantly lower than 100%, the supply pressure of the high pressure supply line can be adjusted appropriately according to the hydraulic pressure conditions of the valve actuators because the energy consumption required for injection of the fuel, together with the fuel injection amount, decreases with the reduction of the engine load.

When the engine load is 70% or less, the hydraulic fluid supply pressure in the high pressure supply pipe is preferably reduced to 75% of the supply pressure for the engine load of 100% at the maximum. Along with the energy savings, this provides a better condition for fuel injection at low engine loads when the injection volume of fuel per engine cycle and the corresponding pressure for injection are reduced. The reduction of hydraulic fluid slows down the operation of the pump piston, and fuel injection is made over a longer period of time, which is desirable for flame spread diffusion, resulting in more desirable combustion.

The pneumatic spring acts on the exhaust valve toward the exhaust valve closing start position, and the air pressure of the pneumatic spring is adjustable, and when the engine speed is increased or decreased, the supply pressure of the high pressure supply pipe and the air pressure of the pneumatic spring are lowered or raised together. In this way, the energy consumption for the supply of hydraulic fluid is further reduced. This utilizes the fact that the valve actuator must overcome the upward force acting on it from the action of air pressure on the piston of the pneumatic spring and the action of cylinder pressure on the bottom of the valve disc. In low speed operation, the drop in air pressure results in the minimum pressure required to open the exhaust valve to a level close to the minimum pressure condition required for the pump drive where the speed is reduced relatively rapidly.

The air chambers at all air pressure springs of the engine in the exhaust valves can be in communication with each other. This means that the pneumatic spring pressure becomes nearly constant during the opening operation of the exhaust valve downward, because some air is discharged to other air chambers and returned during the closing operation of the valve with the resulting reduction in chamber volume. .

In one embodiment, the hydraulic system is configured such that the high pressure supply pipe can support the maximum supply pressure as both concentric pipes, and only the inner pipe delivers the hydraulic fluid during normal operation of the hydraulic system. The annular space formed by the pipes is configured to provide a sensor to detect leaks therein. This configuration is capable of assisting the supply line function and the detection of breakage causes hydraulic fluid to leak into the annular space between the pipes when the inner pipe of the two concentric pipes is damaged while the outer pipe receives the pressure. To function. Therefore, even if the inner pipe is damaged, the detector of the engine detects the damage of the inner pipe so that the engine operation continues.

Hereinafter, with reference to the accompanying drawings showing an embodiment of the present invention will be described in detail the present invention.

The hydraulic system supplies hydraulic fluid to the hydraulic devices of the two-stroke crosshead engine 1 under pressure. The engine comprises a plurality of cylinders 2 as indicated in FIG. 1 by dashed lines around hydraulics associated with the cylinders. More cylinders than those shown in the figure are typically provided with 4 to 14 cylinders. Each cylinder is provided with at least one, typically two or three fuel injectors 3 and an exhaust valve 4 located in the center of the cylinder cover.

The exhaust valve is of the poppet valve type (disc type) and opens as the high pressure supply tube 5 moves downward in the cylinder when it communicates with the pressure chamber 6 of the actuator 7, thereby causing the actuator piston to exhaust. Presses the spindle 8 downward. The pneumatic spring 9 comprises a piston 10 movably disposed in a cylinder with a pressure chamber 12 and fixed to a spindle 8, whereby the air pressure of the pressure chamber continues to act on the valve spindle. The upward force acts in the direction in which the valve is closed. The pressure of the hydraulic fluid in the chamber 6 acts on the spindle 8 with downward force. The conditions for the opening of the exhaust valve are such that the force generated by the valve actuator 7 is upwardly directed against the valve, partly from the action of air pressure on the piston 10 and partly from the gas pressure of the engine cylinder. It must be much greater than force.

The hydraulically driven fuel pump 13 supplies the fuel injectors with the pressurized fuel at an amount suitable for the engine load and when necessary for the engine cycle. The pump piston is driven by the pump drive 14, which is in the form of a cylinder with an actuator piston having a large diameter in relation to the pump piston. The piston device is a stepped piston that supplies fuel at a pressure greater than the pressure in the supply pipe 5 by the ratio between the areas of the large and small pistons. The fuel supplied as above must be supplied at a pressure much higher than the current gas pressure of the engine cylinder, so that a good atomization state is obtained through the nebulizer holes having a predetermined area. The fuel pump can supply fuel to a plurality of injectors in a single cylinder, which is usually carried out in a simultaneous feed, and can also be supplied to fuel injectors in other cylinders, in which case Fueled in time.

The supply of high pressure hydraulic fluid from the supply pipe 5 to the actuators is controlled via the control valve 16 for the fuel pump 13 and the control valve 15 for the exhaust valve 4. The control valves are actuated electronically by at least one electronic control unit 17, which can be a central control unit for a plurality of cylinders. In addition, for example, one control device may be provided for each cylinder to perform distributed control and use a distributed control system as a whole. The signal transmission is made through the signal line s briefly shown in the figure.

The control valves 15, 16 can be in the form of, for example, two positions, one of which connects a pressure chamber with a high pressure supply tube 5 and an actuator piston and the other one To the outlet in the form of return tube (18). The control valves can also be in three positions, in which case the third position is a neutral position in which both the supply tube 5 and the return tube 18 are isolated from the actuator. Of course, other types of control valves and a plurality of control valves may be provided in combination with each actuator device, but such a structure becomes more complicated.

The high pressure supply pipe 5 is supplied with hydraulic fluid from the pump device 19 schematically shown in FIG. 1 as a single pump, in practice the pump device may comprise a plurality of pumps which can be driven in different ways. have. The supply pipe 20 supplies hydraulic pumps having a relatively low pressure of 1 to 8 bar to the pump device. The supply pipe 20 preferably obtains hydraulic fluid from the engine oil of the crosshead engine. Precision filter 21 is to ensure the filtering of the hydraulic fluid. The pump device 19 can adjust the hydraulic fluid supply pressure to the high pressure supply pipe 5 within a wide range, for example, in the range of 150 to 300 bar. The adjustment is controlled by a signal received from the controller 17 via the signal line 22.

FIG. 2 is a longitudinal cross-sectional view of a crosshead engine, each engine cylinder 2 having a cylinder liner 23 forming a combustion chamber 28 together with a cylinder cover 24 having a piston 25 and an exhaust valve. Doing. The piston is connected to the connecting rod journal 30 of the crankshaft 31 of the engine via the piston rod 27, the crosshead 28 and the connecting rods 29. The crankshaft is journaled to a bedplate 32 of the engine, which receives the engine oil and is equipped with an engine frame box 33 on its top and supports the guide face 34 for the crosshead. The upper end of the guide surface is provided with an intermediate bottom portion 35 having a piston rod receiving box 36 and the piston rod receiving box is provided with an engine frame box and a bed plate provided with various moving parts lubricated by engine oil. The cylinder part is positioned on the middle bottom which is completely separated from the inside.

The fuel pump 13 is arranged at the top of the cylinder 2 and supplies fuel through three high pressure pipes 37 each leading to fuel injectors 3. The other high pressure pipe 38 is associated with the control valve 15 and connected to the exhaust valve 4.

Since the engine oil is used as the hydraulic fluid, the hydraulic fluid used in each cylinder is discharged from the pump drive unit and the valve actuator to the return pipe 18 and flows downwardly below the intermediate bottom 35 to the engine frame box 33. It discharges the lubricating oil of the inner side and flows into the oil tank of the bad plate. As shown in FIG. 1, each cylinder may have a discharge tube, which has the advantage that the hydraulic system can be formed without a common return tube.

In one embodiment, the high pressure feed tube 5 may be configured as a double pipe as shown in FIG. 3. The outer pipe 40 can withstand the maximum supply pressure from the pumping device like the inner pipe 41. The two pipes are arranged concentrically. In normal operation of the hydraulic system, the supply of hydraulic fluid is carried out only through the inner pipe 41. An annular space 42 formed between the two pipes is provided with a leak detection sensor 43. When the inner pipe 41 is broken, the sensor 43 generates an alarm signal to notify the drivers so that there is no need for excessive protection against pipe breakage. The supply pipe 5 does not necessarily have to be configured as a double pipe as described above, but provides greater reliability in operation.

Pump drives and valve actuators are designed to operate optimally for only one engine load. This will be described in detail below with reference to FIG. 4. The point A of the optimum operating state is selected as the full engine load point of 100% of the engine load, but the point may be selected otherwise. The pump device 19 is controlled to supply hydraulic fluid at a pressure of 250 bar. Curve a in the figure shows how the condition of the exhaust valve for minimum hydraulic pressure varies with engine load when the engine is directly connected to a fixed pitch propeller. Curve b shows the condition of the exhaust valve for minimum hydraulic pressure when the engine is connected to a power generating generator or variable pitch propeller. In both cases, the engine speed is constant and load independent, and at low loads the effective average pressure of the cylinder is smaller than for a speed adjustable corresponding engine, which requires the valve actuator to have the same high hydraulic pressure as at the low load. Means not to.

Curve c shows how the condition of the pump drive for minimum hydraulic pressure varies with engine load. In higher load ranges, the pressure condition of the pump drive was found to decrease faster than the pressure condition of the exhaust valve, due to a decrease in both the cylinder pressure which must be overcome by the fuel injection and the amount of fuel to be injected. When the engine load is lowered to levels below 50%, the pressure conditions are constant and it is determined by the lowest pressure that produces the required atomization state. There is a significant difference between the course of the curves of the pump drive and the valve actuators, since the hydraulic fluid is supplied through the common supply line 5, of the devices with the highest conditions for minimizing the supply pressure at the load shown. In the case of the embodiment, the supply pressure of the pump device must be controlled according to one, which is a valve actuator. As a result, at low loads the supply pressure up to about 50 bar of the pump drive is higher than necessary for the variable speed engine, but it is partially compensated by the smaller amount of fuel supplied at the lower load. It is clear that the hydraulic system can be constructed with different pressure values than shown, but this does not change the fact that the relative process of the curves is shown.

In a preferred embodiment, all the pressure chambers 12 of the pneumatic springs of the exhaust valve are in communication with one another via a common conduit 44, so that the air pressure in the chamber 12 does not essentially increase the opening of the exhaust valve. There is no need for the extra hydraulic energy required to overcome such pressure increases. Moreover, the air pressure in the chamber 12 can be adjusted by the air pressure controller 45 in accordance with the engine speed in such a way that the air pressure decreases with the speed decrease. This is possible because more time can be used to return the valve spindle to the valve closing position at low speeds. The low corresponding pressure from the pneumatic spring means that the pressure supplied from the pump device 19 can be correspondingly reduced and consequently save energy.

The hydraulic system according to the present invention is simplified by supplying hydraulic fluid to both the hydraulic actuators of the exhaust valves and the pump driving units with a single high pressure supply pipe, thereby reducing the installation cost of the engine and using a common high pressure supply pipe. This improves the reliability of the engine. Half the number of high pressure pipes into two types of devices provides a more economic advantage of producing higher strength high pressure pipes as a special safety measure against problems. In addition, the hydraulic system according to the present invention is able to continuously adjust the supply pressure according to the engine load such that the present minimum supply pressure is equal to one of two types of devices requiring the highest supply pressure in the corresponding operation mode. Energy consumption can be minimized by minimizing energy consumption.

1 is a schematic diagram of a hydraulic system for a two-stroke crosshead engine;

2 is a longitudinal sectional view of the engine.

3 is an enlarged partial view of the hydraulic system shown in FIG.

4 is a graph showing the correlation between the minimum pressure and engine load required to drive a fuel pump and open an exhaust valve;

Claims (11)

The fuel pumps are hydraulically actuated piston pumps whose pump drives 14 are supplied with pressurized hydraulic fluid and the opening of the exhaust valves is carried out by a plurality of hydraulic actuators 7 supplied with pressurized hydraulic fluid. In a hydraulic system for a two-stroke crosshead engine 1 having fuel pumps 13 and a plurality of exhaust valves 4, A single high pressure supply pipe 5 supplies hydraulic fluid to the hydraulic actuators 7 and the pump drives 14 of the exhaust valves, the engine oil of the engine being used as the hydraulic fluid, and the hydraulic fluid is the pump drive ( 14) wherein the valve actuator (7) is returned to the oil tank of the engine. The method of claim 1, The control valves 15 and 16 have two pistons, one of which connects a hydraulic actuator 7 or a pump drive 14 having a drain in the form of a return tube 18. system. The method of claim 1, Each cylinder 2 has an engine frame box at a height below the intermediate bottom portion 35 having a return pipe 18 connecting the drain from the pump drive portion 14 of the cylinder and a piston rod receiving box 36. Hydraulic system, characterized in that the valve actuator (7) having an internal cavity of the installed. The method of claim 3, wherein The return tube is open directly under the middle floor. The method according to any one of claims 1 to 4, Hydraulic system, characterized in that the precision filter (21) filters the hydraulic fluid. The method according to any one of claims 1 to 4, The pressure in the high pressure supply pipe 5 acts on the pistons of the valve actuators 7 and the pump drive 14, the area of the piston being substantially uniform in the engine load range of the valve actuators and the pump drive 100%. Hydraulic systems characterized in that they are adapted to each other to have a fluid pressure condition. The method according to any one of claims 1 to 4, The supply pressure of the high pressure supply pipe (5) is characterized in that it is adjusted according to the hydraulic conditions of the valve actuators (7) when the engine load is substantially lower than 100%. The method according to any one of claims 1 to 4, The supply pressure of the high pressure supply pipe (5) is a hydraulic system, characterized in that when the engine load is 70% or less, at most 75% of the supply pressure at 100% engine load. The method according to any one of claims 1 to 4, The pneumatic spring 9 acts on the exhaust valve 4 in the direction in which the valve faces the closed starting position, the air pressure of the pneumatic spring is adjustable, the supply pressure of the high pressure supply pipe 5 and the air of the pneumatic spring 9 The pressure system is characterized in that the pressure is adjusted downward or upward together as the engine speed decreases or increases respectively. 10. The hydraulic system of claim 9 wherein all pneumatic springs of the engine are connected to each other. The method according to any one of claims 1 to 4, The high pressure supply pipe (5) consists of two concentrically arranged pipes (40, 41) each capable of withstanding the maximum supply pressure, and only the inner pipe (41) transmits the hydraulic fluid during normal operation of the hydraulic system. And an annular space (42) formed of two pipes is provided with a sensor (43) for detecting leaks.