DK173421B1 - Hydraulic system for a two-stroke cross-head motor and with single-strand high-pressure feeder - Google Patents

Description

in DK 173421 B1

The invention relates to a hydraulic system for a two-stroke cross-head motor with multiple fuel pumps and multiple exhaust valves, the fuel pumps being hydraulically driven piston pumps whose pump drives are provided with pressurized hydraulic fluid and the opening of the exhaust valves is effected by hydraulic actuators. with pressurized hydraulic fluid.

It has been known for many years to hydraulically actuate the exhaust valves on the large 10 two-stroke cross-head motors, typically used as propulsion engines in ships. The valve actuator is here provided with hydraulic fluid in the form of a liquid column which is enclosed in a conduit between the pressure chamber in the actuator and a pressure chamber in a cylinder containing a camshaft actuated piston. Danish Patent No. 148,664 also discloses an electronically controlled and hydraulically actuated exhaust valve whose actuator is briefly connected to a high pressure source for hydraulic fluid at constant pressure at the start of the open movement.

20 The duration of the connection to the high pressure source may vary depending on the engine load.

For many years, there have been suggestions that the fuel pumps on a large two-stroke cross-head motor should be hydraulically actuated instead of the 25 well-known camshaft actuation. Applicant's Danish Patent No. 41046 of 1929 proposed a hydraulically driven fuel pump, and more recently, Danish Patent No. 151145, which relates to a special design of a pump piston in a hydraulically driven fuel pump, is proposed.

The various known proposals for clean hydraulic actuation of exhaust valves and fuel pumps on large two-stroke cross-head motors have not found concurrent commercial use on engines due to the complicated design of the hydraulic feed systems 2 DK 173421 B1 in combination with the large energy consumption that can be used for such activation. Minimizing energy consumption is a design criterion for these large engines, which are usually stopped only a few days a year, about 5 any at all. This is also seen by the fact that the overall efficiency of the engines in recent years has been above 50%.

In terms of energy consumption, the two types of devices can be mentioned as follows.

For a given valve actuator, the pressure of the hydraulic fluid 10 must exceed the minimum pressure required to open the exhaust valve against the gas pressure in the engine cylinder at the time of opening. This gas pressure varies with the desired opening time in the motor cycle and with the engine load. If the engine is connected to a propeller with a fixed pitch, the engine speed varies with the engine load, which also demands the minimum hydraulic fluid pressure, because the valve must open faster at higher speeds.

In addition, for the exhaust valve, there are only 20 minor variations in the amount of hydraulic fluid consumed per valve actuation.

For a given pump drive, the hydraulic fluid delivery pressure must exceed a minimum pressure which also varies with the engine load, partly because the fuel 25 at higher load must be injected into the engine cylinder against a higher combustion pressure, and partly because a larger amount of fuel must be delivered. If the engine is connected to a propeller with a fixed pitch and thus has increasing rpm with increasing load, a further increase of the minimum pressure is required, because the larger amount of fuel must be injected over a shorter period of time. Furthermore, the amount of hydraulic fluid consumed varies with the amount of fuel.

The required minimum pressure for the pump drive varies 35 considerably more with the motor load than that required in the minimum pressure for the valve actuator, and the delivery quantities for the two types of units also show large differences. The two types of units thus have different characteristics and thus different requirements for fixed, 5 individual delivery pressures in order to be able to operate energy optimally. This speaks to the use of completely separate feeding systems.

Experimentally, it has been tried to provide a common high pressure pump to supply hydraulic fluid to a first supply line leading to the valve actuators and to a second supply line leading to the pump drives, where the common pump delivered constant at the highest required pressure and where the pump supply to the supply line with lower pressure requirements occurred via a pressure regulator.

15 Such a hydraulic feeding system has been found to be complicated and to cause significant energy losses.

The invention has for its object to provide a two-stroke cross-head motor with clean hydraulic actuation of the pump drives and valve actuators, where the hydraulic feed system is reliable and suitably simple without thereby causing excessive energy consumption.

To this end, the hydraulic system according to the invention is characterized in that a single high-pressure supply line supplies both the hydraulic actuators of the pump drives and the exhaust valves with hydraulic fluid, and that the supply pressure in the high-pressure feed line, and optionally the pressure in air springs in the exhaust valves, is adjustable in the motor. .

By providing the invention with both the valve actuators and the pump drives from a common high pressure feed line, the wiring to the engine cylinders becomes extremely simple, which provides significant savings in engine installation. More importantly, however, the use of a common high pressure feed line improves the engine's reliability because failure risk 4 decreases as the number of fault critical units is reduced. Furthermore, halving the number of high-pressure pipes for the two types of units provides a better economic opportunity to produce the high-pressure pipes with 5 higher strengths as extra security against failure.

The feeding from a common pipe involves the energy disadvantage that the two types of units are supplied with the same delivery pressure, and even if a single motor load is designed to fit the delivery pressure to a single engine load, the different characteristics cause the delivery pressure to be not optimally at other engine loads. The hydraulic system according to the invention partially compensates for this by adjusting the delivery pressure in dependence on the engine load. Thus, the loss of energy due to non-utilization of the full delivery pressure can be minimized, since the delivery pressure can be continuously adjusted to correspond to the instantaneous minimum delivery pressure to either of the two types of units requiring the highest supply pressure at the operating mode concerned.

It is preferred that the pressure in the high pressure feed line affect pistons in the pump drives and in the valve actuators, which piston areas are so mutually adapted for pump drives and valve actuators that they have substantially the same hydraulic pressure demand at a 100% engine load. This provides an optimal utilization of energy consumption for feeding the hydraulically driven units at full engine load, where the hydraulic amount consumed per motor cycle is greatest and 30 where there is the greatest supply pressure.

At substantially lower engine loads than 100%, the delivery pressure in the high-pressure feed line may conveniently be regulated according to the hydraulic pressure requirements of the valve actuators, because the fuel quantity and thus the energy consumption for the injection of the fuel decreases with decreasing engine load.

It is preferred that the delivery pressure in the high pressure feed line be reduced to a maximum of 75% of the delivery pressure at 100% engine load when the engine load 5 is 70% or less. In addition to achieving an energy saving, this gives better fuel injection ratio at lower engine loads, where both the injection pressure and the fuel injection rate per motor cycle is lower. By lowering the hydraulic pressure, the movement of the pump piston becomes slower and the fuel injection is extended over a longer period, giving a more advantageous combustion with the associated advantageous distribution of the heat generation.

15 A further saving in energy can be achieved for the supply of hydraulic fluid by the fact that an air spring affects the exhaust valve towards the closed starting position, that the air pressure in the air spring is adjustable and that the supply pressure in the high-pressure supply line and the air pressure in the air spring are jointly adjustable. in the downward and upward direction as the engine rpm decreases and increases respectively. Hereby it is utilized that the valve actuator must overcome the created force effects from both the effect of the cylinder pressure 25 on the underside of the valve plate and the effect of the air pressure on the piston of the air spring. A lowering of the air pressure at lower rpm causes the minimum pressure requirement to open the exhaust valve to be reduced to a level 30 closer to the minimum pressure requirement for the pump drives, which, as mentioned, decreases relatively sharply with the rpm.

The air chambers in all the engine air springs in the exhaust valves may be interconnected. This means that the air spring pressure is approximately constant, also during the downward opening movement of the exhaust valve, because the consequent reduction of the chamber volume causes some of the air to escape to the other air chambers and is returned during 5 of the valve closing movement.

In one embodiment, the hydraulic system is designed such that the high-pressure feed line is constructed of two concentric tubes, both capable of withstanding the maximum delivery pressure, that only the inner tube carries 10 the hydraulic fluid during normal operation of the hydraulic system, and that one of the two tubes delimited annulus is provided. with a leak monitoring sensor in the annulus. This design provides redundancy in the operation of the feed line as well as failure monitoring, as a breakage of the interior of the two concentric tubes provides leakage of hydraulic fluid to the annulus between the tubes and accompanying signal delivery from the sensor while the outer tube assumes the pressure-bearing function. Therefore, engine operation can continue even if the inner tube breaks, but the engine monitoring system receives notification of failure of the inner tube.

In a particularly simple and thus preferred embodiment, the engine oil of the engine is used as hydraulic fluid, and the pump drives and valve actuators deliver the hydraulic fluid to the engine oil sump. By using the system oil as a hydraulic fluid, the engine becomes more independent of external systems, which improves reliability and at the same time avoids separate tanks with associated pipe connections, etc. for storing 30 hydraulic fluid. Operational safety is also increased by avoiding the use of a hydraulic oil that could contaminate the system oil if leakage to the interior of the engine.

The use of system oil as hydraulic fluid 35 provides a particularly advantageous option for simplifying the hydraulic system, in that for each cylinder there may be a return line connecting sinks from the pump's pump drive and valve actuator to the internal cavity of the engine rack at one level. located under a 5 middle bottom with a piston rod packing box. The spent oil in the pump drives and in the valve actuators can thus be delivered outside the consumption point at a level below and separated from the air supply of the cylinder, and the use of a common return pipe with associated 10 tanks is completely avoided. With this hydraulic system, the oil can be delivered and used, after which it can be delivered inside the engine just like any other part of the system oil. It is preferred that the return line opens immediately below the intermediate bottom for the purpose of obtaining the shortest possible return lines.

Examples of embodiments of the invention will now be described in more detail with reference to the schematic drawing, in which fig. 1 shows a simplified diagram of a hydraulic system for a two-stroke cross-head motor; FIG. 2 is a cross-section through the motor; FIG. 3 is an enlarged view of the hydraulic system of FIG. 1, and FIG. 4 shows a diagram of the relationship between the engine load and the required minimum pressure for opening the exhaust valves and operating the fuel pumps.

A hydraulic system supplies hydraulic fluid under pressure to hydraulic units on a two-stroke cross-head motor 1. The motor has several cylinders 2, which in Fig. 1 are indicated by a dashed line around the hydraulic units belonging to the cylinder. Obviously, there are typically more cylinders than shown, such as from 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 centrally in the cylinder 8 cover.

The exhaust valve is of the plate type, which is opened by moving downwardly in the cylinder when a high pressure feed line 5 is connected to a pressure chamber 6 in an actuator 7, whereby the actuator piston presses the spindle 8 of the exhaust valve downwards. A pneumatic spring 9 comprises a piston 10 which is fixed to the spindle 8 and is slidably positioned in a cylinder with a pressure chamber 12 located below the piston, so that the air pressure 10 in the pressure chamber continuously affects the valve spindle with an upward force acting in the closing direction. The pressure of the hydraulic fluid in the chamber 6 affects the spindle 8 with a downward force. To open the exhaust valve, it is required that this force produced by the valve actuator 7 15 is suitably much greater than the upward force on the valve arising partly from the gas pressure in the engine cylinder and partly from the pressure of the air pressure on the piston 10.

A hydraulically driven fuel pump 13 supplies the fuel injectors with pressurized fuel at the desired time of the motor cycle and in an amount adapted to the engine load. The pump piston is driven by a pump drive 14 in the form of a cylinder with a large diameter actuator piston relative to the pump piston. Thus, the piston unit is a step piston which delivers fuel at a pressure which is the area ratio of the large to the small piston greater than the pressure in line 5. The fuel must be delivered at a pressure which is suitably much greater than the instantaneous gas pressure in the engine cylinder. so that good dusting is achieved through the predetermined area of the nebulizer holes. The fuel pump can deliver fuel to multiple injectors on a single cylinder, which usually happens at the same time, and it can also be designed to deliver fuel to injectors on different 35 cylinders, in which case it delivers the fuel at different times to the various cylinders.

The supply of high pressure hydraulic fluid from the feed line 5 to the actuators is controlled via a control valve 15 for the exhaust valve 4 and a control valve 16 to 5 the fuel pump 13. The control valves are electronically activated from at least one electronic control unit 17, which can be a central unit for several cylinders. It is also possible to use distributed control, for example with one control unit per cylinder, and combinations of 10 overall and distributed control. Signal transmission is via signal lines s, which are only indicated in the figure.

For example, the control valves 15 and 16 may be of a type having two positions, one of which connects the pressure chamber to the actuator piston with the high pressure damper 5, and the other connects the pressure chamber to a drain in the form of a return line 18. The control valves can also be made with three positions, the third being a neutral position, where both the feed and return lines 5, 18 are off the actuator bar. Of course, many other types of control valves and combinations of multiple control valves per actuator unit can be used, but these will be more complicated designs.

25 The high pressure feed line 5 is supplied with hydraulic fluid from a pump unit 19 which in FIG. 1 is shown schematically as a single pump, but in practice the pump unit will comprise several pumps which can be operated in different ways. A supply line 20 supplies the pump unit 30 with hydraulic fluid at a relatively low pressure, such as from 1 to 8 bar. Feed line 20 may fetch the liquid from a tank, but it is preferred that the hydraulic fluid be withdrawn from the system oil of the crosshead engine. A fine filter 21 provides for filtration of the hydraulic fluid.

The pump unit 19 can regulate the supply pressure to high pressure feed line 5 within a wide range, such as from 150 to 300 bar. The control is controlled by signals received from the control unit 17 via the signal line 22.

5 In FIG. 2 shows a cross section through the engine. Each engine cylinder 2 has a cylinder liner 23 which, together with a cylinder cover 24 with the exhaust valve and a piston 25, define a combustion chamber 26. The piston is connected through a piston rod 27, a cross head 28 and a 10 rod rod 29 to a piston rod column 30 on the engine crankshaft 31. The crankshaft is mounted in the engine bottom vessel 32 containing the system oil, and on top of the base vessel is mounted an engine rack 33 carrying the control planes 34 for the crosshead. At the top of the 15 guide planes, there is an intermediate bottom 35 with a piston rod packing box 36 which holds the overlying cylinder portion completely separate from the interior of the bottom vessel and engine rack with the various moving parts lubricated by the system oil.

The fuel pump 13 is located off the top of the cylinder 2 and delivers the fuel through three high pressure pipes 37 which lead to each of their fuel injectors 3. An additional high pressure pipe 38 is connected to the control valve 15 and leads to the exhaust valve 4.

When system oil is used as a hydraulic fluid, the spent hydraulic fluid from each cylinder can be drained from the pump drive and valve actuator to the return line 18 which goes straight down to the area below the intermediate bottom 35 and delivers the lubricating oil inside the engine rack 33 where it runs into the oil sump. in the bottom vessel. As shown in FIG. 1, there may be such a drain line for each cylinder, which gives the special advantage that the hydraulic system can be made without a common return line.

In one embodiment, the high pressure feed line 5 may be constructed as a double tube, as shown in FIG. 3. An outer tube 40, like an inner tube 41, is able to withstand the maximum delivery pressure from the pump unit. The two tubes are concentric. In normal operation of the hydraulic system, the hydraulic fluid is delivered exclusively through the inner tube 41. Between the two tubes there is an annulus 42 which is provided with a sensor 43 for leak monitoring in the annulus. If the inner tube 41 is broken, the sensor 43 emits an alarm signal, so that the operating personnel become aware that there is no longer any additional security against pipe breakage. The design of the conduit 5 as double pipe is not a necessity, but provides greater reliability.

15 As mentioned above, the pump drives and valve actuators can be designed to run optimally at only one engine load. This is described in greater detail with reference to FIG. 4. The point A with optimum operating conditions is here chosen to be the motor full load point 20 with 100% motor load, but could also have been chosen differently. The pump unit 19 is controlled to deliver hydraulic fluid at a pressure of approx. 250 bar. In the figure, curve a shows how the exhaust valve requirements for minimum hydraulic pressure vary with the load of the engine 25 when the engine is directly coupled to a fixed pitch propeller. Curve b shows the exhaust valve requirements for minimum hydraulic pressure when the engine is connected to either a generator for power generation or a variable pitch propeller. In these two cases, the engine speed is constant and independent of the load, and the effective mean pressure of the cylinder is lower at lower loads than that of a corresponding variable speed engine, meaning that the valve actuator does not require an equally high hydraulic pressure at the lower loads.

12 DK 173421 B1

Curve c shows how the pump drive's minimum hydraulic pressure requirements vary with the engine load. In the upper load range, the pressure requirement of the pump drive is seen to decrease faster than the pressure requirement of the exhaust valve 5, because there is both a reduction in the amount of fuel to be injected and a reduction in the cylinder pressure which the injection must overcome. As the engine load comes down to around 50% and lower, the pressure requirement becomes constant and is determined by the lowest pressure that produces the desired atomization. There is seen to be a significant difference between the paths of the curves of the pump drives and the valve actuators, and since the supply of hydraulic fluid is through a common conduit 5, it is necessary to control the delivery pressure of the pump unit according to that of the units having the highest demand for the load. minimal delivery pressure, which in the case shown means the valve actuator. As a consequence, the supply pressure to the pump drive at 20 lower loads up to about 50 bar is higher than necessary for a variable speed engine, but this is partly compensated for by the low load fuel quantity. It is clear that the hydraulic units may be laid out for pressure values other than those shown, but this does not change the relative course of the curves as shown.

In an advantageous embodiment, all of the pressure chambers 12 in the pneumatic springs of the exhaust valves are interconnected through a common conduit 44, which causes the air pressure in the chamber 12 not to increase substantially when opening an exhaust valve, and thus no extra hydraulic energy is used to overcome a such pressure rise. It is furthermore possible by means of an air pressure control unit 45 to regulate the air pressure in the chambers 12 depending on the engine speed of the engine in such a way that the air pressure is reduced with decreasing rpm. This is possible because at lower rpm is longer available to return the valve stem to the 5 closed position. The lower back pressure from the pneumatic spring means that the delivery pressure from the pump unit 19 can be reduced accordingly, thereby achieving an energy saving.

Claims (9)

13 DK 173421 B1 10 PATENT REQUIREMENTS 1. Hydraulic system for a two-stroke cross-head motor (1) with multiple fuel pumps (13) and multiple exhaust valves (4), the fuel pumps being hydraulically driven piston pumps, whose pump drive (14) is provided with pressurized hydraulic fluid and the opening of the exhaust valves is effected by means of hydraulic actuators (7) supplied with pressurized hydraulic fluid, characterized in that a single high pressure feed line (5) supplies hydraulic fluid (7) to both the pump drives (14) and the hydraulic actuators (7) of the exhaust valves, and that the supply pressure in the high pressure feed line (5); any pressure in the air springs in the exhaust valves is adjustable depending on the engine load. Hydraulic system according to claim 1, characterized in that the pressure in the high pressure feed line (5) acts on pistons in the pump drives (14) and in the valve actuators (7), the piston areas of the pistons thus being mutually adapted for pump drives and valve actuators, that they have substantially the same hydraulic jerk demand 30 at a motor load of 100%. Hydraulic system according to claim 1 or 2, characterized in that the delivery pressure in the high pressure supply line (5) is regulated according to the hydraulic jerking requirements of the valve actuators (7) when the engine load is substantially lower than 100%. 14 DK 173421 B1 Hydraulic system according to one of claims 1-3, characterized in that the delivery pressure in the high pressure feed line (5) is at most 75% of the delivery pressure at 100% engine load when the engine load 5 is 70% or less. Hydraulic system according to one of claims 1-4, characterized in that an air spring (9) acts on the exhaust valve (4) in the direction of the closed initial position, that the air pressure in the air spring is adjustable and that the supply pressure in the high pressure feed line (5) and the air pressure in the air spring (9) are jointly adjustable downwards and upwards as the engine rpm decreases and increases respectively. Hydraulic system according to claim 5, characterized in that the air chambers (12) in all the air springs of the engine are interconnected. Hydraulic system according to one of claims 1-6, characterized in that the high pressure feed line (5) is made up of two concentric pipes (40, 41), both of which can withstand the maximum delivery pressure that only the inner tube (41) carries. the hydraulic fluid during normal operation of the hydraulic system and that one of the two pipes defined by the annulus (42) is provided with a sensor (43) for leak monitoring in the annulus. Hydraulic system according to one of claims 1-7, characterized in that the engine system oil is used as hydraulic fluid and that the pump drives (14) and the valve actuators (7) deliver the hydraulic fluid to the engine oil sump. Hydraulic system according to claim 8, characterized in that for each cylinder (2) there is a return line (18) connecting sinks from the pump drive (14) and valve actuator (7) to the internal cavity of the motor stand at a level located below a intermediate bottom 35 (35) with a piston rod packing box (36), preferably opening straight from the line immediately below the intermediate bottom.