KR19980087199A - Hydraulic system - Google Patents

Abstract

The present invention relates to a hydraulic system for an internal combustion engine having a plurality of exhaust valves and fuel pumps, wherein at least one of the high pressure pumps receives energy from the pressurized hydraulic fluid, the hydraulic actuators for the exhaust valves and the fuel pump. Supply to a hydraulic drive means, such as a pump drive means for. The hydraulic system comprises at least three high pressure pumps, at least two of which are main pumps 6 driven by the output shaft of the internal combustion engine, the rotational speed of which is preset according to the rotational speed of the crankshaft of the engine. At least one of the pumps, which varies in proportion, is a control pump 7 in which the discharge flow rate can be controlled and is electrically driven.

Description

Hydraulic system

The present invention relates to a hydraulic system for an internal combustion engine having a plurality of exhaust valves and fuel pumps, wherein at least one of the high pressure pumps receives energy from the pressurized hydraulic fluid, the hydraulic actuators for the exhaust valves and the fuel pump. Supply to a hydraulic drive means, such as a pump drive means for.

For a long time, proposals have been made to carry out hydraulic operation of the exhaust valves and fuel pumps of large two-stroke crosshead engines instead of the well-known camshaft operation. Applicant's 1929 Danish Patent No. 41046 has proposed a hydraulically driven fuel pump, and recently patented a hydraulically driven fuel pump as Danish Patent No. 151145, and Danish Patent No. 148 664 electrically. Patents have been issued for controlled and hydraulically actuated exhaust valves.

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 engines because of the high pressure involved in supplying high pressure hydraulic fluid to the hydraulics. It was due to the complex structure of the hydraulic supply system along with the energy consumption. The prerequisite for the commercial production of an internal combustion engine without a camshaft, i.e. without mechanically operating the fuel pump and exhaust valves, is that the hydraulic drive means has a reasonable design in terms of energy consumption and a reliable hydraulic supply system in operation. To have. When an internal combustion engine is employed as the ship's main engine, reliability is very important.

If the load on the engine is large, the hydraulic fluid feature of the hydraulic drive means is to use a large amount of hydraulic fluid per hour. If a high pressure pump is designed to meet the capacity conditions for hydraulics at full load of the engine, there is a problem of overcapacity at light loads.

It is an object of the present invention to provide a hydraulic system that has operational reliability and has a moderately low energy consumption characteristic.

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

The hydraulic system according to the invention for this purpose comprises at least three high pressure pumps, at least two of which are main pumps driven by the output shaft of the internal combustion engine, the rotational speed of which is the rotational speed of the crankshaft of the engine. According to the change in a preset ratio, at least one of the pump is characterized in that the discharge flow rate can be controlled and electrically driven control pump.

By distributing the discharge flow rate to at least three pumps, the overall reliability of the engine is improved because a failure of one pump does not result in a significant loss of discharge capacity, as in the case of using only two pumps, or auxiliary This is because the pump will not have a significant effect on the operating head without the pump. In addition, since at least two pumps are the main pumps driven by the engine output shaft, the design is considerably simplified than the electronically driven control pump, and the reliability is considerably improved. Moreover, the pump directly connected to the engine output shaft is the most reliable pump driving means. Known as Thus, with the configuration in which the main pumps are connected to the output shaft of the engine, reliable discharge of hydraulic fluid is ensured when the output shaft of the internal combustion engine rotates.

In addition, the hydraulic system of the present invention has several advantages in terms of energy efficiency. First, by dispersing the pump work into a plurality of pumps, the change in discharge flow rate of each pump is small, so that the pumps can operate close to the designed operating conditions. Second, when there are more pumps, the discharge from the pumps can be connected or separated in fine steps. Third, the power transmission loss in the shaft connection of the main pumps is preferably reduced. Fourth, in the structure in which the internal combustion engines are connected so that the rotational speed is changed according to the load change, partial adjustment of the discharge flow rate is automatically achieved in response to the current load, and the main pump likewise changes the rotational speed and the discharge flow rate. Because. These conditions preferably reduce the energy consumption associated with the discharge of high pressure hydraulic fluid. The electrically driven control pump enables fine adjustment of the discharge flow rate with respect to the current hydraulic fluid condition of the drive means. As the control pump is electrically driven, the discharge flow rate of the control pump can be controlled completely independently of the operation mode of the internal combustion engine.

The high reliability and relatively low energy consumption of the high pressure pump allows the hydraulic system provided in the drive means to replace the conventional camshaft of the large two-stroke crosshead engine used as the propulsion engine of the ship.

According to the invention, it is possible to apply to the main pumps, whereby it is possible to adjust the discharge flow rate with control according to the rotational speed of the main pumps, but each main pump is preferably able to provide a constant discharge flow rate per shaft rotation do. This improves reliability as the pumps can be designed to consist of only a few elements, for example standard fixed displacement axial piston pumps.

Since at least some of the main pumps do not require the discharge flow rate to be adjustable at a fixed rotational speed, the main pumps can be more optimized for their operating conditions, and are also more complex than the control pump with adjustable flow rate. It can have a high efficiency.

In order to optimize energy consumption, the control pump is preferably connected to the electric motor and the electric generator device, and the electric generator is operated by using the hydraulic fluid pressurized from the pump mode driven by the electric motor to discharge the pressurized hydraulic fluid. It can be controlled in the driving motor mode. This makes it possible to reduce the size of the control pump and to correspondingly increase the size of the more effective main pumps, which means that the control pump is positive or negative with respect to the discharge flow from the main pump. Because all of the adjustments can be made. If the main pumps discharge more hydraulic fluid than is required, the control pump generates electricity using excess discharge flow, and if the main pumps discharge less hydraulic fluid than is required, the control pump will be The flow rate can be discharged.

In a preferred embodiment, the control pump preferably has a capacity in the range of 40-60%, preferably 50% of the main pump capacity, with the main pumps having substantially the same capacity. This pump size distribution structure reduces the flow rate discharged by the control pump to a minimum and does not change the total discharge flow rate when the control pump is operated at the maximum output as a pump or a motor, and the discharge of the main pump is carried out over a wide range. Allows for step-by-step connection and disconnection.

At least four main pumps and at least two control pumps are preferably provided. This allows the compact size of the pumps to be combined so that the risk of failure in all pumps at the same time is extremely low.

Internal combustion engines have a fixed rotational direction, or are connected to a fixed pitch propeller, which means a marine marine engine or a stationary drive engine of a power plant connected to an adjustable pitch propeller in large two-stroke crosshead engines. As in the case of marine marine engines, it is known to be capable of forward and reverse rotation so that it can be operated at full power under bidirectional rotational conditions. Forward and reverse rotatable engines are mostly diesel type marine engines, and when the drive shafts of the main pumps are able to rotate in both directions at full load, a problem that it is difficult to achieve a sufficiently high level of efficiency and reliability in the main pumps is caused. It is possible to provide a clutch and a reversing gear between each main pump and the drive shaft, but this structure has the problem of reducing the advantages of the main pump on which the shaft is directly driven.

The present invention also provides a hydraulic drive of a main unit having a rotating shaft and operable in reverse direction such that the rotating shaft can rotate in both directions, such as hydraulic actuators for exhaust valves and fuel pump pumps of an internal combustion engine having a crankshaft. A hydraulic system having at least one high pressure pump for discharging a pressurized hydraulic fluid by means.

In order to provide a highly reliable and preferably low energy consumption type hydraulic system, the hydraulic system according to the invention comprises a plurality of main pumps driven by a rotating shaft and the rotational speed of the main pump is dependent on the rotational speed of the shaft. The main pump is connected to or connected to the high pressure pipe through each of the non-return valves to allow only hydraulic fluid to flow away from the connection. It is characterized in that it is mounted to the conduit between two connections which are connected to the low pressure pipe through each of the non-return valves to allow only fluid to flow.

The advantage of using main pumps driven by a shaft is as described above. In connection with the change in the direction of rotation of the drive shaft, the main pumps are made independent of the direction of rotation by placing each pump in a conduit connected at both ends to the low and high pressure pipes. Regardless of whether the pump draws fluid from one end and discharges it to the other end, or vice versa, the hydraulic fluid flows through the two non-return valves and flows toward the main pump from the low pressure pipe. The pressurized hydraulic fluid from is discharged into the high pressure pipe. Unlike the use of the clutch element and the forward and reverse gear to control the pump shaft, the great advantage of non-return valves is that the non-return valve Depending on whether it is in the open or closed position, it works without external control and is extremely reliable. When the direction of rotation of the main pump changes, the fluid pressure also changes, and all four non-return valves automatically switch to the opposite position, thus allowing the flow of fluid to flow in the opposite direction in the conduit provided with the main pump. Thus, the main pumps can all be equally optimal in structure as described above, and can operate at full capacity loads in both directions of rotation so that the drive means use substantially the same hydraulic fluid in both directions of rotation.

The following describes embodiments in which the present invention is applied to a basic structure having an internal combustion engine having a fixed rotational direction and a basic structure having an internal combustion engine capable of forward and reverse rotation.

In a preferred embodiment, each main pump is connected in parallel with an adjustable bypass valve that allows some or all of the hydraulic fluid discharged therefrom to be returned to the inlet side, and the non-return valve in the pressure line of the main pump to the high pressure line. Is disposed between the return pipe with the bypass valve and the high pressure pipe. When the discharge flow from the main pump is not necessary, the bypass valve is fully open as the non-return valve between the high pressure pipe and the bypass valve blocks the pressure of the high pressure pipe from the main pump and the bypass valve. The pressure in the pressure tube of the pump is reduced to almost the pressure level of the low pressure tube. In this state, the pressure difference between the discharge port side and the suction port side of the main pump is generated only by the flow resistance at the time of circulating flow out from the low pressure pipe through the main pump to the return pipe. The pressure difference is very small, and the main pump separates as described above and consumes negligible energy.

In the simplest structure, the bypass valve is a shutoff valve having a closed position and an open position. It is also possible to form a bypass valve as a control valve for controlling the discharge pressure from the main pump. The control of the discharge pressure can be common to all main pumps so that the pressure in the high pressure tube can be adjusted in a preferably simple manner so that there is no unnecessary energy consumption in pressurizing the hydraulic fluid.

In a preferred embodiment, the pressure in the high pressure tube is electrically controlled by a valve which regulates the discharge flow rate of the control pump. By changing the flow rate or discharge flow rate consumed by the control pump to correct the difference between the flow rate discharged by the main pumps and the flow rate consumed, in the hydraulic system due to the failure to use the total discharge pressure of the pumps to the high-pressure pipe The energy loss can be minimized and the discharge pressure is continuously adjusted such that the minimum discharge pressure is equal to the highest discharge pressure required by the hydraulic drive means in the corresponding operation mode.

When the hydraulic system supplies hydraulic fluid to the hydraulic actuators for the exhaust valve of the internal combustion engine and the hydraulic pump means for the fuel pump, the pressure discharged from the high pressure pump is 100% of the engine of the internal combustion engine when the load of the internal combustion engine is 70% or less. It can be up to 75% of discharge pressure under load. This saves a considerable amount of energy in driving the high pressure hydraulic pump.

The first electronic control unit controls the bypass valve of the at least one control pump and the at least one main pump, and the second electronic control unit is the bypass valve of the at least one second control pump and the at least one second main pump. The hydraulic system is preferably designed to control the pressure. The main purpose of controlling by the use of electronic control units is to control the flow rate and discharge pressure currently discharged from the pumps to the flow rate and pressure required for the hydraulic fluid application. In view of reliability, if control is not performed, the result is total discharge flow rate and maximum pressure. The control of the main pumps and the control pumps using a plurality of control units provides an extremely high degree of safety against complete failure of the hydraulic system.

Embodiments of the present invention will be described in more detail with reference to the accompanying drawings showing a simplified schematic structure for a hydraulic system for a two-stroke crosshead engine.

The hydraulic system supplies hydraulic fluid under pressure to the hydraulic units of a two-stroke crosshead engine. The engine is provided with a plurality of cylinders provided with hydraulic actuators 1 such as hydraulic actuators for exhaust valves and pump drive means for fuel pumps. These two types of hydraulics have different propensities for hydraulic fluid consumption at different engine loads, and the requirements for minimum hydraulic pressure may also be very different. For minimum hydraulic pressure, the hydraulic system should be able to provide a discharge flow rate that meets the requirements for maximum discharge engine load, including maximum overall consumption. Normally, the maximum engine load requires the highest discharge pressure.

The hydraulic fluid can be delivered from the storage tank, for example using standard hydraulic oil but engine lubricating oil can also be used as the hydraulic fluid, and the hydraulic system is supplied from the oil tank 2 of the engine. The main pump 3 supplies hydraulic fluid to the low pressure pipe 5 through at least one filter device 4, and the four main pumps 6 and two control pumps 7 are connected to the low pressure pipe. do. The main pump maintains a low pressure pipe, for example, a pressure in the range of 1-5 bar, typically 2 bar, so that the main pumps maintain the total hydraulic fluid at a positive pressure to prevent cavitation. This provides an advantage of preventing the pumps from missing. Thus, the main pumps do not need to be self-contained.

The embodiment shown in the figure supplies hydraulic fluid to a two-stroke crosshead engine capable of forward and reverse rotation of a ship. Marine engines do not have a conventional camshaft and their exhaust valves and fuel pumps are hydraulically driven and electronically controlled. It is also possible to connect a high pressure source for fuel at a constant pressure (normal rail system) or to leave it as fuel pumps for each cylinder, but a hydraulically driven fuel pump is preferred. Moreover, the hydraulic drive device supplied with the hydraulic fluid may be of another type, such as control valves and pumps.

The main pumps 6 are driven directly by means of gears by one or more shafts of the marine engine, typically the crankshaft of the engine. The gear ratio for this is chosen to obtain a suitable rotational speed of the main pumps when the marine engine is running at full load. In order for the marine engine to have a rotation speed of 125 rpm at a cylinder bore of 500 mm and a load of 100%, the main pumps can have a rotation speed 11 times higher than that of the driving crankshaft. Larger marine engines can have lower rotational speeds, and higher gear ratios of the main pumps are allowed. For example, with the main type A4FM, an axial piston pump from Mannesmann Rexrod GmbH can be selected, which has an efficiency of η = 0.95. The pump is a positive displacement pump with a fixed displacement in which the pump capacity depends only on the rotational speed of the pump shaft. It is advantageous to jack pumps of fixed displacement because of the high level of efficiency and reliability and the simplified design.

If the ship's engine is capable of forward and reverse rotation, its rotational speed also changes with the engine load, which is associated with the main pumps as the lower rotational speed at lower loads results in a smaller discharge from the main pump and the consumption of hydraulic fluid is reduced. It is particularly beneficial. The discharge from the main pumps changes in proportion to the speed of the ship engine, while the consumption changes in proportion to the speed of rotation. Thanks to their high efficiency, the total capacity of the main pumps can be selected to ensure an accurate amount of hydraulic fluid consumed by the engine at 100% engine load.

The main pump is mounted to a conduit 8 extending between two connections 9 to the supply pipe 10 and the discharge pipe 11. In these connections, the conduits can be welded together or otherwise bolted to eg a T-shaped connector. The conduits may also be formed as channels drilled into the block-shaped body, in which case the connections are located at places where one channel meets another channel. Supply pipe 10 may be a single conduit starting from low pressure pipe 5 and branching into two lines provided with connections 9. The connection part 9 may have a supply pipe to a low pressure pipe as a modification, respectively. Non-return valves 12, 12 ′ are disposed between the respective connecting portions 9 and the low pressure pipe 5 to allow hydraulic fluid flow from the low pressure pipe to the main pump. The two discharge pipes are preferably combined into a single discharge pipe prior to connection to the high pressure pipe 14 on the discharge side thereof. Non-return valves 13, 13 ′ which allow only the flow of hydraulic fluid from the main pump to the high pressure pipe are arranged in each of the discharge pipes before the discharge pipes merge into a single discharge pipe.

As a result of the above connection of the main pump to the low pressure pipe and the high pressure pipe, the hydraulic fluid can flow from the low pressure pipe to the high pressure pipe regardless of the rotation direction of the main pump. When the main pump is operated in one direction, the hydraulic fluid flows through the branch pipe of the supply pipe provided with the non-return valve 12 'through the conduit section 8 on the left side in the drawing, so that the portion of the discharge pipe provided with the non-return valve 13 is provided. It is discharged to the high pressure pipe via the engine. When the main pump is operated in the opposite direction, the hydraulic fluid flows through the branch pipe of the supply pipe provided with the non-return valve 12 through the conduit section 8 on the right side in the drawing, so that the non-return valve 13 'is provided. It is discharged through the branch pipe to the high pressure pipe. If the engine is capable of forward and reverse rotation, the conduits (10, 11) can be connected directly to the main pump (6) by omitting the supply and discharge pipes with non-return valves (12, 12 ', 13, 13'). have.

The return pipe 15 of each main pump is provided with a bypass valve 16 in the form of an electronically actuated control valve of at least two positions, the bypass valve being shut off at the end position shown in the figure. It is biased with a spring. When the bypass valve is operated by a control signal, it is switched to another position where the return tube is opened. The return pipe starts from the discharge pipe 11 and leads to the low pressure pipe 5 or to another position connected to the suction side of the main pump. The non-return valve 17 of the discharge pipe is disposed between the branch pipe of the return pipe and the high pressure pipe (14). The non-return valve 17 prevents the high pressure of the conduit 14 from acting as a branch pipe of the return pipe.

In another embodiment, although not shown, the bypass valve is formed in the form of a valve pressurized to an adjustable opening pressure. When it is necessary to start or terminate the operation of the main pump to adjust the amount of hydraulic fluid discharged to the current consumer, the opening pressure can be increased to an opening pressure higher than that of the high pressure pipe or lowered below the pressure of the low pressure pipe. .

The control pump 7 is an axial piston pump that is electrically driven and electronically controlled. For example, an axial piston pump from Mannismann Rexrod GmbH, Germany, whose main model is A4VSO with a maximum efficiency of η = 0.90 at full discharge, can be selected. At smaller discharge flow rates the efficiency is significantly lower. It is a positive displacement pump with variable displacement, the pump pistons being pivotally mounted on the disk rotated by the pump shaft and movable in the cylinders of the subrotating drum, the longitudinal axis of the drum being the longitudinal axis of the pump shaft. The angle is adjustable relative to. By the longitudinally movable slider, the inclination of the drum with cylinders can be changed so that the stroke of the piston is changed. The drum has a neutral position coaxially with respect to the extension of the pump shaft such that the pistons have a zero stroke. By controlling the discharge amount of the pump by setting the amount of inclination of the drum, the inclination of the drum can be changed to be disposed on both sides of the neutral position. In this way the pump is adjusted to function like a motor rather than a pump. That is, the pump may be set to a so-called negative (discharge) discharge amount so as to use hydraulic fluid from the high pressure pipe and discharge the fluid to the low pressure pipe.

The control pump is connected to the electric motor / generator unit 19 and the shaft, and the unit drives the control pump when the control pump discharges the hydraulic fluid into the high pressure pipe 14, and the control pump is driven from the high pressure pipe. Hydraulic fluid is used to drive the control pump and produce electricity. The control pump is adjusted by an electronically controlled proportional valve 18, which sets the inclination of the drum and the operating position of the control pump. The control pump controls the pressure of the high pressure pipe by adjusting the valve 18, the valve 18 may be referred to as a pressure control valve. Such adjustment is made based on, for example, the control voltage, and the larger the control voltage, the higher the pressure in the high pressure tube. In large two-stroke crosshead engines, the pressure in the high pressure pipe is suitably controlled to vary between 125 and 300 bar, with low pressure at idling of the engine and a high pressure of 250 bar or more at 100% engine load. This works. By reducing the pressure at lower engine loads, a reduction in energy taken from the engine system for pressurizing the high pressure hydraulic fluid in the conduit 14 is achieved.

The control valve 20 is located between the high pressure pipe 14 and the pump 7. The control valve has two positions, one of which is a position in which the control valve serves as a non-return valve, in which only hydraulic fluid flows in the direction of the high pressure pipe in the flow path to the high pressure pipe, and the control is performed at the other position. The pump 7 opens the flow path so that the hydraulic fluid from the high pressure pipe can be used. The control valve 20 is biased with a spring to maintain the first position, but can be actuated electronically to take the second position. In the event of an electronic control failure, the control valve 20 is automatically switched by the force of the spring to a position that acts as a non-return valve, thus preventing pressure loss from the high pressure pipe. The high pressure tube includes a safety valve, although not shown, which is a hydraulic fluid if the pressure generated by the main pumps without pressure control from the control pump 7 exceeds a preset maximum pressure, for example 310 bar. Can be discharged. In the event of total electronic control failure, all the main pumps are forcibly connected and the control pumps are forcibly separated to allow the total hydraulic fluid to be discharged regardless of consumption. All unused hydraulic fluid is discharged through the safety valve of the high pressure pipe.

Instead of the control valve 20 using other safety means, the control valve can be provided with a mechanical brake, such as a brake disc with brake blocks, which is electrically controlled, the brake blocks being braked by magnetizing current. Away from the disk. In the event of a failure of the electrical system, the magnetization current is lost and mechanical compression springs move the brake blocks to the brake position in contact with the brake disc, causing the control pump to stop.

The control of the hydraulic system is carried out via two electronic control units 21, each of which has two main pumps and a control pump, ie bypass valve 16 and proportional valve 18 and control valve 20. ). In the figure, the control unit 21 with the accessory units is surrounded by a dashed line. In the event that only one of the control valves 21 fails, the other control unit can maintain the pressure control of the high pressure pipe 14.

In use in connection with pressure control, the control unit 21 measures signals from the pressure sensor 23 of the high pressure tube 14 and the pressure sensor 22 of the low pressure tube 14 together with the signal for the current engine load. Receive.

When the internal combustion engine is stopped and put back into the start mode, one of the control pumps 7 starts to cause the high pressure pipe 14 to be pressurized. If the proportional valve 18 does not receive the control voltage from the control unit 21, the control pump 7 can be set to the engine start position, where the control pump is a pre-set amount of oil, e.g. Pump about 20% of the total discharge volume. This discharge amount is suitable for starting operation of the internal combustion engine, at which time the discharge by the main pumps is started. In contrast, the control pumps can be maintained at the hydraulic pressure in the lowest rotational speed range.

All conduits 8, 10, 11 around the main pump 6 can be formed as flow paths in the manifold. That is, it may be channels of holes of a body having a large block shape. This reduces the number of pipe connections and connectors. It is also possible to integrate the control pumps 7 in the manifold. Although the hydraulic system may consist of only two main pumps and a single control pump and a single control unit 21, four or more main pumps are preferred. In view of reliability, at least two control pumps 7 each controlled by a control unit are preferred.

Advantageous Effects According to the present invention, there is an advantage in that it is possible to provide a hydraulic system having operational reliability and an appropriately low energy consumption characteristic.

Claims (11)

A plurality of exhaust valves and fuel pumps, the at least one high pressure pump supplies energy from the pressurized hydraulic fluid to the hydraulic drive means 1, such as the hydraulic actuators for the exhaust valve and the pump drive means for the fuel pump. In a hydraulic system for an internal combustion engine comprising at least three high pressure pumps, at least two of the pumps being main pumps 6 driven by an output shaft of the internal combustion engine, the rotational speed of which is the rotational speed of the crankshaft of the engine. And at least one of the pumps is an electrically driven control pump (7) in which the discharge flow rate can be controlled. 2. Hydraulic system according to claim 1, characterized in that each of the main pumps (6) provides a constant discharge amount per shaft revolution. 3. Hydraulic system according to claim 1 or 2, characterized in that the main pump (6) has a significantly higher efficiency than the control pump (7). 4. The control pump (7) according to any one of the preceding claims, wherein the control pump (7) is connected to an electric motor / generator unit (19) and pressurized from a pump mode driven by an electric motor to discharge the pressurized hydraulic fluid. A hydraulic system, characterized in that it can be controlled in a motor mode to drive an electrical generator using hydraulic fluid. 5. Hydraulic system according to claim 4, characterized in that the control pump (7) has a capacity in the range of 40-60%, preferably 50% of the main pump capacity, and the main pumps (6) have substantially the same capacity. 6. Hydraulic system according to any one of the preceding claims, characterized in that it comprises at least four main pumps (6) and at least two control pumps (7). Hydraulic drive means of the main unit having a rotating shaft and capable of reverse operation such that the rotating shaft can rotate in both directions, such as the hydraulic actuators for the exhaust valve and the fuel pump pump 1 of the internal combustion engine having a crank shaft. 10. A hydraulic system having at least one high pressure pump for discharging a pressurized hydraulic fluid, comprising: a plurality of main pumps 6 driven by a rotating shaft, wherein the rotational speed of the main pump is in relation to the rotational speed of the shaft; The main pump 6 through each of the non-return valves 13 and 13 'to allow only the hydraulic fluid to flow away from the connection portion. Low pressure through each of the non-return valves 12, 12 'to allow only hydraulic fluid to flow to or connected to the high pressure tube 14; 5, the two connecting portions (9), a hydraulic system, characterized in that mounted on the conduit part (8) between which the connection. 8. The main pump (6) according to any one of the preceding claims, wherein each main pump (6) is connected in parallel with an adjustable bypass valve (16) which allows some or all of the hydraulic fluid discharged therefrom to be returned to the inlet side. And a non-return valve (17) in the pressure pipe of the main pump to the high pressure pipe is disposed between the return pipe (15) having a bypass valve and the high pressure pipe. 9. Hydraulic system according to claim 8, characterized in that the high pressure pipe is electronically controlled by a valve (18) for adjusting the discharge amount from the control pump (7). 10. The pressure discharged from the high pressure pumps 6 and 7 is a maximum of 75% of the discharge pressure at 100% of the engine load of the internal combustion engine when the load of the internal combustion engine is 70% or less. Hydraulic system characterized in that. The method according to any one of claims 1, 7 and 8, and 2-6, 9 or 10, wherein the first electronic control unit 21 comprises at least one control pump 7 and at least one main unit. A bypass valve (16) of the pump, wherein the second electronic control unit is adapted to control the bypass valve of the at least one second control pump and the at least one second main pump.