KR100522364B1 - 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 camshafts. 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.

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.

Dispersion of the discharge flow rate into at least three pumps improves the overall reliability of the engine because there is no significant loss of discharge capacity when only two pumps are used, even if one pump fails, or without an auxiliary pump. This is because it will not have a big impact on the. In addition, at least two pumps are made of primary pumps driven by the engine output shaft, which greatly simplifies the design than the electronically driven control pump, which significantly improves reliability. Furthermore, the pump directly connected to the engine output shaft is the most reliable. Known pump driving means. 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, each of the pumps has a small change in discharge flow rate, so that the pumps can operate in close proximity to the optimum operating conditions designed. 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 changes according to the load change, partial adjustment of the discharge flow rate is automatically achieved in response to the current load, which is similarly changed in the main pump. 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 operating conditions 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 correspondingly increase the size of the more efficient main pumps, which means that the control pump is positive or negative relative to the discharge flow from the main pump. This is because all of the adjustment of-) is possible. If the main pump discharges more hydraulic fluid than is required, the control pump generates electricity using excess discharge flow, and if the main pump discharges less hydraulic fluid than 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 makes it possible to reduce the size of the pump, with an extremely low risk of failure in all pumps at the same time.

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 rotatable 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 an internal combustion engine engine having a rotating shaft and operable in a reverse direction such that the rotating shaft can rotate in both directions, such as a hydraulic actuator for an exhaust valve of an internal combustion engine having a crank shaft and a pump driving means for a fuel pump. A hydraulic system having at least one high pressure pump for discharging a pressurized hydraulic fluid by means.

A highly reliable and preferably low energy consumption form that provides compressed fluid to a hydraulic drive such as an actuator for an exhaust valve of an internal combustion engine engine having a rotating shaft and capable of rotating in both directions so that the rotating shaft can rotate in both directions. In order to provide a hydraulic system with at least one high pressure pump, the hydraulic system according to the invention comprises a plurality of main pumps 6 which are driven such that the rotational speed of the main pump is set in advance with respect to the rotational speed of the rotary shaft. It is characterized in that it changes in proportion and changes direction simultaneously with the shaft, wherein at least one of the main pumps is a control pump 7 having a discharge amount which can be changed by changing the stroke of the piston of the pump.

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 pressure conduit and the high pressure conduit. 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 conduit. Unlike the use of clutch elements and forward and reverse gears for the control of the pump shaft, the great advantage of non-return valves is that the front and rear fluid pressures of the valve determine that the non-return valve is in the open or closed position without external control. It works 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 is non-returned in the pressure conduit of the main pump to the high pressure conduit. The valve is disposed between the return conduit with the bypass valve and the high pressure conduit. When the discharge flow from the main pump is not required, the bypass valve is fully open as the non-return valve between the high pressure conduit and the bypass valve blocks the pressure in the high pressure conduit from the main pump and the bypass valve. The pressure in the pressure conduit of the pump is reduced to nearly the pressure level of the low pressure conduit. 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 when circulating flow out from the low pressure conduit through the main pump to the return conduit. 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 conduit 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 conduit is electrically controlled by a valve which regulates the discharge flow rate of the control pump. By varying the flow rate or discharge flow rate consumed by the control pump to compensate for 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 conduit 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 under the corresponding operating conditions.

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 internal combustion engine when the load on the internal combustion engine is 70% or less. At engine load of%, the discharge pressure can be up to 75%. This saves a considerable amount of energy in driving the high pressure hydraulic pump.

Electronic control units are used to regulate the flow. The main purpose of controlling using the electronic control unit 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 has 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 conduit (5) through at least one filter device (4), which is connected to four main pumps (6) and two control pumps (7). do. The main pump maintains a low pressure conduit, for example, in the range of 1 to 5 bar, typically 2 bar, so that the main pump maintains the total hydraulic fluid at a positive pressure to prevent cavitation. This provides the advantage of preventing the pump from running dry. Thus, the main pumps do not need to be self-priming type.

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 the 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 consumption of hydraulic fluid is reduced with lower rotational speeds at lower loads resulting in smaller discharges from the main pump. 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 in a conduit 8 extending between two connections 9 to the supply conduit 10 and the exhaust conduit 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. The supply conduit 10 can be a single conduit starting from the low pressure conduit 5 and branching into two lines provided with connections 9. The connections 9 may each have a high quality conduit up to a low pressure conduit as a variant. Non-return valves 12, 12 ′ are disposed between the respective connections 9 and the low pressure conduit 5 to allow hydraulic fluid flow from the low pressure conduit to the main pump. The two outlet conduits are preferably combined into a single outlet conduit prior to connection to the high pressure conduit 14 at the outlet side. Non-return valves 13, 13 ′ which allow only the flow of hydraulic fluid from the main pump to the high pressure conduit are arranged in each of the outlet conduits before the outlet conduits are combined into a single outlet conduit.

As a result of the above connection of the main pump to the low pressure conduit and the high pressure conduits, hydraulic fluid can flow from the low pressure conduit to the high pressure conduit regardless of the rotational direction of the main pump. When the main pump operates in one direction, the hydraulic fluid flows through the branch conduit of the supply conduit provided with the non-return valve 12 'through the conduit 8 on the left side in the drawing, It is discharged into the high pressure conduit via the branch conduit. When the main pump is operated in the opposite direction, the hydraulic fluid flows through the branch conduit of the supply conduit provided with the non-return valve 12 through the conduit 8 on the right side in the drawing, and the exhaust conduit provided with the non-return valve 13 '. It is discharged into the high pressure conduit via the branch pipe of. If the engine is capable of forward and reverse rotation, the conduits 10, 11 are fed directly to the main pump 6, omitting the supply conduits with non-return valves 12, 12 ', 13, 13' and the branch conduits of the exhaust conduits. Can connect

The return conduit 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, which bypass valve is closed at the end position shown in the drawing. 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 tube starts from the discharge conduit 11 and extends to the low pressure tube 5 or to another position connected to the suction side of the main pump. The non-return valve 17 of the discharge conduit is arranged between the branch pipe of the return pipe and the high pressure conduit 14. The non-return valve 17 prevents the high pressure of the high pressure 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 in order to adjust the amount of hydraulic fluid discharged to the current consumer, the opening pressure can be increased to an opening pressure higher than the pressure of the high pressure conduit 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 a disk rotated by a pump shaft and movable in cylinders of the subrotating drum, the longitudinal axis of the drum being The angle is adjustable relative to the longitudinal axis of the pump shaft. 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 amount to discharge the fluid to the low pressure pipe using hydraulic fluid from the high pressure conduit.

The control pump 7 can be connected to the electric motor / generator unit 19 as a shaft, which drives the control pump when the control pump discharges hydraulic fluid into the high pressure conduit 14, the control pump being a high pressure. When using hydraulic fluid from conduits, the unit is driven by a control pump to 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 conduit by adjusting the proportional valve 18, and thus the proportional valve 18 can be referred to as a pressure control valve. Such adjustment is made, for example, on the basis of a control voltage, and a larger control voltage results in an increase in pressure in the high pressure conduit. In large two-stroke crosshead engines, the pressure in the high pressure conduit is appropriately controlled to vary between 125 and 300 bar, with low pressure at idling of the engine and 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 conduit 14 and the control pump 7. The control valve has two positions, which are defined as the first position of the control valve and the second position of the control valve, one of which is a position in which the control valve serves as a non-return valve, at which time the flow velocity into the high pressure conduit Only allow hydraulic fluid to flow in the direction of the high pressure conduit, and in other locations the flow path is opened so that the control pump 7 can use the hydraulic fluid from the high pressure conduit. The control valve 20 is biased with a spring to maintain the first position of the control valve, but may be electronically actuated to take the second position of the control valve. 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 conduit. The high pressure conduit 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 unconsumed hydraulic fluid is discharged through the safety valve of the high pressure conduit.

Instead of the control valve 20 using other safety means, the control valve may 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 electronic control unit 21 with the accessory units is surrounded by a dashed line. If only one of the electronic control units 21 has failed, the other control unit can maintain the pressure control of the high pressure conduit 14.

In use in connection with pressure control, the control unit 21 measures signals from the pressure sensor 23 of the high pressure conduit 14 and the pressure sensor 22 of the low pressure conduit 5 together with the signals 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 conduit 14 to be pressurized. If the proportional valve 18 does not receive a control voltage from the electronic control unit 21, the control pump 7 can be set to the starting position of the engine, where the control pump is pre-set oil volume, e.g. Pump about 20% of the total discharge volume of the control pump. 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, a single control pump and a single electronic control unit 21, four or more main pumps are preferred. In view of reliability, at least two control pumps 7 each controlled by an electronic 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.

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

Claims (14)

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 device 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. 2. Hydraulic system according to claim 1, characterized in that the main pump (6) has a higher efficiency than the control pump (7). 2. The control pump (7) according to claim 1, wherein the control pump (7) is connected to an electric motor / generator unit (19) and is powered by using a pressurized hydraulic fluid from a pump mode driven by an electric motor to discharge pressurized hydraulic fluid. A hydraulic system which can be controlled in a motor mode of driving the generator. 5. Hydraulic system according to claim 4, characterized in that the control pump (7) has a capacity in the range of 40-60% of the main pump 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 system with at least one high pressure pump having a rotating shaft and for supplying compressed fluid to a hydraulic drive device 1 such as an actuator for an exhaust valve of an internal combustion engine engine capable of forward and reverse rotation of the rotating shaft in both directions. To Including a plurality of main pumps (6) driven by the rotary shaft of the engine, the rotational speed of the main pumps is changed at a predetermined ratio with respect to the rotational speed of the rotary shaft, the rotational direction of the rotary shaft of the engine When this change, the rotation direction of the pump shaft of the main pumps is changed, at least one of the main pump is a control pump (7) characterized in that the discharge amount that can be changed by changing the stroke of the piston of the pump system. The adjustable bypass valve (16) according to any one of claims 1 to 5 or 7, wherein each main pump (6) allows some or all of the hydraulic fluid discharged therefrom to be returned to the inlet side. And a non-return valve (17) disposed between the high pressure conduit and the return conduit with a bypass valve in a pressure line of the main pump to the high pressure conduit. 9. Hydraulic system according to claim 8, characterized in that the high pressure conduit is controlled electronically by a proportional valve (18) which regulates the amount of discharge from the control pump (7). The pressure discharged from the high pressure pump (6,7) according to any one of claims 1 to 5 or 7, wherein 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 up to 75% of the. 8. Hydraulic system according to claim 7, comprising two or more main pumps.  8. Hydraulic pressure according to claim 7, characterized in that each main pump (6) is connected to the high pressure conduit (14) via a discharge conduit (11) having a non-return valve (17) located in the discharge conduit (11). system. 8. Hydraulic system according to claim 7, wherein the rotary shaft is a crankshaft of the engine and the main pumps (6) are driven by the crankshaft via a gear arrangement. 8. Hydraulic system according to claim 7, characterized in that the main pumps (6) have the same capacity.