Main drive seal system for a tunnel boring machine

Abstract

The invention relates to a main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine, comprising at least one pressurization and pressure-control system having at least one electronic controller (80) which comprises: at least one data storage unit; at least one data processing unit; and at least one control command output unit, the electronic controller (80) having a control program which, inter alia, has the following steps: calculating a pressure difference Δpi between the desired value pi-SOLL and the actual value pi-IST, i being the number of the chamber whose actual pressure is being controlled, and checking whether Δpi lies in a range x < 0 < y, x and y being a lower interval limit and an upper interval limit, wherein, if Δpi lies in the range x < 0 < y, the first compressed-air switching valve (21, 21', 31, 41) of the at least one chamber i (P2, P2', P3, P4) and the second compressed-air switching valve (22, 23, 22', 23', 32, 33, 42, 43) of the at least one chamber i (P2, P2', P3, P4) are controlled such that they are in the closed position, wherein, if Δpi is > y, the first compressed-air switching valve (21, 21', 31, 41) of the at least one chamber i (P2, P2', P3, P4) is controlled such that it switches to the open position and the second compressed-air switching valve (22, 23, 22', 23', 32, 33, 42, 43) of the at least one chamber i (P2, P2', P3, P4) is controlled such that it is in the closed position, and wherein, if Δpi is < x, the second compressed-air switching valve (22, 23, 22', 23', 32, 33, 42, 43) of the at least one chamber i (P2, P2', P3, P4) is controlled such that it switches to the open position and the first compressed-air switching valve (21, 21', 31, 41) of the at least one chamber i (P2, P2', P3, P4) is controlled such that it is in the closed position.

Description

Technical Field The present application relates to the technical field of tunnel boring machines, in particular to a liquidbased or earth pressure-based tunnel boring machine with a cutting wheel. Such tunnel boring machines in particular have a main drive shaft seal system for the drive shaft of the cutting wheel. In particular, the present application relates to a main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine having at least one space with a first pressure behind a cutting wheel, having at least one first chamber with a first pressure, wherein the first chamber is preferably a labyrinth chamber filled with a blocking grease (HBW), at least one second chamber with a second pressure, wherein the at least one second chamber is an oil and compressed-air sealing chamber, at least one seal between the at least one first chamber and the at least one second chamber, which can withstand a differential pressure ApL1 between the at least one first chamber and the at least one second chamber, at least one compressed-air input connection, at least one compressed-air discharge line, at least one first compressed-air switching valve of the at least one second chamber with at least one compressed-air inlet and at least one compressed-air outlet, wherein the first compressed-air switching valve of the at least one second chamber is configured to be switchable between an open and a closed position, at least one second compressed-air switching valve of the at least one second chamber having at least one compressed-air inlet and at least one compressed-air outlet, wherein the second compressed-air switching valve of the at least one second chamber is configured to be switchable between an open and a closed position, at least one inlet of the compressed-air input connection configured to be pneumatically connectable to a compressed-air source, at least one outlet of the compressed-air input connection pneumatically connected via a compressed-air line to the at least one compressed-air inlet of the first compressed-air switching valve of the at least one second chamber, wherein the at least one compressed-air outlet of the first compressed-air switching valve of the at least one second chamber is pneumatically connected to the at least one compressed-air inlet of the second compressed-air switching valve of the at least one second chamber and the at least one second chamber, and wherein a compressed-air outlet of the second compressed-air switching valve of the at least one second chamber is pneumatically connected to the compressed-air discharge line, as well as to a method for controlling the pressure in a main drive seal system for a tunnel boring machine. Background The construction of tunnels having a large cross section, a large laying depth, a high water pressure and over large distances is associated with complicated and harsh operating conditions. At high water pressure, for example, when driving under a body of water such as a river or the sea, a liquidbased or earth-pressure-based tunnel boring machine should be used for tunnel construction. At present, a safe and reliable method is the use of a tunnel boring machine with compressed-air support. The main drive is an important part of a liquid-based or earth pressure-based tunnel boring machine. The sealing performance of the main drive directly determines the water and ground pressure load capacity of the tunnel boring machine. At present, a seal system of rubber lip seals is used for the main drive of the tunnel boring machine. In this case, four sealing lips are generally provided. Outside the first sealing lip there is a labyrinth chamber into which HBW grease is continuously injected as loss lubrication in order to counteract the penetration of liquid or earth slurry from the outside. Subsequently, a grease chamber P1 is provided, which is formed by the first and a second sealing lip. This is continuously filled with grease EP2 to loss, which on the one hand further improves the sealing capacity of the main drive and on the other hand lubricates the sealing lips 1 and 2 in order to reduce wear. An oil and compressed-air sealing chamber P2 is then provided, which is formed by the second and third sealing lips. The oil is used to lubricate the seals 2 and 3. If the pressure in the excavation chamber exceeds a certain value, transmission oil and / or air is injected into this chamber to support the sealing lips. The third seal lip and the fourth seal lip are generally installed opposite each other to form a leak detection chamber P3. The fourth seal lip is mainly configured to seal a transmission P4 to prevent the internal transmission oil from leaking. The load capacity of a single rubber lip seal is generally about 3 bar. If the water and soil pressure is less than 3 bar, the external water and soil pressure in the excavation chamber can be absorbed by the grease pressure of the grease chamber P1, so that the seal of the main drive works reliably. If the water and soil pressure is greater than 3 bar and less than 6 bar, the total pressure provided by the oil and compressed-air sealing chamber P2 and the grease chamber P1 as back pressure can also withstand the external water and soil pressure in the excavation chamber. A system for the chamber 1 with HBW and chamber 2 with EP2 is disclosed in CN106223964B. Disclosed herein is a method for controlling a sealing pressure of a main bearing of a shield tunneling machine in the HBW chamber and the EP2 chamber of the seal system. The HBW grease loss lubrication comprises a pneumatic HBW source 1 and a HBW grease injection port 16. In the HBW supply line 2, there are successively installed an HBW supply pressure gauge 3, an HBW two-way solenoid valve 4, an HBW filter 5, a preset HBW proportional pressure reducing valve 6, and an HBW pressure sensor 7. The EP2 grease lubrication comprises a pneumatic EP2 source 8 and an EP2 grease injection port 17. The pneumatic EP2 source 8 and the EP2 grease injection port 17 are connected by the EP2 supply line 9. In the EP2 supply line 9, an EP2 supply pressure gauge 10, an EP2 two-way solenoid valve 22, an EP2 filter 12, a preset EP2 proportional pressure reducing valve 13, and an EP2 pressure sensor 14, and an EP2 multipoint lubrication pump 15 are sequentially installed. The method for controlling the seal pressure comprises the steps: 1. Inputting a Api and Ap2 in a control program of the tunnel boring machine, wherein Api and Ap2 are not 0 and Api > Ap2; Api is the pressure difference between the pressure p0 of the excavation chamber and the pressure pi behind the preset HBW proportional pressure reducing valve 6 measured by the HBW pressure sensor 7, and Ap2 is the pressure difference between the pressure p2 behind the preset EP2 proportional pressure reducing valve i3 measured by the EP2 pressure sensor i4 and the pressure pi behind the preset HBW proportional pressure reducing valve 6. 2. Detecting p0 in the excavation chamber behind the cutting wheel; 3. Setting the HBW pressure p1 in relation to the pressure p0 of the excavation chamber, in which p1 = p0 + Api . 4. Setting the EP2 pressure p2 in relation to the HBW pressure pi, in which p2 = pi-Ap2; as a result, p2 also depends on p0. By the differential pressure-control valves set in advance, the feed pressure in pi and p2 can be changed depending on the setting of the control system of the tunnel boring machine. This provides a closed pressurecontrol system by pressure feedback which provides a relative pressure adjustment in the seal by combining the pressure p0 of the excavation chamber, the pressure pi of the HBW grease leakage lubrication in the HBW chamber and the pressure p2 of the EP2 grease lubrication of the EP2 chamber. The sealability of this system ends at 6 bar. In a case where the shield machine is operated at a great depth and at a high water pressure, the water and ground pressure exceeds 6 bar, so that the conventional multi-lip combined seal is difficult to withstand the external water pressure, and the earth slurry / bentonite suspension / cuttings permeate the seal and enter the main drive, resulting in stoppage of the shield machine and delay of the project. CN2070496i9U and CNi0740i678A disclose a fully mechanically pneumatic differential pressure-control system for a seal system of a main drive shaft of a tunnel boring machine for the chambers of the seal system behind the HBW labyrinth seal and the EP2 grease lubrication chamber, with which the chambers of the seal system lying behind can be mechanically pneumatically pressurized under differential pressure control. A compressed-air source i, a first pressure chamber 5 which is connected to the oil chamber P2 between the second and the third lip seal of the seal system, and a first mechanically pneumatic differential pressure valve 3 between the compressed-air source 1 and the first pressure chamber 5 are provided. Furthermore, a third mechanically pneumatic differential pressure valve 8 is provided which is arranged between the compressed-air source 1 and a third pressure chamber 12, wherein the third pressure chamber 12 is a chamber between the fourth lip seal arranged in the opposite direction and the transmission chamber provided here in an air-tight manner. Furthermore, the third mechanically pneumatic differential pressure valve 8 is connected in parallel to the connection to the third pressure chamber 12 both to a pressure relief valve 7 and to a second mechanically pneumatic differential pressure valve 2. The second mechanically pneumatic differential pressure valve 2 is connected, on the opposite site, to a second pressure chamber 11 which is the leakage chamber P3 between the third and fourth lip seals for connection to the third mechanically pneumatic differential pressure valve 8. The pressure relief valve 7 is connected opposite the connection to the third differential pressure valve 8 with a sound damper 4 as a pneumatic relief. For pressure control, between the pressure chambers 5, 11, 12 and the mechanically pneumatic differential pressure valves 3, 8 and 2 a discharge throttle 9 is provided in each case, which continuously discharges compressed air. The mechanically pneumatic differential pressure valves 3, 8 and 2 and the pressure relief valve 7 are each mechanically adjustable with a pressure difference value Ap that is or can be different for each valve 2, 3, 7, 8. The pressure relief valve 7 serves as a positive pressure relief for the third pressure chamber 12 / P4 and, if appropriate, also for the second pressure chamber 11 / P3. Furthermore, a fourth pressure chamber 13 is provided, which represents the compressed-air bubble 16 of the cutting wheel 14 of the tunnel boring machine and is connected to the excavation chamber 15 behind the cutting wheel 14. The pressure 22 of the liquid or the earth slurry acts on the compressed-air bubble in the fourth pressure chamber. The fourth pressure chamber thus serves as a reference pressure for the control of the seal system. The first differential pressure valve 3 is pneumatically connected at its + connection to the fourth pressure chamber 13 / 16 and at its - connection to the first pressure chamber 5 / P2. The second differential pressure valve 2 is pneumatically connected at its + connection to the first pressure chamber 5 / P2 and at its - connection to the second pressure chamber 11 / P3. The third differential pressure valve 8 is pneumatically connected at its + connection to the second pressure chamber 11 / P3 and at its -connection to the third pressure chamber 12 / P4. The pressure relief valve 7 is pneumatically connected at its + connection to the second pressure chamber 11 / P3 and at its - connection to the third pressure chamber 12 / P4. However, the Ap of the third differential pressure valve 8 and the pressure release valve 7 are different. By mechanically adjusting the pressure difference values of the first differential pressure valve 3, the second differential pressure valve 2, the third differential pressure valve 8 and the pressure relief valve 7, the corresponding pressure in the respective pressure chamber is controlled by the respective differential pressure valve and the throttle 9 in the event of a pressure change in the fourth reference pressure container 13 / 16. The flow valve is dynamically balanced to ensure that the pressure of each pressure chamber can be adjusted and maintained according to the pressure difference values to maintain the pressure differences in the pressure chambers. The pressure relief valve may provide dynamic protection in the event of system over pressure to maintain the stability of the system. EP3854990 discloses an approach to a main drive seal system for a tunnel boring machine having a mechanically pneumatic feedback and follow-up control. The tunnel boring machine has a cutting wheel. The space behind the cutting wheel is connected fluidically to a compressed-air bubble in a compressed-air chamber ACB. The main drive seal system includes an HBW labyrinth seal P0, a grease chamber P1, an oil and air sealing chamber P2, a leak detection chamber P3, and a transmission chamber P4. The chambers P1, P2, P3 and P4 are separated from each other by lip seals. The chambers P2, P3, P4 can be pressurized by introducing compressed air via compressed-air lines. For this purpose, a compressed-air input connection is provided. In order to achieve pressure regulation, mechanically pneumatic differential pressure-control valves 21, 22, 23 are provided in the compressed-air lines. Furthermore, an exhaust air line is provided. The exhaust air line is connected via mechanically pneumatic differential pressure-control valves 51, 52, 53 to the chambers P2,  P3, P4 in order to delivery pressure from the chambers in a controlled manner. If the pressure difference between the compressed-air chamber ACB and the oil and compressed-air sealing chamber P2 is greater than or equal to a first preset value, the first differential positive pneumatic pressure-control valve 21 is opened, and the first differential negative pneumatic pressure-control valve 51 is in a closed state ("in a closed state" means that the valve element is closed at this time or has been closed in advance, the same applies hereinafter); and if the pressure difference between the compressed-air 8 chamber and the oil and compressed-air sealing chamber P2 is less than or equal to a second preset value, the first differential negative pneumatic pressure-control valve 51 is opened, and the first differential positive pneumatic pressure-control valve 21 is in a closed state. The "first preset value" is set according to the minimum opening value preset in the first positive pneumatic differential pressure-control valve 21 (i.e., the first positive pneumatic differential pressurecontrol valve 21 is opened and released when the pressure difference reaches or exceeds this value) and the minimum closing value preset in the first negative pneumatic differential pressure-control valve 51 (i.e., the first negative pneumatic differential pressurecontrol valve 51 is closed and sealed when the pressure difference reaches or exceeds this value). Preferably, the first preset value corresponds to the minimum opening value of the first positive pneumatic differential pressure-control valve 21, and is greater than or equal to the minimum closing value of the first negative pneumatic differential pressure-control valve 51. The "second preset value" is set according to the maximum closing value preset in the first positive pneumatic differential pressure-control valve 21 (i.e., the first positive pneumatic differential pressurecontrol valve 21 is closed and shut off when the pressure difference reaches or falls below this value) and the maximum opening value preset in the first negative pneumatic differential pressure-control valve 51 (i.e., the first negative pneumatic differential pressure-control valve 51 is opened and unlocked when the pressure difference reaches or falls below this value). Preferably, the second preset value corresponds to the maximum opening value of the first negative pneumatic differential pressure-control valve 51, and is equal to or smaller than the maximum closing value of the first positive pneumatic differential pressurecontrol valve 21. Therefore, when the pressure difference between the compressed-air chamber ACB and the oil and compressed-air sealing chamber P2 increases to or exceeds the first preset value, the first differential positive pneumatic pressure-control valve 21 is opened and the first differential negative pneumatic pressure-control valve 51 is in a closed state, and compressed air is charged into the oil and compressed-air sealing chamber P2 (i.e., the oil and compressed-air seal container 11) after passing through the compressed-air input connection and the first differential positive pneumatic pressure-control valve 21. The oil and air sealing chamber P2 is continuously filled until the total pressure of the oil and air sealing chamber P2 and the grease chamber P1 can equalize the external water and soil pressure, so that the main driving seal reliably holds, and preferably at this time, the pressure difference between the air sealing chamber ACB and the oil and air sealing chamber P2 reaches an intermediate value (which is less than or equal to the first preset value and less than or equal to the rated pressure of the grease chamber P1) preset in the first positive differential pressure pneumatic valve 21, and the first positive differential pressure pneumatic valve 21 is closed (or, in other specific embodiments, the first positive differential pressure pneumatic valve 21 may still be in an open state in which the discharge capacity of the first positive differential pressure pneumatic valve is small, to balance the leakage). If the pressure in the compressed-air chamber ACB decreases, when the pressure difference between the compressed-air chamber ACB and the oil and air sealing chamber P2 is less than or equal to the second preset value, the first negative pneumatic differential pressure-control valve 51 is opened and the first positive differential pressure pneumatic valve 21 is in a closed state, and at this time, the compressed air in the oil and air sealing chamber P2 is discharged through the first negative pneumatic differential pressure-control valve 51; and the compressed air in the oil and compressed-air sealing chamber P2 is continuously discharged until the pressure difference between the compressed-air chamber ACB and the oil and compressed-air sealing chamber P2 reaches an intermediate value (which is larger than the second preset value) set in the first negative pneumatic differential pressure-control valve 51, and the first negative pneumatic differential pressure-control valve 51 is closed. Further disclosed is main drive seal system compressed-air path comprising the oil and compressed-air sealing chamber P2, a transmission P4, a second positive differential pressure pneumatic valve 22, and second negative pneumatic differential pressure-control valve 52. If the pressure difference between the oil and air sealing chamber P2 and the transmission P4 is greater than or equal to a third preset value, the second positive differential pressure pneumatic valve 22 is opened and the second negative pneumatic differential pressure-control valve 52 is in a closed state; and when the pressure difference between the oil and air sealing chamber P2 and the transmission P4 is less than or equal to a fourth preset value, the second negative pneumatic differential pressure-control valve 52 is opened and the second positive differential pressure pneumatic valve 22 is in a closed state. The "third preset value" is set according to the minimum opening value preset in the second positive pneumatic differential pressure-control valve 22 (i.e., the second positive pneumatic differential pressurecontrol valve 22 is opened and released when the pressure difference reaches or exceeds this value) and the minimum closing value preset in the second negative pneumatic differential pressure-control valve 52 (i.e., the second negative pneumatic differential pressurecontrol valve 52 is closed and sealed when the pressure difference reaches or exceeds this value). Preferably, the third preset value corresponds to the minimum opening value of the second positive pneumatic differential pressure-control valve 22, and is greater than or equal to the minimum closing value of the second negative pneumatic differential pressure-control valve 52. The "fourth preset value" is set according to the maximum closing value preset in the second positive pneumatic differential pressure-control valve 22 (i.e., the second positive pneumatic control valve 22 is closed and shut off when the pressure difference reaches or falls below this value) and the maximum opening value preset in the second negative pneumatic differential pressure-control valve 52 (i.e., the second negative pneumatic differential pressure-control valve 52 is opened and unlocked when the pressure difference reaches or falls below this value). Preferably, the fourth preset value corresponds to the maximum opening value of the second negative pneumatic differential pressure-control valve 52 and is less than or equal to the maximum closing value of the second positive pneumatic differential pressure-control valve 22. In order to prevent leakage of the transmission oil in the transmission due to positive pressure, when the pressure difference between the oil and air sealing chamber P2 and the transmission P4 is greater than the third preset value, the second positive pneumatic differential pressure-control valve 22 is opened and the second negative pneumatic differential pressurecontrol valve 52 is in a closed state, and the compressed air is charged into the transmission P4 after passing through the compressed-air input and the second positive pneumatic differential pressure-control valve 22 to charge the transmission. The transmission P4 is continuously charged until the pressure difference between the oil and air sealing chambers P2 and the transmission P4 reaches or falls below an intermediate value (which is less than the third preset value) preset in the second positive pneumatic differential pressure-control valve 22, and at this time, the second positive pneumatic differential pressure-control valve 22 is closed (or, in other specific embodiments, the second positive pneumatic differential pressure-control valve 22 may still be in an open state in which the discharge capacity of the second positive pneumatic control valve is small to compensate for leaks). If the pressure in the compressed-air chamber ACB decreases, the pressure in the oil and compressed-air sealing chamber P2 also decreases, and when the pressure difference between the oil and compressed-air sealing chamber P2 and the transmission P4 is less than or equal to the fourth preset value, the second negative pneumatic differential pressure-control valve 52 is opened and the second positive pneumatic differential pressurecontrol valve 22 is in a closed state, and at this time, the compressed air in the transmission P4 is discharged through the second negative pneumatic differential pressure-control valve 52. The compressed air in the transmission P4 is continuously discharged until the pressure difference between the oil and compressed-air sealing chamber P2 and the transmission P4 reaches an intermediate value (which is larger than the fourth preset value) set in the second negative pneumatic differential pressure-control valve 52, and the second negative pneumatic differential pressurecontrol valve 52 is closed. Further disclosed is a compressed-air path of the main drive seal system including the transmission P4, a leak detection chamber P3, a third positive differential pressure pneumatic pressure-control valve 23, and a third negative pneumatic differential pressure-control valve 53. If the pressure difference between the transmission P4 and the leak detection chamber P3 is greater than or equal to a fifth preset value, the third positive pneumatic differential pressure-control valve 23 is opened and the third negative pneumatic differential pressure-control valve 53 is in a closed state; and when the pressure difference between the transmission P4 and the leak detection chamber P3 is less than or equal to a sixth preset value, the third negative pneumatic control valve 53 is opened and the third positive pneumatic control valve 23 is in a closed state. The "fifth preset value" is set according to the minimum opening value preset in the third positive pneumatic differential pressure-control valve 23 (i.e., the third positive pneumatic differential pressurecontrol valve 23 is opened and released when the pressure difference reaches or exceeds this value) and the minimum closing value preset in the third negative pneumatic differential pressure-control valve 53 (i.e., the third negative pneumatic differential pressurecontrol valve 53 is closed and sealed when the pressure difference reaches or exceeds this value). Preferably, the fifth preset value corresponds to the minimum opening value of the third positive pneumatic differential pressure-control valve 23, and is greater than or equal to the minimum closing value of the third negative pneumatic differential pressure-control valve 53. The "sixth preset value" is set according to the maximum closing value preset in the third positive pneumatic differential pressure-control valve 23 (i.e., the third positive pneumatic differential pressurecontrol valve 23 is closed and shut off when the pressure difference reaches or falls below this value) and the maximum opening value preset in the third negative pneumatic control valve 53 (i.e., the third negative pneumatic control valve 53 is opened and unlocked when the pressure difference reaches or falls below this value). Preferably, the sixth preset value corresponds to the maximum opening value of the third negative pneumatic differential pressure-control valve 53 and is equal to or smaller than the maximum closing value of the third positive pneumatic differential pressure-control valve 23. If the pressure difference between the transmission P4 and the leak detection chamber P3 is equal to or larger than the fifth preset value, the third positive differential pressure pneumatic pressure-control valve 23 is opened, and the third negative pneumatic differential pressure-control valve 53 is in a closed state, and the compressed air is charged into the leak detection chamber P3 after passing through the compressed-air input connection, the second positive differential pressure pneumatic pressure-control valve 22, and the third positive differential pressure pneumatic pressure-control valve 23. The leak detection chamber P3 is continuously pressurized until the total pressure of the leak detection chamber P3, the oil and compressed-air sealing chamber P2, and the EP2 grease chamber P1 can balance the external water and soil pressures, so that the main drive seal is reliable, preferably at this time, the pressure difference between the transmission P4 and the leak detection chamber P3 reaches or is less than an intermediate value (which is less than the fifth preset value) preset in the third positive differential pressure pneumatic valve 23, and the third positive differential pressure pneumatic valve 23 is closed (or, in other specific embodiments, the third positive pressure pneumatic valve 23 may still be in an open state in which the discharge capacity of the third positive differential pressure pneumatic valve is small to balance the leakage. If the pressure in the compressed-air chamber ACB decreases, the pressure in the leak detection chamber P3 also decreases, and when the pressure difference between the transmission P4 and the leak detection chamber P3 is less than or equal to the sixth preset value, the third negative pneumatic differential pressure-control valve 53 is opened, and the third positive pneumatic differential pressurecontrol valve 23 is in a closed state, at which time the compressed air in the leak detection chamber P3 is discharged through the third pneumatic differential pressure-control valve 53. The compressed air in the leak detection chamber P3 is continuously discharged until the pressure difference between the transmission P4 and the leak detection chamber P3 reaches an intermediate value (which is larger than the sixth preset value) set in the third negative pneumatic differential pressure-control valve 53, and the third negative pneumatic differential pressure-control valve 53 is closed. OBJECTIVE The previously described systems of mechanically pneumatic differential pressure control are very complex in installation, adjustment and repair. There is a very high risk of making errors during assembly, which can then lead to damage which is expensive to repair. Furthermore, the systems are complex in adapting to seal wear and changing parameters. Furthermore, the seal systems have problems in the area of the rear sealing chambers if they are system-related without pressurization. Here, it can easily lead to malfunctions of the seals, which can then lead to oil losses from one chamber into the adjacent chamber. The object of the invention is to provide a main drive seal system for a tunnel boring machine which overcomes the aforementioned disadvantages. DESCRIPTION OF THE INVENTION This objective is achieved according to the invention in that at least one electronic controller is provided, which has at least one data storage unit, at least one data processing unit and at least one control command output unit, in that at least one control circuit based on the at least one electronic controller is provided for controlling the second pressure in the at least one second chamber, in that at least one first pressure detection device is connected to the at least one space or the at least one first chamber in order to measure the pressure in the space or the current pressure in the at least one first chamber, wherein the at least one first pressure detection device is electronically connected to the at least one electronic controller for transmitting the pressure, in that at least one second pressure detection device is connected to the at least one second chamber in order to measure the current pressure in the at least one second chamber, wherein the at least one second pressure detection device is electronically connected to the at least one electronic controller for transmitting the pressure, in that the at least one first compressed-air switching valve of the at least one second chamber is connected to the at least one control device, so that the at least one first compressed-air switching valve of the at least one second chamber is electrically switchable by the control device, in that the at least one second compressed-air switching valve of the at least one second chamber is connected to the at least one control device, so that the at least one second compressed-air switching valve of the at least one second chamber is electrically switchable by the control device, and that the electronic controller has a control program with the following steps: receiving and storing the pressure p0 and / or the pressure p1-ACTUAL, defining and storing the differential pressure ApL1-CONTROL, wherein a checking step is preferably provided to check that the ApL1-CONTROL is smaller than or equal to the differential pressure ApL1; defining and storing a pressure offset Ap1 and calculating a pressure p1-TARGET according to the formula p1-TARGET = p0 + Ap1, wherein a checking step is preferably provided to check that p1-TARGET is greater than p0, defining a reference pressure pREF, wherein pREF is one of the following pressures: p0 + Ap1 or p1-ACTUAL, storing the pressure p2-ACTUAL, calculating a pressure p2-TARGET according to the formula p2-TARGET = pREF-ApL1-CONTROL, wherein a checking step is provided to check that p2-TARGET lies in a range between pREF and pREF-ApL1, receiving and storing the pressure p2-ACTUAL of the second chamber, calculating and storing a pressure difference Ap2 between p2-TARGET and p2-ACTUAL; and checking whether Ap2 is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit, wherein, if Ap2 is in the range x < 0 < y, the first compressed-air switching valve of the at least one second chamber and the second compressed-air switching valve of the at least one second chamber are controlled by the controller such that the first compressed-air switching valve and the second compressed-air switching valve are closed, wherein, if Ap2 > y, the control command output unit sends a signal for opening the first compressed-air switching valve of the at least one second chamber to the first compressed-air switching valve of the at least one second chamber, wherein the second compressed-air switching valve of the at least one second chamber is controlled so as to be closed, and wherein, if Ap2<x, the control command output unit transmits a signal for opening the second compressed-air switching valve of the at least one second chamber to the second compressed-air switching valve of the at least one second chamber, wherein the first compressed-air switching valve of the at least one second chamber is controlled so as to be closed. It is advantageous here that the system according to the invention, despite the reservation of experts that only mechanically pneumatic differential pressure systems are safe, that the system is cost-effective and space-saving to install and that it can be installed, set, maintained and adjusted simply and without errors, also by a corresponding simple adjustment in the control program. The interval limits x, y, are switching conditions for the respective first and second compressed-air switching valves belonging to the chambers P2, P2’, P3, P4. The skilled worker would find the interval limits x, y as an upper and a lower limit value for the pressure differences Ap2, and the pressure differences Ap2’, Ap3, Ap4 described below as reasonable limit values for maintaining the respective target pressure conditions in the chambers P2, P2’, P3, P4, optionally also as a function of the pressure p0 in the excavation chamber, x, y are in the ranges from -1 to +1 bar, -0.5 to +0.5 bar, -0.25 to +0.25 bar, -0.1 to +0.1 bar, -0.05 to +0.05 bar, -0.025 to +0.025 bar, -0.01 to +0.01 bar, or lower - / + pressures. These serve to illustrate that x, y are merely values to be set in the controller as a function of the respective components of the main drive seal system and pressure conditions in which it is used. A further solution of the invention provides that at least one further second chamber with a further second pressure is provided downstream of the at least one second chamber, wherein the at least one further second chamber is an oil and compressed-air sealing chamber, that at least one seal is provided between the at least one second chamber and the at least one further second chamber, which seal can resist a differential pressure ApL2 between the at least one second chamber and the at least one further second chamber, that at least one first compressed-air switching valve of the at least one further second chamber is provided with at least one compressed-air inlet and at least one compressed-air outlet, wherein the first compressed-air switching valve of the at least one further second chamber is configured such that it can be switched between an open and a closed position, that at least one second compressed-air switching valve of the at least one further second chamber is provided with at least one compressed-air inlet and at least one compressed-air outlet, wherein the second compressed-air switching valve of the at least one further second chamber is configured such that it can be switched between an open and a closed position, that at least one control circuit based on the at least one electronic control is provided for controlling the further second pressure in the at least one further second chamber, that at least one further second pressure detection device is connected to the at least one further second chamber in order to measure the current pressure in the at least one second chamber, wherein the at least one further second pressure detection device is electronically connected to the at least one electronic control for transmitting the pressure, that the at least one first compressed-air switching valve of the at least one further second chamber is connected to the at least one control device, such that the at least one first compressed-air switching valve of the at least one further second chamber can be electrically switched by the control device, that the at least one second compressed-air switching valve of the at least one further second chamber is connected to the at least one control device, such that the at least one second compressed-air switching valve of the at least one further second chamber is electrically switchable by the control device, that the at least one outlet of the compressed-air input connection, which is pneumatically connected via a compressed-air line to the at least one compressed-air inlet of the first compressed-air switching valve of the at least one further second chamber, wherein the at least one compressed-air outlet of the first compressed-air switching valve of the at least one further second chamber is pneumatically connected to the at least one compressed-air inlet of the second compressed-air switching valve of the at least one further second chamber and the at least one further second chamber, and wherein a compressed-air outlet of the second compressed-air switching valve of the at least one further second chamber is pneumatically connected to the compressed-air discharge line, and that the control program of the electronic control has the further steps of: defining and storing the differential pressure ApL2-CONTROL, wherein a checking step is provided to check that the ApL2-CONTROL is smaller than or equal to the differential pressure ApL2; receiving and storing the pressure p2’-ACTUAL of the further second chamber, calculating and storing a pressure p2’-TARGET according to the formula p2’-TARGET = p2-ACTUAL - ApL2-CONTROL or according to the formula p2’-TARGET = pREF -ApL1-CONTROL - ApL2-CONTROL, wherein a checking step is provided to check that p2’-TARGET lies in a range between p2-ACTUAL and p2-ACTUAL - ApL2, calculating and storing a pressure difference Ap2’ between p2’-TARGET and p2’-ACTUAL, and checking whether Ap2’ is in a range x < 0 < y, wherein x, y are a lower interval boundary and an upper interval boundary, wherein when Ap2’ is in the range x < 0 < y, the first compressed-air switching valve of the at least one further second chamber and the second compressed-air switching valve of the at least one further second chamber are controlled to be closed, wherein if Ap2’ > y, the control command output unit sends a signal for opening the first compressed-air switching valve of the at least one further second chamber to the first compressed-air switching valve of the at least one further second chamber, wherein the second compressed-air switching valve of the at least one further second chamber is controlled so as to be closed, and wherein, if Ap2’ <x, the control command output unit sends a signal for opening the second compressed-air switching valve of the at least one further second chamber to the second compressed-air switching valve of the at least one further second chamber, wherein the first compressed-air switching valve of the at least one further second chamber is controlled so as to be closed. The provision of the further second chamber, which is likewise designed as an oil and compressed-air sealing chamber, has the advantage that an additional sealing stage is provided in comparison with previous systems with an EP2 grease lubrication chamber, which is likewise relevant for the pressure dissipation. A further solution of the invention provides that at least one third chamber is provided with a third pressure downstream of the at least one second chamber or that downstream of the at least one further second chamber, wherein the at least one third chamber is a leak detection chamber, that at least one seal is provided between the at least one second chamber or that at least one seal is provided between the at least one further second chamber and the at least one third chamber, which seal can resist a differential pressure ApL2 between the at least one second chamber or that can resist a differential pressure ApL2’ of the at least one further second chamber and the at least one third chamber, that at least one first compressed-air switching valve of the at least one third chamber is provided with at least one compressed-air inlet and at least one compressed-air outlet, wherein the first compressed-air switching valve of the at least one third chamber is configured such that it can be switched between an open and a closed position, at least one second compressed-air switching valve of the at least one third chamber having at least one compressed-air inlet and at least one compressed-air outlet is provided, wherein the second compressed-air switching valve of the at least one third chamber is designed such that it can be switched between an open and a closed position, that at least one control circuit based on the at least one electronic controller is provided for controlling the third pressure in the at least one third chamber, that at least one third pressure detection device is connected to the at least one third chamber in order to measure the current pressure in the at least one third chamber, wherein the at least one third pressure detection device is electronically connected to the at least one electronic 23 controller for transmitting the pressure, that the at least one first compressed-air switching valve of the at least one third chamber is connected to the at least one control device, such that the at least one first compressed-air switching valve can be electrically switched by the control device, that the at least one second compressed-air switching valve of the at least one third chamber is connected to the at least one control device, so that the at least one second of the at least one third chamber is electrically switchable by the control device, that the at least one outlet of the compressed-air input connection, which outlet is pneumatically connected via a compressed-air line to the at least one compressed-air inlet of the first compressed-air switching valve of the at least one third chamber, wherein the at least one compressed-air outlet of the first compressed-air switching valve of the at least one third chamber is pneumatically connected to the at least one compressed-air inlet of the second compressed-air switching valve of the at least one third chamber and the at least one third chamber, and wherein a compressed-air outlet of the second compressed-air switching valve of the at least one third chamber is pneumatically connected to the compressed-air discharge line, and that the control program of the electronic control system has the following steps: defining and storing the differential pressure ApL2-CONTROL or the differential pressure ApL2’-CONTROL, wherein a checking step is provided to check that the differential pressure ApL2-CONTROL is smaller than or equal to the differential pressure ApL2 or that the differential pressure ApL2’-CONTROL is smaller than or equal to the differential pressure ApL2’; receiving and storing the pressure p3-ACTUAL of the third chamber, calculating and storing a pressure p3-TARGET according to the formula p3-TARGET = (p2-ACTUAL or p2’-ACTUAL)-(ApL2-CONTROL or ApL2’-CONTROL) or according to the formula p3-TARGET = pREF-ApL1-CONTROL-ApL2-CONTROL-ApL2’-CONTROL, wherein a checking step is provided in each case that p3-TARGET lies in a range between p2-ACTUAL and p2-ACTUAL-ApL2 or between p2’-ACTUAL and p2’-ACTUAL-ApL2, calculating and storing a pressure difference Ap3 between p3-TARGET and p3-ACTUAL, and checking whether Ap3 is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit, wherein if Ap3 is in the range x < 0 < y, the first compressed-air switching valve of the at least one third chamber and the second compressed-air switching valve of the at least one third chamber are controlled to be closed, wherein if Ap3 > y, the control command output unit transmits a signal for opening the first compressed-air switching valve of the at least one third chamber to the first compressed-air switching valve of the at least one third chamber, wherein the second compressed-air switching valve of the at least one third chamber is controlled so as to be closed, and wherein if Ap3<x, the control command output unit transmits a signal for opening the second compressed-air switching valve of the at least one third chamber to the second compressed-air switching valve of the at least one third chamber, wherein the first compressed-air switching valve of the at least one third chamber is controlled so as to be closed. This provides a simple control of the pressure in the leak detection chamber. A further solution of the invention provides that at least one fourth chamber with a fourth pressure is provided downstream of the at least one third chamber, wherein the at least one fourth chamber is a transmission chamber, that at least one seal is provided between the at least one third chamber and the at least one fourth chamber, which seal can resist a differential pressure ApL3 between the at least one third chamber and that of the at least one fourth chamber, that at least one first compressed-air switching valve of the at least one fourth chamber is provided with at least one compressed-air inlet and at least one compressed-air outlet, wherein the first compressed-air switching valve of the at least one fourth chamber is configured such that it can be switched between an open and a closed position, that at least one second compressed-air switching valve of the at least one fourth chamber is provided with at least one compressed-air inlet and at least one compressed-air outlet, wherein the second compressed-air switching valve of the at least one fourth chamber is configured such that it can be switched between an open and a closed position, that at least one control circuit based on the at least one electronic control is provided for controlling the fourth pressure in the at least one fourth chamber, that at least one third pressure detection device is connected to the at least one fourth chamber in order to measure the current pressure in the at least one third chamber, wherein the at least one fourth pressure detection device is electronically connected to the at least one electronic control for transmitting the pressure, that the at least one first compressed-air switching valve of the at least one fourth chamber is connected to the at least one control device, such that the at least one first compressed-air switching valve of the at least one fourth chamber is electrically switchable by the control device, that the at least one second compressed-air switching valve of the at least one fourth chamber is connected to the at least one control device, such that the at least one second compressed-air switching valve of the at least one fourth chamber is electrically switchable by the control device, that the at least one outlet of the compressed-air input connection, which is pneumatically connected via a compressed-air line to the at least one compressed-air inlet of the first compressed-air switching valve of the at least one fourth chamber, wherein the at least one compressed-air outlet of the first compressed-air switching valve of the at least one fourth chamber is pneumatically connected to the at least one compressed-air inlet of the second compressed-air switching valve of the at least one fourth chamber and the at least one fourth chamber, and wherein a compressed-air outlet of the second compressed-air switching valve of the at least one fourth chamber is pneumatically connected to the compressed-air discharge line, and that the control program of the electronic control system comprises the further steps: defining and storing a pressure offset Ap4-ADDITION, calculating and storing a pressure p4-TARGET according to the formula p4-TARGET = p3-ACTUAL + Ap4-ADDITION, defining and storing the differential pressure ApL3-CONTROL, wherein a checking step is provided to check that the ApL3-CONTROL is smaller than or equal to the differential pressure ApL3; receiving and storing the pressure p4-ACTUAL of the fourth chamber, calculating and storing a pressure difference Ap4 between p4-TARGET and p4-ACTUAL, and checking whether Ap4 is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit, wherein if Ap4 is in the range x < 0 < y, the first compressed-air switching valve of the at least one fourth chamber and the second compressed-air switching valve of the at least one fourth chamber are controlled to be closed, wherein if Ap4 > y, the control command output unit transmits a signal for opening the first compressed-air switching valve of the at least one fourth chamber to the first compressed-air switching valve of the at least one fourth chamber, wherein the second compressed-air switching valve of the at least one fourth chamber is controlled so as to be closed, and wherein if Ap4<x, the control command output unit transmits a signal for opening the second compressed-air switching valve of the at least one fourth chamber to the second compressed-air switching valve of the at least one fourth chamber, wherein the first compressed-air switching valve of the at least one fourth chamber is controlled so as to be closed. This provides a simple control of the pressure in the transmission chamber. A further solution of the invention provides that the at least one compressed-air outlet of the second compressed-air switching valve of the at least one second chamber, the at least one further second chamber, the at least one third chamber and / or the at least one fourth chamber is pneumatically connected to the compressed-air discharge line, which is preferably connected to the environment via a sound damper, and / or is pneumatically connected to an air suction line, which is connected to a vacuum pump, wherein the vacuum pump is preferably controllable via the controller. By means of the two variants of the compressed-air delivery, either passive or active as suction, it is possible to discharge the pressure in one or more of the chambers in a targeted manner and with the desired accuracy. A further solution of the invention provides that at least one of the chambers is connected to at least one third compressed-air switching valve which is pneumatically connected with its compressed-air outlet to an air suction line which is connected to a vacuum pump, so that a pressure lower than atmospheric pressure can be set in the connected chamber, wherein the vacuum pump can preferably be controlled via the controller. The third compressed-air switching valve thus enables a second path to reduce the pressure. The reduction is controlled by the vacuum pump. It has furthermore surprisingly been shown that it is thereby possible to provide a pressure in one or more chambers which is less than the atmospheric pressure. It has surprisingly been found that the sealing effect in the chambers can be increased by the seal being suctioned onto the shaft to be sealed. A further solution of the invention provides that a series of the target pressures of the chambers is stored in the controller: p0<p1-TARGET > p2-TARGET > p2’-TARGET > p3-TARGET < p4-TARGET, wherein the further second chamber and its pressure can be omitted. This prevents a loss of lubricant, which facilitates operation and makes it more cost-effective and environmentally compatible. A further solution of the invention provides that, if the target pressure is calculated to be less than atmospheric pressure in at least one of the chambers, the target pressure is set in the controller to atmospheric pressure or to a defined value between 0 bar and atmospheric pressure, which can then be adjusted by switching the third compressed-air switching valve of the respective chamber by the controller, the air extraction line and the vacuum pump, wherein the vacuum pump can preferably be controlled by the controller. It has surprisingly been 29 found that it is thereby possible to provide a pressure in one or more chambers which is less than atmospheric pressure. It has surprisingly been found that the sealing effect in the chambers can be increased by the seal being suctioned onto the shaft to be sealed. A further solution of the invention provides that, if p0 + Api is smaller than ApLi-CONTROL, the target pressures of the chambers in the control are set to atmospheric pressure or at least one of the target pressures of the chambers in the control is set to a defined value between 0 bar and atmospheric pressure, which is then adjustable via the switching of the third compressed-air switching valve of the respective chamber by the control, the air extraction line and the vacuum pump, wherein preferably the vacuum pump is controllable via the control. A further solution of the invention provides that a circulation pump for the oil located in the chamber is provided for at least one of the chambers, which circulation pump is connected fluidically via at least one line to at least one suction point of the chamber for suctioning the oil from the chamber and via at least one further line to at least one introduction point of the chamber for introducing the oil into the chamber. It is advantageous here if the oil is filtered upstream or downstream of the circulation pump, or foreign substances are separated from the oil and / or the quality of the oil is checked. The circulation of the oil in the respective chamber enables a better lubricant supply in the chamber. Furthermore, it has been found that this achieves better lubrication of the seal(s) of the chambers in a simple manner, in particular in the upper region of the seal. A further solution of the invention provides that the air suction line is connected to at least one negative pressure accumulator, which is preferably connected to a pressure detection device. This makes it possible in a simple manner to damp the under certain circumstances pulsating action of the vacuum pump and at the same time to temporarily exhaust air for pressure compensation without causing the vacuum pump to be actuated. It is furthermore advantageous that the actual pressure p2 of the chamber P2 to be regulated is less than or equal to the pressure p1-ACTUAL of the chamber P1, that the actual pressure p2’ of the chamber P2’ to be regulated is less than or equal to the pressure p2-ACTUAL of the chamber P2, and that the actual pressure p3 of the chamber P3 to be regulated is less than or equal to the pressure p2-ACTUAL of the chamber P2 or p2’-ACTUAL of the chamber P2’ and less than or equal to the pressure p4-ACTUAL of the chamber P4. This prevents in a simple manner the lip seal from being opened to the adjacent chamber and a medium, such as oil, located in the chamber to be controlled can pass through the respective seal into the adjacent chamber. It is furthermore advantageous that the actual pressure p2 of the chamber P2 to be controlled is greater than or equal to the pressure p1-ACTUAL of the chamber P1 -the pressure difference ApL1 of the lip seal L1, that the actual pressure p2’ of the chamber P2’ to be controlled is greater than or equal to the pressure p2-ACTUAL of the chamber P2 - the pressure difference ApL2’ of the lip seal L2’, and that the actual pressure p3 of the chamber P3 to be controlled is greater than or equal to (the pressure p2-ACTUAL of the chamber P2 or p2’-ACTUAL of the chamber P2’)-(the pressure difference ApL1 of the lip seal L1 or the pressure difference ApL2’ of the lip seal L2’) and greater than or equal to the pressure p4-ACTUAL of the chamber P4 -the pressure difference ApL3 of the lip seal L3 that the lip seal fails because the pressure difference between two chambers is greater than the pressure difference that can be held by the lip seal and thus the seal is damaged. Furthermore, the objective according to the invention is achieved by a method for regulating the pressure in a main drive seal system in a main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine, in particular according to one of the features described above, having at least one space P0 having a first pressure p0 behind a cutting wheel of the tunnel boring machine, wherein the space P0 is connected to a pressure detection device, and wherein the main drive seal system has the following features: at least one first chamber P1 having a first pressure p1, wherein the first chamber P1 is preferably a labyrinth chamber filled with a blocking grease (HBW), wherein the first chamber P1 is connected to a pressure detection device, at least one second chamber P2 having a second pressure p2, wherein the at least one second chamber P2 is an oil and compressed-air sealing chamber P2, wherein the second chamber P2 is connected to a pressure detection device, preferably at least one further second chamber P2’ with a further second pressure p2’, wherein the at least one further second chamber P2’ is an oil and compressed-air sealing chamber P2’, wherein the further second chamber P2’ is connected to a pressure detection device, at least one third chamber P3 with a third pressure p3 wherein the at least one third chamber P3 is a leak detection chamber, wherein the third chamber P3 is connected to a pressure detection device, at least one fourth chamber P4 with a fourth pressure p4, wherein the at least one fourth chamber P4 is a transmission chamber, wherein the fourth chamber P4 is connected to a pressure detection device, at least one lip seal L1,  L2,  L2’, L3 in each case between the chambers P1, P2, P2’, P3, P4, which can in each case resist a differential pressure ApL1, ApL2, ApL2’, ApL3 between the adjacent chambers, and at least one electronic controller, which has at least one data storage unit, at least one data processing unit and at least one control command output unit, wherein at least one program for providing a control loop based on the at least one electronic controller for the pressure p2-ACTUAL, p2’-ACTUAL, p3-ACTUAL, p4-ACTUAL to be controlled is executed in the controller, with the method steps: measuring, receiving and storing the pressure p0 and / or the pressure p1-ACTUAL, defining and storing a pressure offset Ap1 and calculating a pressure p1-TARGET according to the formula p1-TARGET = p0 + Ap1, wherein a checking step is preferably provided that p1-TARGET is greater than p0, calculating a reference pressure pREF, the reference pressure being the pressure p0 in the first space P0 + pressure offset Ap1 or the pressure p1-ACTUAL in the first chamber P1, measuring and receiving at least one actual pressure to be regulated p2-ACTUAL, p2’-ACTUAL, p3-ACTUAL, p4-ACTUAL; defining a differential pressure of at least one lip seal ApL1-CONTROL, ApL2-CONTROL, ApL2’-CONTROL, ApL3-CONTROL, defining and storing a pressure supplement Ap4-ADDITION between the third and fourth chambers P3, P4, calculating a target pressure p2-TARGET, p2’-TARGET, p3-TARGET, p4-TARGET with at least one of the following formulae: 1. p2-TARGET = pREF-ApL1-CONTROL 2.  p2’- TARGET = p2-ACTUAL-ApL2-CONTROL or p2’-TARGET = pREF-ApL1-CONTROL-ApL2-CONTROL, 3. p3-TARGET = (p2-ACTUAL or p2’-ACTUAL)-(ApL2-CONTROL or ApL2’-CONTROL)   or p3- TARGET = pREF-ApL1-CONTROL-ApL2-CONTROL-ApL2’-CONTROL, and 4. p4-TARGET = p3-ACTUAL + Ap4-ADDITION or p4-TARGET = pREF-ApL1-CONTROL-ApL2-CONTROL-ApL2L2’-CONTROL + Ap4-ADDITION, calculating a pressure difference Api between pi-TARGET and pi-ACTUAL, wherein i is the number of the chamber of which the ACTUAL pressure is controlled, and checking whether Api is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit, wherein if Api is in the range x < 0 < y, the first compressed-air switching valve of the at least one chamber i and the second compressed-air switching valve of the at least one chamber i are controlled to be closed, wherein if Api > y, the first compressed-air switching valve of the at least one chamber i is controlled so as to be open, wherein the second compressed-air switching valve of the at least one chamber i is controlled so as to be closed, and wherein if Api<x, the second compressed-air switching valve of the at least one chamber i is controlled so as to be open, wherein the first compressed-air switching valve of the at least one chamber i is controlled so as to be closed. Furthermore, the previously known main drive seal systems have a need for improvement in that the sealing action of the lips is to be improved if only atmospheric pressure would have to be present in the chambers P2 to P4, since the lip seals L1 to L3 then press sealingly on the shaft only with a differential pressure of about 0.2 bar. For improvement, therefore, a main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine is provided, having at least one space (P0) with a first pressure (p0) behind the cutting wheel, having at least one first chamber (P1) with a first pressure (p1), wherein the first chamber (P1) is preferably a labyrinth chamber filled with a blocking grease (HBW), at least one second chamber (P2) with a second pressure (p2), wherein the at least one second chamber (P2) is an oil and compressed-air sealing chamber (P2), at least one seal (L1) between the at least one first chamber (P1) and the at least one second chamber (P2), which can resist a differential pressure ApL1 between the at least one first chamber (P1) and the at least one second chamber (P2), preferably at least one further second chamber (P2’) with a further second pressure (p2’) downstream of the at least one second chamber (P2), wherein the at least one further second chamber (P2’) is an oil and compressed-air sealing chamber (P2’), at least one seal (L2) between the at least one second chamber (P2) and the at least one further second chamber (P2’) which can resist a differential pressure ApL2 between the at least one second chamber (P2) and the at least one further second chamber (P2’), at least one third chamber (P3) with a third pressure (p3) following the at least one second chamber (P2) or the at least one further second chamber (P2’), wherein the at least one third chamber (P3) is a leak detection chamber (P3), at least one seal (L2’) between the at least one further second chamber (P2’) and the at least one third chamber (P3), which seal can resist a differential pressure ApL2 between the at least one further second chamber (P2’) and that of the at least one third chamber (P3), at least one fourth chamber (P4) with a fourth pressure (p4) following the at least one third chamber (P3), wherein the at least one fourth chamber (P4) is a transmission chamber (P4), at least one seal (L3) between the at least one third chamber (P3) and the at least one fourth chamber (P4), which seal can withstand a differential pressure ApL3 between the at least one third chamber (P3) and that of the at least one fourth chamber (P4), characterized in that at least one second chamber (P2), at least one further second chamber (P2’), at least one third chamber (P3) and / or at least one fourth chamber (P4) is pneumatically connected to an air suction line which is pneumatically connected to a vacuum pump, so that a pressure which is less than the atmospheric pressure can be set in at least one of the chambers via the vacuum pump. It has surprisingly been found that it is thus possible in a simple manner to provide a pressure in one or more chambers which is less than atmospheric pressure. It has furthermore surprisingly been shown that the sealing effect in the chambers can be increased by the seal being suctioned onto the shaft to be sealed. A further solution of the invention provides that between one of the chambers and the vacuum pump and at least one compressed-air switching valve and / or at least one throttle is provided in the air extraction line (93), and that preferably the at least one compressed-air switching valve and / or the at least one throttle can be electrically switched. It is furthermore advantageous that at least one of the chambers for detecting an actual pressure of the chamber is connected to at least one pressure detection device. A further solution of the invention provides that a controller (80) is provided which is electrically connected to the vacuum pump (95), the at least one compressed-air switching valve (23, 23’, 33, 43) and / or the at least one throttle (233, 233’, 333, 433) and / or the at least one pressure detection device (24, 24’, 34, 44). It has been shown that these are simple solutions with which it is possible in a simple manner to lower and maintain the pressure under atmospheric pressure in a correspondingly controlled manner. A further solution of the invention provides that a controller (80) is provided, which has at least one data storage unit, at least one data processing unit and at least one control command output unit, and that at least one control circuit, which is based on the at least one electronic controller (80), is provided for controlling the ACTUAL pressure in one of the chambers (P2, P2’, P3, P4), which control circuit has a program step: defining a TARGET pressure for one of the chambers (P2, P2’, P3, P4), receiving an ACTUAL pressure for one of the chambers (P2, P2’, P3, P4), calculating a pressure difference Api between pi-TARGET and pi-ACTUAL, controlling the vacuum pump (95), the at least one compressed-air switching valve (23, 23’, 33, 43) and / or the at least one throttle (233, 233’, 333, 433) for changing pi-ACTUAL to pi-TARGET. A further solution of the invention provides that a series of the target pressures of the chambers (P1, P2, P2’, P3, P4) is stored in the controller (80): p0<p1-TARGET > p2-TARGET > p2’-TARGET > p3-TARGET< p4-TARGET, wherein the further second chamber (P2’) and its pressure p2’-TARGET can be omitted. Furthermore, the previously known main drive seal systems may have difficulties in providing adequate lubrication throughout the entire operating time of the tunnel boring machine. Often, a sump lubrication is used in this case, in which the oil collects at the lowest point of the seal and is then carried upwards by the rotation of the shaft. It cannot always be ensured that sufficient lubricant is sufficiently provided at the uppermost point of the seal. For improvement, therefore, a main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine is provided, having at least one first chamber P1, wherein the first chamber P1 is preferably a labyrinth chamber filled with a blocking grease (HBW), at least one second chamber P2, wherein the at least one second chamber P2 is an oil and compressed-air sealing chamber P2, at least one seal L1 is provided between the at least one first chamber P1 and the at least one second chamber P2, preferably at least one further second chamber P2’, following the at least one second chamber P2, wherein the at least one further second chamber P2’is an oil and compressed-air sealing chamber P2’, at least one third chamber P3 following the at least one second chamber P2 or provided on the at least one further second chamber P2’, wherein the at least one third chamber P3 is a leak detection chamber P3, at least one seal L2 between the at least one second chamber P2 or the at least one further second chamber P2 and the at least one third chamber P3, at least one fourth chamber P4 following the at least one third chamber P3, wherein the at least one fourth chamber (P4) is a gear chamber P4, at least one seal L3 between the at least one third chamber P3 and the at least one fourth chamber P4, characterized in that for at least one of the second, further second, third and / or fourth chambers P2, P2‘, P3, P4, at least one third chamber P3 is provided on the side of the at least one third chamber P2, P2’, P4 is connected to a circulation pump for the oil located in the chamber, and that the connection is provided via at least one line fluidically to at least one suction point of the chamber P2, P2’, P4 for suctioning the oil from the chamber P2, P2’, P4 and via at least one further line fluidically to at least one introduction point of the chamber P2, P2’, P4 for introducing the oil into the chamber P2, P2’, P4. It is advantageous here if the oil is filtered upstream or downstream of the circulation pump, or foreign substances are separated from the oil and / or the quality of the oil is checked. The circulation of the oil in the respective chamber enables a better lubricant supply in the chamber. Furthermore, it has been found that this achieves better lubrication of the seal(s) of the chambers in a simple manner, in particular in the upper region of the seal. A further solution of the invention provides that a filter for filtering the oil is provided upstream or downstream of the circulation pump. A further solution of the invention provides that a separator for separating solids or liquids in the oil is provided upstream or downstream of the circulation pump. A further solution of the invention provides that quality control of the oil takes place during the circulation of the oil. Furthermore, if the leak detection chamber P3 is also filled with oil, it can also be provided with a circulation pump. BRIEF DESCRIPTION OF THE DRAWINGS For better illustration of the technical solutions of embodiments of the present application or the conventional technology, the drawings referred to for describing the embodiments or the conventional technology will be briefly described below. Obviously, 39 the drawings in the following description are only some examples of the present application, and other drawings can be obtained based on these drawings without any creative efforts by those skilled in the art. In the drawings: figure 1 shows a schematic diagram of the main drive seal for a shield machine according to an embodiment of the present application , and figure 2       shows a schematic diagram of an inventive pressurization and pressurecontrol system of the main drive seal structure; and figures 3-6 show schematic representations of pressure profiles in the main drive seal as a function of an output pressure p0. DETAILED DESCRIPTION OF THE EMBODIMENTS Figure 1 shows the basic design of a main drive seal system according to the invention. In front of the main driving seal system there is provided a space P0 which is the space behind the cutting wheel (not shown) of the tunnel boring machine and in which there is located a ground slurry of dissolved soil / rock, water / bentonite suspension and optionally foam. Fluidly connected to this is the main drive seal system, which seals the gap between the shaft of the main drive system and the tunnel boring machine. The seal functions both statically and dynamically as the cutting wheel and thus the shaft rotates. The main drive seal system is constructed from left to right as set forth below. First, a chamber P1 is effected, which is connected fluidically to the space P0. The chamber P1 is preferably a so-called labyrinth chamber, into which a blocking grease (preferably HBW) is introduced under pressure. A second chamber P2 follows this. The chamber P1 is separated from the chamber P2 by a seal L1. Preferably, the seal L1 is an oriented lip seal. For this purpose, the lip seal has an upper body on which a lip is arranged movably over a hinge-like region. The orientation is provided in such a way that a pressure applied in the chamber P1 presses on the lip part of the seal L1, so that the latter is pressed against the shaft. In the prior art, a lubricating grease, for example EP2, is usually introduced into the chamber P2 with, for example EP2. According to the invention, chamber P2 is designed to be an oil and compressed air sealing chamber that can be pressurized with compressed air and is hereinafter referred to synonymously as the first chamber P2, chamber P2, or oil chamber P2. Adjacent to the chamber P2 is an oil and compressed-air sealing chamber P2’ which is pressurized with compressed air and is hereafter referred to as chamber P2’, second chamber P2’, or oil chamber P2’ in the following as synonymously. The further chamber P2’ is separated from the chamber P2 by a seal L2. Preferably, a lip seal is again provided here as seal L2, which is oriented toward the chamber P2. The chamber P2’ is also a pressurized oil chamber. If necessary, further chambers P2’ can be provided as an oil chamber in the connection. As shown here, the chamber P2’ is followed by the chamber P3, which is also referred to as leakage chamber P3 or leak detection chamber P3 in the following, and which is separated from the chamber P2’ by a seal L2’. The chamber P3 is a leak detection chamber. It is usually provided without a lubricant filling. It can be pressurized by pressurized air. The orientation of lip seal L2’ between chamber P2’ and chamber P3 is aligned with chamber P2’. The chamber P3 serves to detect whether one of the seals has failed by the entry of earth slurry / liquid from the space P0, lubricating oil from the chamber P2 / P2’ and / or transmission oil from the chamber P4 into the chamber P3. The chamber P4, which is the transmission chamber, follows chamber P3. A seal L3 is provided between the chamber P3 and the chamber P4. Seal L3 is preferably designed as a lip seal and is oriented toward chamber P4, and is thus arranged opposite seals L1, L2, L2’. The chamber P4 is also filled with oil - here transmission oil - and can be pressurized with compressed air. A pressure p1 prevails in the chamber P1. The pressure p1 is set to be larger than the pressure p0 because the chamber P1 is designed as a grease-loss barrier chamber. This means that the blocking grease (HBW) is pressure-pressed into the chamber P1 and, since the blocking grease is not a so-called life grease, is forced out forward into the space P0 through the labyrinth gap. This is effected by pressing in the barrier grease at the pressure p1, which results as the pressure p0 + a pressure offset Api. The pressure offset Api is usually 0.5 bar. The seals L1, L2, L2’ and L3 are designed so that they are able to withstand a certain applied pressure until the seal is damaged and thus becomes permeable. In the case of a lip seal, damage takes place as a result of the lip pressed onto the shaft striking through. In the case of the seals, a distinction is made between the permissible static differential pressure of the seal and the permissible dynamic differential pressure of the seal. The static differential pressure is significantly higher than the dynamic differential pressure. Depending on the type of seal, the static differential pressure can be 12 bar and the dynamic differential pressure can be 5 bar, for example. For safety reasons, the permissible dynamic differential pressure in the design of the seal system is not set fully, but rather a lower differential pressure is set, so that a safety buffer is present. In the case of a dynamic seal which has, for example, 5 bar permissible dynamic differential pressure, this is preferably 3 bar. This pressure difference is referred to as ApLi, wherein the "Li" stands for the respective number of the chamber. Preferably, the ApLi can be taken into account, for example, to conserve the seal, smaller than that of the previously set ApLi. This is referred to as ApLi-CONTROL (ApLi-ST) hereinafter. In order for the seal system to be tight with respect to the applied pressure p0 in the space P0, the seal system must provide the pressure p0 prevailing there with a counterpressure which, as a whole, is at least as great as the applied pressure p0. This is achieved by taking into account the differential pressures of the seals L1 to L3 and the pressurizing chambers P1 to P4. Surprisingly, it has been found that the lips of the seals L1 to L4 can be pulled to the shaft with a greater extent by providing a pressure in a chamber on the rear side of the seal which is less than atmospheric pressure, and that the sealing effect of the seal can thus be improved in the event that atmospheric pressure or a pressure which is only slightly greater than atmospheric pressure prevails on the front side of the seal. In order to prevent transmission oil from leaking from the chamber P4 into the leak detection chamber P3, P4 is further set at a pressure p4 that is higher than the pressure p3 in the chamber P3. For this purpose, an Ap4-ADDITION is provided in the chamber P4 here for increasing the pressure relative to the pressure in the chamber P3. This improves the sealing effect of the seal L3 and prevents the seal L3 from opening if the pressure p3 in the chamber P3 is greater than the pressure p4 without Ap4-ADDITION in the chamber P4, wherein the lip part would lift off from the shaft and at the same time transmission oil could escape from the chamber P4 through the opening into the chamber P3. Figure 2 shows the schematic structure of the pressurization and pressure-control system 10 with which the chambers P2 to P4 can be pressurized. At the same time, the means are shown by which pressures in the chambers can be adjusted as a function of a changing reference pressure. For this purpose, at least one control circuit based on an electronic control 80 is provided in particular for regulating the pressures p1 to p4 in the respective chambers. Figure 2 shows a pressurization and pressure-control system 10 according to the invention in order to be able to pressurize the chambers P2 to P4 of the seal system and to be able to control the pressures as a function of a reference pressure that changes if appropriate. For this purpose, the chamber P2 is fluidically connected to a level compensation tank 20. Both the chamber P2 and the leveling tank 20 contain lubricating oil. The chamber P2 and the leveling tank 20 are fluidly connected to each other via a line 60 so that the oil level in the leveling tank 20 and the chamber P2 can level. At the same time, the level compensation tank 20 and the chamber P2 are fluidically connected to one another via a compressed-air line 61. By means of this compressed-air line 61, the pressure can be compensated in the chamber P2 starting from the level compensation tank 20. The above-mentioned construction also applies to the chamber P2’ which is connected fluidically to a level compensation tank 20’ via an oil line 60 and a compressed-air line 61. Further, the chamber P4 is also connected to the leveling tank 40 through an oil line 60 and a compressed-air line 61 in the same manner. Transmission oil is present in each of the leveling tank 40 and the chamber P4. The chamber P3 is also connected to the leveling tank 30 via an oil line 60 and a compressed-air line 61. However, the leveling tank 30 serves primarily as a compressed air tank. However, it can also be determined via the level compensation tank 30 whether oil or liquid / foreign substances enter the chamber P3, which is operated regularly free of oil, either from the chamber P2 / P2’ or P4 due to a disturbance. To drain this accumulated oil, chamber P3 is connected to a collection vessel 35 via a line 36 and a drain 37, which is preferably located in the sump of P3. Furthermore, at least one of the chambers P2, P2’ and P4 is preferably provided with a circulation pump 25, 25’, 45 which are connected via a line 26, 26’, 46 to a suction point 27, 27’, 47 of the chamber P2, P2’, P4 for the suction of the oil from the chamber P2, P2’, P4. Furthermore, the circulation pump 25,  25’,  45 is connected fluidically via a line 28, 28’, 48 to an introduction point 29, 29’, 49 of the chamber P2, P2’, P4 for introducing the oil into the chamber P2,  P2’, P4. The circulation of the oil in the respective chamber P2, P2’, P4 enables a better lubricant supply in the chamber P2, P2’ and P4 or a better lubrication of the seal L2, L2’, L4 thereof, in particular in the upper region of the seal. If, for example, oil lubrication is also provided in the chamber P3, it would be advantageous to provide a corresponding circulation pump (not shown) in the same way. In addition, a filter or a separator for separating foreign substances from the oil may be provided (not shown) in front of or behind the circulation pump 25, 25’,  45. Furthermore, quality control of the oil can preferably be provided in order to determine any oil exchange or the need for cleaning the oil. Symbolically represented is the space P0 behind the excavation chamber, which is connected to a pressure detection device 4 in order to measure the pressure p0. The measurement result is digitally converted and transmitted to the controller 80 connected to the pressure detection device 4. These measurement data are correspondingly stored in the controller 80 and used for further calculation. The chambers P1, P2, P2’, P3 and P4 are also each connected to a pressure detection device 14, 24, 24’, 34, 44 in order to measure the respective ACTUAL pressure in the chambers P1, P2, P2’, P3, P4. These measured actual pressures p1-ACTUAL, p2-ACTUAL, p2’-ACTUAL, p3-ACTUAL, p4-ACTUAL are digitally converted and transmitted to the controller 80 connected to the pressure detection device 14,  24,  24’,  34,  44. These measurement data are correspondingly stored in the controller 80 and used for further calculation. The pressurization system 10 further comprises a source of pressurized air 100 connected to an inlet 71 of a pressurized air input connection 70. The compressed-air input connection 70 has an outlet 72 which is connected to a compressed-air line 91. The compressed-air switching valves 21, 21’, 31, 41 are fluidically connected to the compressed-air line 91 via their compressed-air inlet 211, 211’, 311, 411. On the outlet side, the compressed-air switching valve 21, 21’, 31, 41 has a compressed-air outlet 212, 212’, 312, 412 which is connected fluidically to the level compensation tank 20, 20’, 30, 40. The compressed-air switching valves 21, 21’, 31, 41 are connected to the controller 80 to receive therefrom switching commands for switching between an open and a closed position and to transmit the switching status to the controller. Furthermore, a throttle 213, 213’, 313, 413 can be provided in front of the compressed-air inlet 211, 211’, 311, 411 or behind the compressed-air outlet 212, 212’, 312, 412. The throttle can preferably be controllably connected to the controller and controllable. With the throttle 213, 213’, 313, 413, it is possible to adjust the flow rate of the compressed air before or after the compressed-air switching valve 21, 21’, 31, 41. This is preferably effected via control commands from the controller 80. Furthermore, a pressure relief line 92 is provided, which is designed to be open at one end to the environment and thus to the atmospheric pressure. A silencer 96 is preferably provided between the environment and the line. Furthermore, the pressure discharge line 92 is connected to a second compressed-air switching valve 22, 22’, 32, 42 of the respective chamber P2, P2’, P3, P4 via its compressed-air outlet 222, 222’, 322, 422. The compressed-air inlet 221, 221’, 321, 421 is fluidically connected to the leveling tank 20, 20’, 30, 40 either directly or to the line between the leveling tank 20, 20’, 30, 40 and the compressed-air outlet 212, 212’, 312, 412. The compressed-air switching valves 22, 22’, 32, 42 are connected to the controller 80 for receiving therefrom switching commands for switching between open and closed positions and communicating the switching status to the controller. Furthermore, an air suction line 93 is provided, which is connected on the output side to a vacuum pump 95. The vacuum pump 95 has a drain into the atmosphere. The air suction line 93 is connected to a third compressed-air switching valve 23, 23’, 33, 43 of the respective chamber P2, P2’, P3, P4 via its compressed-air outlet 232, 232’, 332, 432. The compressed-air inlet 231, 231’, 331, 431 of the third compressed-air switching valve 23, 23’, 33, 43 is fluidically connected to the level compensation tank 20, 20’, 30, 40. The compressed-air switching valves 23, 23’, 33, 43 are connected to the controller 80 to receive therefrom switching commands for switching between an open and a closed position and to transmit the switching status to the controller. The vacuum pump 95 is also connected to the controller 80. The first compressed-air switching valve 21, 21’, 31, 41, the second compressed-air switching valve 22, 22’, 32, 42 and / or the third compressed-air switching valve 23, 23’, 33, 43 are connected to the controller 80 respectively. By means of corresponding control commands, the controller can bring about the opening and closing of the compressed-air switching valves. The (pressure) suction line 93 is furthermore preferably connected to a vacuum reservoir 97 which has a pressure detection device 94. The pressure detection device 94 is connected to the controller 80 for transmitting the measured values. With the vacuum reservoir 97, it is possible to damp the possibly pulsating action of the vacuum pump 95 and at the same time to temporarily exhaust air for pressure compensation without causing the vacuum pump 95 to be actuated. In front of the compressed-air inlet or compressed-air outlet of the second compressed-air switching valve 22, 22’, 32, 42 and / or third compressed-air switching valve 23, 23’, 33, 43, a throttle 223, 223’, 323, 423 or 233, 233’,  333,  433 can furthermore be provided. This is preferably connected to the controller 80. Furthermore, the throttle 223, 223’, 323, 423 or 233, 233’, 333, 433 is preferably adjustable, so that the flow rate of the compressed air through the compressed-air switching valves 22,   22’,   32,   42 or 23,   23’,   33,   43 is adjustable. The electronic controller 80 includes at least one data storage unit, at least one data processing unit, and at least one control command output unit. The units themselves are not shown in Figure 2. The pressurization system receives a control circuit through the control 80 for regulating the pressures p2, p2’, p3, p4 in the chambers P2, P2’. P3, P4. For this purpose, a control program is provided in the controller 80 with the following steps: receiving and storing the pressure p0 from the pressure detection device 4 and / or the pressure p1-ACTUAL from the pressure detection device 14. Defining and storing a pressure offset Api  and calculating the pressure p1-TARGET according to the formula pi-TARGET = p0 plus Api. The fixing is effected either directly by a value provided in the program or by a user inputting a value via an input device of the controller 80. A checking step is preferably provided 49 in which it is checked that p1-TARGET > p0. Only in this case is it ensured that the chamber P1 is operated in the blocking grease loss mode. If the pressure p1-TARGET were lower than the pressure p0, there would additionally be the risk that earth slurry or liquid located in the space P0 could penetrate into the chamber P1. As another step, the program provides defining and storing the differential pressure ApL1-CONTROL (ApL1-ST), ApL2-CONTROL (ApL2-ST), ApL2’-CONTROL (ApL2’-ST), ApL3-CONTROL (ApL3-ST). If seals are not provided in the seal system, the fixing and storage of the respective differential pressure of this seal is dispensed with. The same applies if additional seals are provided. For these, a corresponding ApL would then likewise be defined and stored. Preferably, a checking step is provided in the setting that ApLi-CONTROL is smaller than or equal to the pressure difference ApLi that of the gasket Li. "Li" is the number of the gasket here. The setting itself is carried out either by a value specified in the program or by the input by an operator via an operating unit. If the ApLi-CONTROL is selected to be smaller than the ApLi value specified by the manufacturer, this can serve to reduce the wear of the seal or to increase the safety with respect to the respective seal. A further preferred program step is defining a reference pressure pREF, wherein pREF = p0 + Ap1 and / or pREF = p1-ACTUAL. The defining of the actual ACTUAL pressure in the chamber P1 would be advantageous here, but has the disadvantage that pressures in the blocking grease are difficult to measure precisely because of the friction of the blocking grease and the temperature dependence of the viscosity of the blocking grease. Therefore, P0 + Ap1 is preferred as the reference pressure pREF. As a further program step, provision is made for the pressure pi-ACTUAL of the respective chamber Pi to be received and stored via the respective pressure detection device 24,  24’,  34,  44 of the respective chamber P2, P2’, P3, P4. If a pressure pi of a chamber Pi is not to be controlled, the reception and storage of this ACTUAL pressure can be omitted accordingly. A further provided program step is calculating a pressure p2-TARGET according to the formula p2-TARGET = pREF-ApL1-CONTROL, or calculating a pressure p2’-TARGET according to the formula p2’-TARGET = pREF-ApL1-CONTROL-ApL2-CONTROL or according to the formula p2’-TARGET = p2-ACTUAL-ApL2-CONTROL, calculating a pressure p3-TARGET according to the formula p3-TARGET = pREF-ApL1-CONTROL - ApL2-CONTROL - ApL2’-CONTROL or according to the formula p3-TARGET = p2’-ACTUAL -ApL2’-CONTROL. Preferably, a checking step is provided for p2-TARGET to check that p2-TARGET lies in a range between pREF and pREF-ApL1. If p2-TARGET is larger than pREF, there is a risk that the seal L1 is opened and lubricating oil enters the chamber P1, thereby degrading the barrier effect of the barrier grease. If p2-TARGET is less than pREF-ApL1, the risk increases that the seal L1 fails and is pressed inward in the worst case. Preferably, a checking step is provided for p2’-TARGET to check that p2’-TARGET lies in a range between p2-ACTUAL and p2-ACTUAL-ApL2. If p2’-TARGET is greater than p2-ACTUAL, there is the risk that the seal L2 is opened and lubricating oil enters the chamber P2. If p2’-TARGET is less than p2-ACTUAL-ApL2, the risk of the seal L2 failing and, in the worst case, being pressed inward increases. Preferably, a checking step is provided for p3-TARGET to check that p3-TARGET lies in a range between p2’-ACTUAL and p2’-ACTUAL-ApL2’ and in a range between p4-ACTUAL and p4-ACTUAL-ApL3. If p3-TARGET is greater than p2’-ACTUAL or p4-ACTUAL, there is a risk that the seal L2’ or the seal L3 is opened and oil enters the chamber P3. If p3-TARGET is less than p2’-ACTUAL-ApL2’ or p4-ACTUAL-ApL3, the risk of the seal L2 or the seal L3 failing and being pressed inward in the worst case increases. For controlling the pressure p2-ACTUAL / p2’-ACTUAL / p3-ACTUAL, the program provides for calculating and storing a pressure difference Ap2 / Ap2’ / Ap3 = p2-TARGET-p2-ACTUAL / p2’-TARGET-p2’-ACTUAL / p3-TARGET-p3ACTUAL and checking whether the pressure difference Ap2 / Ap2’ / Ap3 is in a range x < 0 < y, wherein x represents a lower interval limit and y represents an upper interval limit. The control of the compressed-air switching valves 21, 22, 23 / 21’, 22’, 23’ / 31, 32, 33 for controlling the pressure p2-ACTUAL / p2’-ACTUAL / p3-ACTUAL in the chamber P2 / P2’ / P3 takes place in this case after the following steps: If Ap2 / Ap2’ / Ap3 lies in a range x < 0 < y, then the first compressed-air switching valve 21, 21’, 31 and the second compressed-air switching valve 22, 22’, 32 and optionally also the third compressed-air switching valve 23, 23’, 33 are controlled by the controller in such a way that they are closed. If Ap2 / Ap2’ / Ap3 > y, the control command output unit of the controller 80 outputs a signal for opening the first compressed-air switching valve 21, 21’, 31 to the first compressed-air switching valve 21, 21’, 31, and the second compressed-air switching valve 22, 22’, 32 and / or the third compressed-air switching valve 23, 23’, 33 are controlled to be closed. If Ap2 / Ap2’ / Ap3<x, the control command output unit of the controller 80 outputs a signal for opening the second compressed-air switching valve 22, 22’, 32 and / or the third compressed-air switching valve 23, 23’,  33 to the second compressed-air switching valve 22, 22’, 32 and / or the third compressed-air switching valve 23, 23’, 33, the first compressed-air switching valve 21, 21’, 31 being controlled to be closed. By opening and closing the compressed-air switching valves 21, 22, 23 / 21’, 22’, 23’ / 31, 32, 33, the pressure p2-ACTUAL / p2’-ACTUAL / p3-ACTUAL is adjusted to the pressure p2-TARGET / p2’-TARGET / p3-TARGET by compressed air being either added or discharged or sucked out via the compressed-air switching valves 21, 22, 23 / 21’, 22’, 23’ / 31, 32, 33. For controlling the pressure p4 of the chamber P4 (transmission chamber), the control program of the electronic control provides the steps defining and storing a pressure offset Ap4-ADDITION (Ap4-ADD); calculating and storing a pressure p4-TARGET according to the formula p4-TARGET = P3-ACTUAL + Ap4-ADDITION; defining and storing the differential pressure ApL3-CONTROL, wherein a checking step is preferably provided that ApL3-CONTROL is smaller than or equal to the differential pressure ApL3 of the seal L3; receiving and storing the pressure p4-ACTUAL and calculating the pressure difference Ap4 between p4-TARGET and p4-ACTUAL, and checking whether the pressure difference Ap4 is in a range x < 0 < y, wherein x represents a lower interval boundary and y represents an upper interval boundary. The control of the compressed-air switching valves 41, 42, 43 for controlling the pressure p4-ACTUAL in the chamber P4 takes place in this case after the following steps: If Ap4 is in a range x < 0 < y, the first compressed-air switching valve 41 and the second compressed-air switching valve 42 and, if appropriate, also the third compressed-air switching valve 43 are controlled by the controller in such a way that they are closed. If Ap4 > y, the control command output unit of the controller 80 outputs a signal for opening the first compressed-air switching valve 41 to the first compressed-air switching valve 41, and the second compressed-air switching valve 42 and / or the third compressed-air switching valve 43 are controlled to be closed. If Ap4<x, the  control command output unit of the controller 80 outputs a signal for opening the second compressed-air  switching  valve  42 and / or  the  third compressed-air  switching  valve 43 to  the  second compressed-air  switching  valve  42 and / or  the  third compressed-air  switching  valve 43, and  the  first compressed-air switching valve 41 is controlled so as to be closed. By opening and closing the compressed-air switching valves 41, 42, 43, the pressure p4-ACTUAL is adjusted to the pressure p4-TARGET by either adding or discharging or respectively extracting compressed air via the compressed-air switching valves 41, 42, 43. The pressure release from a chamber P2 to P4 is preferably effected via the second compressed-air switching valve 22, 22’, 32, 42 via the compressed air release line 92 and the sound damper 96 and / or via the third compressed-air switching valves 23, 23’, 33, 43 and the air suction line 93 and the vacuum pump 95. If the calculation for a target pressure indicates that it is less than or equal to atmospheric pressure, atmospheric pressure can be applied to the corresponding chamber by having the control unit 80 open the second pneumatic control valve 22,  22’,  32, 42, thereby allowing atmospheric pressure to be established in the corresponding chamber via the compressed air exhaust line 92 without the need for further control. The method according to the invention for pressure control is preferably carried out according to the previously described steps of the control program. Alternatively, a pressure that is less than the atmospheric pressure can also be set in the corresponding chamber. For this purpose, the second compressed-air switching valve 22,  22’,  32,  42 then remains closed and the controller 80 controls the vacuum pump 95 in order to set the actual pressure to a pressure less than the atmospheric pressure via the air suction line 93 after opening the respective third compressed-air switching valve 23, 23’, 33, 43 in the corresponding chamber P2 to P4. The TARGET pressure is set or calculated to a necessary value of low atmospheric pressure. Alternatively, the pressures in the chambers P2 to P4 can also be controlled with regard to this by opening the first compressed-air switching valve 21, 21’, 31, 41 by the controller 80 and likewise opening the second compressed-air switching valve 22, 22’, 32, 42 and / or the third compressed-air switching valve 23, 23’, 33, 43. The throttles 213, 223, 233, 213’, 223’, 233’, 313, 323, 333, 413, 423, 433 of the compressed-air switching valves 21, 21’, 31, 41, 22, 22’, 32, 42, 23, 23’, 33, 43 are then adjusted in such a way that, in order to maintain the actual pressure in the respective chamber P2-P4, exactly the same amount of compressed air flows into the respective chamber P2-P4 via the first compressed-air switching valve 21, 21’, 31, 41 as flows out via the second compressed-air switching valve 22, 22’, 32, 42 and / or the third compressed-air switching valve 23, 23’, 33, 43. If the reference pressure pREF then changes, either compressed-air switching valves are briefly opened or closed in order to correspondingly change the ACTUAL pressure or the setting of the throttles is correspondingly changed, so that, in order to increase the ACTUAL pressure in the chamber, more compressed air flows into the chamber via the first compressed-air switching valve 21, 21’, 31, 41 than flows out via the second compressed-air switching valve 22,  22’,  32,  42 and / or the third compressed-air switching valve 23, 23’, 33, 43, or in order to reduce the ACTUAL pressure in the chamber, less compressed air flows into the chamber via the first compressed-air switching valve 21,  21’,  31,  41 than flows out via the second compressed-air switching valve 22, 22’, 32, 42 and / or the third compressed-air switching valve 23, 23’, 33, 43. The setting of the throttles for increasing / decreasing the pressure is correspondingly maintained until the actual pressure of the respective chamber reaches the TARGET pressure. It is also possible to control the pressures in the respective chambers of a seal system via a combination via the control valves or the throttles. Figures 3-6 show different pressure profiles across the chambers P1 to P4 and the seals of the seal system located therebetween. In this case, the respective prevailing pressure is plotted on the y-axis and the respective chamber and seal on the x-axis. The x-axis itself has the atmospheric pressure value represented as P-ATMOS. Figure 3 shows a pressure curve in which all chambers P1-P4 are correspondingly pressurized in order to provide a pressure equilibrium and generate a counterpressure for the pressure p0 prevailing in the space P0. First, Api is added to the pressure p0, so that a higher pressure value p1 is obtained. A pressure difference ApLi-ST in the seal Li is removed therefrom, so that a pressure p2 is established in the chamber P2 by the control. In the seal L2 between the chambers P2 and P2’, the pressure difference ApL2-ST is then removed, so that the pressure p2’ must be established in order to provide the equilibrium in the chamber P2’. Since the pressure reduction ApL2’-ST in the seal L2’ is not sufficient to not pressurize the chamber P3, the pressure p3 greater than the atmospheric pressure must be provided in the chamber P3. In order to increase the sealing effect of the seal L3 and to reduce the risk of the seal L3 being opened, the pressure p4 in the chamber P4 is preferably increased by Ap4-ADDITION. The procedure is also correspondingly followed in figure 4. Here, however, P0 is smaller than in figure 3, so that it is possible to set the chamber P2’ to atmospheric pressure via Api-ST and Ap2-ST. In figure 4, the pressure in P3 is then also set to atmospheric pressure. The sealing action of the seal L2’ of about 0.2 bar with which the lip seal L2’ presses on the shaft is sufficient here to prevent the seal L2’ from opening and oil from the chamber P2’ from emerging into the chamber P3. In order to prevent the seal L3 from opening and transmission oil from the chamber P4-ADDITION being transferred into the chamber P3, an Ap4 is again preferably added to the pressure p3 in chamber P3 in order to set the pressure p4 in chamber P4. The pressure difference Ap4-ADDITION must be smaller than the pressure difference ApL3 acceptable by the seal L3. Figure 5 shows the same pressure curve as figure 4 up to chamber P2’, To increase the sealing effect of seal L2’ relative to chamber P3, a pressure below atmospheric pressure is set in chamber P3 via vacuum pump 95 and third compressed-air switching valve 33. The pressure difference between the pressure p2’ and the pressure p3 must be smaller than the ApL2’ of the seal L2’. The pressure p4 is again increased with an Ap4-ADDITION compared to the set pressure p3. An overpressure in P4 is shown here. Alternatively, the atmospheric pressure can also be present in the chamber P4 here. Figure 6 shows a pressure profile in which the differential pressure of the lip seal ApL1 is already sufficient to provide a sufficient counterpressure against P0. In this case, the chambers P2 to P4 could all be pressurized with atmospheric pressure. However, it has been found, as in figure 6, that the sealing effect of the lip seals L1-L3 is improved accordingly if a negative pressure < atmospheric pressure is provided in the chambers P2-P3, and therefore the seals L1-L3 are sucked up to the shaft for enhancing the sealing effect with respect to the shaft. A corresponding negative pressure with respect to atmospheric pressure is shown in figure 6 in the chambers P2,  P2’ and P3. Values permanently set for this are preferably stored in the controller 80. P4 may then be again added with an offset and set to either atmospheric or positive or negative pressure with respect to atmospheric pressure. From the standpoint of control, atmospheric pressure is preferred here, since only the compressed-air switching valve 42 has to be opened for this purpose and no further control by opening and closing compressed-air switching valves has to take place. During the control, certain maximum conditions and minimum conditions have to be maintained for the pressures of the individual chambers P1 to P4. The maximum pressure in P1 is set by the pressure offset Ap1. A higher pressure by pressing in the blocking grease HBW is possible, but may not be expedient. The minimum pressure in P1 is to be used as the pressure p0 of the space P0. If the pressure in chamber P1 is less than p0, there is the risk that foreign objects will enter the seal from space P0. In order that the seal L1 does not open due to the pressure in P2, the maximum pressure p2 in the chamber P2 may be the ACTUAL pressure in P1. The minimum pressure in P2 must not be less than the actual pressure in P1 minus the pressure difference ApL1 of the seal L1. If p2-TARGET is equal to p1-ACTUAL-ApL1-ST is less than or equal to atmospheric pressure, either atmospheric pressure or negative pressure can be set in P2. In order to prevent the seal L2 from opening between P2 and chamber P2’, the maximum pressure P2’ must be equal to the pressure P2-ACTUAL. Here again, the minimum pressure P2’ is P2-ApPL2 to prevent the seal L2 from failing. If the pressure in P2’ = P2-ACTUAL - ApL2 is equal to or lower than the atmospheric pressure, the pressure P2’ -TARGET may be set to the atmospheric pressure or a negative pressure. 10 The maximum actual pressure p3 must not exceed the pressure p2-ACTUAL or p4-ACTUAL in order to prevent the seals L2’ or L3 from opening. In order to avoid failure of the seals, p3-ACTUAL must not be smaller than the difference between p2’-ACTUAL-ApL2’ or p4-ACTUAL-ApL3. According to the above-mentioned conditions, the pressure p3 may be set as an atmosphere or a negative pressure. The same applies analogously to p4. Overall, pressures must be set in the chambers which, together with the differential pressures of the seals, are capable of equilibrium with p0.

Claims

1. A main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine havingat least one space (P0) with a first pressure (p0) behind the cutting wheel, having at least one first chamber (P1) with a first pressure (p1), wherein preferably the first chamber (P1) is a labyrinth chamber filled with a blocking grease (HBW),at least one second chamber (P2) with a second pressure (p2), wherein the at least one second chamber (P2) is an oil and compressed-air sealing chamber (P2),at least one seal (L1) between the at least one first chamber (P1) and the at least one second chamber (P2), which can withstand a differential pressure ApL1 between the at least one first chamber (P1) and the at least one second chamber (P2),at least one compressed-air input connection (70),at least one compressed-air discharge line (92, 93),at least one first compressed-air switching valve (21) of the at least one second chamber (P2) having at least one compressed-air inlet (211) and at least one compressed-air outlet (212), wherein the first compressed-air switching valve (21) of the at least one second chamber (P2) is configured to be switchable between an open and a closed position,at least one second compressed-air switching valve (22, 23) of the at least one second chamber (P2) having at least one compressed-air inlet (221, 231) and at least one compressed-air outlet (222, 232), wherein the second compressed-air switching valve (22, 23) of the at least one second chamber (P2) is configured to be switchable between an open and a closed position,at least one inlet (71) of the compressed-air input connection (70) configured to be pneumatically connectable to a compressed-air source (100),at least one outlet (72) of the compressed-air input connection (70) pneumatically connected via a compressed-air line (91) to the at least one compressed-air inlet (211) of the first compressed-air switching valve (21) of the at least one second chamber (P2), wherein the at least one compressed-air outlet (212) of the first compressed-air switching valve (21) of the at least one second chamber (P2) is pneumatically connected to the at least one compressed-air inlet (221,  231) of the second compressed-airswitching valve (22,  23) of the at least one secondchamber (P2) and the at least one second chamber (P2), and wherein a compressed-air outlet (222, 232) of the second compressed-air switching valve (22, 22, 23) of the at least one second chamber (P2) is pneumatically connected to the compressed-air discharge line (92, 93), characterized in that at least one electronic controller (80) is provided, which has at least one data storage unit, at least one data processing unit and at least one control command output unit,in that at least one control circuit based on the at least one electronic controller (80) is provided for controlling the second pressure (p2) in the at least one second chamber (P2),in that at least one first pressure detection device (4, 14) is connected to the at least one space (P0) or the at least one first chamber (P1) in order to measure the pressure (p0) in the space or the current pressure (p1-ACTUAL) in the at least one first chamber (P1), wherein the at least one first pressure detection device (4) is electronically connected to the at least one electronic controller (80) for transmitting the pressure,in that at least one second pressure detection device (24) is connected to the at least one second chamber (P2) in order to measure the current pressure (p2-ACTUAL) in the at least one second chamber (P2),wherein the at least one second pressure detection device (24) is electronically connected to the at least one electronic controller (80) for transmitting the pressure,in that the at least one first compressed-air switching valve (21) of the at least one second chamber (P2) is connected to the at least one control device (80), so that the at least one first compressed-air switching valve (21) of the at least one second chamber (P2) is electrically switchable by the control device (80),in that the at least one second compressed-air switching valve (22, 23) of the at least one second chamber (P2) is connected to the at least one control device (80), so that the at least one second compressed-air switching valve (22, 23) of the at least one second chamber (P2) is electrically switchable by the control device (80), andin that the electronic control (80) has a control program with the following steps:receiving and storing the pressure p0 and / or the pressure p1-ACTUAL;defining and storing the differential pressure ApL1-CONTROL (ApL1-ST), wherein a checking step is preferably provided that the ApL1-CONTROL (ApL1-ST) is smaller than or equal to the differential pressure ApL1;defining and storing a pressure offset Ap1 and calculating a pressure p1-TARGET according to the formula p1-TARGET = p0 + Ap1, wherein a checking step is preferably provided that p1-TARGET is greater than p0,defining a reference pressure pREF, wherein pREF is one of the following pressures: p0 + Ap1 or p1-ACTUAL,receiving and storing the pressure p2-ACTUAL of the second chamber (P2),calculating and storing a pressure p2-TARGET according to the formula p2-TARGET = pREF-ApL1-CONTROL, wherein a checking step is provided to check that p2-TARGET lies in a range between pREF and pREF-ApL1, calculating and storing a pressure difference Ap2 between p2-TARGET and p2-ACTUAL; andchecking whether Ap2 is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit,wherein if Ap2 is in the range x < 0 < y, the first compressed-air switching valve (21) of the at least one second chamber (P2) and the second compressed-air switching valve (22, 23) of the at least one second chamber (P2) are controlled by the controller such that the first compressed-air switching valve (21) and the second compressed-air switching valve (22, 23) are closed,wherein if Ap2 > y, the control command output unit sends a signal for opening the first compressed-air switching valve (21) of the at least one second chamber (P2) to the first compressed-air switching valve (21) of the at least one second chamber (P2), wherein the second compressed-air switching valve (22, 23) of the at least one second chamber (P2) is controlled so as to be closed, andwherein if Ap2<x, the control command output unit sends a signal for opening the second compressed-air switching valve (22,  23) of the at least one secondchamber (P2) to the second compressed-air switching valve (22, 23) of the at least one second chamber (P2), wherein the first compressed-air switching valve (21) of the at least one second chamber (P2) is controlled so as to be closed.

2. The main drive seal system for a tunnel boring machine as claimed in claim 1, characterized in that at least one further second chamber (P2’) is provided with a further second pressure (p2’) following the at least 64one second chamber (P2), wherein the at least one further second chamber (P2’) is an oil and compressed-air sealing chamber (P2’),in that at least one seal (L2) is provided between the at least one second chamber (P2) and the at least one further second chamber (P2’), which can resist a differential pressure ApL2 between the at least one second chamber (P2) and the at least one further second chamber (P2’),in that at least one first compressed-air switching valve (21’) of the at least one further second chamber (P2’) is provided with at least one compressed-air inlet (211’) and at least one compressed-air outlet (212’), wherein the first compressed-air switching valve (21’) of the at least one further second chamber (P2’) is designed such that it can be switched between an open and a closed position,in that at least one second compressed-air switching valve (22’, 23’) of the at least one further second chamber (P2’) is provided with at least one compressed-air inlet (221’, 231’) and at least one compressed-air outlet (222’, 232’), wherein the second compressed-air switching valve (22’, 23’) of the at least one further second chamber (P2’) is designed such that it can be switched between an open and a closed position,in that at least one control circuit based on the at least one electronic controller (80) for controlling the further second pressure (p2’) is provided in the at least one further second chamber (P2’),in that at least one further second pressure detection device (24’) being connected to the at least one further second chamber (P2’) in order to measure the current pressure (p2’-ACTUAL) in the at least one second chamber (P2’), wherein the at least one further second pressure detection device (24’) iselectronically connected to the at least one electronic controller (80) for transmitting the pressure,in that the at least one first compressed-air switching valve (21’) of the at least one further second chamber (P2’) is connected to the at least one control device (80), so that the at least one first compressed-air switching valve (21’) of the at least one further second chamber (P2’) is electrically switchable by the control device (80), that the at least one second compressed-air switching valve (22’, 23’) of the at least one further second chamber (P2’) is connected to the at least one control device (80), so that the at least one second compressed-air switching valve (22’, 23’) of the at least one further second chamber (P2’) is electrically switchable by the control device (80),in that the at least one outlet (72) of the compressed-air input connection (70), which is pneumatically connected via a compressed-air line (91) to the at least one compressed-air inlet (211’) of the first compressed-air switching valve (21’) of the at least one further second chamber (P2’), wherein the at least one compressed-air outlet (212’) of the first compressed-air switching valve (21’) of the at least one further second chamber (P2’) is pneumatically connected to the at least one compressed-air inlet (221’,  231’)  of the second compressed-air switchingvalve (22’,  23’) of the at least one further secondchamber (P2’) and the at least one further second chamber (P2’), and wherein a compressed-air outlet (222’,  232’) of the second compressed-air switchingvalve (22’,  23’) of the at least one further secondchamber (P2’) is pneumatically connected to the compressed-air discharge line (92, 93), andin that the control program of the electronic controller (80) comprises the further steps of:defining and storing the differential pressure ApL2-CONTROL, wherein a checking step is provided tocheck that the ApL2-CONTROL is smaller than or equal to the differential pressure ApL2;receiving and storing the pressure p2’-ACTUAL of the further second chamber (P2’),calculating and storing a pressure p2’-TARGET according to the formula p2’-TARGET = p2-ACTUAL - ApL2-CONTROL or according to the formula p2’-TARGET = pREF -ApL1-CONTROL - ApL2-CONTROL, wherein a checking step is provided to check that p2’-TARGET lies in a range between p2-ACTUAL and p2-ACTUAL - ApL2,calculating and storing a pressure difference Ap2’ between p2’-TARGET and p2’-ACTUAL, andchecking whether Ap2’ is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit,wherein, if Ap2’ is in the range x < 0 < y, the first compressed-air switching valve (21’) of the at least one further second chamber (P2’) and the second compressed-air switching valve (22’, 23’) of the at least one further second chamber (P2’) are controlled to be closed,wherein, if Ap2’ > y, the control command output unit sends a signal for opening the first compressed-air switching valve (21’) of the at least one further second chamber (P2’) to the first compressed-air switching valve (21’) of the at least one further second chamber (P2’), wherein the second compressed-air switching valve (22’, 23’) of the at least one further second chamber (P2’) is controlled so as to be closed, andwherein, if Ap2’ < x, the control command output unit sends a signal for opening the second compressed-air switching valve (22’,  23’)  of  the  at  least onefurther second chamber (P2’) to the second compressed-air switching valve (22’,  23’)  of  the  at  least onefurther second chamber (P2’), wherein the first compressed-air switching valve  (21’) of the at leastone further second chamber (P2’) is controlled so as tobe closed.

3. The main drive seal system for a tunnel boring machine as claimed in claim 1 or 2, characterized in that at least one third chamber (P3) with a third pressure (p3) is provided following the at least one second chamber (P2) or the at least one further second chamber (P2’), wherein the at least one third chamber (P3) is a leak detection chamber (P3),in that at least one seal (L2) is provided between the at least one second chamber (P2) or that at least one seal (L2’) is provided between the at least one further second chamber (P2’) and the at least one third chamber (P3), which can resist a differential pressure ApL2 between the at least one second chamber (P2) or a differential pressure ApL2’ of the at least one further second chamber (P2’) and the at least one third chamber (P3),in that at least one first compressed-air switching valve (31) of the at least one third chamber (P3) is provided with at least one compressed-air inlet (311) and at least one compressed-air outlet (312), wherein the first compressed-air switching valve (31) of the at least one third chamber (P3) is configured such that it can be switched between an open and a closed position,in that at least one second compressed-air switching valve (32, 33) of the at least one third chamber (P3) is provided with at least one compressed-air inlet (321, 331) and at least one compressed-air outlet (322, 323), wherein the second compressed-air switching valve (32, 33) of the at least one third chamber (P3) is configured such that it can be switched between an open and a closed position,in that at least one control circuit based on the at least one electronic controller (80) is provided forcontrolling the third pressure (p3) in the at least one third chamber (P3),in that at least one third pressure detection device (34) is connected to the at least one third chamber (P3) in order to measure the current pressure (p3-ACTUAL) in the at least one third chamber (P3), wherein the at least one third pressure detection device (34) is electronically connected to the at least one electronic controller (80) for transmitting the pressure,in that the at least one first compressed-air switching valve (31) of the at least one third chamber (P3) is connected to the at least one control device (80), so that the at least one first compressed-air switching valve (31) can be electrically switched by the control device (80), that the at least one second compressed-air switching valve (32, 33) of the at least one third chamber (P3) is connected to the at least one control device (80), so that the at least one second compressed-air switching valve (32, 33) of the at least one third chamber (P3) can be electrically switched by the control device (80),in that the at least one outlet (72) of the compressed-air input connection (70), which outlet is pneumatically connected via a compressed-air line (91) to the at least one compressed-air inlet (311) of the first compressed-air switching valve (31) of the at least one third chamber (P3), wherein the at least one compressed-air outlet (312) of the first compressed-air switching valve (31) of the at least one third chamber (P3) is connected to the at least one compressed-air inlet (321, 331) of the second compressed-air switching valve (32, 33) of the at least one third chamber (P3) and the at least one third chamber (P3) are pneumatically connected, and wherein an outlet (322, 332) of the second compressed-air switching valve (32, 33) of the at least one third chamber (P3) ispneumatically connected to the compressed-air discharge line (92, 93), andin that the control program of the electronic controller (80) comprises the following steps:defining and storing the differential pressure ApL2-CONTROL or the differential pressure ApL2’-CONTROL, wherein a checking step is provided to check that the differential pressure ApL2-CONTROL is smaller than or equal to the differential pressure ApL2 or that or the differential pressure ApL2’-CONTROL is smaller than or equal to the differential pressure ApL2’;receiving and storing the pressure p3-ACTUAL of the third chamber (P3),calculating and storing a pressure p3-TARGET according to the formula p3-TARGET = (p2-ACTUAL or p2’-ACTUAL)-(ApL2-CONTROL or ApL2’-CONTROL) or according to the formula p3-TARGET = pREF-ApL1-CONTROL-ApL2-CONTROL-ApL2’-CONTROL, wherein a checking step is provided in each case that p3-TARGET lies in a range between p2-ACTUAL and p2-ACTUAL-ApL2 or between p2’-ACTUAL and p2’-ACTUAL-ApL2,calculating and storing a pressure difference Ap3 between p3-TARGET and p3-ACTUAL, andchecking whether Ap3 is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit,wherein if Ap3 is in the range x < 0 < y, the first compressed-air switching valve (31) of the at least one third chamber (P3) and the second compressed-air switching valve (32, 33) of the at least one third chamber (P3) are controlled to be closed,wherein if Ap3 > y, the control command output unit sends a signal for opening the first compressed-air switching valve (31) of the at least one third chamber (P3) to the first compressed-air switching valve (31) of the at least one third chamber (P3), wherein the second compressed-air switching valve (32, 33) of theat least one third chamber (P3) is controlled so as to be closed, andwherein if Ap3 < x, the control command output unit transmits a signal for opening the second compressed-air switching valve (32, 33) of the at least one third chamber (P3) to the second compressed-air switching valve (32, 33) of the at least one third chamber (P3), wherein the first compressed-air switching valve (31) of the at least one third chamber (P3) is controlled so as to be closed.

4. The main drive seal system for a tunnel boring machine as claimed in claim 3, characterized in that at least one fourth chamber (P4) with a fourth pressure (p4) is provided following the at least one third chamber (P3), wherein the at least one fourth chamber (P4) is a transmission chamber (P4),in that at least one seal (L3) is provided between the at least one third chamber (P3) and the at least one fourth chamber (P4), which seal can resist a differential pressure ApL3 between the at least one third chamber (P3) and that of the at least one fourth chamber (P4),in that at least one first compressed-air switching valve (41) of the at least one fourth chamber (P4) is provided with at least one compressed-air inlet (411) and at least one compressed-air outlet (412), wherein the first compressed-air switching valve (41) of the at least one fourth chamber (P4) is configured such that it can be switched between an open and a closed position,in that at least one second compressed-air switching valve (42,  43) of the at least one fourthchamber (P4) is provided with at least one compressed-air inlet (421, 431) and at least one compressed-air outlet (422,  423), wherein the second compressed-airswitching valve (42, 43) of the at least one fourthchamber (P4) is configured such that it can be switched between an open and a closed position,in that at least one control circuit based on the at least one electronic controller (80) is provided for controlling the fourth pressure (p4) in the at least one fourth chamber (P4),in that at least one third pressure detection device (44) is connected to the at least one fourth chamber (P4), in order to measure the current pressure (p4-ACTUAL) in the at least one third chamber (P4), wherein the at least one fourth pressure detection device (44) is electronically connected to the at least one electronic controller (80) for transmitting the pressure,in that the at least one first compressed-air switching valve (41) of the at least one fourth chamber (P4) is connected to the at least one control device (80), so that the at least one first compressed-air switching valve (41) of the at least one fourth chamber (P4) is electrically switchable by the control device (80), that the at least one second compressed-air switching valve (42, 43) of the at least one fourth chamber (P4) is connected to the at least one control device (80), so that the at least one second compressed-air switching valve (42, 43) of the at least one fourth chamber (P4) is electrically switchable by the control device (80),in that the at least one outlet (72) of the compressed-air input connection (70) is pneumatically connected via a compressed-air line (91) to the at least one compressed-air inlet (411) of the first compressed-air switching valve (41) of the at least one fourth chamber (P4), wherein the at least one compressed-air outlet (412) of the first compressed-air switching valve (41) of the at least one fourth chamber (P4) is pneumatically connected to the at least one compressed-air inlet (421, 431) of the second compressed-air switching valve (42, 43) of the at leastone fourth chamber (P4) and the at least one fourth chamber (P4), and wherein an outlet (422, 432) of the second compressed-air switching valve (42, 43) of the at least one fourth chamber (P4) is pneumatically connected to the compressed-air discharge line (92, 93), andin that the control program of the electronic controller (80) has the further following steps:defining and storing a pressure offset Ap4-ADDITION (Ap4-ZU), calculating and storing a pressure p4-TARGET according to the formula p4-TARGET = p3-ACTUAL + Ap4-ADDITION (Ap4-ZU), defining and storing the differential pressure ApL3-CONTROL, wherein a checking step is provided to check that the ApL3-CONTROL is smaller than or equal to the differential pressure ApL3;receiving and storing the pressure p4-ACTUAL of the fourth chamber (P4),calculating and storing a pressure difference Ap4 between p4-TARGET and p4-ACTUAL, and checking whether Ap4 is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit,wherein if Ap4 is in the range x < 0 < y, the first compressed-air switching valve (41) of the at least one fourth chamber (P4) and the second compressed-air switching valve (42, 43) of the at least one fourth chamber (P4) are controlled to be closed, wherein if Ap4 > y, the control command output unit sends a signal for opening the first compressed-air switching valve (41) of the at least one fourth chamber (P4) to the first compressed-air switching valve (41) of the at least one fourth chamber (P4), wherein the second compressed-air switching valve (42, 43) of the at least one fourth chamber (P4) is controlled so as to be closed, andwherein, if Ap4 < x, the control command output unit transmits a signal for opening the secondcompressed-air switching valve (42, 43) of the at least one fourth chamber (P4) to the second compressed-air switching valve (42, 43) of the at least one fourth chamber (P4), the first compressed-air switching valve (41) of the at least one fourth chamber (P4) is controlled so as to be closed.

5. The main drive seal system for a tunnel boring machine as claimed in one of claims 1 to 4, characterized in that the at least one compressed-air outlet (222, 232, 222’, 232’, 322, 332, 422, 432) of the second compressed-air switching valve (22, 23, 22’, 23’, 32, 33, 42, 43) of the at least one second chamber (P2), of the at least one further second chamber (P2’), of the at least one third chamber (P3) and / or of the at least one fourth chamber (P4) is pneumatically connected to the compressed-air discharge line (92), which is preferably connected to the environment via a sound damper (96), and / or is pneumatically connected to an air suction line (93), which is connected to a vacuum pump (95), wherein preferably the vacuum pump (95) is controllable via the controller (80).

6. The main drive seal system for a tunnel boring machine as claimed in one of claims 1 to 5, characterized in that at least one of the chambers (P2, P2’, P3, P4) is connected to at least one third compressed-air switching valve (23, 23’, 33, 43), which is pneumatically connected by its compressed-air outlet (232, 232’, 332, 432) to an air suction line (93), which is connected to a vacuum pump (95), so that a pressure lower than the atmospheric pressure can be set in the connected chamber, wherein preferably the vacuum pump (95) can be controlled via the controller (80).

7. The main drive seal system for a tunnel boring machine as claimed in one of claims 1 to 6, characterized in that a series of the target pressuresof the chambers (P1, P2, P2’, P3, P4) is stored in the controller (80): p0 < pl-TARGET >p2-TARGET >p2’-TARGET > p3-TARGET ^ p4-TARGET, wherein the further second chamber (P2’) and its pressure p2’-TARGET can be omitted.

8. The main drive seal system for a tunnel boring machine as claimed in one of claims 1 to 7, characterized in that, if the target pressure of low atmospheric pressure is calculated in at least one of the chambers (P2, P2’, P3, P4), the target pressure is set in the controller to 1 bar or to a defined value between 0 bar and atmospheric pressure, which can then be adjusted by the controller (80), the air suction line (93) and the vacuum pump (95) via the switching of the third compressed-air switching valve (23, 23’, 33, 43) of the respective chamber (P2, P2’, P3, P4), wherein preferably the vacuum pump (95) can be controlled via the controller (80).

9. The main drive seal system for a tunnel boring machine as claimed in one of claims 1 to 8, characterized In that, if p0 + Ap1 is smaller than ApL1-CONTROL, the target pressures of the chambers (P2, P2’,  P3,  P4) in the controller (80) are set toatmospheric pressure or at least one of the target pressures (p2-TARGET, p2’-TARGET, p3-TARGET, p4-TARGET) of the chambers (P2, P2’, P3, P4) in the controller (80) is set to a defined value between 0 bar and atmospheric pressure, which is then set by the controller (80) via the switching of the third compressed-air switching valve (23, 23’, 33, 43) of the respective chamber (P2, P2’, P3, P4), the air suction line (93) and the vacuum pump (95) can be adjusted, wherein the vacuum pump (95) can preferably be controlled via the controller (80).

10. The main drive seal system for a tunnel boring machine as claimed in one of claims 1 to 9, characterized in that for at least one of the chambers (P2, P2’, P4) a circulation pump (25, 25’, 45) for the oil located in the chamber is provided, which is connected via at least one line (26,   26’,   46)fluidically to at least one suction point (27, 27’, 47) of the chamber (P2, P2’, P4) for suctioning the oil from the chamber (P2, P2’, P4) and via at least one further line (28, 28’, 48) fluidically to at least one introduction point (29,  29’,  49) of the chamber (P2,P2’, P4) for introducing the oil into the chamber (P2, P2’, P4).

11. The main drive seal system for a tunnel boring machine as claimed in one of claims 6 to 10, characterized in that the air suction line (93) is connected to at least one vacuum reservoir (97), which is preferably connected to a pressure detection device (94).

12. A method for controlling the pressure in a main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine having at least one space (P0) with a first pressure (p0) behind the cutting wheel of the tunnel boring machine, in particular as claimed in one of claims 1 to 11, wherein the space (P0) is connected to a pressure detection device (4), and wherein the main drive seal system has the following features:at least one first chamber (P1) with a first pressure (p1),  wherein  the first  chamber  (P1)  ispreferably a labyrinth chamber filled with a blocking grease (HBW),  wherein  the first  chamber  (P1)  isconnected to a pressure detection device (4),at least one second chamber (P2) with a second pressure (p2), wherein the at least one second chamber (P2) is an oil and compressed-air sealing chamber (P2),wherein the second chamber (P2) is connected to a pressure detection device (24),preferably at least one further second chamber (P2’) with a further second pressure (p2’), wherein the at least one further second chamber (P2’) is an oil and compressed-air sealing chamber (P2’), wherein the further second chamber (P2’) is connected to a pressure detection device (24’),at least one third chamber (P3) with a third pressure (p3), wherein the at least one third chamber (P3) is a leak detection chamber (P3), wherein the third chamber (P3) is connected to a pressure detection device (34),at least one fourth chamber (P4) with a fourth pressure (p4), wherein the at least one fourth chamber (P4) is a transmission chamber (P4), wherein the fourth chamber (P4) is connected to a pressure detection device (44),at least one lip seal (L1, L2, L2’, L3) between the chambers (P1, P2, P2’, P3, P4), each of which is able to resist a differential pressure (ApL1, ApL2, ApL2’, ApL3) between the adjacent chambers, andat least one electronic controller (80), which has at least one data storage unit, at least one data processing unit and at least one control command output unit, wherein at least one program for providing a control loop for the pressure (p2-ACTUAL, p2’-ACTUAL, p3-ACTUAL, p4-ACTUAL) to be controlled is executed in the controller, having the method steps:measuring, receiving and storing the pressure p0 and / or the pressure p1-ACTUAL,defining and storing a pressure offset Ap1 and calculating a pressure p1-TARGET according to the formula p1-TARGET = p0 + Ap1, wherein preferably a checking step is provided to check that p1-TARGET is greater than p0,calculating a reference pressure (pREF), wherein the reference pressure is the pressure p0 in the firstspace (P0) + pressurization Ap1 or the pressure (p1-ACTUAL) in the first chamber (P1),measuring and receiving at least one actual pressure to be regulated (p2-ACTUAL, p2’-ACTUAL, p3-ACTUAL, p4-ACTUAL);defining a differential pressure of at least one lip seal (ApL1-CONTROL, ApL2-CONTROL, ApL2’-CONTROL, ApL3-CONTROL),defining and storing a pressure supplement (Ap4-ADDITION) between the third and fourth chambers (P3, P4),calculating a target pressure (p2-TARGET, p2’-TARGET, p3-TARGET, p4-TARGET) with at least one of the following formulae:

1. p2-TARGET = pREF-ApLl-CONTROL 2. p2’-TARGET = p2-ACTUAL-ApL2-CONTROL or p2’-TARGET = pREF-ApL1-CONTROL-ApL2-CONTROL, 3. p3-TARGET = (p2-ACTUAL or p2’-ACTUAL)-(ApL2-CONTROL or ApL2’-CONTROL) or p3-TARGET = pREF-ApL1-CONTROL-ApL2-CONTROL-ApL2’-CONTROL, and 4. p4-TARGET = p3-ACTUAL + Ap4-ADDITION or p4-TARGET =    pREF-ApL1-CONTROL-ApL2-CONTROL-ApL2’-CONTROL + Ap4-ADDITION,calculating a pressure difference Api between pi-TARGET and pi-ACTUAL, wherein i is the number of the chamber of which the ACTUAL pressure is controlled, and checking whether Api is in a range x < 0 < y, wherein x, y are a lower interval limit and an upper interval limit,wherein if Api is in the range x < 0 < y, the first compressed-air switching valve (21, 21’, 31, 41) of the at least one chamber i (P2, P2’, P3, P4) and the second compressed-air switching valve (22,  23,  22’,23’, 32, 33, 42, 43) of the at least one chamber i (P2, P2’, P3, P4)  are controlled to be closed, wherein ifApi > y, the first compressed-air switching valve (21, 21’,  31,  31,  41)  of the at least one chamber i (P2,P2’, P3, P4) is controlled so as to be open, the second compressed-air switching valve (22, 23, 22’, 23’, 32, 33, 42, 43) of the at least one chamber i (P2, P2’, P3, 78P4) is controlled so as to be closed, and if Api<x, the second compressed-air switching valve (22, 23, 22’, 23’, 32, 33, 42, 43) of the at least one chamber i (P2, P2’, P3, P4) is controlled so as to be open, the first compressed-air switching valve (21, 21’, 31, 41) of the at least one chamber i (P2, P2’, P3, P4) is controlled so as to be closed.

13. The main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine, havingat least one first chamber (P1), wherein the first chamber (P1) is preferably a labyrinth chamber filled with a blocking grease (HBW),at least one second chamber (P2), wherein the at least one second chamber (P2) is an oil and compressed-air sealing chamber (P2),at least one seal (L1) between the at least one first chamber (P1) and the at least one second chamber (P2),preferably at least one further second chamber (P2’) adjoining the at least one second chamber (P2), wherein the at least one further second chamber (P2’) is an oil and compressed-air sealing chamber (P2’),at least one third chamber (P3) is provided adjoining the at least one second chamber (P2) or the at least one further second chamber (P2’), wherein the at least one third chamber (P3) is a leak detection chamber (P3),at least one seal (L2) is provided between the at least one second chamber (P2) or the at least one further second chamber (P2’) and the at least one third chamber (P3),at least one fourth chamber (P4) is provided adjoining the at least one third chamber (P3), wherein the at least one fourth chamber (P4) is a transmission chamber (P4),at least one seal (L3) is provided between the at least one third chamber (P3) and the at least one fourth chamber (P4),characterized in that for at least one of the second, further second, third and / or fourth chambers (P2, P2’, P4), a circulation pump (25, 25’, 45) for the oil located in the chamber is connected, and that the connection is provided via at least one line (26, 26’, 46) fluidically with at least one suction point (27, 27’, 47) of the chamber (P2, P2’, P4) for suctioning the oil from the chamber (P2, P2’, P4) and via at least one further line (28, 28’, 48) fluidically with at least one introduction point (29,  29’,  49) of thechamber (P2, P2’, P4) for introducing the oil into the chamber (P2, P2’, P4).

14. The main drive seal system for a tunnel boring machine as claimed in claim 13, characterized in that a filter for filtering the oil and / or a separator for separating solids or liquids is provided in front of or behind the circulation pump (25, 25’, 45).

15. The main drive seal system for a drive shaft of a cutting wheel of a tunnel boring machine having at least one space (P0) with a first pressure (p0) behind the cutting wheel, havingat least one first chamber (P1) with a first pressure (p1), wherein preferably the first chamber (P1) is a labyrinth chamber filled with a blocking grease (HBW),at least one second chamber (P2) with a second pressure (p2), wherein the at least one second chamber (P2) is an oil and compressed-air sealing chamber (P2),at least one seal (L1) between the at least one first chamber (P1) and the at least one second chamber (P2), which can resist a differential pressure ApL1 between the at least one first chamber (P1) and the at least one second chamber (P2),preferably at least one further second chamber (P2’) with a further second pressure (p2’) downstream of the at least one second chamber (P2), wherein the at least one further second chamber (P2’) is an oil and compressed-air sealing chamber (P2’),at least one seal (L2) between the at least one second chamber (P2) and the at least one further second chamber (P2’) which can resist a differential pressure ApL2 between the at least one second chamber (P2) and the at least one further second chamber (P2’),at least one third chamber (P3) with a third pressure (p3) following the at least one second chamber (P2) or the at least one further second chamber (P2’), wherein the at least one third chamber (P3) is a leak detection chamber (P3),at least one seal (L2) between the at least one further second chamber (P2’) and the at least one third chamber (P3), which seal can resist a differential pressure ApL2 between the at least one further second chamber (P2’) and that of the at least one third chamber (P3),at least one fourth chamber (P4) with a fourth pressure (p4) following the at least one third chamber (P3), wherein the at least one fourth chamber (P4) is a transmission chamber (P4),at least one seal (L3) between the at least one third chamber (P3) and the at least one fourth chamber (P4), which seal can resist a differential pressure ApL3 between the at least one third chamber (P3) and that of the at least one fourth chamber (P4), characterized in that at least one second chamber (P2), at least one further second chamber (P2’), at least one third chamber (P3) and / or at least one fourth chamber (P4) is pneumatically connected to an air suction line (93), which is pneumatically connected to a vacuum pump (95), so that a pressure which is less than the atmospheric pressure can be set in at least one of the chambers via the vacuum pump.

16. The main drive seal system for a tunnel boring machine as claimed in claim 15, characterized in thatbetween one of the chambers  (P2, P2’, P3, P4) and the5  vacuum  pump (95),  and at  least one compressed-airswitching valve (23, 23’, 33, 43) and / or at least one throttle (233, 233’, 333, 433) is provided in the air suction line (93), and that preferably the at least one compressed-air switching valve (23, 23’, 33, 43) and / or 10 the at least one throttle (233, 233’, 333, 433) can be electrically switched.

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