Patent Publication Number: US-2022221883-A1

Title: Pressure control valve and device comprising such a pressure control valve , for open-loop or closed-loop control of the pressure of a pressurized fluid in a pilot pressure chamber

Description:
The present invention relates to a pressure control valve for open-loop or closed-loop control of a pressure of a compressed fluid in a pilot pressure chamber. The invention also relates to a device with such a pressure control valve, with which the pressure of the compressed fluid in the pilot pressure chamber can be regulated. 
     Hydraulic fluids or compressed air are usually used as compressed fluids. Pilot pressure chambers in hydraulically or pneumatically operated devices are used for open-loop or closed loop control of pilot-operated valves, which often are also designed as hydraulic or pneumatic sliders. If pilot-operated valves are designed as proportional valves or proportional sliders, the volume flows that flow through the proportional valve or the proportional slider can be, within certain limits, continuously adjusted with the pressure in the pilot pressure chamber. 
     An example of such hydraulically or pneumatically operated devices are vibration dampers in motor vehicles, in which the damping characteristic depends on the volume flow of the compressed fluid used flowing through the proportional valve. Depending on the volume flow, a more comfort-oriented, softer damping or a sportier, harder damping can be set. In the case of vibration dampers, an actuation device that can be energized is used, with which several damping characteristics can be specified by the driver or automatically set by an on-board computer depending on the driving condition of the motor vehicle or the condition of the ground surfacing along which the motor vehicle is currently moving. However, it must be ensured that in the event of a failure of the electrical energy and consequently the failure of the actuation device, a fail-safe device, also referred to as a “failsafe”, is available. This ensures that the vehicle can continue to be operated with a certain damping characteristic even in the event of a failure of the electrical energy. A medium damping characteristic that is neither too hard nor too soft is usually aimed for here. 
     These requirements result in a relatively complex structure of the device, in particular the vibration damper, as can be seen, for example, from US 2016/0091044 A1 and WO 2016/066314 A1. The structure becomes particularly complex because a plurality of sliders have to be used. Further vibration dampers are disclosed in US 2016/0369862 A1, JP 2009-115319 A, U.S. Pat. No. 5,147,018 A, WO 2011/023351 A1 and US 2005/0016086 A1. In particular, the vibration damper disclosed in EP 2 678 581 B1 also offers a medium damping characteristic in “fail-safe” mode. 
     The object of one embodiment of the present invention is to provide a pressure control valve for closed-loop control of a pressure of a compressed fluid in a pilot pressure chamber, which is simple in structure and regulates the pressure in the pilot pressure chamber to a determinable level even when there is no electrical energy to energize the actuation device. Furthermore, it is the object of one embodiment of the present invention to create a device, with which the pressure of the compressed fluid in the pilot pressure chamber can be regulated and which can be operated with such a pressure control valve. 
     This object is achieved with the features specified in claims  1  and  14 . Advantageous embodiments are the subject of the dependent claims. 
     One embodiment of the invention relates to a pressure control valve for closed-loop control of a pressure of a compressed fluid in a pilot pressure chamber, comprising
         a valve housing with at least one inlet, which can be fluidically connected to the pilot pressure chamber, and at least one outlet,   a wall section which is securely arranged in the pressure control valve and which
           has a passage channel through which the compressed fluid can flow, and   which forms a first valve seat,   
           a tappet, which is mounted in the valve housing so as to be movable along a longitudinal axis by means of an actuation device that can be energized,   a first sealing element, which
           forms a second valve seat,   is mounted in the valve housing so as to be movable along the longitudinal axis and   is biased by means of a first spring against the actuation direction of the actuation device into a closure position in which the first sealing element bears against the first valve seat and can be moved by the compressed fluid in the actuation direction,   
           a second sealing element, which is secured to the tappet and, by energizing the actuation device, can be moved by means of the tappet along the longitudinal axis between a first position, in which the second sealing element bears against the wall section and closes the passage channel, and a second position, in which the second sealing element bears against the second valve seat, the second valve seat being arranged axially offset to the first valve seat with respect to the longitudinal axis, and   a second spring, which biases the second sealing element into the first position.       

     The essential property of the proposed pressure control valve is that it has at least two valve seats, through which the compressed fluid can flow when the respective valve seat is open. The pressure control valve is designed in such a way that the compressed fluid can flow through the pressure control valve when at least one of the valve seats is open. In this respect, the first valve seat and the second valve seat are connected in parallel to one another in relation to the opening behavior. 
     While the second valve seat can be opened and closed directly or indirectly as a result of the actuation device being energized and the resulting movement of the second sealing element, the first valve seat is opened due to the pressure acting in the pressure control valve. In other words, the second valve seat is actively opened by being energized, while the first valve seat is passively opened due to the prevailing pressure conditions. The second spring ensures that the passage channel is closed if the actuation device fails. 
     This has the consequence that even if the electrical energy for energizing the actuation device is not available, a flow through the pressure control valve is possible. The pressure in the pilot pressure chamber can therefore be open-loop or closed-loop controlled even if the power supply fails, so that a fail-safe device, also referred to as a “failsafe”, can be provided with just a single pressure control valve. The damping characteristic that arises in the event of the fail-safe is determined by the choice of the spring constant and the spring bias of the first spring. 
     The pressure control valve can also be closed when the second sealing element is in the second position and the second sealing element bears against the second valve seat. Then, however, no flow through the pressure control valve and therefore neither open-loop or closed-loop control of the pressure in the pilot pressure chamber is possible, so that the second sealing element is usually not moved into the second position when the pressure control valve is in operation. 
     The first valve seat and the second valve seat are arranged axially offset from one another with respect to the longitudinal axis in order to be able to ensure the movability of the second sealing element along the longitudinal axis. The provision of the second sealing element for throttling enables the opening points and the desired damping characteristics to be set very precisely. In the pressure control valve disclosed in EP 2 678 581 B1, the throttling and the opening and closing of the valve seats are carried out with the tappet. The pressure control valve shown there does not have a second sealing element. As a result, the desired damping characteristics cannot be set as precisely as with the present pressure control valve. In addition, with the present pressure control valve, the damping characteristics can be changed in a simple manner by using a second sealing element with different dimensions. In the case of the pressure control valve disclosed in EP 2 678 581 B1, the entire tappet has to be changed for this, which is significantly more complex. 
     Contrary to the pressure control valve disclosed in EP 2 678 581 B1, the proposed pressure control valve does not have a movable valve chamber with a movable wall section. Rather, the wall section is securely connected to the valve housing. As a result, the damping characteristics can be adjusted more precisely. In addition, the mounting of the movable components is simplified compared to the pressure control valve disclosed in EP 2 678 581 B1. 
     According to another embodiment, the first sealing element has a first surface to which the compressed fluid can be applied and which points away from the wall section, and a second surface to which the compressed fluid can be applied and which points toward the wall section, the second surface being larger than the first surface. In the event that no electrical energy is available for energizing the actuation device, the second sealing element is moved by means of the second spring into the first position, in which the second sealing element closes the passage channel. As a result, the compressed fluid cannot flow through the passage channel, so that a pressure builds up upstream of the second sealing element, which acts both on the first surface and on the second surface of the first sealing element. Due to the fact that the second surface is larger than the first surface, but the same pressure acts on both the first surface and the second surface, the compressed fluid applies a fluid force to the first sealing element, which acts in the actuation direction of the actuation device and thus against the bias of the first spring. The first sealing element is therefore moved along the actuation direction until a force equilibrium is established between the bias of the first spring and the fluid force applied by the compressed fluid to the first sealing element. The first valve seat is opened so that the compressed fluid can flow through it. Consequently, a flow through the pressure control valve is made possible even if there is no electrical energy for operating the actuation device (“failsafe”). 
     According to a further embodiment, the second valve seat is formed by a tube arranged in the first sealing element. In particular, if structural changes are to be made to the pressure control valve that require a different positioning of the second valve seat, only the diameter and/or the length of the tube and the corresponding receptacle in the first sealing element need to be changed. The valve housing itself can remain unchanged. 
     According to a further developed embodiment, the tube is connected to the first sealing element so as to be movable along the longitudinal axis. It is advantageous here to connect the tube to the first sealing element by means of a frictional connection, for example by means of a certain interference with said sealing element, so that the position of the second valve seat is clearly retained when the pressure control valve is in operation. However, the frictional connection can be overcome with suitable tools during the assembly of the pressure control valve, so that the position of the second valve seat can be adjusted. In this way, magnetic forces, which can be different as a result of tolerance differences, can be standardized. Opening points that deviate from the target value due to manufacturing tolerances can be corrected in a relatively simple manner. 
     According to a further embodiment, the passage channel is formed by an annular gap between the wall section and the tappet. In this embodiment, the passage channel can be implemented in a structurally simple manner. 
     According to a further developed embodiment, the wall section has a through-hole through which the compressed fluid can flow and which cannot be closed by the first sealing element. The through-hole is used for guiding the compressed fluid downstream of the first valve seat, i.e., after the pressure of the compressed fluid has been adjusted to the desired level. As a result, it is possible to guide the compressed fluid through the pressure control valve with short paths, which requires few structural changes. 
     According to a further developed embodiment, the cross-sectional area of the passage channel or of the annular gap is larger than the cross-sectional area of a throttle gap originating from the second sealing element. The above-mentioned open-loop or closed loop control of the pressure in the pilot pressure chamber takes place essentially by throttling the flow of the compressed fluid in the pressure control valve. The amount of throttling is determined by the smallest cross-section through which fluid can flow. When flowing through the pressure control valve, the compressed fluid passes essentially two cross-sections, namely on the one hand the annular gap and on the other hand the throttle gap formed by the second sealing element or the tappet. While the annular gap is structurally predetermined and its cross-sectional area cannot be changed, the cross-sectional area of the throttle gap can be changed as a result of a stronger or less strong energization of the actuation device. Due to the fact that the cross-sectional area of the throttle gap in every position of the tappet is smaller than the cross-sectional area of the annular gap or of the passage channel, it is ensured that the pressure in the pilot pressure chamber can be changed by energizing the actuation device. 
     According to a further developed embodiment, the cross-sectional area of the first annular gap and of the second is larger than the cross-sectional area
         of the first throttle gap formed between the second sealing element and the second valve seat, or   of the second throttle gap formed between the second sealing element and the first sealing element, or   of the third throttle gap formed between the second sealing element and the wall section.       

     If the second sealing element is located between the first position and the second position, the compressed fluid is initially directed radially outward by the second sealing element, seen in the flow direction, then parallel to the longitudinal axis and then radially inward again. If the compressed fluid flows radially outward, it flows through a first throttle gap extending parallel to the longitudinal axis. When flowing parallel to the longitudinal axis, the compressed fluid flows through a second throttle gap, whereas it flows through a third throttle gap when flowing radially inward. The first throttle gap is formed between the second sealing element and the second valve seat. The second throttle gap is formed between the second sealing element and the first sealing element, whereas the third throttle gap is formed between the second sealing element and the wall section. 
     Depending on the position of the second sealing element, the cross sections of the first and the third throttle gap change. The throttle gap which has the smallest cross-sectional area should be referred to as the active throttle gap, since this determines the degree of throttling of the flow of the compressed fluid. The pressure control valve is designed in such that, regardless of the position of the tappet, the cross-sectional area of the annular gap is larger than the cross-sectional area of the active throttle gap. As a result, it is ensured that the pressure in the pilot pressure chamber can be changed by energizing the actuation device. 
     According to a further embodiment, the pressure control valve is designed as a proportional valve. In this embodiment, the volume flow through the pressure control valve can be regulated in the following way: as mentioned, the second sealing element can be moved back and forth between the first position and the second position by means of the actuation device. The proportional valve is designed in such that the throttle gap changes linearly, so that the volume flow is also changed linearly. The pressure in the pilot pressure chamber can therefore be controlled proportionally to the energization of the actuation device. 
     In a further embodiment, the wall section can be designed as a first spring plate and/or the second sealing element as a second spring plate. In this embodiment, the wall section and the second sealing element are sufficiently stable with a low wall thickness as well as comparatively simple to manufacture. 
     According to a further developed embodiment, the second sealing element is connected to the tappet by means of a clearance fit. This allows tolerances to be compensated for in a simple manner. 
     A further developed embodiment is characterized in that the spring plate is press-fit on the tappet. In this way, sufficient fastening of the spring plate on the tappet can be achieved in a simple manner. 
     According to a further embodiment, the actuation device comprises a magnet through which the compressed fluid can flow. Actuation devices which use magnets to move a tappet are common, so that such actuation devices can be used when manufacturing the present pressure control valve. If the compressed fluid can flow through the magnet, however, there is the advantage that the compressed fluid acts as a coolant, since it can dissipate at least some of the heat from the magnet that is generated during operation of the magnet. This reduces the thermal load on the magnet and increases its durability. 
     One embodiment of the invention relates to a device for open-loop control of or closed-loop control of a pressure in a pilot pressure chamber, comprising
         a primary circuit for a compressed fluid,   a working machine arranged in the primary circuit for conveying the compressed fluid in the primary circuit along a conveying direction,   a hydraulic or pneumatic slider,   a secondary circuit for the compressed fluid,
           which starts from a branch of the primary circuit, which branch is arranged downstream of the working machine with respect to the conveying direction, and   which flows back into the primary circuit at a junction,   
           a pilot pressure chamber arranged in the secondary circuit, and   a pressure control valve according to one of the previous embodiments, arranged between the pilot pressure chamber and the junction in the secondary circuit, wherein   the slider is arranged and designed so that the slider can block or unblock the flow of the compressed fluid in the primary circuit between the branch and the junction depending on the pressure in the pilot pressure chamber.       

     The advantages and technical effects that can be achieved with the proposed device correspond to those that have been explained with the pressure control valve according to one of the previously discussed embodiments. In summary, it should be pointed out that with only one pressure control valve and only one slider, both active and passive control of the pressure in the pilot pressure chamber can be achieved and the structural complexity of the device can be kept low. 
     According to a further embodiment, the slider is designed as a proportional slider. In a closed position, the slider blocks the primary circuit between the branch and the junction depending on the pressure in the pilot pressure chamber. In this case, the compressed fluid can only flow from the branch to the junction via the secondary circuit. As soon as the pressure in the pilot pressure chamber is exceeded or not reached, depending on the design of the device, the slider is moved into an open position so that the fluid can also flow between the branch and the junction in the primary circuit. However, simple sliders can only be moved between the open position and the closed position, so that the flow of the compressed fluid between the branch and the junction in the primary circuit is either completely unblocked or blocked. However, if the slider is designed as a proportional slider, the volume flow of the compressed fluid between the branch and the junction in the primary circuit can be adjusted depending on the pressure in the pilot pressure chamber. Since the pressure in the pilot pressure chamber can in turn be adjusted with the energization of the actuation device, the volume flow of the compressed fluid between the branch and the junction in the primary circuit can accordingly also be adjusted with the energization of the actuation device and at the same time a fail-safe can be realized in the event that the actuation device fails. 
     Another embodiment is characterized in that the actuation device of the pressure control valve comprises a magnet through which the compressed fluid can flow and in that the magnet is fluidically connected to the pilot pressure chamber or to an external compressed fluid circuit. As mentioned, actuation devices which use magnets to move a tappet are widespread, so that such actuation devices can be used. If the compressed fluid can flow through the magnet, however, there is the advantage that the compressed fluid acts as a coolant, since it can dissipate at least some of the heat from the magnet that is generated during operation of the magnet. This reduces the thermal load on the magnet and increases its durability. 
     If the magnet is fluidically connected to the pilot pressure chamber, the pressure prevailing there can be used as the delivery pressure for the compressed fluid, so that no further delivery elements have to be used. The construction of the device is not significantly complicated. In the event that the magnet is fluidically connected to an external compressed fluid circuit, the volume flow through the magnet can be changed independently of the volume flow and the pressure conditions in the secondary circuit. 
     Another embodiment is characterized in that the working machine is a pump, a compressor or a vibration damper. The vibration dampers can be designed as two-tube or three-tube vibration dampers. Such working machines can be open-loop or closed-loop controlled particularly well in a simple manner by means of the proposed device as a result of the regulation in the pilot pressure chamber. In the event that the working machine is designed as a vibration damper, the damping characteristics can be adjusted by energizing the actuation device so that harder or softer damping results. If the actuation device fails, damping is also ensured, which depends on the spring bias and the spring constant of the first spring. 
    
    
     
         FIG. 1  is a circuit diagram of an embodiment of a proposed device for open-loop control of or closed-loop control of a pressure of a compressed fluid in a pilot pressure chamber; 
         FIG. 2A  is a sectional view through an embodiment of a proposed pressure control valve; 
         FIG. 2B  is an enlarged illustration of the section X marked in  FIG. 2A ; 
         FIG. 2C  is a separate illustration of the first sealing element; 
         FIG. 3A  is a basic and not-to-scale enlarged illustration of part of the section X marked in  FIG. 2A , in which the pressure control valve is in a first operating state; 
         FIG. 3B  is a basic and not-to-scale enlarged illustration of part of the section X marked in  FIG. 2A , in which the pressure control valve is in a second operating condition; and 
         FIG. 3C  is a basic and not-to-scale enlarged illustration of part of the section X marked in  FIG. 2A , in which the pressure control valve is in a third operating condition. 
     
    
    
       FIG. 1  shows a circuit diagram of a device  10  for open-loop or closed-loop control of a pressure of a compressed fluid in a pilot pressure chamber  12 . A hydraulic fluid or compressed air can be used as the compressed fluid, the following description relating to a compressed fluid which is designed as a hydraulic fluid. The device  10  comprises a primary circuit  14  in which the compressed fluid can be conveyed by means of a working machine  16 . A working machine  16  is to be understood as a component with which, in particular, mechanical work can be transferred to the compressed fluid in such that it is conveyed in the primary circuit  14  in the conveying direction indicated by the arrow P 1 . 
     In relation to the conveying direction indicated by the arrow P 1 , a branch  18  is arranged downstream of the working machine  16 , from which a secondary circuit  20  starts, through which the compressed fluid can likewise flow. The exact configuration of the secondary circuit  20  will be discussed in greater detail later. 
     Downstream of the branch  18 , a junction  22  is provided in the primary circuit  14 , at which the secondary circuit  20  enters again into the primary circuit  14 . In the example shown, the junction  22  is realized by means of a low-pressure chamber  23 . 
     Starting from the low-pressure chamber  23 , the primary circuit  14  flows back into the working machine  16 . 
     As can be seen from  FIG. 1 , a slider  24  is arranged downstream of the branch  18 , which in the illustrated embodiment is designed as a proportional slider  26  which interacts with a spring  25 . The secondary circuit  20  cannot be blocked by the slider  24 . The slider  24  is adjustable between two positions, wherein in a first position, which is shown in  FIG. 1 , the slider  24  blocks the primary circuit  14  between the branch  18  and the junction  22 . In the second position, on the other hand, the fluid connection between the branch  18  and the junction  22  in the primary circuit  14  is provided. The slider  24  is designed as a 2/2 valve. 
     The spring  25  interacts with the slider  24  in such a way that it is biased into the first position. A first control line  27 , which is connected to the slider  24 , extends between the working machine  12  and the branch  18 . Furthermore, a second control line  29  extends from the pilot pressure chamber, which, like the first control line  27 , is also connected to the slider  24 . The compressed fluid conveyed to the slider  24  via the first control line  27  acts in the opposite direction on the slider  24  compared to the compressed fluid conveyed via the second control line  29  to the slider  24 . The compressed fluid conveyed to the slider  24  via the second control line  29  acts in the same direction as the spring  25 . 
     Starting from the branch  18 , a throttling main orifice  28  is provided downstream of the slider  24  in the secondary circuit  20 . The secondary circuit  20  then enters into the already mentioned pilot pressure chamber  12 . 
     Downstream of the pilot pressure chamber  12  a pressure control valve  30  is arranged, the function of which can be understood as a solenoid-controlled 3/2 valve and a purely hydraulically controlled 3/2 valve connected in parallel thereto. The exact structural design of the pressure control valve  30  will be discussed in greater detail later. 
     Downstream of the pressure control valve  30 , a first line  32  extends directly to the low-pressure chamber  23 , while a second line  34  splits into a first sub-line  36  and a second sub-line  38 , with a check valve  40  arranged in the first sub-line  36  and a secondary orifice  42  arranged in the second sub-line  38 . The check valve  40  and the secondary orifice  42  are connected in parallel to one another. Downstream of the check valve  40  and the secondary orifice  42 , the first sub-line  36  and the second sub-line  38  merge again. From there, the second line  34 , like the first line  32 , leads to the low-pressure chamber  23 . As already mentioned, the secondary circuit  20  in the low-pressure chamber  23  enters again into the primary circuit  14 . 
     As already mentioned, the proposed pressure control valve  30  can be understood in terms of its function as a solenoid-controlled 3/2 valve and a pressure-controlled 3/2 valve connected in parallel thereto, which in the example shown comprises an inlet  41  and two outlets  43 . As will be apparent from the explanations below, the pressure control valve  30  can be operated as a 3/3 valve. However, it is also possible to design the pressure control valve  30  in such a way that its function can be interpreted as a solenoid-controlled 2/2 valve and a pressure-controlled 2/2 valve connected in parallel thereto. In this case, the pressure control valve  30  has one inlet  41  and only one outlet  43 . Instead of the first line  32  and the second line  34 , there is then only one common line (not shown). 
     In the example shown, the solenoid-controlled valve has a magnet  44  through which the compressed fluid, in this case the hydraulic fluid, can flow. However, it is just as possible to design the magnet  44  in such a way that no fluid can flow through it. In the exemplary embodiment shown in  FIG. 1 , the magnet  44  is connected to an external compressed fluid circuit  46 , which has a feed pump  48  for conveying the compressed fluid in the external compressed fluid circuit  46 . An embodiment in which the magnet  44  is fluidically connected to the primary circuit  14  and/or secondary circuit  20  is not shown. For example, the magnet  44  can be fluidically connected to the pilot pressure chamber  12  and the low-pressure chamber  23 . 
     In  FIG. 2A , an embodiment of the proposed pressure control valve  30  is shown as a sectional view. The section X marked in  FIG. 2A  is shown enlarged in  FIGS. 2B and 3A . Consequently, the following description relates both to  FIG. 2A  and to  FIGS. 2B and 3A . To facilitate understanding, the pilot pressure chamber  12  and the low-pressure chamber  23  are also shown in  FIGS. 2A and 3A . 
     The pressure control valve  30  comprises a valve housing  50 , in which the above-mentioned slider  24  is arranged on the left with respect to the chosen illustration in  FIG. 2A . In addition, the primary circuit  14 , which can be opened or closed by the slider  24 , is indicated in  FIG. 2A . 
     Furthermore, the pressure control valve  30  comprises a tappet  52 , which is mounted in the valve housing  50  so as to be movable along a longitudinal axis L and can be moved along a movement direction B by means of an actuation device  49  that can be energized. The movement direction B extends in parallel with the longitudinal axis L. In the following, valve housing  50  should be understood to mean all components which in any way form walls and cavities of the pressure control valve  30 . The valve housing  50  can have a plurality of such components. 
     In addition, a wall section  51  is permanently arranged in the pressure control valve  30  and forms a passage channel  60  ( FIG. 3A ) through which the compressed fluid can flow and which is designed as an annular gap  62 . The annular gap  62  is formed between the wall section  51  and the tappet  52 . The wall section  51  also forms a first valve seat  58  and, in the illustrated embodiment, is designed as a first spring plate  53 . In addition, the wall section  51  has at least one through-hole  73  which will be discussed in more detail below. 
     The pressure control valve  30  shown in  FIGS. 2A to 2C  has a first sealing element  54   1  according to a first exemplary embodiment, which is likewise mounted in the valve housing  50  so as to be movable along the longitudinal axis L. The first sealing element  54  is biased by means of a first spring  56  against the valve seat  58  (see  FIG. 3A ), which is formed by a wall section  51  permanently connected to the valve housing  50 . 
     In addition, the proposed pressure control valve  30  shown comprises a second sealing element  64  (see  FIGS. 2B and 3A ) which is attached to the tappet  52  and can be moved by means of the tappet  52  along the longitudinal axis L between a first position, in which the second sealing element  64  bears against the wall section  51  and closes the passage channel  60  (see  FIGS. 2B and 3A ), and a second position, in which the second sealing element  64  bears against a second valve seat  66  (not shown). As can be seen in particular from  FIG. 2C , the second valve seat  66  is formed by the first sealing element  54   1  according to the first exemplary embodiment.  FIGS. 3A to 3C  show a second exemplary embodiment of the first sealing element  54   2 , which differs in particular from the first sealing element  54   1  according to the first exemplary embodiment in that the second valve seat  66  is formed by a tube  67  which is connected to the first sealing element  54   2  to form a frictional connection. As a result, the tube  67  can be moved along the longitudinal axis L when a sufficiently large force is applied to the tube  67 . When the tube  67  is moved, the position of the second valve seat  66  also changes, as a result of which the opening points of the pressure control valve  30  can be easily changed. 
     As can be seen from  FIG. 3A , the tube  67  has an inside diameter D RI  and an outside diameter D RA . In addition, the tappet  52  has an outside diameter D SA  at the end pointing toward the tube  67 . In the embodiment shown of the pressure control valve  30 , the outside diameter D SA  of the tappet  52  is smaller than the inside diameter D RI  of the tube  67 . An embodiment in which the outside diameter D SA  of the tappet  52  is larger than the inside diameter D RI  but smaller than the outside diameter D RA  of the tube  67 , is not shown. 
     The pressure control valve  30  furthermore comprises a second spring  68  (see  FIG. 2A ), which interacts with the tappet  52  in such that the second sealing element  64  is biased into the first position and is consequently pressed against the wall section  51 . In this respect, the wall section  51  forms a third valve seat  70  for the second sealing element  64 . 
     The second sealing element  64  is designed as a second spring plate  72 , which is fastened to the tappet  52  by means of a clearance fit. The clearance fit is designed in such a way that the spring plate  72  can be moved to a minimal extent both along the longitudinal axis L and perpendicular thereto. The fastening can take place by press-fitting the tappet  52  at the end. The spring plate  72  has a thickness of 0.1 to 0.5 mm. 
     In  FIGS. 2A, 2B and 3A , the pressure control valve  30  is in a first operating state, while the pressure control valve  30  in  FIG. 3B  and  FIG. 3C , which analogously represent part of the section X marked in  FIG. 2A , is in a second and third operating state, respectively. 
     In  FIG. 3A , the device  10  is in the unpressurized state, in which the first sealing element  54   2  is pressed against the wall section  51  and the first valve seat  58  by means of the first spring  56 , and the second sealing element  64  is pressed against the wall section  51  and the third valve seat  70  by means of the second spring  68 . Consequently, the compressed fluid cannot flow through the pressure control valve  30 , so that the second valve seat  66  is also closed indirectly. The through-hole  73  is located radially outside the first valve seat  58  so that it cannot be closed by the first sealing element  58 . 
     In  FIG. 3B , the pressure control valve  30  is in a second operating condition, which corresponds to the intended operation of the pressure control valve  30 . Due to the energization of the actuation device  49 , the tappet  52  is moved along the actuation direction B, which points left with respect to  FIGS. 2 to 3C  and extends in parallel with the longitudinal axis, as a result of which the second sealing element  64  moves away from the wall section  51  and from the third valve seat  70 , and consequently no longer closes the passage channel  60 . The compressed fluid, which is conveyed by the working machine  16  through the secondary circuit  20 , can consequently flow through the pressure control valve  30 , as indicated by the arrow P 2  in  FIG. 3B , and thus reach the low-pressure chamber  23 . The compressed fluid flows through the above-mentioned through-hole  73  and a through-opening  84  arranged in the housing  50 . 
     Based on a flow directed parallel to the longitudinal axis L, when entering the pressure control valve  30  and after flowing through the second valve seat  66 , the compressed fluid is first deflected radially outward by the second sealing element  64  and must flow through a first throttle gap  74   1 . The compressed fluid is then deflected in such a way that it flows substantially parallel to the longitudinal axis L and has to flow through a second throttle gap  74   2 . Thereafter, the compressed fluid is deflected radially inward, so that it flows through a third throttle gap  74   3  before it enters the passage channel  60  with a flow directed substantially parallel to the longitudinal axis L. After the compressed fluid has flowed through the passage channel  60 , as well as through the through-hole  73  and the through-opening  84 , it enters the low-pressure chamber  23 . 
     The outside diameter D SA  of the tappet  52  is smaller than the inside diameter D RI  of the tube  67 . As a result, the first throttle gap  74   1  is formed starting at the second sealing element  64 . In an embodiment that is not shown, in which the outside diameter D SA  of the tappet  52  at the end pointing toward the tube  67  is larger than the inside diameter D RI  but smaller than the outside diameter D RA  of the tube  67 , the first throttle gap  74   1  starts at the tappet  52 . 
     The second throttle gap  74   2  and the third throttle gap  74   3  start at the second sealing element  64 . The first throttle gap  74   1  has a first cross-sectional area A 1  extending substantially parallel to the longitudinal axis L and which cross-sectional area is formed between the second valve seat  66  and the tappet  52 . The second throttle gap  74   2  forms a second cross-sectional area A 2  extending substantially perpendicular to the longitudinal axis L and which cross-sectional area extends between the second sealing element  64  and the first sealing element  54   2 . The third throttle gap  74   3  has a third cross-sectional area A 3  extending substantially parallel to the longitudinal axis L and which cross-sectional area is formed between the second sealing element  64  and the wall section  51  and in particular the third valve seat  70 . 
     A comparison of  FIG. 3A  and  FIG. 3B  shows that before the start of the energization, the third cross-sectional area A 3  is equal to zero and thus the passage channel  60  is closed. If the energization is now started, the tappet  52  together with the second sealing element  64  move in the actuation direction B away from the wall section  51  and toward the second valve seat  66 . As a result, the third cross-sectional area A 3  increases, while the first cross-sectional area A 1  decreases. Regardless of this, the second cross-sectional area A 2  remains constant. Regardless of the size of the first cross-sectional area A 1 , the second cross-sectional area A 2  and the third cross-sectional area A 3 , the cross-sectional area A 4  of the passage channel  60  is selected so that it is always larger than at least one of the first, second and third cross-sectional areas A 1 , A 2 , A 3 . 
     For reasons of controllability, it has proven to be advantageous if the throttling is carried out with the first throttle gap  74   1 . The energization of the actuation device  49  must therefore be carried out in such a way that the second sealing element  64 , together with the tappet  52 , is moved as quickly as possible beyond the middle of the distance between the third valve seat  70  and the second valve seat  66 . This can be achieved by an initial peak current. As soon as the second sealing element  64  is located to the left of the middle between the third valve seat  70  and the second valve seat  66  as illustrated in  FIGS. 2A to 3B , the first cross-sectional area A 1  of the first throttle gap  74   1 is the smallest of the first, second and third cross-sectional area A 1 , A 2 , A 3 , such that the throttling of the compressed fluid is determined by the first throttle gap  74   1 . 
     When flowing through, the compressed fluid is throttled, the throttling being determined by the throttle gap  74  which has the smallest cross-sectional area A. Depending on how much the compressed fluid is throttled when flowing through the pressure control valve  30 , the pressure in the pilot pressure chamber  12  also changes. The more it is throttled, the more the pressure in the pilot pressure chamber  12  increases. The throttling can take place continuously and depends on the strength of the energization of the actuation device  49 . Since the volume flow is also influenced by the pressure control valve  30  as a result of the throttling and can be continuously adjusted, the pressure control valve  30  is designed as a proportional valve  75 . 
     With reference to  FIG. 1 , the effect of the pressure in the pilot pressure chamber  12  on the slider  24  will now be explained. In the event that the pressure in the pilot pressure chamber  12  is greater than or equal to the pressure upstream of the slider  24  in the primary circuit  14 , the slider  24  remains in the position shown in  FIG. 1 , so that the primary circuit  14  is blocked between the branch  18  and the junction  22 . A fluid connection between the branch  18  and the junction  22  is only available via the secondary circuit  20 . However, to facilitate the opening of the slider  24 , the main orifice  28  is provided downstream of the slider  24  in the secondary circuit  20 , which causes the pressure downstream of the slider  24  in the secondary circuit  20  to drop at least slightly. If, in addition, the pressure in the pilot pressure chamber  12  falls due to the above-described energization of the actuation device  49  and the throttling of the compressed fluid caused by this, the slider  24  can open and unblock the primary circuit  14  between the branch  18  and the junction  22 . As mentioned, the slider  24  is designed as a proportional slider  26 , which means that the slider  24  unblocks the primary circuit  14  between the branch  18  and the junction  22  to a greater or lesser extent, depending on the pressure in the pilot pressure chamber  12 . Thus, the volume flow between the branch  18  and the junction  22  can be set proportionally to the pressure in the pilot pressure chamber  12  by energizing the actuation device  49 . 
     A third operating state of the pressure control valve  30  is shown in  FIG. 3C , in which no electrical energy is available for energizing the actuation device  49 . In this case, the second spring  68  (see  FIG. 2 ) returns the second sealing element  64  to the first position, in which the second sealing element  64  bears against the third valve seat  70  and closes the first passage channel  53 . This intermediate position is similar to the first operating state shown in  FIG. 3A . 
     As can be seen in particular from  FIGS. 2B and 2C , according to the first exemplary embodiment, the first sealing element  54   1  has a first surface C 1  to which the compressed fluid can be applied and which points away from the wall section  51 , and a second surface C 2  to which the compressed fluid can be applied and which points toward the wall section  51 . In this case, the second surface C 2  is larger than the first surface C 1 . The forces acting on the first sealing element  54   1  as a result of the pressure from the compressed fluid are not the same due to the differently sized surfaces C 1 , C 2 ; rather, a resulting force directed in the actuation direction B is established, as a result of which the first sealing element  54   1  moves in the actuation direction B. The first spring  56  is compressed until an equilibrium of forces is reached between the resulting force and the bias of the spring  56 . This state is shown in  FIG. 3C . It should be noted that the first sealing element  54   1  according to the first exemplary embodiment does not differ from the first sealing element  542  according to the second exemplary embodiment with regard to the first surface C 1  and the second surface C 2 . 
     The first sealing element  54   2  is consequently moved away from the first valve seat  58  so that a gap  76  opens between the wall section  51  and the first sealing element  54   2 , through which gap the compressed fluid can flow and consequently reach the low-pressure chamber  23  (arrow P 3 ). Depending on the cross-sectional area A of this gap  76 , the compressed fluid is throttled to a greater or lesser extent when it flows through the pressure control valve  30 . The size of the cross-sectional area A of the gap  76  can be adjusted with the spring bias and the spring constant of the first spring  56 . Consequently, even if the actuation device  49  fails, it is ensured that the slider  24  enters and the primary circuit  14  is unblocked between the branch  18  and the junction  22 . As already explained, the extent to which the slider  24  enters depends on the amount of throttling. Consequently, in the event of a failure of the supply of the actuation device  49  with electrical energy, the degree to which, when and how far the slider  24  opens can be selected with the spring bias and the spring constant of the first spring  56  (“fail-safe”). 
     From the above explanations it follows that the pressure control valve  30  according to the invention is operated as a 3/3 valve. 
     As mentioned, the second line  34  of the secondary circuit splits into the first sub-line  36  and the second sub-line  38  (see  FIG. 1 ). The connected secondary orifice  42  arranged there and the check valve  40  ensure damping of the entire device  10  by absorbing pressure peaks. 
     Finally, it should be pointed out that the working machine  16  can be configured as a pump  78 , a compressor  80  or a vibration damper  82  of a motor vehicle. In particular, in the case where the working machine  16  is designed as a vibration damper  82 , it may be necessary to provide hydraulic synchronization so that regardless of the load direction of the vibration damper  82 , the fluid is always conveyed in the direction shown in  FIG. 1  through the primary circuit  14  and the secondary circuit  20 . The device  10  according to the invention can be used for two-tube or three-tube vibration dampers  82 . 
     LIST OF REFERENCE SYMBOLS 
     
         
           10  device 
           12  pilot pressure chamber 
           14  primary circuit 
           16  working machine 
           18  branch 
           20  secondary circuit 
           22  junction 
           23  low-pressure chamber 
           24  slider 
           25  spring 
           26  proportional slider 
           27  first control line 
           28  main orifice 
           29  second control line 
           30  pressure control valve 
           32  first line 
           34  second line 
           36  first sub-line 
           38  second sub-line 
           40  check valve 
           41  inlet 
           42  secondary orifice 
           43  outlet 
           44  magnet 
           46  external compressed fluid circuit 
           48  feed pump 
           49  actuation device 
           50  valve housing 
           51  wall section 
           52  tappet 
           53  first spring plate 
           54  first sealing element 
           54   1 ,  54   2  first sealing element 
           56  first spring 
           58  first valve seat 
           60  passage channel 
           62  annular gap 
           64  second sealing element 
           66  second valve seat 
           67  tube 
           68  second spring 
           70  third valve seat 
           72  second spring plate 
           73  through-hole 
           74  throttle gap 
           74   1 - 74   3  first to third throttle gap 
           75  proportional valve 
           76  gap 
           77  recess 
           78  pump 
           80  compressor 
           82  vibration damper 
           84  through-opening 
         A cross-sectional area 
         A 1 -A 4  first to fourth cross-sectional area 
         B actuation direction 
         C 1  first surface 
         C 2  second surface 
         D RA  outside diameter of the tube 
         D RI  inside diameter of the tube 
         D SA  inside diameter of the tappet 
         L longitudinal axis 
         P 1 -P 3  arrow