Abstract:
The invention relates to a valve arrangement with a continuously variable directional control valve, wherein the valve slide thereof can be adjusted in the direction of five positions in order to control a user in two directions, to carry out a quick motion, to switch into a floating position or to close off the pressure means connection to the user (neutral position).

Description:
CROSS-REFERENCE 
     The invention described and claimed hereinbelow is also described in PCT/EP2008/009448, filed on Nov. 8, 2008, DE 10 2007 057 654.6, filed on Nov. 28, 2007, and DE 10 2008 008 092.6, filed on Feb. 8, 2008. These German Patent Applications, whose subject matter is incorporated here by reference, provide the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a valve system. 
     A valve system of this type is used, e.g., to activate hydraulic consumers of a mobile working machine, such as a wheel loader, a bulldozer, a crawler dozer, a telescopic loader, or an underground loader. 
     Data sheet RD 64 284/06.00 from Mannesmann Rexroth AG describes an LUDV mobile control block, in which the pressure-medium supply to the consumers is controlled via sections of directional control valves, using one proportional directional valve in each case. It includes one speed part, which is formed by a metering orifice, and a direction part which determines the direction of flow of pressure medium to and from the consumer. An LUDV pressure compensator is assigned to the metering orifice. In a mobile control block of this type, a load-independent flow distribution (LUDV) is given for consumers that may be activated simultaneously. As stated in a highly simplified manner, in LUDV systems of this type, when the activated consumers are under-supplied, i.e., when a pump is unable to meet the desired demand for pressure medium, the pressure differences across all open metering orifices decrease, and therefore the quantities of pressure medium that flow to the activated consumers are reduced by the same proportion. In this manner, it is ensured that individual consumers are not brought to an unwanted standstill. The present invention is not limited to LUDV systems, however. 
     In the known solution, the proportional directional valve may be moved from a neutral or centered position into the direction of first positions, in which, e.g., a hydraulic cylinder is retracted. When displaced in the other direction, the hydraulic cylinder is extended. Furthermore, the directional-control valve section may be moved into a floating position by switching over a floating-position valve and simultaneously activating the valve spool in the “lower” direction; in the floating position, the two consumer ports and the pressure port are connected to the tank port, and therefore, e.g., a dozer blade of a crawler dozer lies on the ground simply under its own weight. The disadvantage of this solution is that a separate floating-position valve is required. 
     Publication DE 103 36 684 A1 shows a valve system in which the directional control valve is equipped with four positions (neutral position, raise, lower, floating position) of a valve spool. The term “position” is understood to mean a large number of intermediate positions, in each of which an opening cross section that is active in terms of the functions “neutral”, “raise”, “lower”, and “floating position” may be changed. 
     DE 196 08 758 A1 discloses a solution, in the case of which a valve spool of the directional control valve may be displaced into five positions (floating position, lower, neutral position, vibration damping, and extend); in the “vibration damping” position, an annular chamber of the hydraulic cylinder that is active in the direction of retraction is connected to the tank. 
     In none of these solutions is it possible, by displacing the valve spool, to obtain a quick- action function in addition to the functions “neutral setting”, “extend”, “retract”, and “floating position”, in which the pressure medium, which has been displaced out of the contracting pressure chamber of the consumer, e.g., the annular chamber of a hydraulic cylinder, is added to the volumetric flow of pressure medium being supplied to the other pressure chamber of the consumer. To realize a quick-action function of this type in the known solutions, a separate valve device must be provided, via which, when the “quick-action” function is activated, the volumetric flow of pressure medium flowing out of the contracting pressure chamber circumvents the directional control valve and is added to the volumetric flow of pressure medium that is flowing to the pressure chamber which is expanding. 
     SUMMARY OF THE INVENTION 
     In contrast, the present invention is based on the object of creating a valve system in which quick-action operation and floating-position operation are made possible using a simple design. 
     According to the present invention, the valve system includes a proportional directional valve that has a valve spool that is guided in a valve bore, which may be moved out of a spring-preloaded neutral position and into a first direction, in which a pressure-medium flow path is controlled open between a consumer port and the inlet port, and between another consumer port and an outlet port. When the valve spool is displaced in the other direction, in a first position, a pressure-medium flow path is controlled open between the other consumer port and the inlet port, and between the aforementioned consumer port and the outlet port. Preferably, this is an “extension” position, in which pressure medium flows out of the pressure chamber—on the piston rod side—of a differential cylinder, and in which pressure medium flows into the pressure chamber on the side opposite the piston rod. 
     According to the present invention, when the valve spool is displaced further in the other direction, the volumetric flow of pressure medium flowing away from a consumer port is added to that volumetric flow of pressure medium that flows toward the other consumer port; the directional control valve is then in a quick-action position. 
     When the valve spool is moved past the quick-action position, the two consumer ports and the inlet port are connected to the outlet port, thereby displacing the directional control valve into the floating position. 
     As a result, the valve system according to the present invention is designed to include a directional control valve, the valve spool of which may be moved into five positions, the floating position being reached preferably after the quick-action position has been passed. 
     According to the concept according to the present invention, these functions are activated by adjusting the directional control valve, and so, in contrast to the state of the art described initially, no additional control valves, which must be switched manually or via precontrol, or the like need to be provided. 
     The concept according to the present invention may be used for LUDV directional control valves, and for IS directional control valves, in which the pressures in front of and behind a metering orifice act on a pressure compensator, and for directional control valves for throttle controls (6-way valves with circulatory channel). 
     In a preferred embodiment of the present invention, in the quick-action position of the directional control valve, a residual cross section in the pressure-medium flow path between the one consumer port and the outlet port is controlled open. 
     In a specific solution, the valve spool is provided with a control edge, using which, when displaced in the other direction, an opening cross section in the pressure-medium flow path between the one consumer port and the outlet port may be controlled open, and in which at least one control or extension groove is formed on the valve spool at a distance from this control edge, using which, upon displacement in the other direction, an opening cross section between the one consumer port and the outlet port may be controlled open, and using which this opening cross section may be controlled closed upon further displacement of the valve spool in the direction of the quick-action position. Upon further displacement in the direction of the floating position, the aforementioned opening cross section is controlled open using the control edge. 
     That is, using this extension groove, the pressure-medium connection of the one consumer port to the outlet port is initially controlled open. Upon further displacement in the direction of the quick-action position, this pressure-medium connection is closed, and it is opened once more when the valve spool is displaced in the direction of its end position, in order to set the floating function using the control edge. 
     The extension groove is particularly easy to create when it is designed as a pocket—which is closed around the circumference—on the outer circumference of the valve spool. 
     In a preferred embodiment of the present invention, a longitudinal groove that determines the aforementioned residual cross section is designed parallel—in terms of hydraulics—to the extension groove, and using which a residual cross section in the pressure-medium flow path from one consumer port to the outlet port is controlled open when the valve spool is displaced to the quick-action function. This longitudinal groove has a smaller effective cross section than the extension groove. 
     In one variant of the present invention, the valve spool is preloaded into its neutral position using a centering spring system. This centering spring system includes a pressure-point spring that becomes operatively engaged when the valve spool is displaced in the direction of the floating position, thereby ensuring that the operator must set this floating position deliberately, by overcoming a resistance. 
     A centering spring system of this type typically includes two centering springs that act on the valve spool in both directions; one of these centering springs bears against the pressure point spring that is acted upon by a greater preload, and therefore the pressure point spring is not compressed initially when the valve spool is displaced. 
     In a solution having a very simple design, the pressure point spring is held captive on a stop bolt that is preloaded against a stop that is secured in the housing, and against which the valve spool moves, directly or indirectly, upon displacement in the direction of the floating position, and so the preload of the pressure point spring must be overcome for displacement to continue. 
     The design of the valve system is particularly simple when a quick-action channel is provided, using which—when the valve spool is displaced into its quick-action position and the directional control valve is circumvented—a return line that is connected to the one consumer port is connected to an inlet line that is connected to the inlet port; a return valve that blocks in the direction toward the consumer port is provided in the quick-action channel. When the opening cross section between the one consumer port and the outlet port is controlled closed via the extension groove, the pressure medium may then flow from the consumer via the quick-action channel to the other pressure chamber, and therefore the consumer is moved at a high rate of speed. 
     The directional control valve of the valve system is preferably designed as an LUDV directional control valve having a direction part and a speed part, the later being formed by a metering orifice. Located downstream thereof is an individual pressure compensator which is acted upon by the highest load pressure of all activated consumers in order to reduce the pressure-scale opening cross section, and is acted upon by the pressure downstream of the metering orifice to enlarge the opening cross section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the present invention is explained below in greater detail with reference to schematic drawings. In the drawings: 
         FIG. 1  shows a circuit diagram of a directional-control valve section of a mobile control block that includes a valve system according to the present invention; 
         FIG. 2  shows a specific design of the directional-control valve section depicted in  FIG. 1 , in a sectional view; 
         FIG. 3  shows an enlarged view of a directional control valve of the directional-control valve section depicted in  FIG. 2 , and 
         FIGS. 4   a  through  4   d  show the directional-control valve section depicted in  FIG. 2 , in the positions “retract”, “extend”, “quick-action”, and “float”. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a circuit diagram of a directional-control valve section  1  of a mobile control block of a mobile working machine, e.g., a crawler dozer. A mobile control block of this type includes a large number of directional-control valve sections which may be used to activate the individual hydraulic consumers of the working machine. In the following embodiments, it is assumed that directional-control valve section  1 , which is depicted in  FIG. 1 , is used to activate a lifting cylinder of a dozer blade in order to hold it in a predetermined position, lower or raise it, lower it quickly, or operate it in a floating position. In the depiction shown in  FIG. 1 , only those components of directional-control valve section  1  are shown that are essential to understanding the present invention. Further details are presented in the figures which are described below. The basic design of directional-control valve section  1  is known from aforementioned data sheet RD 64 284/06.00, and so only those elements that are essential to understanding the present invention will be described here. 
     As shown in the circuit diagram in  FIG. 1 , directional-control valve section  1  includes a pressure port P, two working ports A, B, tank ports T 1  T, a control port pst, and a control oil outlet port L. Pressure port P is connected to a pump line  2  that is connected to the pressure port of a not-depicted pump which is activated via an LS pump regulator as a function of the highest load pressure of all activated consumers in the working machine. This load pressure is tapped by the consumers via the LS port and a load-sensing channel  4 . The pumped quantity is adjusted via this pump regulator in a manner such that the pump pressure lies above the highest load pressure by a predetermined differential pressure. 
     Consumer ports A, B of the directional-control valve section are connected via consumer lines  6 ,  8  to a cylindrical chamber  10  on the bottom side, and to an annular chamber  12 , which is situated on the piston-rod side, of a hydraulic cylinder  14 . The direction of motion and the speed of hydraulic cylinder  14  are adjusted via a proportional directional valve  16 . It is provided with a speed part, which is formed by a metering orifice  18 , and a direction part  20 ; the pressure-medium volumetric flow to hydraulic cylinder  14  is determined via metering orifice  18 , and the direction of flow to or from pressure chambers  10 ,  12  is determined via direction part  20 . 
     According to the present invention, directional control valve  16  is provided with five settings, and a valve spool, which is described in greater detail below, is preloaded via a centering spring system  22  in a neutral position ( 0 ) in which the aforementioned ports are blocked. The valve spool is displaced using precontrol valves  24 ,  26 , which are designed, e.g., as pressure control valves, the pressure port of which is connected to control line pst, the tank port of which is connected to L, and the control output of which is connected to a control chamber on the valve spool. 
     When the valve spool is moved to the right (as indicated in  FIG. 1 ), the valve spool is first brought into the positions “extend”, which are labelled (A), in which hydraulic cylinder  14  extends and the dozer blade is lowered. When the valve spool is displaced further toward the right, the positions labelled (E) are reached, in which hydraulic cylinder  14  is operated using quick action. In this quick-action function, the volumetric flow of pressure medium from contracting annular chamber  12  is added to the volumetric flow of pressure medium being supplied to cylindrical chamber  10  via metering orifice  18 . By displacing the valve spool in the direction of its positions labelled (F), a floating position is attained, in which the dozer blade rests on the ground under its own weight and may follow uneven terrain. 
     When the valve spool is moved out of the neutral position ( 0 ) and in the opposite direction, i.e., to the left in  FIG. 1 , the valve spool settings labelled (H) are reached, in which hydraulic cylinder  14  is retracted and the dozer blade is lifted. 
     In the embodiment shown, an individual pressure compensator  28  is located downstream of metering orifice  18 , which is acted upon by the pressure in load-sensing channel  4 , i.e., by a control pressure that corresponds to the highest load pressure, in order to reduce the flow area, and it is acted upon by the pressure downstream of metering orifice  18  to increase the flow area. 
     The inlet port of individual pressure compensator  28  is connected via a pressure compensator channel  30  to a pressure port P′, and the outlet port of the pressure compensator channel is connected via a curved channel  32  to port P″ of directional control valve  16 . A load-holding valve  34  is located in curved channel  32  to support the load in a zero-leakage manner. A working port A of directional control valve  16  is connected via a forward-flow channel  36  to consumer port A, and consumer port B of directional control valve section  1  is connected via a return channel  38  to working port B of directional control valve  16 . Tank ports T, T 1  of directional control valve  16  are connected via outlet channels  40 ,  42 , respectively, to tank ports T, T 1  of directional-control valve section  1 . Pressure port P of directional control valve  16  is connected via an inlet channel  44  to pressure port P of directional-control valve section  1 . 
     As shown in  FIG. 1 , return channel  38  is connected via a quick-action channel  46  to the section of curved channel  32  that lies between pressure port P″ and load-holding valve  34 . A return valve  48  which opens in the direction toward pressure port P″ is provided in quick-action channel  46 . When the valve spool is moved into the “quick action” position (E), pressure medium that is displaced from annular chamber  12  may flow via quick-action channel  46  and return valve  48 , which is opening, toward port P″ of directional control valve  16 , and therefore this outflowing volumetric flow of pressure medium is added to the volumetric flow of pressure medium that is flowing from metering orifice  18  to cylindrical chamber  10 . 
     As likewise indicated in  FIG. 1 , in the case in which the pressure downstream of metering orifice  18  is greater than the pressure in load-sensing channel  4  in that instant, the pressure-compensator sliding element is moved to its left end position, as shown in  FIG. 1 , and therefore this pressure, which is present downstream of metering orifice  18 , is signaled in load-sensing channel  4 . 
       FIG. 2  shows a specific embodiment of directional-control valve section  1  depicted in  FIG. 1 , in a sectional view. As mentioned, directional-control valve section  1  is part of a mobile control block that is formed of a large number of directional-control valve sections of this type, and of an input element and an end plate. Directional-control valve section  1  includes a valve disc  50 , in which a valve bore  54  that accommodates valve spool  52  is formed. As shown in  FIG. 2  and in the enlarged depiction in  FIG. 3 , valve bore  54  expands to include, as viewed from left to right, a tank chamber  56 , a forward-flow channel  58 , a pressure-compensator outlet chamber  60 , a pressure-compensator inlet chamber  62 , an inlet chamber  64 , a further pressure-compensator outlet chamber  66 , a return chamber  68 , and a further tank chamber  70 . The expressions “forward-flow . . . ”, “return . . . ”, etc. are selected merely to simplify the description; depending on the switching position of directional control valve  16 , return chamber  68  may also lie in the forward flow, for example. As indicated in  FIG. 2 , tank chamber  56  is connected via outlet channel  40  to tank port T, forward-flow chamber  58  is connected via forward-flow channel  36  to consumer port A, and pressure-compensator outlet chamber  60  is connected via quick-action channel  46  and return valve  48  to return chamber  68 ; in the embodiment shown in  FIG. 1 , pressure-compensator outlet chamber  60  corresponds to port P″. Return chamber  68  is connected via return channel  38  shown in  FIG. 2  to consumer port B. Finally, tank chamber  70  has a pressure-medium connection via outlet channel  42  to tank port T 1 . 
     The design of valve spool  52  will be described with reference to the enlarged depiction in  FIG. 3 . As shown in  FIG. 3 , valve spool  52  is subdivided via a plurality of interspaced annular grooves into two end collars  72 ,  74 , a tank control collar  76 , an inlet collar  78 , a control collar  80  that determines the opening cross section of metering orifice  18 , an intermediate collar  82 , and an inlet collar  84 . A tank control edge  85  is formed on tank control collar  76 , an inlet control edge  86  is formed on inlet collar  78 , a metering-orifice control edge  88 ,  90  is formed on each end face of control collar  80 , an inlet control edge  92  is formed on inlet collar  84 , and a floating-position control edge  94  is formed on the opposite annular end face of end collar  74 . 
     Aforementioned control edges  85 ,  86 ,  88 ,  90 ,  92 ,  94  are each provided with control grooves or control windows  96  in known manner; only one of the control windows that is assigned to floating-position control edge  94  is provided with a reference numeral, as an example, in  FIG. 3 . 
     At a distance from control windows  96  of floating-position control edge  94 , an extension groove  100 , which extends parallel to directional-control valve axis  98 , is formed on the outer circumference of valve spool  52 , the right—as shown in FIG.  3 —end section of which is covered, in the neutral position ( 0 ), by the annular segment between control chambers  68 ,  70 . The left—as shown in FIG.  3 —end section of extension groove  100  is not connected to adjacent control windows  96 , and therefore extension groove  100  is formed as a pocket that is closed around the circumference. 
     Situated parallel to and at a distance from extension groove  100 , a longitudinal groove  102  is formed on the outer circumference of end collar  74 , the width (as viewed in the circumferential direction) and length (as viewed in the axial direction) of which are less than those of extension groove  100 . As shown in  FIG. 3 , longitudinal groove  102  leads into lower control window  96  of floating-position control edge  94 . In the neutral position ( 0 ) shown, longitudinal groove  102  is open toward return chamber  68 . As shown in  FIG. 2 , return chamber  68  is connected via quick-action channel  46 , which is designed as an angled bore, and return valve  48  inserted therein, to pressure-compensation outlet chamber  60 ; the return valve opens toward pressure-compensation outlet chamber  60 . 
     In the neutral position ( 0 ) of valve spool  52  shown in  FIGS. 1 through 3 , ports P, A, B, P′, P″, T, T 1  of directional control valve  16 , which are visible in  FIG. 1 , are blocked. Accordingly, as shown in  FIG. 3 , the pressure-medium connection between chambers  56 ,  58  is blocked via tank control edge  85 , the pressure-medium connection between chambers  58 ,  60  is blocked via inlet control edge  86 , the pressure-medium connection between chambers  64  and  62  is blocked via metering-orifice control edges  88 ,  90 , the pressure-medium connection between chambers  66 ,  68  is blocked via inlet control edge  92 , and pressure-medium connection between chambers  70 ,  68  is blocked via extension groove  100 , and therefore the consumer is fixed in its position shown. 
     Individual pressure compensator  28  shown in  FIG. 1  has been inserted into a pressure-compensator bore  104  that extends perpendicularly to directional-control valve axis  98 ; a pressure-compensator piston  106  is acted upon on the end face, i.e., from the bottom to the top as shown in  FIG. 2 , by the pressure in pressure-compensator inlet chamber  62 , and it is acted upon on the back side by the highest load pressure tapped in load-sensing channel  4 , which is present in a rear annular chamber  108  of pressure-compensator bore  104 . When the pressure-compensator cross section is controlled fully open (pressure-compensator piston  106  is displaced upwardly in the figure), the pressure in pressure-compensator inlet chamber  62  is signaled via inner bores  110  in pressure-compensator piston  106  into annular chamber  108  and, therefore, into load-sensing channel  4 . 
     Centering spring system  22  shown in  FIG. 1  is accommodated, as shown in  FIG. 2 , in spring housings  112 ,  114 , into which the two end sections of valve spool  52  extend. In the left—as shown in FIG.  2 —spring housing  115 , a centering spring  116  is supported, and acts via a spring bushing  118  on the adjacent end face of valve spool  52 ; the displacement of spring bushing  118  to the right—as shown in FIG.  2 —is limited by a stop  120  that is secured in the housing. The displacement of valve spool  52  to the left—as shown in FIG.  2 —is limited by a displacement-limiting element  122 . 
     A centering spring  124  is likewise supported in right spring housing  112 , and acts via a spring plate  126  on an annular end face of valve spool  52  that enters centering spring  124  via a radially recessed end section  128 . 
     A pressure-point spring  130  is provided, approximately in the extension of centering spring  124 , in spring housing  112 ; pressure-point spring  130  is fixed on a stop bolt  132  between a stop ring  134  and a support ring  136  of stop bolt  132 . Rings  134 ,  136  bear against stop bolt  132  in opposite directions. Centering spring  124  bears against support ring  136 , and the spring preload of pressure point spring  130  is greater than that of centering spring  124 . In the neutral position shown, stop bolt  132  is preloaded via centering spring  124  via its stop ring  134  against a stop  138  in the spring housing; spring plate  126  bears against a stop in the housing. In neutral position ( 0 ) shown, a left —as shown in FIG.  2 —end face  142  of stop bolt  132  is located with axial clearance from the adjacent end face of end section  128  of valve spool  52 . When the valve spool is moved to the right, end section  128  moves toward end face  142  of stop bolt  132 , which is then moved along—while the pressure point spring is shortened—to an end stop  144  of spring housing  112 . 
     Pressure control valve  24 , which is used to activate the directional control valve, is also apparent on the directional-control valve section shown in  FIG. 2 . 
     The function of aforementioned directional-control valve section  1  will be explained with reference to  FIG. 4 , in which positions (A), (E), (F) and (H) per  FIG. 1  are shown. 
     In the illustration shown in  FIG. 4   a , valve spool  52  is displaced, by setting a suitable control pressure, to the left via pressure-control valve  26  into its positions labelled (H), in which a pressure-medium connection between inlet chamber  64  and pressure-compensator inlet chamber  62  is controlled open via metering-orifice control edge  90 ; this controlled-open cross section forms the flow area of metering orifice  18 . The pressure medium may then flow, via individual pressure compensator  28  and curved channel  32  to pressure-compensator outlet chamber  66 , and, from there, enters return chamber  68  via the cross section that was controlled open by floating-position control edge  94 ; from return chamber  68 , it flows to consumer port B and, from there, via consumer line  8  to annular chamber  12  of lifting cylinder  14 . The pressure medium that is displaced out of contracting cylindrical chamber  10  enters—via consumer line  6 , consumer port A, forward-flow channel  36 , which now functions practically as a return channel—forward-flow chamber  58  which is connected via tank control edge  85  to tank chamber  56 , and therefore the pressure medium flows via outlet channel  40  and tank port T of directional-control valve section  1  to tank. That is, when valve spool  52  is moved into positions (H), lifting cylinder  14  is retracted, and the dozer blade is therefore raised. 
     To lower the dozer blade, directional valve spool  52  as shown in  FIG. 4   b  is moved to the right by setting a suitable control pressure via precontrol valve  24 , as shown in the illustrations in  FIGS. 1 through 3 ; the opening cross section of metering orifice  18  between inlet chamber  64  and pressure-compensator inlet chamber  62  is then determined via metering-orifice control edge  88 . The pressure medium that flows away from individual pressure compensator  28  flows via curved channel  32  into pressure-compensator outlet chamber  60  and, from there, through the cross section, which was controlled open via inlet control edge  86 , into inlet chamber  58 , and then via forward-flow channel  36 , consumer port A, and consumer line  6  into cylindrical chamber  10 . The pressure medium that is displaced from annular chamber  12  flows via consumer port B, return channel  38 , return chamber  68 , and then via the cross section that was controlled open via extension groove  100  into tank chamber  70  and, from there, to the tank. Parallel to the opening cross section, which is determined by extension groove  100 , an opening cross section between chambers  68 ,  70  is likewise opened, via small longitudinal groove  102 . 
     As a result, when the valve spool is in positions (A), lifting cylinder  14  is extended in order to lower the dozer blade. 
     When valve spool  52  is displaced further to the right—as shown in  FIG. 4   c —into the quick-action positions labelled (E) in  FIG. 1 , the left—as shown in  FIG. 4   c —end section of extension groove  100  overlaps the annular segment between chambers  68 ,  70 , and therefore the pressure-medium connection is blocked via extension groove  100 . However, only the relatively small residual cross section remains via longitudinal groove  102  which is still open toward return chamber  68  and toward tank chamber  70 . Floating-position control edge  94  is likewise ineffective in this position. Via longitudinal groove  102 , a certain quantity of pressure medium therefore flows toward the tank; this partial flow is lost to the actual quick-action volumetric flow. The main portion of the pressure-medium volumetric flow flows from return chamber  68  via quick-action channel  46  and return valve  48 , which then opens, into pressure-compensation outlet chamber  60 , where it is added to the pressure-medium volumetric flow that flows from inlet chamber  64  via the metering-orifice cross section, which has been controlled open by metering-orifice control edge  88 , to individual pressure compensator  28  and, from there, via curved channel  32  into pressure-compensator outlet chamber  60 . This relatively great quick-action volumetric flow is then directed via the cross section that was controlled open by inlet control edge  86 , forward-flow chamber  58 , and consumer port A to cylindrical chamber  10  of lifting cylinder  14 . 
     Due to the design of control edge  86  to include control windows having a flow area that is smaller than an entire flow area, it is made possible for such a pressure to build up in annular chamber  12  that the load does not drop in an uncontrolled manner, but rather that the speed of the load is specified by the quantity of pressure medium that is pumped by the pump. Due to control edge  86 , the pressure decreases from the high pressure in annular chamber  12  to the lower pressure in cylindrical chamber  10 . 
     The quantity of pressure fluid that is not useful for quick action and flows away via longitudinal groove  102  is dependent on the pressure in cylindrical chamber  12  of lifting cylinder  14 . 
     As  FIG. 4   c  also shows, in this position (E), end section  128  of the directional-control valve piston moves toward end face  142  of stop bolt  132 , and this displacement of valve spool  52  initially takes place only against the force of centering spring  124 —pressure point spring  130  has not yet contracted. This is the case because it is preloaded with a greater amount of force than is exerted by spring  124  in position (E). 
     Valve spool  52  may then be displaced in the direction of floating position (F) only against the force of pressure point spring  130 . Floating position (F) is shown in  FIG. 4   d . In this position, the connection between inlet chamber  64  and pressure-compensation inlet chamber  62  is blocked by the right—as shown in  FIG. 4   d —end section of inlet collar  78 . However, inlet chamber  64  is connected in a throttled manner via metering-orifice control edge  90  to pressure-compensation outlet chamber  66  which is open toward return chamber  68 . The latter is connected via floating-position control edge  94  to tank chamber  70 , thereby enabling the pressure medium to flow from inlet chamber  64  to the tank. Accordingly, consumer port B is likewise connected via return chamber  68 , floating-position control edge  94 , and tank chamber  70  to the tank. The other consumer port A is likewise connected to the tank via forward-flow chamber  58  and tank chamber  56 , which has therefore been controlled open via the annular groove between collars  72 ,  76 , thereby enabling the dozer blade, in this floating position, to track uneven terrain or to flatten it using its weight. As explained above, floating position (F) may be attained only by overcoming the preload of pressure point spring  130 , and therefore the operator receives clear feedback as to when floating position (F) has been reached. When pressure point spring  130  contracts, stop bolt  132  is driven by end section  128  of valve spool  52  until the right—as shown in  FIG. 4   c —end section of stop bolt  132  moves toward end stop  144 . Further displacement toward the right is prevented. 
     In the above-described solution, valve spool  52  may be displaced into five positions in order to implement the functions “extend/retract lifting cylinder”, “quick action of the lifting cylinder”, “floating position of the lifting cylinder”, and “move to a neutral position”. 
     Disclosed herein is a valve system that includes a proportional directional valve, the valve spool of which may be displaced in the direction of five positions in order to activate a consumer in two directions, move it using quick action, operate a floating position, or block the pressure-medium connection to the consumer (neutral position).