Abstract:
The invention relates to a valve that comprises at least one pump connection ( 10 ), one tank connection ( 14 ) and one consumer connection ( 18 ), and a valve piston ( 22 ) that is displaced within the valve box ( 12 ). Said valve piston separates the pump connection ( 10 ) from the tank connection ( 14 ) in at least one blocked position and interacts with an energy accumulator ( 24 ). A fluid stream that flows between the consumer connection ( 18 ) and the tank connection ( 14 ) is controlled by means of a control device ( 26 ). The control device ( 26 ) is configured as a fluid stream control that is integrated in the valve piston ( 22 ) and that allows, contrary to known valves which use a diaphragm construction, reduction, by a constant value, of the volume flow to the consumer in a load-independent manner, thereby allowing for a proportional load-independent control.

Description:
FIELD OF THE INVENTION 
     The invention relates to a valve having at least one pump connection, one tank connection, and one appliance connection and a valve piston positionable inside the valve housing, which piston separates the pump connection from the tank connection in at least one blocked position and which operates in conjunction with an energy accumulator, a self-adjusting fluid flow being controllable by means of a control device between the appliance connection and the tank connection. 
     BACKGROUND OF THE INVENTION 
     Such valves are routinely used in so-called hydraulic load sensing systems or control means and operate there like a piston manometer, directing an unneeded pump feed flow back to the tank. In order to prevent leakages in the appliance circuit from raising the appliance pressure to the performance level of the pump and thereby possibly disabling the load sensing system, the load on the appliance connection to the tank is to be removed. Such load removal is currently effected in a cost-effective manner by use of aperture control means, the aperture preferably being integrated directly into the piston manometer or being used separately in a control unit which is part of the load sensing control mechanism. 
     A disadvantage of these known solutions with the aperture design feature is the pressure dependence of the volume flow draining to the tank. In the case of appliances whose volume flow is independent of load, proceeds by way of proportional valves, for example, this then results in constant slowing of the appliance with increase in the load pressure, something which has an especially negative effect in the case of appliances with a low volume flow. 
     SUMMARY OF THE INVENTION 
     On the basis of this state of the art the invention pursues the object of further improving known valves to the end that such valves will not be characterized by the disadvantages described, especially when employed in so-called load sensing systems. In addition, it is to be possible to reduce the valve cost efficiently and so that the valve occupies little space. The object as thus formulated is attained by means of a valve having the features specified in claim  1 . Since, as specified in the descriptive portion of claim  1 , the control device consists of a fluid flow controller integrated into the valve piston it is possible, in contrast with known valve solutions, to use the aperture design to reduce the volume flow to the appliance, independently of the load, by a constant value, so that proportional load-independent control is effected. The disadvantages of the state of the art as described, in the form of slowing of the appliance in particular, are thus reliably excluded. The solution with the fluid flow controller claimed for the invention can be cost effectively applied and space-saving installation in the valve itself is possible as a result of integration of the fluid flow controller into the valve box. Since the valve claimed for the invention has only a few structural components, reliability of operation is ensured which benefits the load sensing system as a whole. 
     Other advantageous embodiments are specified in the dependent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The valve claimed for the invention is explained in detail in what follows with reference to the drawing, in which, in diagrammatic form and not to scale, 
     FIG. 1 presents a longitudinal section through the valve claimed for the invention; 
     FIG. 2 in the form of a circuit diagram, illustrates use of the valve as shown in FIG. 1 in the case of a load sensing system with an operating cylinder as hydraulic appliance. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The valve shown in longitudinal section in FIG. 1 has a pump connection  10 , specifically on the front end of a valve box  12 , designed as a screw-in cartridge to be secured in control units or the like for subsequent use. Configuration as a built-in set or the like is also possible. The valve box  12  has at its end facing the pump connection  10  two first tank connections  14  diametrically opposite each other. As viewed in the line of sight to FIG. 1, mounted above them (as shown in the left half of the illustration) is another separate tank connection  16  whose free open cross-section is smaller than the corresponding diameter area of the first tank connections  14 . On the other hand, another cross bore which serves as appliance connection  18  has been introduced into the valve box  12 . The tank connections  14  and  16  also are in the form of cross bores in the valve box  12 . The connections  14 ,  16 , and  18  in question extend more or less transversely to the longitudinal axis  20  of the valve box  12 . The pump connection  10 , in contrast, is mounted along the longitudinal axis  20  of the valve box  12 , on the front side of the latter. 
     Mounted in the valve box  12  so as to be longitudinally positionable is a valve piston  22  the external circumference of which is provided with pressure relief ducts by conventional means, which accordingly are not described in detail. In one of its blocked positions as shown in FIG. 1 this valve piston in any event separates the pump connection  10  from the tank connection  14 . Furthermore, the valve piston  22  operates in conjunction with an energy accumulator  24 , it being possible to activate a self-adjusting fluid flow between the appliance connection  18  and the tank connection  14  by means of a control device identified as a whole as  26 . The control device  26  in question consists in particular of a fluid flow regulator which is integrated into the valve piston  12  and is explained in greater detail in what follows with respect to its structure and function. 
     The fluid flow regulator in question has a flow regulating piston  28  which is controlled in the valve piston  22  so as to be longitudinally positionable, the inner circumference of the valve piston  22  encircling the outer circumference of the flow regulating piston  28 . The flow regulating piston  28  in turn rests on another energy accumulator  30 , the direction of operation of which is opposite that of the first energy accumulator  24 . Along the longitudinal axis  20  of the valve box  12 , and so in the center, the flow regulating piston  28  has a fluid channel  32 , which, at least in one displaced position of the flow regulating piston  28  as shown in FIG. 1, discharges into a fluid channel  34  the valve piston  22  which, again in the displaced position shown in FIG. 1, establishes a fluid-conducting connection with the separate tank connection  16  in the valve box  12 . In each displaced position of the valve piston  22  the latter separates the first tank connections  14  from the other separate tank connection  16 . 
     The fluid channel  32  of the flow regulating piston  28  may, on its side facing the appliance connection  18 , be sealed by a control piston  36  which is held in the direction of this locking position by way of the first energy accumulator  24 . On its end in this direction the fluid channel  32  has a throat and, as shown in FIG. 1, discharges into the open at its end with reduced cross-section. The control piston  36  in question has as contact component a cup  38  which is in the form of a hemisphere and, with its curved frontal engaging surface, is provided for fluid-conducting introduction into the fluid channel  32  of the flow regulating piston  28 . In the position illustrated and in every other shifted position the cup  38  leaves the free end of the fluid channel  32  with its reduced cross-section clear for passage of fluid. As is to be seen in the line of sight to FIG. 1, a flange-like enlargement  40  is mounted above the cup  38 ; the free end of the pressure spring which forms the first energy accumulator  24  rests on this enlargement. The other free end of the pressure spring as energy accumulator  24  is in contact with an end stop  42  which is screwed into the valve box  12  on the end opposite the pump connection  10  and is secured in this manner. On its end facing the end stop  42  the control piston  36  has a stop face  44  which maintains axial spacing from the end stop as seen in the longitudinal direction of the longitudinal axis  20  also when the valve is in the usual operating state. 
     As a result of the action of the energy accumulator  24  and of the control piston  36 , the flow regulating piston  28  is held down in the direction of a lower position, as viewed in the line of sight toward FIG.  1 . Acting against the direction of action in question, within the integrated system represented by flow regulating piston  28  and valve piston  22 , there is another energy accumulator  30  in the form of a pressure accumulator one lower end of which rests on the valve piston  22  and the other end of which rests on the flow regulating piston  28  in such a way that it is introduced into the fluid channel  32  of the flow regulating piston  28 . For the purpose of such introduction the diameter of the fluid channel  32  of the flow regulating piston  28  is enlarged in the direction of its lower free end. 
     The flow regulating piston  28  is guided in the interior of the valve piston  22 , which for this purpose has a cylindrical interior recess; when a fluid connection has been established among the separate tank connection  16 , the fluid channel  34 , and the fluid channel  32 , the upper front ends of valve piston  22  and flow regulating piston  28  come together while more or less level in one plane which extends transversely to the longitudinal axis  20 . In the configuration in question the lower free end of the flow regulating piston  28  is spaced an axial distance from the lower receiving end of the valve piston  22  such that the latter comes to rest flush against the upper edge of the part of the fluid channel  34  which faces the interior of the valve piston  22 . The side of the fluid channel  34  facing away from the valve piston  22  widens into an annular recess  46  the upper edge of which fits snugly, in the circuit diagram shown in FIG. 1, against the separate tank connection  16 . In addition, the lower free end of the other energy accumulator  30  in the form of the pressure spring is received into an interior recess on the bottom side of the valve piston  22  and in this way supported in this position. The appliance connection  18  discharges into a valve space  48  of the valve box  12  through which extend the control piston  36  and the first energy accumulator  24 . In addition, the valve box  12  has for the valve piston  22 , on its side facing the valve space  48 , a stop surface  50 , in the form of a retaining ring (not shown), for example. As a result, the valve piston  22  may be freely positioned downward in the line of sight to FIG. 1 of the pump connection  10 , while the positioning path is limited in the opposite direction. 
     As a function of the pressure loads on the appliance connection  18 , also designated as load connection, the cup  38  as closing component is held back against the action of the energy accumulators  24  and  30  and/or the flow regulating piston  28  is positioned downward in the valve piston  22  as viewed in the line of sight to FIG. 1, so that fluid channel  32  is fully released. The configuration in question may be adjusted so that the volume flow to the appliance may be reduced free of load by a constant value so that proportional load-independent control is also possible if leaks occur. 
     The block diagram presented in FIG. 2 shows how proportional load-independent control may be effected for this purpose. This figure illustrates a basic circuit concept of a so-called load sensing system, a fixed-displacement pump  52  being employed in the embodiment shown in FIG.  2 . Variable-displacement pumps (not shown) may be appropriately used rather than the fixed-displacement pumps in question. The purpose of the load sensing referred to is achievement of optimized energy utilization, the load pressure returned to a regulating element in the form of the valve being employed to adjust the output provided hydraulically by way of the fixed-displacement pump  52  to that of an appliance, in this instance in the form of a hydraulic working cylinder  54 . Proportional control elements are generally employed to drive the appliance, in this instance in the form of the hydraulic working cylinder  54 , even on the basis of the operating comfort desired; exclusively for the sake of greater simplicity of presentation an adjustable throttle  56  is used here in place of the proportional control valves as drive component for the hydraulic working cylinder  54 . The appliance volume flow may be varied, and accordingly the working cylinder  54  actuated, by way of the control throttle or control stop  56 . The appliance volume flow is determined from the free throttle opening cross-section Q and the pressure difference Δp at the throttle  56  as measured at sensing points  58  upstream and downstream from the throttle  56 . 
     In the load sensing systems in question the valve piston  22  is assigned the function of a kind of piston manometer, the flow regulating piston  28  as part of the control device  26  reducing the volume flow to the appliance  54  independently of load by a constant value in the event of leaks in the hydraulic appliance circuit  62 . The difference Δp as measured between the two sensing points  58  is accordingly predetermined by the spring tension of the energy accumulator  24  which engages the piston manometer in the form of the valve piston  22  and is kept constant by adjustment of the piston manometer. Equilibrium then more or less prevails at the valve piston  22  as piston manometer:          Δ                 p     =         spring                 tension                 of                 energy                 accumulator                 24       surface                 area                 of                 valve                 piston                 22       =   constant                            
     Consequently, a directly proportional relationship is obtained between the free cross-section Q of the control throttle  56  and the appliance volume flow proper. If an additional force in the form of an additional load in the direction of the appliance circuit  62  is applied to the cylinder rod  64  of the working cylinder  54 , the piston manometer in the form of the valve piston  22  is forced into its blocked position as shown in FIG. 2, in which the pump connection  10  is separated from the first tank connection  14  and the fixed displacement pump  52  correspondingly delivers to the piston side  66  of the working cylinder  54  the amount of fluid required to offset the additional load applied. If, however, the working cylinder  54  removes load in the opposite direction, the applied load in question must be offset by a constant load and the fixed-displacement pump  52 , which otherwise is secured in the direction of the tank  68  by a pressure control valve  60 , now pumps directly by way of the freed connection to the first tank connections  14 , the valve piston  22  as piston manometer being retracted in a suitably elevated displacement position in the direction of the appliance connection  18  (see FIG.  1 ). 
     If a plurality of appliances is connected to a load sensing system and is supplied by a common fixed-displacement pump  52 , the load sensing lines must be linked so that suitable load sensing control of the valve configuration described may be exerted. 
     If leaks occur in the hydraulic circuit  62  to which the appliance  54  is connected or in the appliance  54  itself, the control device designated as a whole as  26  makes certain that the appliance pressure does not rise undesirably to the pump level, something which would have the result that the load sensing would be disabled. This is prevented by the control device  26 , which relieves the load on the appliance connection  18  to the tank  16 . The volume flow to the appliance is reduced by a constant value independently of load by the flow regulating device, so that proportional load-independent control is provided. Slowing of the operating process by the appliance  54  with increase in load pressure is reliably prevented. Integration of the flow regulating device into the piston manometer results in a compact structure with a small number of components and the maintenance situation is improved in the case of the valve claimed for the invention.