Patent Publication Number: US-6904938-B2

Title: Locking block

Description:
The invention relates to a stop block for connecting an operating port to a pressure port and a tank or low-pressure port. 
   Stop blocks of this kind are used, for instance, in the mobile hydraulics for controlling double-acting hydraulic cylinders which are provided, for example, for operating front-end power lifts, rear-end power lifts or other peripheral machines, such as cutter bars, packers etc. The control of the hydraulic cylinders is effected, for instance, via a valve arrangement as it is known from DE 197 34 479 A1. This valve arrangement has a disk design and includes a proportional valve including a directional member and a speed member through which a pressure port can be connected alternatively to two operating ports. The two operating ports are communicated with a cylinder chamber and an annular chamber, resp., of the hydraulic cylinder to be controlled. A generic stop block designed as a pilot controlled check valve arrangement is assigned to each of the operating ports. In its non-return function the stop block permits a fluid supply from the proportional valve to the assigned operating port, while the stop block connected in parallel and assigned to the other operating port controls in its return function the return pass of the fluid from the hydraulic cylinder to a tank or low-pressure port. 
   Each stop block includes a main piston biased against a valve seat which controls to increase a connection between the pressure port and the assigned operating port in the non-return function. For controlling to open the main piston in the return function a push piston to which a control pressure is applicable is assigned to the former, by which push piston the main piston can be brought into its opening position so as to increase the connection between the operating port and the tank port. The push piston opens an advanced opening of the main piston so that the front face thereof effective in the closing direction is relieved and the push piston is adapted to lift the main piston off the valve seat by the effect of the control pressure. The push piston is supported at the neighboring front face of the main piston by a spring. In this pressure chamber receiving the spring the pressure, i.e. the pump pressure, is applied to the pressure port in the non-return function (extending the hydraulic cylinder). On the other hand, in the return function (run-in of the hydraulic cylinder) the load pressure is applied to the consumer in this pressure chamber. When changing over from the non-return function to the return function or vice versa first the respective pressure has to be reduced in the pressure chamber before the respective other function can become effective. In the known solution, for instance, when changing over from the non-return function to the return function during the axial displacement of the push piston caused by applying a control pressure a tank passage is increased via a control edge so that the pressure chamber is relieved toward the tank. In the initial phase, however, the pump pressure still acts in said pump chamber so that the response characteristic of the valve arrangement, especially when it is quickly changed over, does not meet the requirements under particular operating conditions. 
   Compared to that, the object underlying the invention is to provide a stop block which permits a quick change-over between the return function and the non-return function and vice versa. 
   This object is achieved by a stop block as described herein. 
   In accordance with the invention, the pressure chamber between the main piston and a push piston is always relieved toward a tank or low-pressure port so that delayed response characteristic representing a drawback in the prior art cannot occur due to the required pressure reduction in said pressure chamber. 
   In such an especially preferred embodiment an end portion of the push piston is sealingly guided in a front recess of the main piston so that the pressure chamber is only confined by the push piston and the main piston designed to have an advanced opening. 
   The latter is preferably designed as a step piston, the surface difference being effective in the closing direction so that the push piston can be returned to its closing position as soon as possible. 
   In the case of the valve according to the invention the advanced opening of the principal cone is opened through the push piston in the return function so that a rear chamber of the main piston is relieved toward the tank or low-pressure port. 
   The annular chamber confined by the radial shoulder of the main piston is hydraulically connected, on the one hand, to a pilot passage downstream of the pilot valve seat and, on the other hand, to the operating port. In the fluid flow path from the annular chamber to the operating port a nozzle is provided whose effective diameter is considerably smaller than that of the advanced opening so that an effective relief of the pressure is possible in the annular chamber and in the pilot passage. In an especially simple embodiment this nozzle is formed by an axial groove at the outer periphery of the main piston. 
   The smaller diameter of the main piston preferably has the same diameter as the push piston. 
   It is especially simple to manufacture the stop block according to the invention if a passage through which the pressure chamber is connected to the tank or low-pressure port is formed in the push piston. 
   In a particularly preferred embodiment the hydraulic connection between the pilot passage and the annular chamber is reduced when the main piston is lifted off its valve seat and the opening cross-section between the annular chamber and the assigned operating port is increased so that differences in pressure due-to a leakage via the increased advanced opening and thus shifts of the return characteristic can be avoided. 
   With a further displacement of the push piston a connection between the operating port and the tank port is increased so that the fluid can flow off from the hydraulic cylinder to the tank. 
   A check spring arrangement biasing the main piston in the closing direction on the one hand acts as a check valve spring permitting the flow to the consumer in the non-return function and, on the other hand, as a control spring for controlling the return pass from the consumer to the tank. 
   As a check valve spring this spring should be designed to be relatively weak so that no major pressure losses occur above the check valve. As a control spring, on the other hand, the spring should have a steeper characteristic curve to permit a good response characteristic during the return pass control. 
   In order to ensure these contradicting requirements to the check spring arrangement, the check valve arrangement is formed by combining a is weak check spring and a control spring having a steep characteristic curve, wherein the comparatively weak check spring determines the non-return function while the control spring having a steep spring characteristic is operatively connected only after a predetermined axial movement of the main piston to control the return function. 
   The structure of the stop block is especially simple when the main piston is guided in a sleeve inserted in a valve housing (valve disk) at the outer periphery of which a flange is provided for sealing. At the outer periphery of the main piston preferably a slide ring sealing is formed so that the leakage of the check valve is minimal even in the case of high load pressures. 
   Other advantageous further developments of the invention are also described herein. 

   
     Hereinafter two preferred embodiments of the invention are described in detail by way of schematic drawings in which: 
       FIG. 1  shows a section across a stop block according to the invention and 
       FIG. 2  shows a variant of the stop block illustrated in FIG.  1 . 
   

     FIG. 1  shows a longitudinal section across a stop block  1  which is inserted in a location hole  4  of a plate-like valve housing  2 . 
   A control passage  6 , a tank passage  8 , an operating passage  10  and a pressure passage  12  which are connected to a control port S, a tank port T, an operating port A and a pressure port P, resp., of the valve arrangement open into this location hole  4  via annular chambers. 
   In the location hole  4  there is inserted a sleeve  14  in which a main piston  16  is guided in an axially movable manner. In the embodiment shown in  FIG. 1  the sleeve  14  extends from the face of the valve housing on the right in  FIG. 1  to the operating passage A. In this area a flange  18  which is sealingly adjacent to the circumferential wall of the location hole  4  when inserting the sleeve  14  is formed at the outer periphery in the sleeve  14 . 
   The main piston  16  is a step piston, wherein a part  22  having a larger diameter D3 is guided in sections in a radially extended area of an inside bore  20  of the sleeve  14 . This radially extended part  22  of the main piston axially projects from the sleeve  14  and is biased in the represented home position via a check spring arrangement  24  against a valve seat  26  formed in the area between the pressure passage  12  and the operating passage  10  at the location hole  4 . In the area of the valve seat  26  the main piston  16  is provided with a radially projecting annular collar  28  which immerses in an appropriately formed graduation of the location hole  4 . The annular collar  28  controls a further flow cross-section positioned in series with a flow cross-section at the valve seat  4  between its one 360 degree edge and a 360 degree edge in the location hole  4  of the valve housing  2 . This further flow cross-section namely starts to open when the flow cross-section at the valve seat is already wide open. By way of such a design the forces originating from the flow of fluid and acting in the closing direction are kept low. The annular collar  28  moreover enlarges the surface at the main piston  16  at which a pressure acting in the opening direction can be provided. On the whole, in this way the pressure drop is kept low with a flow of the fluid from the pressure passage  12  through the main piston  16  to the operating passage  10 . 
   The section  22  of the main piston  16  having the diameter D3 is stepped back via a radial shoulder  32  to the diameter D1, wherein this stepped back end section  30  is guided in an appropriately radially reset area of the inside bore  20 . The end section  30  has a slide ring sealing  34  at its outer periphery so that an annular chamber confined by the radial shoulder  32  of the main piston  16  and the opposite shoulder of the inside bore  20  of the sleeve  14  is sealed hydraulically against a spring chamber  36  for the check spring arrangement  24 . This spring chamber  36  is closed in axial direction by a sealing plug  38  screwed into the sleeve  14 . 
   The main piston  16  is designed to have an advanced opening and has a front recess  40  in the bottom of which a pilot passage  42  passing through the end section  30  of the main piston  16  ends. In the mouth area of the pilot passage  42  a pilot valve seat  44  is formed against which a pilot valve member  46  is biased by a weak pilot spring  48 . The latter is supported at a bolt  50  which is screwed into the pilot passage  42  and whose end section on the right in  FIG. 1  axially projects from the main piston  16 . A check spring  52  of the check spring arrangement  24  supported at the screwed sealing plug  38  acts on this end section of the bolt  50  so that the main piston  16  is biased in the home position shown in  FIG. 1  via this comparatively weak check spring  52  against its valve seat  26 . 
   The check spring arrangement  24  moreover includes a control spring  54  having a steeper spring characteristic curve than the aforementioned weak check spring  52 . This control spring  54  is supported at a spring plate  56  formed at an axial distance from the face of the end section  30  shown on the right in FIG.  1 . This spring plate  56  is supported at a radial shoulder in the inside bore  20  of the sleeve  14 . The other end section of the control spring  54  is adjacent to the screwed sealing plug  38 . The control spring  54  only becomes effective when the end section  30  of the main piston  16  abuts against the spring plate  56 . Several radial bores  58  connected with the annular chamber  34  in the closing position of the main piston  16  are ending in the pilot passage  42 . In the area of the radial bores  58  the main piston  16  has a control edge  60  by which the connection between the annular chamber  34  and the radial bores  58  can be controlled to be closed when the main piston  16  is lifted off the valve seat  26 . 
   The spring chamber  36  is connected by a bore  62  indicated in broken lines and passing through the end portion  30  to the chamber of the main piston  16  confined by the front recess  40 . 
   In the area between the annular chamber  34  and the operating passage  10  axial grooves  64  are formed at the outer periphery of the part  22  of the main piston  14 , the grooves being narrowed toward the annular chamber  34  to form a nozzle  66 . The effective cross-section of this nozzle  66  is considerably smaller than the diameter of the pilot valve seat  44 . In the case of an axial displacement of the main piston  16  the narrowed portion of the axial grooves  64  forming the nozzle  66  is displaced into the annular chamber  34  so that the opening cross-section is increased for the connection of the annular chamber  34  to the operating passage  10 . 
   In the location hole  4  moreover a push piston  68  is guided whose end portion on the right in  FIG. 1  sealingly immerses into the front recess  40  of the main piston  16 . At the bottom of the front recess  40  a spring  70  is supported via which the push piston  68  is biased against a front face  72  of the location hole  4  in the area of the control passage  6 . At its right-hand end portion the push piston  68  has an axial projection  74  which during an axial displacement of the push piston  68  abuts against the pilot valve body  46  and lifts the same off its pilot valve seat  44 . The pressure chamber  76  formed between the push piston  68  and the main piston  16  is connected to the tank passage  8  via at least one angular bore  78  passing through the push piston  68 , said angular bore extending from the front face on the right in  FIG. 1  to the outer periphery of the push piston  68  in the area of the tank passage  8 . The opening area of the angular bore  78  in the area of the tank passage  8  is selected such that the pressure chamber  76  is constantly connected to the tank passage  8 . 
   In the area of this tank passage  8  at the outer periphery of the push piston  68  a control recess  80  is provided forming another control edge  82  over which there extends the connection between the tank passage  8  and that space  84  which extends from the opening area of the pressure passage  12  to the valve seat  26  so that a hydraulic connection is opened between the operating passage  10  and the tank passage  8  when the main piston  16  is lifted off. The axial position of the control edge  82  is selected such that the connection between the operating passage  10  and the tank passage  8  is not increased before the larger opening cross-section of the axial grooves  64  is opened. 
   The outer diameter of the push piston  68  has the same diameter D1 as the end portion  30  of the main piston  16 . 
   As mentioned in the beginning, a proportional valve by which the pressure passage  12  can be connected to the pump or can be blocked is added ahead of the stop block  1 . In the non-return function the pump pressure is applied to the pressure passage  12  so that a resultant pressure force effective in the opening direction acts upon the annular front face confined by the diameters D3 and D1. Then the main piston  16  is lifted off its valve seat  26  when this resultant pressure force effective in the opening direction is larger than the resultant pressure force in the annular chamber  34  acting on the radial shoulder  32  in the closing direction and the force of the check spring  52  and the frictional force generated by the slide ring sealing  35 . As the check spring  52  is designed to be relatively weak, the pressure loss is minimal in the non-return function. The pressure chamber  76  is constantly connected to the tank passage  8  by the angular bore  78 . 
   When reversing to the return function, the connection of the pressure passage  12  to the pump is blocked via the proportional valve and a control pressure acting upon the rear end face of the push piston  68  is applied to the control passage  6  so that pressure is applied to the right of the push piston in the representation according to FIG.  1 . As the pressure chamber  76  is relieved from pressure due to its connection to the tank passage  8 , the push piston  68  can be displaced to the right by the effect of the control pressure against the force of the spring  70  so that the axial projection  74  abuts against the pilot valve body  46  and lifts the same off its valve seat  44  against the force of the pilot spring  48 —the advanced opening of the main piston  16  is increased. Thereby the control oil provided in the annular chamber  34  and in the pilot passage  42  can flow off through the advanced opening into the pressure chamber  76  and from there via the angular bore  78  to the tank passage  8  so that the pressure forces applied to the main piston  16  in the closing direction are reduced. The push piston  68  successively abuts against the main piston  16  so that the latter is lifted off its valve seat  26  due to the control pressure effective in the opening direction. The nozzle  66  effective when the main piston  16  is lifted off and the diameter of the pilot valve seat  44  are designed such that even when a high pressure is prevailing in the operating passage  10  the pressure effective in the annular chamber  34  can be reduced toward the tank passage  8 . 
   As soon as the main piston  16  is lifted off the valve seat  28 , the connection between the radial bores  58  and the annular chamber  34  is controlled to be closed by the control edge  60  and successively the larger opening cross-section of the axial grooves  64  is increased so that differences in pressure due to leakage can be prevented by the pilot valve arrangement and thus displacements of the reflux pass characteristic can be prevented. In the case of a further axial displacement of the main piston  16 , the connection between the tank passage  8  and the operating passage  10  is then increased via the further control edge  82  so that the fluid can flow off from the hydraulic cylinder to the tank passage  8 . Before the further control edge  82  increases the connection between the tank passage  8  and the operating passage  10 , the main piston  16  abuts against the spring plate  56  so that the further increase in the return function is substantially effected against the force of the stronger control spring  54  which is adapted to this control task in an optimum way. In the spring chamber  36  of the control spring  54  and the check spring  52  constantly the tank or low pressure prevailing in the pressure chamber  76  is applied, because this spring chamber  36  is connected to the pressure chamber  76  through the bore  62 . 
     FIG. 2  illustrates a simplified embodiment of the stop block  1  from FIG.  1 . In this embodiment the nozzle  66  is not formed by one or plural axial grooves  64  but by a jacket bore  86  which passes through the sleeve  14  in the area between the flange  18  and the end section adjacent to the operating passage  10 . The jacket bore  86  on the one hand opens into the annular chamber  34  and, on the other hand, in an axial passage  88  which is formed between the outer periphery of the sleeve  14  and the inner circumferential wall of the location hole  4 . The main piston  16  has a control edge  90  in the area of the radial shoulder  32  by which the jacket bore  86  is controlled to be closed after the main piston  16  is lifted off. In the case of a further axial displacement of the main piston  16  an opening cross-section realized by a radially reset circumferential section  94  of the main piston  16  is increased by an additional control edge  92 . 
   In the embodiment shown in  FIG. 2  moreover the annular collar  28  of the main piston  16  was renounced in the area of the valve seat  26  so that the basic structure of the main piston  16  is simplified vis-à-vis the solution described in the beginning. Otherwise the solution shown in  FIG. 2  corresponds to the embodiment described in the beginning so that further explanations can be dispensed with. 
   There is disclosed a stop block for controlling a hydraulic consumer in which a main piston designed to have an advanced opening can be lifted off a valve seat by a push piston in a return function. A pressure chamber confined by the main piston on the one hand and by the control piston on the other hand is connected to a tank or low-pressure passage both in the return function and in the non-return function of the stop block so that the reversal from the return function to the non-return function and vice versa can be effected very quickly. 
   LIST OF REFERENCE NUMERALS 
   
       
         1  stop block 
         2  valve housing 
         4  location hole 
         6  control passage 
         8  tank passage 
         10  operating passage 
         12  pressure passage 
         14  sleeve 
         16  main piston 
         18  flange 
         20  inside bore 
         22  part of the main piston 
         24  check spring arrangement 
         26  valve seat 
         28  annular collar 
         30  end section 
         32  radial shoulder 
         34  annular chamber 
         35  slide ring sealing 
         36  spring chamber 
         38  screwed sealing plug 
         40  front recess 
         42  pilot passage 
         44  pilot valve seat 
         46  pilot valve body 
         48  pilot spring 
         50  bolt 
         52  check spring 
         54  control spring 
         56  spring plate 
         58  radial bores 
         60  control edge 
         61  bore 
         64  axial grooves 
         66  nozzle 
         68  push piston 
         70  spring 
         72  front face 
         74  axial projection 
         76  pressure chamber 
         78  angular bore 
         80  control recess 
         82  further control edge 
         84  chamber 
         86  jacket bore 
         88  axial passage 
         90  control edge 
         92  control edge 
         94  circumferential section