Patent Publication Number: US-6220288-B1

Title: Electrohydraulic control device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on an electro-hydraulic control device and, more particularly, to an electro-hydraulic control device for a hydraulic servo motor for controlling a volume flow, having a blocking valve arranged in a housing, whose movable seat valve body is inserted into a connection between a motor chamber and a return flow chamber for securing the motor chamber, and having a proportional magnet with an armature-actuated tappet for actuating the blocking valve. 
     2. Prior Art 
     This type of electro-hydraulic control device is already known from U.S. Pat. No. 3,667,722, by means of which a delicate proportional volume control is possible. The check valve protecting the hydraulic servo motor with its load is here designed as a pilot seat valve, so that the leakage is as small as possible. This control device can be used as a lowering brake valve, wherein the actuating forces are as low as possible and therefore the proportional magnet can be made small. It is disadvantageous in connection with this control device that only a 2/3 valve function can be represented, wherein no additional valve functions can be performed by the lowering element designed in accordance with seat valve techniques. In order to keep the actuating forces low here, a one-armed lever, with which a force transfer is performed, is placed between the proportional magnet and the actual seat valve. The force for actuating the check valve is transmitted by an unblocking member, which is made in a pin shape and with a narrow diameter, so that it cannot take on additional functions. The volume flow appearing during the lowering of a load is here only controlled by a valve cone at a seat valve body, so that the flow forces appearing particularly at high loads can considerably interfere with the proportional work functioning of the check valve. Therefore the seat valve body, which here is controlled purely hydraulically, easily tends to oscillate, particularly when pulling loads or changing load directions occur. The ball in the seat valve body, which operates as a pilot member, does not have pressure compensation. In addition, the control device is relatively elaborately constructed, to which the transmitting lever and the valve case for the check valve in particular contribute. 
     Furthermore, an electro-hydraulic control device had already been proposed in an older patent application, P 195 22 746.8, which operates with 4/2 valve modules. In this case two such 4/2 valve modules with additional non-return valves are arranged in a circuit in such a way that a control valve for a double-acting servo motor results. A seat valve element and a slide element are combined with each other in each 4/2 valve module in such a way, that they have a common, one-piece control member. In this not prepublished control device, this one-piece construction of the control member in the 4/2 valve module leads to a relatively elaborate construction; in addition, difficulties arise in this 4/2 valve module because of close longitudinal tolerances when adjusting the control edges to each other. Form and play tolerances are harder to control with relatively long slides in particular. Furthermore, stepped slides in stepped bores with little play make high demands in respect to deviations from running true; in addition, the stepped slides cannot be ground centerless. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved electro-hydraulic control device of the above-described type, especially for a hydraulic servo motor for controlling a volume flow, which does not have the above-described disadvantages. 
     According to the invention the electro-hydraulic control device for a hydraulic servo motor for controlling a volume flow, has a blocking valve arranged in a housing, whose movable seat valve body is inserted into a connection between a first motor chamber and a return flow chamber for securing the motor chamber, and has a proportional magnet with an armature-actuated tappet for actuating the blocking valve, and has a longitudinally movable unblocking member, which is separated from the blocking valve and slidingly guided in the housing, which is inserted into the operation connection between the tappet of the proportional magnet and the blocking valve, and is characterized in that, the unblocking member and the tappet of the proportional magnet are arranged coaxially with respect to each other and the unblocking member is embodied as a longitudinal slide which, with one control edge, controls the connection between an inflow chamber and a second motor chamber, wherein the latter is arranged in the slide bore receiving the longitudinal slide next to the return flow chamber and that the longitudinal slide essentially has the same exterior diameter as the seat valve body, and that upon actuation by the proportional magnet both connections are opened or closed in the same direction. 
     In contrast hereto, the electro-hydraulic control device of the invention has the advantage, that with a simple construction it represents a 4/2 valve function, wherein a lowering element designed in accordance with seat valve technology keeps the leakage as small as possible. The control device can be used in many ways because of its 4/2 function, and in addition is constructed in a cost-efficient and compact way. The control device can be employed as a lowering brake valve, by means of which a sensitive proportional volume control is possible. Because of the two-piece construction, a control edge adjustment can be realized in a simple manner by the length adaptation of the transfer edges. 
     Advantageous further developments and improvements of the electro-hydraulic control device possible by means of the measures noted in the dependent claims and the following disclosure. 
     In a preferred embodiment of the invention the seat valve body and the longitudinal slide are guided in a continuous slide bore, particularly with a generally uniform diameter, in which, lying next to each other and arranged spaced from each other in a direction toward the proportional magnet, four chambers are provided for the first motor connection, the return flow connection, the second motor connection and the inflow connection. A valve seat, in particular with a smaller diameter in comparison with the slide bore, which is associated with the seat valve body, is arranged in this slide bore between the first motor chamber and the return flow chamber. It is possible to achieve a particularly advantageous compact structure which, with its four working chambers, is assembled in a particularly space-saving manner. 
     Other advantageous embodiments are possible in which the blocking valve is a pilot valve, whose seat valve body receives a pilot member, which can be unblocked by the longitudinal slide via a transfer bolt. Preferably the pilot member is a pressure-compensated pilot cone. This makes it possible to achieve small actuation forces by hydraulic unblocking, so that proportional magnets of small size can be employed. 
     In another preferred embodiment an axially oriented extension, which protrudes into the return flow chamber, has a transfer bolt on its end, and a transfer shoulder associated with the seat valve body is arranged on the extension. The extension is provided between the longitudinal slide and the seat valve body on one of the two components, preferably on the longitudinal slide on its side facing away from the proportional magnet. In this embodiment the seat valve body and the control slide can cooperate like a mutual, one-piece control member, wherein the control slide takes the seat valve body along mechanically, as is the case in connection with a conventional control device. In this case pulling loads in particular can be better managed. 
     A particularly simple and cost-effective embodiment, which is mainly suitable for small regulating directional control valves with relatively low switching capacity, results when the longitudinal slide can be directly actuated by the armature tappet, and is pressure-compensated with respect to the pressures in the inflow chamber, the second motor chamber and the return flow chamber. 
     Other embodiments may be used in a wide diversity of possible applications. In one of these embodiments a piston section supporting the control edge on the longitudinal slide has an auxiliary control edge which, in an initial position, relieves the second motor chamber into the return flow chamber, and in an operating position blocks this connection. In another embodiment the seat valve body in the slide bore delimits a pressure chamber, in which a spring is arranged which, together with the pressure acting on the front face of the latter, charges the seal valve body in the direction toward the blocking position, in which it rests with its seat edge, which has a smaller diameter in comparison with the diameter of the slide bore, against the valve seat fixed in place on the housing, and in the process encloses an annular chamber, which is located upstream of the valve seat and delimited by the seat valve body, and whose pressure charges the seat valve body in the opening direction via an associated annular surface, and which annular chamber is separated from the first motor chamber by means of the control edge, on whose pressure charges the seat valve body in the opening direction via an associated annular surface, and which annular chamber is separated from the first motor chamber by means of the control edge, on which precision regulating recesses are arranged, particularly located on the circumference of the seat valve body. 
     In another preferred embodiment the longitudinal slide can be actuated by the proportional magnet via a hydraulic sequence control device. Thus hydraulic amplification is provided for actuating the control slide so that the control device is suitable for regulating directional control valves for higher switching capacities. 
     This hydraulic amplification can be achieved by a particular simple, cost-effective and compact construction in an embodiment in which the sequence control device has a pilot slide, which can be actuated by the proportional magnet against a regulating spring and is arranged centered on the longitudinal slide and slidingly guided. Preferably an unblocking piston is arranged in the longitudinal slide, which is used for unblocking the blocking valve in the lowering element by means of a transfer bolt, which is slidingly guided in the longitudinal slide. The pilot slide and the unblocking piston preferably have the same exterior diameter and are slidingly guided in the longitudinal slide in the same longitudinal bore. The control oil flow, which is used for the hydraulic sequence control device and is conducted from the inflow chamber to the return flow chamber, is advantageously conducted over a throttle arranged in the unblocking piston. 
     A characteristic valve curve can be set when, with its front face facing the proportional magnet, the longitudinal slide delimits a control chamber in the slide bore, which chamber receives an adjusting screw, against which the regulating spring is supported, fixed in place on the housing, which charges the pilot slide against the magnetic force. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Two exemplary embodiments of the invention are represented in the drawings and will be explained in more detail in the following description. 
     FIG. 1 shows a longitudinal section through a first control device in a simplified representation, 
     FIG. 2 shows a longitudinal section through a second control device in a simplified representation, 
     FIG. 3 shows a top view of a portion of the second control device in accordance with FIG. 2, and 
     FIG. 4 shows a circuit arrangement with the first, or respectively second control device in accordance with FIG. 1, or respectively  2 . 
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     FIG. 1 shows a longitudinal section through a first electro-hydraulic control device  10  in a simplified representation, such as can be used for a hydraulic servo motor for the control of volume flows. The control device  10  is embodied as a 4/2 valve module, wherein a lowering element  11  produced in accordance with seat valve technology and a lifting element  12  produced in accordance with slide technology are combined with each other. 
     In a housing  13 , the control device  10  has a continuous slide bore  14 , which is closed at its front faces by a cover  15  and a proportional magnet  16 . Chambers are formed in the slide bore  14  by means of ring-shaped widenings placed next to each other and embodied in the direction starting at the cover  15  and viewed in the direction toward the proportional magnet  16  as a first motor chamber  17 , a return flow chamber  18 , a second motor chamber  19  and in inflow chamber  21 . A first motor connection B, a return connection R, a second motor connection A and an inflow connection P are associated to these chambers  17  to  21  in a corresponding manner. A valve seat  22 , whose effective diameter is made less than the diameter of the slide bore  14 , is embodied in the slide bore  14  in the area between the first motor chamber  17  and the return flow chamber  18  close to the latter, which valve seat  22  represents a part of the lowering element  11 . 
     A pilot seat valve is arranged in the lowering element  11  as a blocking valve, whose seat valve body  23  is slidingly guided in the slide bore  14  and receives a pilot cone  24  in its interior. With its front face  26 , which is stressed by a spring  25 , the seat valve body  23  delimits a pressure chamber  27 , whose pressure, together with the force of the spring  25 , presses the seat valve body  23  against the valve seat  22 . In the blocking position, the valve seat body  23  contacts the valve seat  22  with a seat edge  28 , wherein the diameter of the seat edge  28  is less than the diameter of the slide bore  14 . The seat valve body  23  is guided in the slide bore  14  by means of a shaft  29  and on this shaft  29  it has a first control edge  31 , which is followed by precision control recesses  32  on the exterior circumference of the shaft  29 . An annular chamber  33 , to which an annular surface  34  on the seat valve body  23  is assigned, is enclosed in the slide bore  14  by the stepped embodiment of the seat valve body  23  between the notch-like precision control recesses  32  and the seat edge  28  of reduced. diameter. The cross section of the slide bore  14 , reduced by this annular surface  34 , results in a pressure face  35 , whose size is determined by the effective seat edge  28 . The shaft  29  is seated with sufficient play in the slide bore  14 , so that the load pressure prevailing in the first motor chamber  17  can also be built up in the pressure chamber  27  and in the annular chamber  33  via the gaps acting as throttle points. 
     The pilot cone  24  arranged in the seat valve body  23  is designed in a pressure-compensated manner, to which end the diameters of its cone edge  36  and its shaft section  37  are embodied to be of the same size. The pilot cone  24  controls the connection from an annular chamber  38  to the return flow chamber  18  with its cone edge  36 , wherein the annular chamber  38  has a connection with the pressure chamber  27  via a bore  39 . By means of the long structure of the shaft element  37 , which only has a little play, the pilot cone  24  seals the annular chamber  38  very well against a spring chamber  41 , in which a pilot spring  42  is arranged, which presses the pilot cone  24  on its seat. The spring chamber  41  is connected with the return flow chamber  18  via conduits  43  arranged in the pilot cone  24 , so that the pilot cone  24  is relieved of pressure on all sides. 
     An unblocking member  44  has been placed between the pilot blocking valve in the lowering element  11  and the proportional magnet  16 , which is here designed as a longitudinal slide  45  slidingly arranged in the slide bore  14 . The longitudinal slide  45  controls the connection between the inflow chamber  21  and the second motor chamber  19  with a second control edge  46 , wherein notch-like precision control recesses  47  are also arranged on the second control edge  46 . On its end located opposite the precision control recesses  47 , the piston section  48  supporting the second control edge  46  has an auxiliary control edge  49 , which controls the connection from the second motor chamber  19  to the return flow chamber  18 . The inflow chamber  21  is blocked by the positive covering of the second control chamber  46  in the initial position of the longitudinal slide  45  represented, while the auxiliary control edge  49  relieves the second motor chamber  19  into the return flow chamber  18 . The longitudinal slide  45  is furthermore pressure-compensated by its annular groove  51  in respect to the pressure in the inflow chamber  21 . The two front faces of the longitudinal slide  45  are connected with each other via compensating bores  52 . On its front face facing the proportional magnet  16 , the longitudinal slide  45  rests directly against a tappet  53 , actuated by the armature, of the magnet  16 . An extension  54  is formed on the oppositely located front face of the longitudinal slide, which protrudes into the return flow chamber  18  and which forms a transfer bolt  55  with its trailing end, which rests against the pilot cone  24 . The extension  54  additionally forms a transfer shoulder  56 , which is associated with the seat valve body  23  and whose contact surface is located at a distance from the end face of the transfer bolt  55 . 
     The functioning of the first control device  10  will be explained as follows: 
     With the proportional magnet  16  not excited, the lowering element  11  and the lifting element  12  take up the initial position represented, which corresponds to the neutral position. In this case the inflow connection P is hydraulically blocked by the longitudinal slide  45 , since the second control edge  46  blocks the connection to the motor connection A. On the other side the motor connection A is relieved via the auxiliary control edge  49  into the return flow chamber  18 , so that no pressure can build up in it, even in case of a possibly occurring leak flow. As a rule, the servo motor is connected with its load side to the motor connection B, wherein the pressure in the first motor chamber  17  can also be built up in the pressure chamber  27  and in the annular chamber  38  via the gap formed by the shaft  29 . On a remaining difference surface, which corresponds to the pressure surface  35 , the seat valve body  23  is pressed on the valve seat  22  by the pressure in the pressure chamber  27  and by the force of the spring  25 , and in the process provides a sealing of the motor connection B with few leaks. The load pressure in the motor connection B can also be built up in the annular chamber  38  from the pressure chamber  27  via the bore  39  where, however, it is dependably sealed in respect to the return flow chamber  18  by means of the cone edge  36  and the long shaft of the pilot cone  24 . In the initial position represented, the pilot spring  42  maintains the pilot cone  24  on its seat, and via the transfer bolt  55  maintains the longitudinal slide  45  in the position represented, in which it rests against the tappet  53  of the proportional magnet  16 . 
     If the proportional magnet  16  is now excited, and in the process the longitudinal slide  45  is deflected toward the left into the work position, it first opens the pilot cone  24  by means of the transfer bolt  55 , by means of which the pressure chamber  27  is relieved into the return flow chamber  18 . Less pressure medium can flow into the pressure chamber  27  via the gap of the shaft  29  acting as a throttle point, than flows off via the pilot cone  24 , so that the pressure in the pressure chamber  27  is relieved. A pressure possibly still remaining in the annular chamber  33  acts on the annular surface  34  and pushes the seat valve body  23  toward the left against the force of the spring  25 , so that this annular chamber  33  is relieved into the return flow chamber  18  via the seat edge  28 . In this way the seat valve body  23  is hydraulically unblocked in this way, and during the left movement of the longitudinal slide  45  is now taken along by the transfer shoulder  56 , which has been placed against the front face of the seat valve body  23 . Now the precision control recesses  32  on the seat valve body  23  first open and connect the motor connection B with the return flow chamber  18 , and thereafter—with negative covering—the precision control recesses  47  on the longitudinal slide  45  open the connection from the motor connection A to the inflow chamber  21 . Thus the volume flows, from B to R on the one side, and on the other from P to A, are proportionally controlled by means of these precision control recesses. Therefore the switching capacity of the control device  10  is essentially a function of those pressure drops which are effective on the control edges  31 , or respectively  46 . It is relatively simple for the lifting element  12  to keep the pressure drop via the second control edge  46  relatively small and constant. This can be achieved, for example, by means of a pressure scale, through which a load pressure-compensated volume flow can be controlled. 
     The switching load is relatively low at the lowering element  11  when the load pressure is applied at the motor connection B. Because of occurring flow forces, the volume flow flowing through the lowering element  11  tries to move the seat valve body  23  toward the right, i.e. to pull it shut. This closing force is all the greater, the greater the volume flow and the pressure drop are. By means of an appropriate layout of the seating angle  58  at the valve seat  22  and of the effective seat diameter it can now be achieved that the pressure is built up in the annular chamber  33 . This built-up pressure acts in the annular chamber  33  on an annular surface  34  of the seat valve body  23 , and therefore counter to the flow force. By means of this it is possible to achieve a considerable flow force reduction, which leads to an essential increase in the switching capacity even at high load pressures. With the present control device  10  the seat valve body  23  is mechanically taken along after unblocking of the blocking valve, such as is the case per se with a slide device, so that stable functioning can be achieved. In particular, in contrast to hydraulically actuated locking blocks, wherein instabilities occur in case of pulling loads, it is possible by means of the mechanical coupling of the seat valve body  23  and the longitudinal slide  45  to achieve stable work conditions even with unfavorable operating conditions. Because of the immediate, direct actuation of the longitudinal slide  45  by the proportional magnet  16 , a very simple, cost-effective and compact construction results, which can be advantageously used in particular with smaller switching capacities. Because of the flow force reduction, it is possible in spite of the direct actuation to achieve a relatively high switching capacity, even with relatively small sized proportional magnets. In the working positions the proportional magnet  16  pushes the longitudinal slide  45  with the seat valve body  23  resting against it to the left against the force of the spring  25 , wherein the size of the stroke is proportional to the size of the magnetic force. The precision control recesses  32  and  47  are actuated corresponding to the amount of deflection, so that the two volume flows from B to R, or respectively P to A, are controlled proportionally to the size of the electrical input signal at the proportional magnet  16 . 
     FIG. 2 shows a longitudinal section through a second control device  60 , which differs from that in FIG. 1 in the following way, wherein the same reference numerals were used for the same components. 
     The lowering element  11 , the proportional magnet  16  and the slide bore  14  with its chambers remain unchanged in the second control device  60 , but the lifting element  12  has a different longitudinal slide  61 , which can be actuated by the proportional magnet  16  via a hydraulic sequence control device  62 . In this way the second control device  60  can achieve higher switching capacities in comparison with the first control device  10 . Here, the longitudinal slide  61  is embodied to be hollow, and receives a pilot slide  64  in a blind bore-like longitudinal bore  63 , which is arranged centered and open toward the proportional magnet  16 . The pilot slide  64  is sealingly and slidingly guided by means of a piston section  65  in the longitudinal bore  63  and, together with the radial bore  66  in the longitudinal slide  61 , constitutes an adjustable throttle point  67 , which is placed into a control line  68  of the sequence control device  62 . This control line  68  leads from the inflow chamber  21  via the radial bores  66 , the adjustable throttle point  67 , the hollowly embodied pilot slide  64 , a portion of the longitudinal bore  63 , a throttle  62  in an unblocking piston  71  and via oblique bores  72  in the longitudinal slide  61  into the return flow chamber  18 . The pilot slide  64  projects with a cylindrical section  73  into a control chamber  74  formed in the slide bore  14  between the longitudinal slide  61  and the proportional magnet  16 . An adjusting screw  75 , which can be axially adjusted by means of a worm, not represented in detail, is arranged in this control chamber  74 , on which a regulating spring  76 , which is fixed in place on the housing, is supported, whose other end is supported on the cylindrical section  73  and maintains the pilot slide  64  in contact against the tappet  53  of the proportional magnet  16 . 
     The unblocking piston  71  is slidingly guided at the inner end of the longitudinal bore  63  of the pilot slide  64  and is in operative connection with a transfer pin  77 . This transfer pin  77  is slidingly seated in the extension  54  and rests against the pilot cone  24  of the blocking valve in the initial position of the control device  60 . It is particularly useful here that the pilot slide  64  with its piston section  65  and the unblocking piston  71  have the same exterior diameter, so that they can be slidingly arranged in a single longitudinal bore  63 . In this way the longitudinal slide  61  makes a one-piece construction possible because of its longitudinal bore  63  embodied in the manner of a blind bore, which is particularly advantageous to produce in connection with production technology. 
     FIG. 3 shows a partial longitudinal section along III—III in FIG. 2, wherein the seat valve body  23 , the longitudinal slide  61  and the adjusting screw  75  are shown in a top view. 
     In principle, the functioning of the second control device  60  corresponds to that of the first control device  10  in accordance with FIG. 1, however, greater switching capacities can be achieved because of the hydraulic sequence control device  62 . 
     In the represented initial position of the second control device  60 , which corresponds to a neutral position, the first motor chamber  17  as well as the inflow chamber  21  are hydraulically blocked. In the initial position, the pilot slide  64  is maintained resting against the tappet  53  by the regulating spring  76 , and thus in a position fixed on the housing. The axial position of the longitudinal slide  61 , which just closes the adjustable throttle point  67 , is also fixed in place in this way. 
     When actuating the second control device  60 , the proportional magnet  16  merely needs to act against the force of the regulating spring  76 , since the pilot slide  64  is pressure-compensated on all sides. When the pilot slide opens the adjustable throttle point  67 , a control oil flow is formed via the control line  68 , wherein the pressure built up at the throttle  69  actuates the unblocking piston  71  and thereby opens the pilot cone  24 , so that the blocking valve in the lowering element  11  is unblocked. Otherwise the longitudinal slide  61  follows the stroke of the pilot slide  64 , wherein an intermediate pressure builds up in the control chamber  74  for actuating the longitudinal slide  61  and amplifies the magnetic force. In the process, the longitudinal slide  61  and the pilot slide  64  work together in a manner known per se in the form of a hydraulic sequence control device. The prestress of the regulating spring  76  can be changed with the aid of the adjusting screw  75 , and the position of the characteristic valve curve can be set with this. 
     FIG. 4 shows a circuit in a simplified representation, wherein two first control devices  10  of FIG. 1 have been arranged to form a directional control valve  80  for a double-acting servo motor. In this case the two P connections of both control devices  10  are connected parallel to a control pump  82 , while their two connections R are relieved into a tank  83 . An inflow line  84 , or respectively  85 , leads from each connection A of each control device  10  to one of the consumer connections  86 , or respectively  87 , on the servo motor  81 . Here each inflow line  84 ,  85  is conducted over a check valve  88 , or respectively  89 , which protects the load. The two connections B at each control device  10  are respectively connected by means of an outflow line  91 , or respectively  92 , with the respectively other consumer connection  87 , or respectively  86 . A load pressure signal is picked up at the inflow lines  84 ,  85  and reported to the control pump  82 . A 3-position valve has been realized by means of the control valve  80 , which securely seals the servo motor  91  when the control devices  10  are not actuated. To keep the leakage low, the consumer connection  86  is securely blocked on the one side by the check valve  88 , and on the other side by the blocking valve in the lowering element  11  of the right control device  10 . Similar is true for the other consumer connection  87 . By actuating the left control device  10 , the servo motor  81  can be operated in one direction with the piston rod extending, while by actuating the right control device the servo motor  81  can be controlled in the other direction with the piston rod retracting, wherein a proportional operation is achieved. By means of processing the load pressure signal in the control pump  82  it is possible to keep the pressure drop constant in the lifting element  12  via the second control edge  46 , so that a load-compensated volume flow control becomes possible. 
     Changes in the exemplary embodiments represented are of course possible without departing from the scope of the invention. Although the pilot blocking valve in the control device is particularly advantageous, it is also possible to employ a directly controlled blocking valve having a blocking valve body which has been pressure-relieved to a large extent. The continuous slide bore can also be designed in such a way that in the area of the lowering element it has a slightly larger diameter than in the lifting element, so that the interior diameter of the valve seat  22  approximately corresponds to the diameter of the slide bore. Also, in the wiring in accordance with FIG. 4 it is possible to use the second control devices  60  in place of the first control devices  10 . In this case the regulating valve  80  can also be embodied in such a way that it has four operating positions. A constant pump with a pressure scale is also conceivable in place of the control pump  82 .