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Title: Hydraulic drive for the die closing unit of an injection molding machine
Claims: I claim the following: 1. In a hydraulic linear actuator of the cylinder and piston type, whose motion is switchable from a travel mode in which a movable assembly is advanced or retracted at accelerated speed and with comparatively little force to a power mode in which the assembly is subjected to a greatly increased pressure, when the piston is at or near one end of its travel stroke, which actuator is advantageously applicable as a drive for the die closing unit of an injection molding machine, the combination comprising: a closed power cylinder with hydraulic connections at both extremities for double-acting operation; a power piston fixedly seated on a piston rod and arranged for longitudinal travel inside said cylinder over the length of a piston stroke; the piston rod having a forward rod portion extending from the forward end of the power cylinder, which rod portion is connected to a movable assembly arranged for travel between an open position on one end of the piston stroke and a closed position on the other end of the stroke, and a rear rod portion extending from the opposite end of the power cylinder; and the power piston further dividing the space of the power cylinder into a high pressure space on that side of the piston which needs to be pressurized to urge the movable assembly into its closed position and a low pressure space on the opposite side of the piston; a plurality of bypass channels extending generally axially across the body of the power piston from the high pressure side thereof to the low pressure side; an annular valve seat on the power piston, on its high pressure side, arranged so as to surround the openings of the bypass channels; a hollow valve plunger sealingly surrounding a cylindrical guide surface on the piston rod on the high pressure side of the power piston, said plunger being guided for axial motion toward and away from the power piston, between a closed position in which a shoulder of the valve plunger sealingly abuts against the valve seat and an open position located a distance away from said seat, and the valve plunger has at least one axial end face exposed to the fluid in the high pressure space; means for moving the valve plunger between its open and closed positions in response to fluid pressure; and an auxiliary cylinder cooperating with the rear piston rod portion so as to define a coaxial auxiliary linear actuator capable of driving the same movable assembly via the piston rod; and wherein: the auxiliary cylinder has a much smaller hydraulically effective cross section than the power cylinder, so that, when the auxiliary cylinder is supplied with pressurized fluid while the valve plunger is in its open position, the piston rod and the movable assembly travel at a comparatively high rate of speed, while the power piston moves through the fluid contained inside the power cylinder, as the latter passes through its bypass channels from side to side of the power piston. 2. A hydraulic linear actuator combination as defined in claim 1, wherein: the movable assembly is in its closed position when the power piston has reached the rear end of its stroke; the high pressure space in the power cylinder is that portion of the cylinder space which is located forward of the power piston; and the pressurization of the high pressure space, with the power piston bypass channels closed, causes the piston rod to pull the movable assembly toward its closed position. 3. A hydraulic linear actuator combination as defined in claim 1, wherein: the movable assembly is in its closed position when the power piston has reached the forward end of its stroke; the high pressure space in the power cylinder is that portion of the cylinder space which is located to the rear of the power piston; and the pressurization of the high pressure space, with the power piston bypass channels closed, causes the piston rod to push the movable assembly toward its closed position. 4. A hydraulic linear actuator combination as defined in claim 1, wherein: the rear portion of the piston rod has a larger diameter than its forward portion, so that the power piston operates as a differential piston which, when the power piston bypass channels are open and both pressure spaces in the power cylinder are evenly pressurized, moves to the rear, together with the movable assembly, as a result of the larger effective area of the forwardly located pressure space; and the rear portion of the piston rod projects freely into the auxiliary cylinder so as to define a pressure space therein to which the rear extremity of the piston rod is exposed and which, when pressurized while the power piston bypass channels are open, causes the piston rod and the movable assembly to travel to the fore. 5. A hydraulic linear actuator combination as defined in claim 4, wherein the difference in the effective areas of the power cylinder pressure spaces is approximately equal to the effective cross-sectional area of the rear portion of the piston rod. 6. A hydraulic linear actuator combination as defined in claim 1, wherein: the rear portion of the piston rod has a smaller diameter than its forward portion, so that the power piston operates as a differential piston which, when the power piston bypass channels are open and both pressure spaces in the power cylinder are evenly pressurized, moves to the fore, as a result of the larger effective area of the rearwardly located pressure space; and the piston rod carries on the rear extremity of its rear piston rod portion an auxiliary piston engaging the wall of the associated auxiliary cylinder so as to define a pressure space forward of the auxiliary piston which, when pressurized while the power piston bypass channels are open, causes the piston rod and the movable assembly to travel to the rear. 7. A hydraulic linear actuator combination as defined in claim 6, wherein the forward portion of the piston rod has approximately the same diameter as the auxiliary piston on its rear extremity. 8. A hydraulic linear actuator combination as defined in claim 1, further comprising: at least one additional parallelly spaced power cylinder with a substantially identical power piston, piston rod, piston bypass channels, valve seat, cooperating valve plunger with valve plunger moving means, and coaxial auxiliary cylinder; and wherein the forward portions of the piston rods are connected to the same movable assembly; a first one of the piston rods carries on the rear extremity of its rear piston rod portion an auxiliary piston engaging the wall of the associated auxiliary cylinder so as to define a pressure space forward of the auxiliary piston which, when pressurized while the power piston bypass channels are open, causes this piston rod, the movable assembly, and the other piston rod to travel to the rear; and a second one of the piston rods has its rear piston rod portion freely projecting into the associated auxiliary cylinder so as to define a pressure space therein to which the rear extremity of the piston rod is exposed and which, when pressurized while the power piston bypass channels are open, causes this piston rod, the movable assembly and the other piston rod to travel to the fore. 9. A hydraulic linear actuator combination as defined in claim 8, wherein the hydraulically effective cross-sectional areas of the aforementioned two pressure spaces are substantially identical in size, which latter is a fraction of the hydraulically effective cross-sectional area of the power piston, when its bypass channels are blocked by the valve plunger. 10. A hydraulic linear actuator combination as defined in claim 1, wherein the piston rod has the same diameter on its forward portion as on its rear portion, as well as on an intermediate portion on which the power piston is seated; and the power piston rod further includes an annular groove near the low pressure side of the power piston and a split abutment ring which is seated in this groove and radially protrudes therefrom, said ring serving to transmit axial forces from the piston to the rod, in the sense of urging the movable assembly into its closed position. 11. A hydraulic linear actuator combination as defined in claim 1, wherein: the power piston further includes an axial recess on its high pressure side located radially inwardly adjacent to its valve seat; and the bypass channels of the power piston open into this radial recess. 12. A hdyraulic linear actuator combination as defined in claim 11, wherein: the valve plunger includes a tapered seating face which is oriented outwardly and away from the power piston; and the valve seat of the power piston has a radially narrower, similarly oriented tapered face. 13. A hydraulic linear actuator combination as defined in claim 1, wherein: the power piston has a central bore with which it is fixedly seated on the piston rod, over a first length portion of said bore which is located adjacent to the low pressure side; a second length portion of the power piston bore and the guide surface on the piston rod define together an annular plunger cylinder, the outer wall of said cylinder being defined by the piston bore, and its concentric inner wall being defined by the piston rod, said cylinder space being open to the high pressure space; the hollow valve plunger has corresponding concentric inner and outer walls in contact with the concentric cylinder walls; and one axial end of the annular plunger cylinder is closed against the piston rod, thereby defining a valve plunger pressure space at this end of the cylinder as part of said valve plunger moving means, said pressure space being connected to a source of hydraulic pressure, via a channel in the piston rod, so that the valve plunger is moved away from it, when it is pressurized. 14. A hydraulic linear actuator combination as defined in claim 13, wherein: the annular plunger cylinder is arranged axially inside the valve seat on the power piston; the valve plunger pressure space is located at the inner end of the plunger cylinder; a portion of the valve plunger length is sealingly engaged inside the plunger cylinder and thus located axially inside the valve seat; and the valve plunger shoulder which cooperates with the valve seat is part of an enlarged collar on the non-engaged portion of the valve plunger. 15. A hydraulic linear actuator combination as defined in claim 14, wherein the valve plunger moving means further includes a compression spring arranged inside the valve plunger pressure space, the spring bearing against the closed end of the latter and against the near extremity of the valve plunger, thereby urging the latter toward its open position. 16. A hydraulic linear actuator combination as defined in claim 13, wherein: the annular plunger cylinder is arranged axially outside the valve seat on the power piston, the outer wall of said cylinder being larger in diameter than the diameter of the valve seat; the valve plunger pressure space is located at the outer, i.e. more distant, end of the plunger cylinder, its closed end being constituted by an end cover; the near end of the plunger cylinder is open to the high pressure space; the valve plunger is sealingly engaged inside the plunger cylinder between the end cover and the valve seat; and the valve plunger shoulder which cooperates with the valve seat is part of an end face at the near extremity of the valve plunger. 17. A hydraulic linear actuator combination as defined in claim 1, wherein: the valve plunger is located axially outside the power piston in the high pressure space of the power cylinder; the valve plunger shoulder which cooperates with the valve seat is part of a near end face at the near extremity of the valve plunger; and the valve plunger moving means includes an enclosed valve plunger pressure space to which an opposite, far axial face of the valve plunger is exposed, the pressure space being connected to a source of hydraulic pressure, via a channel in the piston rod, so that, when the pressure space is pressurized, the valve plunger is moved toward the valve seat on the power piston. 18. A hydraulic linear actuator combination as defined in claim 17, wherein the valve plunger moving means further includes a compression spring arranged inside the valve plunger pressure space, the spring bearing against the piston rod and against the valve plunger, thereby urging the latter toward the valve seat on the power piston. 19. A hydraulic linear actuator combination as defined in claim 17, wherein: the valve plunger has the shape of a sleeve, with a guide bore, i.e. an inner cylindrical surface, sealingly engaging the piston rod guide surface and an outer cylindrical surface at a diameter which corresponds to the outer diameter of the valve plunger pressure space; the piston rod includes an annular member having a cylindrical surface adapted for sealing and sliding engagement with the outer cylindrical surface of the valve plunger; and the valve plunger pressure space is defined between the piston rod and the valve plunger, the annular member of the piston rod including an axial face bordering this pressure space in opposition to the far axial face of the valve plunger. 20. A hydraulic linear actuator combination as defined in claim 19, wherein: the diameter of the valve seat on the power piston is smaller than the outer diameter of the valve plunger pressure space, so that a pressurization of the high pressure space creates an axial force on the valve plunger in the direction away from the valve seat; and the inner diameter of the valve plunger pressure space is smaller than the diameter of the valve seat, so that, when the valve plunger is in its closed position and both pressure spaces are evenly pressurized, the valve plunger is maintained in its closed postion. 21. A hydraulic linear actuator combination as defined in claim 20, wherein: the annular member of the piston rod includes a removable cylinder sleeve, its outer cylindrical surface being that of a cylindrical bore which is open toward the power piston, but closed in the other direction at said axial face which borders the valve plunger pressure space; and the outer cylindrical surface of the valve plunger engages said bore from the inside. 22. A hydraulic linear actuator combination as defined in claim 20, wherein: the annular member of the piston rod includes a fixed collar on the piston rod, its outer cylindrical surface being that of a short cylinder; the outer cylindrical surface of the valve plunger is that of an enlarged cylindrical bore portion in the valve plunger which is open toward the far extremity of the valve plunger and axially adjacent its guide bore; and the valve plunger surrounds and engages the fixed collar on the piston rod from the outside. 23. A hydraulic linear actuator combination as defined in claim 22, wherein the annular member of the piston rod is a removable ring having a substantially rectangular cross section. 24. A hydraulic linear actuator combination as defined in claim 22, wherein: the annular member of the piston rod is removable from the piston rod and has the shape of a flange bushing, the flange part of the member being said fixed collar, and the bushing part of the member being a tubular extension seated on the piston rod and extending toward the power piston; and the cylindrical guide surface on the piston rod is constituted by the outer surface of the bushing part of the annular member. 25. A hydraulic linear actuator combination as defined in claim 24, wherein: the piston rod and the annular member have matching male and female threads; the power piston has a clamping face on the side that faces toward the high pressure space; and the threaded annular member is adapted to serve as a clamping nut, engaging the clamping face of the power piston when tightened against it. 26. A hydrualic linear actuator combination as defined in claim 25, wherein: the high pressure space of the power cylinder and the valve plunger are located to the rear of the power piston; the forward portion of the piston rod is larger in diameter than its rear portion, so that the power piston operates as a differential piston; the piston rod has a clamping shoulder engaging the forward side of the power piston; the power piston and the annular member are seated on an intermediate length portion of the piston rod which is larger in diameter than its rear portion by approximately twice the radial height of said male thread, but smaller in diameter than its forward portion, so as to define said clamping shoulder; and the piston rod carries on its rear portion as auxiliary piston of approximately the same diameter as the forward piston rod portion, which piston engages the wall of the associated auxiliary cylinder. 27. A hydraulic linear actuator combination as defined in claim 26, wherein the ratio between the diameter of the rear portion of the piston rod and the diameter of the auxiliary piston is approximately 15 to 12. 28. A hydraulic linear actuator combination as defined in claim 25, wherein: the outer diameter of the bushing part of the annular member is approximately equal to the diameter of the forward piston rod portion; the power piston further includes an axial recess in its rear side radially inwardly adjacent to its valve seat; the bypass channels in the power piston are bores oriented in parallel to the piston rod axis and extending from the foward side of the piston to said recess, the bores being arranged on a center circle whose diameter is approximately equal to the outer diameter of the valve plunger pressure space and a small amount larger than the diameter of the valve seat; and the bypass channels are bores of a diameter that is approximately equal to the difference between the diameter of their center circle and the diameter of the forward piston rod portion. 29. A hydraulic linear actutor combination as defined in claim 28, wherein: the valve plunger further includes a tapered seating face which is oriented at approximately 45.degree. outwardly and away from the power piston; the valve seat has a radially much narrower, similarly oriented tapered face; and the power piston further includes a narrow planar rear face radially outwardly adjacent its valve seat, and a tapered face continuing radially outwardly from the latter in parallel to the tapered seating face of the valve plunger, so as to define a parallel-tapered flow gap therebetween. Other info: Inventors: Hehl, Karl (7291 Lossburg, DT) Application Number: 546036 Filing Date: 1975-01-31 Publication_date: 1976-02-03 Assignee: Primary Class(es): 91/517 91/519, 92/146, 425/451.2, 425/590 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Geoghegan, Edgar W. Assistant Examiner: Attorney: Geiger; Joseph A. |
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