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Hydraulic unit and method for providing a pressurized hydraulic fluidRelated Patent Categories: Pumps, ProcessesHydraulic unit and method for providing a pressurized hydraulic fluid description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070286740, Hydraulic unit and method for providing a pressurized hydraulic fluid. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to a hydraulic unit and a method for providing a pressurized hydraulic fluid. [0002] Hydraulic units are employed in the most diverse possible technical sectors. In particular, the hydraulic unit is also used in a machine tool which has to execute an axial movement with high force during a machining operation. Such a machine tool is, for example, a press or a punching machine, in which a hole is punched out or a punching element punched in with the aid of an axially displaceable ram. [0003] The hydraulic unit serves, in particular, also in the sector of riveting technology, for connection to a setting appliance for setting a rivet, in particular a blind rivet. In the case of a blind rivet, this is introduced, with its rivet sleeve in front, from one side into a bore of two components to be connected, until its setting head comes to lie on the upper component. In the rivet sleeve, a rivet plug is arranged, which is drawn in the axial direction with the aid of the setting appliance. In this case, the rivet sleeve is deformed and forms a closing head, so that the components to be connected are clamped between the closing head and setting head. Where specific tensile force is overshot, the plug tears off, and the operation of setting the blind rivet is concluded. A continuous pressure build-up occurs during the setting operation. In this case, first, under low pressures, comparatively long axial strokes are executed. At the end of the setting operation until the rivet plug is torn off, high deformation forces and consequently high pressures must be provided, along with comparatively low axial strokes. In order to achieve as short cycle rates as possible, therefore, the hydraulic unit must be capable both of executing long axial travels quickly and of applying very high forces. [0004] In process automation, in particular, for example, in the automobile industry, efforts are aimed at a fully automated and monitored blind rivet setting operation with the aid of an industrial robot. In this case, however, there is a problem that hydraulic lines have to be led from the fixed hydraulic unit to the robot and along its robot arms to a rivet setting appliance fastened to the robot hand. The routing of the hydraulic lines is difficult under these circumstances. Particularly in confined workspace situations, for example in body components of a motor vehicle, there is the additional problem that only very little space is available to the robot and there is the risk of chafing of the hydraulic lines on sharp-edged components. [0005] The object on which the invention is based is to specify a compact hydraulic unit which can be employed, in particular, in combination with an industrial robot. The object on which the invention is based is, furthermore, to specify a method for providing a pressurized hydraulic fluid. [0006] The object relating to the hydraulic unit is achieved, according to the invention, by means of the features of patent claim 1. Accordingly, a hydraulic unit for providing a pressurized hydraulic fluid is provided at an outlet of the unit which has an electric motor and at least one pump for pressure generation, operated via the electric motor and designed, in particular, as a piston pump. In this case, for the hydraulic fluid sucked in by the pump, a storage space with a variable compensating volume is provided, in which the hydraulic fluid is stored free of gas. [0007] The invention in this case proceeds from the consideration that, because of the problems of routing the hydraulic lines along the robot, it is advantageous for the hydraulic unit to be arranged directly on the robot, in particular on the robot hand, so that no hydraulic lines are routed via a movable robot axis. This presents the problem, however, that, in a conventional hydraulic unit, air or gas would pass into the hydraulic fluid on account of the acceleration, so that a reliable and defined hydraulic actuation of a machine tool, for example of a blind rivet setting head, would not be possible. [0008] Owing to the arrangement of the storage volume with a variable compensating volume in which the hydraulic fluid is arranged so as to be free of gas, the penetration of air into the hydraulic fluid and the foaming of the latter are avoided. The change in a hydraulic volume of the machine tool, occurring during the operation of the machine tool, leads to a variation in the compensating volume of the storage space. Here, therefore, in contrast to conventional hydraulic units, no air is used for volume compensation in the compensating volume. In the hydraulic unit proposed here, therefore, rapid movements and, in particular, abrupt accelerations, for example direction changes, do not lead to a foaming of the hydraulic fluid. [0009] The hydraulic unit proposed here is therefore arranged, in particular, on machine parts which are accelerated during operation. These are, in particular, the robot hand of an industrial robot, crane or gripper devices, motor vehicles, in particular motor trucks, and, for example, mobile entertainment equipment for amusement parks. When an industrial robot is concerned, accelerations of, for example, 20 times gravitational acceleration and above may in this case occur. The mobile hydraulic unit is capable of executing such high accelerations, without its functioning capacity being impaired. [0010] Expediently, in this case, the hydraulic fluid in the storage space has an overpressure with respect to an ambient pressure. Foaming is thereby reliably avoided. Preferably, this overpressure is in the region of a few 10.sup.5 Pa, in particular between 3 and 50.times.10.sup.5 Pa. [0011] To form the variable compensating volume, according to an expedient development a compensating wall of the storage space is arranged displaceably in the manner of a piston and so as to be sealed off with respect to a stationary housing wall of the storage space. This design having the mechanically particularly rigid compensating wall achieves a very robust construction. Moreover, the preferred configuration as a piston has the advantage of a simple construction. The pressure generation unit is therefore designed in the manner of a piston storage space. Alternatively to the mechanically rigid configuration, the compensating wall is designed, for example, as an elastic diaphragm. [0012] To generate the overpressure in the storage space, in this case, the compensating wall can expediently be acted upon by a counterforce or a counterpressure. For this purpose, advantageously, on the outside facing away from the storage space a pressure space is provided to which a pressure line can be connected. The generation of the counterforce therefore takes place, in particular, pneumatically or else hydraulically. In principle, a mechanical application of the counter-pressure, for example by means of a spring element, is also possible. By contrast, the advantage of pneumatic or hydraulic pressure action is that the magnitude of the counterpressure can be controlled in a simple way. The pressure unit for generating the counterpressure is therefore designed, in the case of pneumatic pressure generation, in the manner of a media converter, that is to say converts pneumatic pressure into hydraulic pressure. Preferably, in this case, the pressure unit is designed in such a way that pressure intensification is achieved. [0013] In order, in particular, to ensure reliable operation, in particular, for example, in the event of an interruption of the pneumatic line for generating the counterpressure, in a preferred version a securing spring is additionally provided for generating the counterpressure. A securing spring is in this context to be understood, in general, to mean an elastic element which exerts a fixed elastic restoring force. Preferably, in this case, a spring element in the actual sense, for example a compression spring, is employed. Alternatively to the additional arrangement of the spring element, this is provided instead of the pressure space. [0014] In order to achieve as compact a construction of the hydraulic unit as possible, the electric motor and the pump are arranged in a housing of the unit, and the inner space surrounded by the housing forms the storage space, that is to say is filled with hydraulic fluid. The electric motor and the pump are therefore arranged in the hydraulic fluid, in particular hydraulic oil. The housing is sealed off, overall, hermetically relative to the outside. By virtue of this configuration, a separate compensating vessel is not required. Furthermore, there is no need for any supply lines from the compensating vessel to a suction-intake side of the pump. [0015] Furthermore, with a view to as compact a construction as possible, the housing is preferably closed by an, in particular, end-face function block in which a plurality of hydraulic components are integrated. Hydraulic components of this type are, for example, hydraulic lines and valves. The function block therefore forms a cover of the housing and consequently of the unit. By the hydraulic components being integrated into the cover, there is no need for a separate space requirement for these components and the unit overall can have a very compact construction. [0016] Expediently, the function block is designed for controlling and routing the hydraulic fluid provided at the outlet. For this purpose, a multiplicity of lines and also hydraulic control elements, such as valves, are arranged in the function block. The function block therefore serves, for example, for shutting off or releasing the pressurized hydraulic fluid generated by the pump. [0017] Preferably, the pressure side of the pump is connected via a line to the function block. All further hydraulic components following the pump on the pressure side are integrated in the function block. By all the hydraulic function elements being arranged within the function block, the construction of the remaining unit is kept comparatively simple and robust. [0018] According to a particularly preferred embodiment, at least two pumps are provided for the provision, on the one hand, of a low-pressure part stream and, on the other hand, of a high-pressure part stream of the hydraulic fluid. A two-stage hydraulic unit is thus provided. The advantage of this is that different pressure stages are provided at a low energy outlay as a function of the respective application. Different pressure requirements are therefore served simply and in an energy-saving way. Particularly in a blind rivet setting operation, there is no need for high pressure to be provided at the commencement of the setting operation. [0019] Expediently, the at least two different pumps are actuated jointly by the electric motor. A plurality of hydraulic part streams of different pressures and/or of different feed quantities are therefore generated via one and the same electric motor, so that the most diverse possible pressure requirements can be fulfilled by means of only one electric motor and therefore in a highly space-saving way. Particularly in two-stage or multistage machining operations in which different pressure requirements are demanded within one operation, this embodiment is of particular advantage. For example, long axial strokes must be executed at only low pressure and short axial strokes at high pressure, as, for example, in a blind rivet setting operation. [0020] Expediently, in this case, the pumps are actuated jointly via an eccentric shaft of the electric motor and are therefore arranged approximately annularly around the eccentric shaft. The pumps are therefore actuated directly by the electric motor, without a gear being interposed. In the provision of two hydraulic part streams, in this case, expediently a plurality of pumps are provided for generating the low pressure part stream and a plurality of pumps are provided for generating the high-pressure part stream, a pump for the high-pressure part stream and a pump for the low-pressure part stream preferably being alternately adjacent to one another. [0021] Preferably, furthermore, a valve arrangement for controlling the at least two part streams is provided, which is designed in such a way that in each case only one part stream is provided at the outlet of the hydraulic unit. There is therefore no need for any external control valves outside the unit for changing over from one part stream to the other part stream, so that, overall, a compact construction is achieved. The valve arrangement is in this case designed, in particular, in such a way that an automatic changeover between the part streams takes place as a function of the current pressure requirement. [0022] This valve arrangement is in this case integrated, in particular, in the function block. Preferably, the valve arrangement has a pressure switching valve which automatically switches off the low-pressure part stream when a predeterminable pressure of the hydraulic fluid provided at the outlet is overshot. [0023] In order to keep energy necessary for generating the pressure as low as possible, furthermore, the valve arrangement is preferably designed in such a way that in each case one of the part streams can be switched to pressureless. There is therefore provision, in particular, for in each case one of the part streams to be pressureless during operation. The electric motor therefore needs to build up pressure in only one part stream and can therefore have a lower-power and compact design. [0024] According to an expedient development, the electric motor is controllable and, in particular, regulatable. The electric motor is in this case started only as required, that is to say when there is a pressure requirement. The pressure is therefore generated, only as required, in an energy-saving way without a pressure accumulator. Continue reading about Hydraulic unit and method for providing a pressurized hydraulic fluid... Full patent description for Hydraulic unit and method for providing a pressurized hydraulic fluid Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Hydraulic unit and method for providing a pressurized hydraulic fluid patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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