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Axially driven piston/cylinder unitRelated Patent Categories: Pumps, Motor Driven, Fluid Motor, Rectilinearly Reciprocating Cylinder And Piston-type MotorAxially driven piston/cylinder unit description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080008606, Axially driven piston/cylinder unit. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates to an axially driven piston-cylinder unit and compressors comprising the same. [0002] Such a piston-cylinder unit is disclosed in U.S. Pat. No. 5,525,845. This piston-cylinder unit of prior art comprises a piston driven by a linear drive, the piston being connected to the linear drive by means of a piston rod. This piston rod is rigid in the axial direction and is flexible in the lateral direction, i.e. in the radial direction. This design of the piston rod is intended to ensure that the piston is guided free from friction in the air bearing of the cylinder even when the drive axis does not run parallel with the cylinder axis. This unspecific flexible design of the piston rod may, however, lead to a situation where transverse forces act on the piston causing the piston to tilt in the cylinder or giving rise to a lateral offset of the piston axis relative to the cylinder axis. This results in asymmetries in the air gap between the outer circumference of the piston and the inner circumference of the cylinder, so that the fluid bearing is weakened in the region in which the distance between the outer piston circumference and the inner cylinder circumference is increased because the pressure of the bearing fluid is reduced at this point. However, this reducing pressure enables the fluid compressed in the cylinder volume to penetrate the bearing gap at this weakened point as soon as the fluid pressure increases, further expanding the bearing gap until the piston finally bears against the cylinder wall at the radially opposite point on the piston, causing undesirable friction. [0003] The object of this invention is to further develop a generic piston-cylinder unit so that reliable operation of the fluid bearing, and hence reliable guidance of the piston in the cylinder, is guaranteed even when there is a lateral offset between the drive axis and the piston axis or where there is an inclination of both these axes relative to each other. [0004] This object is achieved by the features specified in the claims. [0005] The provision of the two joint sections in the piston rod first of all ensures that the piston rod is given the required flexibility, at defined points, to be able to compensate for a lateral offset of the axes. Because of the arrangement according to the invention of the piston-side joint of the piston rod in the rear region of the piston facing away from the piston crown, transverse forces acting on the piston are supported radially by the fluid bearing in the rear piston region, and away from the front piston-crown-side peripheral edge of the piston so that the fluid bearing is not influenced or is not substantially influenced by these harmful transverse forces. The risk that the piston may experience a lateral offset in the piston-cylinder unit of the invention due to transverse forces introduced into the piston by the piston rod in its front piston-crown-side region, which offset results in the state of the art in the detrimental weakening of the fluid bearing, is almost eliminated in the piston-cylinder unit according to the invention. [0006] The second piston-side joint is preferably provided in the direction of the longitudinal axis of the piston at a point which lies level with the rear region of the piston-side bearing surface. This guarantees that any transverse forces introduced by the piston rod into the piston are directly supported at this point in the piston-side bearing surface on the fluid bearing. [0007] Each joint section is preferably pivotable about at least one axis. However, it is also preferable for each joint section to be pivotable about two axes which are orthogonal to each other. [0008] A particularly preferred design comprises joint sections which move in the manner of a ball and socket joint. This ensures that any offset relative to the radial direction between the drive axis and the cylinder axis can be compensated for without special alignment of the piston in the circumferential direction. [0009] The fluid bearing preferably has a plurality of outlet nozzles for the fluid provided in the inner circumferential wall of the cylinder. [0010] Here the outlet nozzles are arranged, in a particularly preferred embodiment, so that when the piston is in its second piston position, first outlet nozzles supply the front region of the piston-side bearing surface relative to the longitudinal extension of the piston, and second discharge nozzles supply the central or rear region of the piston-side bearing surface relative to the longitudinal piston extension, with pressure fluid. [0011] If the outlet nozzles are provided in the front and rear regions of the piston-side bearing surface, an extremely uniform support of the piston over its longitudinal extension is achieved in the compression position of the piston. However, it is also advantageous for the first outlet nozzles to be provided in the front region and the second outlet nozzles to be provided in the central region, whereby the centre of gravity of the bearings extends forwards, i.e. towards the piston crown. Consequently a higher pressure is developed in the fluid bearing between the piston and cylinder in the region of the front end of the annular gap between the piston and cylinder, which pressure offers a higher resistance to the compressive pressure in the cylinder volume and is even better at preventing compressed pressure fluid from the cylinder volume from penetrating the bearing gap, even when a transverse force acts on the piston. [0012] In a further optional embodiment the outlet nozzle are arranged so that when the piston is in its first piston position, the second outlet nozzles supply the front region of the piston-side bearing surface relative to the longitudinal piston extension with pressure fluid, and third outlet nozzles supply the rear region of the piston-side bearing surface relative to the longitudinal piston extension with pressure fluid. These optionally provided third outlet nozzles in the rear region can provide improved support of the piston in its retracted position, particularly during the action of a transverse force. [0013] It is particularly preferable for the fluid bearing to be formed by a gas pressure bearing, the outlet nozzles being formed by gas outlet nozzles; an advantageous and particularly preferred embodiment is that of an air bearing. [0014] A plurality of outlet nozzles preferably form nozzle devices. [0015] The nozzle devices are preferably arranged annularly about the cylinder axis, preferably separated from each other in the axial direction of the piston-cylinder unit. As a result of this an extremely uniform fluid or gas cushion is developed between the piston and the cylinder. [0016] For the formation of an extremely uniform fluid or gas cushion between the piston and the cylinder it is also advantageous for each nozzle ring to have a plurality of outlet nozzles uniformly separated from each other in the circumferential direction. [0017] The outlet nozzles are preferably formed by micro holes drilled by means of an energy-rich jet, which bores are preferably of a conical design, their narrowest cross-section being located on the opening into the cylinder-side bearing surface. The micro holes produced in this manner generate a fluid or gas cushion of high uniformity and high load carrying capacity. [0018] These micro holes are preferably drilled by means of a laser jet. [0019] If the pressure fluid for supplying the outlet nozzles is derived from a fluid flow generated by compression of the cylinder volume, from the outlet duct, for example, a simple structure of the piston-cylinder unit can be achieved and at the same time an additional pressure generator for the pressure fluid for supplying the outlet nozzles may be dispensed with, thereby contributing to low cost production of such a piston-cylinder unit. [0020] This piston-cylinder unit is particularly preferred when the piston is loaded by a moving part of a linear drive for the back and forth drive movement. [0021] A particularly noteworthy and advantageous application of the piston-cylinder unit according to the invention takes place in a compressor for generating a pressure fluid, preferably in a linear compressor driven by a linear motor. [0022] The invention is explained in detail in the following by way of an example with reference to the drawing, in which: [0023] FIG. 1 shows a piston-cylinder unit according to the invention with the piston in a retracted position; [0024] FIG. 2 shows the same piston-cylinder unit with the piston in the vicinity of the compression position. Continue reading about Axially driven piston/cylinder unit... Full patent description for Axially driven piston/cylinder unit Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Axially driven piston/cylinder unit 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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