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Linear compressor and corresponding drive unitRelated Patent Categories: Pumps, Motor Driven, Electric Or Magnetic MotorLinear compressor and corresponding drive unit description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080008607, Linear compressor and corresponding drive unit. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This invention relates to a linear compressor, in particular for use for compressing refrigerant in a refrigerating device, and in particular a drive unit for driving an oscillating piston movement for such a linear compressor. [0002] U.S. Pat. No. 6,506,032B2 discloses a linear compressor whose drive unit comprises a frame and an oscillating body mounted in the frame by means of a diaphragm spring. The oscillating body comprises a permanent magnet, a piston rod rigidly connected to the permanent magnet and a piston articulated to the piston rod, which piston moves back and forth in a cylinder. The movement of the piston is driven by an electromagnet arranged around the cylinder, which electromagnet interacts with the permanent magnet. A disc-shaped diaphragm spring is screwed centrally to the piston rod and the outer edge of the diaphragm spring is connected to a yoke which surrounds the cylinder, the electromagnet and the permanent magnet. [0003] The oscillating body and the diaphragm spring form an oscillating system whose natural frequency is determined by the mass of the oscillating body and the diaphragm spring, as well as by the stiffness of the diaphragm spring. The diagram spring only permits small oscillation amplitudes because any deflection of the oscillating body is associated with an expansion of the diaphragm spring. Due to the low oscillating amplitude it is difficult to reduce the dead volume of the cylinder reliably. However, the higher the dead volume the lower the efficiency of the compressor. The short stroke also necessitates designing the cylinder with a diameter that is proportional to the length in order to achieve a given throughput. It is expensive to seal the correspondingly large circumference of the piston sufficiently. [0004] Since the oscillating body is only retained in the radial direction by its connection to the spring, it is possible that the head of the piston rod supporting the piston may oscillate back and forth and grind against the cylinder wall. To prevent this a compressed gas bearing is provided for the piston, i.e. the cylinder wall covered by the piston has openings which are connected to the high pressure outlet of the linear compressor to form a gas cushion between the inner wall of the cylinder and the piston. However, such a compressed gas bearing only functions if the required excess pressure is present at the outlet of the linear compressor, i.e. not when the compressor starts or stops. At these times there is a risk that the piston will grind against the cylinder wall, resulting in premature wear of the compressor. [0005] A linear compressor is disclosed in U.S. Pat. No. 6,641,377 B2. In this double-piston linear compressor each piston is retained by two two-armed diaphragm springs. [0006] Due to the curvature of the limbs a longer piston stroke is possible. The limbs are more easily deformable, in the longitudinal direction of the piston, than transversely to it, so that they counteract a contact between the piston and the cylinder wall. [0007] To achieve a desired throughout of the compressor the oscillating frequency of the piston must not be too low. This oscillating frequency is all the higher the stiffer the diaphragm spring. However, there is a risk that too rigid a diaphragm spring may result in fatigue at high oscillation amplitudes. [0008] The object of this invention is to provide a drive unit for a linear compressor with a frame and an oscillating body mounted by means of a diaphragm spring, in which the diaphragm spring permits a long stroke of the oscillating body without risk of fatigue and which is able to achieve a high throughput with a small piston diameter. [0009] To achieve a long stroke without the risk of material fatigue, the limbs of the at least one diaphragm spring should be produced from a very thin material. Its strength may be just sufficient to prevent lateral deflection of the oscillating body. However, such a weak diaphragm spring would result in a low natural frequency of the drive unit and hence, at a predetermined stroke, in a low throughput of a compressor driven by the drive unit. In order to achieve a natural frequency of the drive unit adequate for a required throughput, a readjusting spring is therefore assigned, according to the invention, to each limb, which spring counteracts a deformation of the limb so that the diaphragm spring, together with the readjusting springs, forms an elastic system whose stiffness is considerably greater than that of the diaphragm spring alone. [0010] In the simplest case each limb has an individual section curved in one direction. Each such limb also exerts a torque on the oscillating body supported by it when deflected, so that together with the back and forth movement a rotary oscillation of the oscillating body is also excited. To prevent such a rotary oscillation from having a disturbing effect, a rotationally symmetrical structure of at least parts of the compressor may be required. [0011] However, pairs of limbs curved in opposite directions may also be provided. In such a structure the torques induced on the differently curved limbs are mutually compensating, so that the oscillating body performs absolutely no or hardly any rotary oscillation in connection with its back and forth movement. [0012] Each limb preferably has two sections curved in different directions. Since the differently curved sections also generate torques in opposite directions in this case too, the torque of each individual limb may therefore be made very small or caused to disappear altogether. [0013] It is also advantageous to provide at least a second diaphragm spring whose limbs engage on a region of the oscillating body which is distant from the region of engagement of the first diaphragm spring in the direction of the oscillating movement. The oscillating body is reliably guided linearly in the direction of the desired oscillating movement by the two diaphragm springs, and a lateral deflection movement, which could result in contact between a piston supported by the oscillating body and a cylinder surrounding the piston, can be avoided. [0014] The limbs of the same diaphragm spring are preferably joined integrally together at their ends engaging on the frame and/or at their ends engaging on the oscillating body. The ends engaging on the frame may also be connected by a frame integral with the leaf springs. [0015] The effective spring constant of the combination of diaphragm and readjusting spring may be made adjustable so that the natural frequency of the drive unit can be adapted as required. [0016] A helical spring is preferably used as the readjusting spring. [0017] A further subject matter of the invention is a linear compressor with a working chamber, a piston that can be moved back and forth in the working chamber to compress a working fluid, and a drive unit of the type described above, coupled to the piston, for driving the back and forth movement. [0018] Further features and advantages of the invention are evident from the following description of exemplary embodiments with reference to the attached figures. [0019] FIG. 1 shows a diagrammatic section through a linear compressor; [0020] FIG. 2 shows an elevation of a diaphragm spring for use in the linear compressor in FIG. 1 according to the invention; and [0021] FIG. 3 shows an elevation of a second design of a diaphragm spring. [0022] FIG. 1 shows a partially cut side view of a linear compressor. The compressor has a frame with a central chamber 21, in which openings are formed in two opposing walls, here with reference to the representation in the figure designed as ceiling 22 and floor 23, for the sake of clarity, through which openings a rod-shaped oscillating mass 24 extends with a certain clearance. Chamber 21 is provided to accommodate electromagnets, not shown, for driving a back and forth movement of a permanent magnet inserted in oscillating mass 24. [0023] The ends of oscillating mass 24 are fastened to central regions 16 of two diaphragm springs 8 of by means of screws or rivets 25 [0024] One of diaphragm springs 8 is shown in elevation in FIG. 2. Diaphragm spring 8 has a closed outer ring or frame 13 which is rectangular in shape, which is stabilised before installation in the compressor and protects against distortion. Four limbs 14 extend from the corners of frame 13 towards central region 16, each of them being formed from three rectilinear sections 17 and two curved sections 18, 19 connecting sections 17. The two sections 18, 19 of each limb 14 are each curved in opposite directions. Four bores 20 for fastening the diaphragm spring are located in the corners of frame 13. Continue reading about Linear compressor and corresponding drive unit... Full patent description for Linear compressor and corresponding drive unit Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Linear compressor and corresponding drive 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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