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Linear compressor and corresponding drive unitRelated Patent Categories: Pumps, Motor Driven, Electric Or Magnetic Motor, Reciprocating Rigid Pumping Member, Reciprocating Motor, Unitary Pump And Motor Working MemberLinear compressor and corresponding drive unit description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080089796, 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 refrigerants in a refrigerating device, and in particular a drive unit for driving an oscillating linear piston movement for such a linear compressor. [0002] U.S. Pat. No. 6,506,032 B2 discloses a linear compressor whose drive unit comprises a frame and an oscillating body mounted in the frame by means of one 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 can be moved 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, but each diaphragm spring exerts a torque on the piston when deflected. If this torque is not exactly compensated for, the piston performs a rotary oscillation in addition to its linear oscillating movement, and wobble movements of the piston may be excited which may result in contact between the piston and cylinder and consequently to increased wear. [0007] The object of this invention is to provide a low-wear 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 and which is able to achieve a high throughput with a small piston diameter. [0008] The object is achieved in that the plurality of limbs of the diaphragm spring each engage with one end on the frame and with the other end on the oscillating body, and in that the limbs have pairs of sections with opposing curvature between the two ends. The limbs do not therefore extend along the shortest path between the two ends, so that when the oscillating body is deflected, they stretch and my approach the rectilinear shape without the material of the limbs having to be expanded for this purpose. Within the same workpiece it is very easy to produce the limbs so that their torques exactly compensate each other; if, as described in U.S. Pat. No. 6,641,377 B2, two diaphragm springs are provided with limbs covered in different directions, deviations in material strength from one spring to another may prevent such compensation or at least render it extremely difficult. [0009] The diaphragm spring preferably has pairs of limbs with sections curved in opposite directions. [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, but this is compensated for by the limb paired with it and curved in the opposite direction. [0011] 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. [0012] 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. [0013] 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. [0014] To provide a long stroke without 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 dimensioned so small that it is only 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. To achieve a natural frequency of the drive unit sufficient for the required throughput, each limb is preferably assigned a readjusting spring which counteracts deformation of the limb so that the diaphragm spring, together with the readjusting springs, form an elastic system whose stiffness is considerably higher than that of the diaphragm spring alone. [0015] The effective spring constant of the correlation of diaphragm and readjusting spring may be made adjustable so that the natural frequency of the drive unit can be adapted as required. A helical spring is preferably used as the readjusting spring. [0016] 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. [0017] Further features and advantages of the invention are evident from the following description of exemplary embodiments with reference to the attached figures. [0018] FIG. 1 shows a diagrammatic section through a linear compressor; [0019] FIG. 2 shows an elevation of a diaphragm spring for use in the linear compressor in FIG. 1 according to the invention; [0020] FIG. 3 shows an elevation of a second design of a diaphragm spring; [0021] FIG. 4 shows a partially cut side view of a linear compressor with the diaphragm spring shown in FIG. 3; and [0022] FIG. 5 shows a further design of a diaphragm spring. [0023] The linear compressor shown in FIG. 1 for a refrigerating device comprises a compressor chamber 1, which is delimited by a moving piston 2 on the one hand and a cylinder 3 on the other, joined together by a pipe section 4 and a cover 5. Cover 5, not shown, incorporates in an intrinsically known manner a suction connection, a pressure connection and valves which allow refrigerant to flow into the compressor chamber only via the suction connection and discharge only via the pressure connection. [0024] Pipe section 4 is surrounded concentrically by a second pipe section 6 and is connected to it by a radial flange 7. The circumference of a diaphragm spring 8 is fastened to the end of pipe section 6 facing away from flange 7. An oscillating body 9, which is composed of a piston rod 10, to which piston 2 is articulated, a flange 11 fastened to piston rod 10 and a permanent magnet 12, which is fastened to flange 11 and projects into the interval between pipe sections 6, 4, is fitted in the centre of diaphragm spring 8. Electromagnets, also accommodated in the interval, for exerting a force in the direction of piston rod 10 on permanent magnets 12, are omitted in the figure. 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. 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