Oscillating compressor

Abstract: The hermetic compressor casing (1) contains the motor block (3) with the stator (3a). A piston rod (5) is reciprocating and/or rotating inside the motor block, actuated by the mover magnet (3b) attached to it. The cylinder (4) and the valve plate (7) can be positioned in the axial direction and so change the length of stroke of the piston. A method of modifying the piston stroke and obtaining an oscillation damping is to pressurize the cooling gas in the compressor casing (1) and the cylinder casing (4) and regulating the pressure difference. The adjustment may be facilitated by the spring (22). The suction (20) and discharge pipes (10) can contain a slidable fitting for stress reduction. A control unit (26) can be provided to regulate pressure based on the information of a piston position sensor (23). Another electronic control unit (218) uses piston position (214) and external operating parameters (223) such as ambient temperature or cooling fluid temperature changes to modify the amplitude of the oscillations. Another control circuit controls the flow rate by changing the motor frequency. For the axial support and centering of a horizontal piston rod 2 bearings (413,414a,414b,415a,415b) for the 2 end positions of the pistons are provided. The piston stroke variation due to temperature changes can be compensated by integrating a shape memory alloy part into the piston rod (416). If the compressor is operated in vertical position, the control circuit uses the input of a displacement sensor (319) and a voltage or current detector (321). In the case of a vertically oscillating piston rod, the behaviour of the oscillating system can be predicted. If the oscillating movement is combined with a rotary movement, the vertical piston rod is aligned by providing lubricating fluid into the clearance (5) between piston and cylinder (4).

Description: The present invention relates to an oscillation-type compressor preferably used in a refrigerator and an air-conditioner. Various conventional oscillation-type compressors are disclosed in Published Japanese Applications Nos. Kokai 51-57009, Kokai 8-247025, Kokai 9-324764 and Kokai 4-347460. The oscillation-type compressors basically comprise a movable element including a piston and a stationary element including a cylinder, so that gas is introduced into a compression chamber defined by the piston and the cylinder and compressed by the piston that reciprocates in the axial direction. DE 2 441 604 A1 discloses an oscillation type compressor having two cylinders one either side of a reciprocating double-ended piston. An object of some embodiments of the present invention is to provide an oscillation-type compressor capable of minimizing the top clearance of the piston in a given piston stroke and maintaining efficient compressor operations. Another object of some embodiments of the present invention is to realize a practical cooling device, such as a refrigerator, which is capable of automatically increasing the stroke of the piston in response to a high ambient air temperature so that the cooling power can be sufficiently obtained even in such a high load condition and is also capable of automatically reducing the stroke of the piston in response to a decreased ambient air temperature, thereby realizing efficient compressor operation in accordance with the driving conditions of the cooling device without using additional detecting and control devices. According to the present invention, there is provided an oscillation-type compressor comprising: a tightly closed casing having an inside space for storing cooling gas; a block accommodated in said tightly closed casing; a motor including a stator fixed to said block and a mover; a piston connected to said mover of said motor; a movable element including said mover of said motor and said piston; and a stationary element including said stator of said motor and said block; characterised by: an elastic element having a portion fixed to said movable element and another portion fixed to said stationary element; a cylinder receiving said piston and shiftable in an axial direction with respect to said block; and a shifting device for shifting said cylinder in said axial direction. Optionally, the compressor may further comprise a cylinder head fixed to the cylinder, back-pressure chambers formed in the coolant gas space and airtightly partitioned by an integral unit including at least one of the cylinder and the cylinder head, and at least one of the back-pressure chambers being held at a low pressure level and another one of the back-pressure chambers being held at a high pressure level. It is preferable that this oscillation-type compressor further comprises an elastic member having one end connected to the integral unit including at least one of the cylinder and the cylinder head and the other end connected to the stationary element, and further comprises a cylinder position detecting sensor fixed to one of the stationary element and the cylinder. Also optionally, the compressor may further comprise a cylinder head fixed to the cylinder, an auxiliary pipe having one end shiftable in the axial direction with respect to one of an exhaust pipe and an intake pipe and the other end fixed to one of the cylinder and the cylinder head. The above and other features and advantages of the present invention will become more apparent from the following detailed description of exemplary embodiments which is to be read in conjunction with the accompanying drawings, in which: Fig. 1 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a first embodiment of the present invention; Fig. 2 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a second embodiment of the present invention; Fig. 3 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a third embodiment of the present invention; Fig. 4 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a fourth embodiment of the present invention; Fig. 5 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a fifth embodiment of the present invention; Fig. 6 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a sixth embodiment of the present invention; Fig. 7 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a seventh embodiment of the present invention; Fig. 8 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with an eighth embodiment of the present invention; Fig. 9 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with. a ninth embodiment of the present invention; and Fig. 10 is a vertical cross-sectional view showing an operated condition of the oscillation-type compressor in accordance with the ninth embodiment of the present invention. Preferred embodiments of the present invention will be explained in more detail with reference to the attached drawings. Identical parts are denoted by the same reference numerals throughout the drawings. First Embodiment Fig. 1 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a first embodiment of the present invention. The oscillation-type compressor comprises a tightly closed casing 1 having an inside space 1a for storing coolant gas and a main body 2. A motor 3 includes a stator 3a and a mover 3b. The mover 3b is fixed to a piton 5. The main body 2 is roughly constituted by a movable element 12 and a stationary element 13. The movable element 12 includes the mover 3b of the motor 3 and the piston 5. The stationary element 13 includes a cylinder 4, the stator 3a of the motor 3 and a block 6. The main body 2 is elastically supported by a suspension spring (not shown) in the tightly closed casing 1. Lubrication oil 11 is stored in the lower portion of the tightly closed casing 1. An elastic element 8 comprises a plurality of elastic members 8a stacked or multilayered in an axial direction and spaced via intervening radially outer spacers 8d and an radially inner spacers 8e. An inner cylindrical edge 8b of each elastic element 8 is fixed to the piston 5. An outer cylindrical edge 8c of the elastic element 8 is fixed to the block 6. The cylinder 4 and the elastic element 8 cooperatively support the piston 5 so as to be slidable and reciprocate in the axial direction. The cylinder 4 and the piston 5 cooperatively define a compression chamber 9. Next, compression mechanism of the above-described oscillation-type compressor will be explained. First, alternating current of an AC power source is half-wave rectified and supplied to the stator 3a. A magnetic field generated by the stator 3a attracts the mover 3b fixed to the piston 5 based on the principle of magnetic variable resistance. When the mover 3b shifts in the axial direction, the elastic element 8 disposed between the mover 3b and the block 6 resiliently deforms in response to the shift movement of the piston 5, storing an elastic force therein. When the elastic force stored in the elastic element 8 is sufficiently increased, the mover 3b is pushed back to the original position. Continuous repetition of this cycle reciprocates the piston 5 in the axial direction. Coolant gas of a cooling system (not shown) is introduced into a low-pressure chamber 7a of a cylinder head 7, and then enters the compression chamber 9 of the cylinder 4 via an intake valve (not shown) disposed in the cylinder head 7. The coolant gas introduced in the compression chamber 9 is compressed by the piston 5 which reciprocates in the above-described manner. The compressed coolant gas then enters a high-pressure chamber 7b of the cylinder head 7 via an exhaust valve (not shown), and then exits the cylinder head 7 to the cooling system. According to the first embodiment, the cylinder 4 is integral with the cylinder head 7 and shiftable in the axial direction with respect to the block 6 when driven by a shifting device 16. The shifting device 16 comprises a rack 16a provided on an axially extending surface of the cylinder 4. A pinion 16b, rotatably supported to the stationary element 13, such as the block 6, meshes with the rack 16a so as to a constitute a rack-and-pinion mechanism. Thus, the first embodiment provides the shifting device 16 for flexibly shifting the piston 5 in the axial direction with respect to the block 6. Operation of the oscillation-type compressor in accordance with the first embodiment will be explained hereinafter. During a compressing operation of the compressor, the cooling power can be reduced by lowering the voltage applied to the motor 3 so as to reduce the stroke of the piston 5. In this case, the top clearance of the piston 5 may increase in proportion to reduction of the piston stroke. However, according to the first embodiment, the shifting device 16 can shift the cylinder 4 toward the compression chamber 9 so as to reduce the volume of the compression chamber 9, thereby canceling the increased top clearance and maintain the top clearance at a constant value. Thus, re-expansion loss is reduced and efficiency can be maintained adequately. Furthermore, when an increased cooling power is required, an increased voltage is applied to the motor 3 so as to increase the stroke of the piston 5. In this case, the top clearance decreases due to the increased stroke of the piston 5. The piston 5 may collide with the cylinder head 7. However, according to the first embodiment, the shifting device 16 can shift the cylinder 4 away from the compression chamber 9 so as to increase the volume of the compression chamber 9, thereby canceling the reduced top clearance and preventing the piston 5 from colliding with the cylinder head 7. As described above, the first embodiment provides the oscillation-type compressor comprising the tightly closed casing 1 having the inside space 1a for storing coolant gas, the block 6 accommodated in the tightly closed casing 1, the motor 3 including the stator 3a and the mover 3b, the piston 5 connected to the mover 3b of the motor 3, the movable element 12 including the mover 3b of the motor 3 and the piston 5, the stationary element 13 including the stator 3a of the motor 3 and the block 6, the elastic element 8 having a portion fixed to the movable element 12 and another portion fixed to the stationary element 8, the cylinder 4 shiftable in the axial direction with respect the block 6, and the shifting device 16 for shifting the cylinder 4 in the axial direction. With this arrangement, it becomes possible to minimize the top clearance adequately in accordance with a given piston stroke. The compressor can be always operated with better efficiencies. Second Embodiment Fig. 2 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a second embodiment of the present invention. In Fig. 2, the cylinder 4 is put between two stopper projections 17a and 17b provided on an inner surface of the block 7 so that the cylinder 4 can shiftable in the axial direction with respect to the block 7 in a limited range restricted by the stopper projections 17a and 17b. Two back-pressure chambers 18a and 18b, formed in the tightly closed casing 1 and airtightly partitioned by the integral unit of the cylinder 4 and the cylinder head 7, communicate with the outside via back-pressure pipes 19a and 19b, respectively. An intake pipe 20 directly extends from the cylinder head 7 to the outside of the tightly closed casing 1. A pressure control mechanism 21 is disposed between the back-pressure chambers 19a, 19b and intake and exhaust pipes 20 and 10. More specifically, the pressure control mechanism 21 comprises a total of four pressure control valves 21a, 21b, 21c and 21d. Connecting pipes 21e and 21f extend from the intake pipe 20 to the pressure control valves 21a and 21b, respectively. Connecting pipes 21g and 21h extend from an exhaust pipe 10 to the pressure control valves 21c and 21d, respectively. A pressure pipe 21i connects the pressure control valves 21a and 21c to the back-pressure pipe 19a. A pressure pipe 21j connects the pressure control valves 21b and 21d to the back-pressure pipe 19b. Operation of the oscillation-type compressor in accordance with the second embodiment will be explained hereinafter. The pressure control mechanism 21 introduces the low pressure gas from the intake pipe 20 and the high pressure gas from the exhaust pipe 10 and adjusts the pressures of the introduced gases by the pressure control valves 21a, 21b, 21c and 21d to produce adjusted gases having arbitrary pressures in a range from the original high pressure to the original low pressure. The adjusted gases are supplied into the back-pressure chambers 18a and 18b. When the ambient air temperature is high, an increased cooling power is required. In such a case, the pressure control valve 21c is closed while the pressure control valve 21a is opened. Thus, the back-pressure chamber 18a is held at a low pressure level. Meanwhile, the pressure control valve 21d is opened and the pressure control valve 21b is closed. Thus, the pressure of the back-pressure chamber 18b is increased to a high level. The cylinder 4, which is integral with the cylinder head 7, shifts in the axial direction toward the stopper projection 17a due to a pressure imbalance between the back-pressure chambers 18a and 18b. In this case, the top clearance of the piston 5 increases in accordance with the shift movement of the cylinder 4. However, the increased top clearance can be canceled by applying an increased voltage to the motor 3 so as to increase the piston stroke. Thus, the second embodiment makes it possible to maintain the top clearance at a constant value. Accordingly, it becomes possible to automatically increase the stroke of the piston in response to a high ambient air temperature so that the cooling power can be sufficiently obtained even in such a high load condition. Thus, efficient compressor operation can be realized in accordance with the driving conditions of the cooling device without using additional detecting and control devices. Next, when the ambient air temperature is low, a decreased cooling power is required. In such a case, the pressure control valve 21a is closed while the pressure control valve 21c is opened. Thus, the pressure of the back-pressure chamber 18a is increased to a high level. Meanwhile, the pressure control valve 21b is opened and the pressure control valve 21d is closed. Thus, the back-pressure chamber 18b is held at a reduced low pressure level. The integral unit of the cylinder 4 and the cylinder head 7 shifts in the axial direction toward the other stopper projection 17b due to a reversed pressure imbalance between the back-pressure chambers 18a and 18b. In this case, the top clearance of the piston 5 decreases in accordance with the shift movement of the cylinder 4. However, the decreased top clearance can be canceled by applying a decreased voltage to the motor 3 so as to decrease the piston stroke. Thus, the second embodiment makes it possible to maintain the top clearance at the constant value. Accordingly, it becomes possible to automatically decrease the stroke of the piston in response to a low ambient air temperature. Thus, efficient compressor operation can be realized in accordance with the driving conditions of the cooling device without using additional detecting and control devices. As described above, the second embodiment of present invention provides the oscillation-type compressor comprising the tightly closed casing 1 having the inside space 1a for storing coolant gas, the block 6 accommodated in the tightly closed casing 1, the motor 3 including the stator 3a and the mover 3b, the piston 5 connected to the mover 3b of the motor 3, the movable element 12 including the mover 3b of the motor 3 and the piston 5, the stationary element 13 including the stator 3a of the motor 3 and the block 6, the elastic element 8 having one portion 8b fixed to the movable element 12 and another portion 8c fixed to the stationary element 13, the cylinder 4 shiftable with respect the block 6, the cylinder head 7 fixed to the cylinder 4, back-pressure chambers 18a and 18b formed in the coolant gas space 1a and airtightly partitioned by an integral unit including at least one of the cylinder 4 and the cylinder head 7, and at least one of the back-pressure chambers 18a, 18b being held at a low pressure level and another one of the back-pressure chambers 18a, 18b being held at a high pressure level. With this arrangement, it becomes possible to realize a practical cooling device, such as a refrigerator, which is capable of automatically increasing the stroke of the piston in response to a high ambient air temperature so that the cooling power can be sufficiently obtained even in the high load condition and is also capable of automatically reducing the stroke of the piston in response to a decreased ambient air temperature. Thus, efficient compressor operation can be realized in accordance with the driving conditions of the cooling device without using additional detecting and control devices. Although the second embodiment of the present invention discloses the pressure control mechanism 21 which controls the pressures in the back-pressure chambers 18a and 18b. However, in is needless to say that similar effects can be obtained even when the pressure control mechanism 21 is replaced by any other comparable pressure control device. Third Embodiment Fig. 3 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a third embodiment of the present invention. As shown in Fig. 3, an elastic member 22 resiliently holds or supports the integral unit of the cylinder 4 and the cylinder head 7 midway between two stopper projections 17a and 17b. Operation of the oscillation-type compressor in accordance with the third embodiment will be explained hereinafter. When a large voltage is suddenly applied to the motor 3, the piston 5 may collide with the cylinder head 7. Accordingly, during a start-up operation of the compressor, the voltage applied to the motor 3 is gradually increased to avoid the collision of the piston 5. In this case, the top clearance of the piston gradually decreases with a significant elapse of time until the pressure conditions of the system reach the predetermined values. However, according to the third embodiment of the present invention, the elastic member 22 resiliently holds or supports the cylinder 4 at a position closer to the top dead center of the piston 5 when the compressor is stopped. Thus, even when the compressor is driven with a smaller stroke during the start-up operation, the top clearance can be maintained at a smaller value by the elastic member 22. Subsequently, the pressure of the compressed air increases and the piston stroke increases responsively. The cylinder 4 is gradually pushed toward the stopper projection 17a by the compression force, while the elastic member 22 resiliently receives or supports the cylinder 4 so as to maintain the top clearance at a constant value. Thus, the pressure conditions of the system can quickly reach the predetermined optimum values, realizing efficient compressor operation. When the compressor is operated stably, the cylinder 4 may oscillate together with the piston 5. However, the elastic member 22 acts as a damping means for suppressing the oscillation of the cylinder 4. Thus, the third embodiment reduces the fluctuation of the top clearance of the piston 5 caused by the co-oscillation between the piton 5 and the cylinder 4, preventing the cooling power from deteriorating. Furthermore, the third embodiment can stabilize the position of the cylinder 4 and suppress the vibration and noise. As described above, according to the third embodiment of the present invention, the oscillation-type compressor comprises the elastic member 22 having one end connected to the integral unit of the cylinder 4 and the cylinder head 7 and the other end connected to the stationary element 13. With this arrangement, it becomes possible to suppress the top clearance of the piston 5 to a small value even in the start-up operation where the piston is operated at short strokes, thereby realizing efficient compressor operation. Furthermore, it becomes possible to stabilize the cylinder position during an ordinary operation, when compared with a case where the cylinder position is controlled by a gas pressure imbalance. Thus, vibration and noise can be suppressed effectively. Fourth Embodiment Fig. 4 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a fourth embodiment of the present invention. In Fig. 4, a sensor 23, detecting the position of the piston 5, is fixed to the block 6. Another sensor 24, detecting the position of the cylinder 4, is fixed to the block 6. A control unit 26 receives the signals produced from the position detecting sensors 23 and 24, and controls the pressure control valves 21a, 21b, 21c and 21d. Operation of the oscillation-type compressor in accordance with the fourth embodiment will be explained hereinafter. When the stroke of piston 5 increases in response to changed operating pressure conditions of the compressor, the piston 5 may collide with the cylinder head 7. In this case, the control unit 26 feedback controls the pressure control mechanism 21 based on the signals sent from the position detecting sensors 23 and 24. More specifically, the pressure control valve 21c is closed, while the pressure control valve 21a is opened. Thus, the back-pressure chamber 18a is held at a low pressure level. Meanwhile, the pressure control valve 21d is opened and the pressure control valve 21b is closed. Thus, the back-pressure chamber 18b is held at an increased high pressure level. The integral unit of the cylinder 4 and the cylinder head 7 shifts in the axial direction toward the stopper projection 17a due to a pressure imbalance between the back-pressure chambers 18a and 18b. In this case, the top clearance of the piston 5 increases in accordance with the shift movement of the cylinder 4, preventing the piston 5 from colliding with the exhaust valve and eliminating noise. The stroke of the piston 5 decreases in response to the operating pressure conditions of the compressor. In this case, the oscillation center of the piston 5 shifts in a direction opposed to the compression chamber 9. As a result, the piston 5 cannot reach the top dead center due to the shifting of the oscillation center. The position detecting sensors 23 and 24 continuously monitor the positions of the piston 5 and the cylinder 4, respectively. When an increased top clearance is detected based on the signals of the position detecting sensors 23 and 24, the controller 26 closes the pressure control valve 21a and opens the pressure control valve 21a to hold the back-pressure chamber 18a at an increased high pressure level. Meanwhile, the controller 26 opens the pressure control valve 21b and closes the pressure control valve 21d. Thus, the back-pressure chamber 18b is held at a decreased low pressure level. The integral unit of the cylinder 4 and the cylinder head 7 shifts in the axial direction toward the stopper projection 17b due to a pressure imbalance between the back-pressure chambers 18a and 18b. In this case, the top clearance of the piston 5 decreases in accordance with the shift movement of the cylinder 4. Thus, the piston position is always optimized with respect to the cylinder position. In other words, it becomes possible to minimize the top clearance, preventing the cooling power from deteriorating due to the increase of the top clearance. Efficient compressor operation can be realized. As described above, according to the fourth embodiment of the present invention, the oscillation-type compressor of the present invention comprises the cylinder position detecting sensor 24 fixed to one of the stationary element 13 and the cylinder 4. With this arrangement, it becomes possible to optimize the piston position with respect to the cylinder position irrespective of changed operating pressure conditions, thereby minimizing the top clearance and realizing efficient compressor operation. Furthermore, it becomes possible to prevent the piston from colliding with the exhaust valve when the piston stroke is increased, thereby eliminating any damage and noise. According to the above-described fourth embodiment, the control unit 26 feedback controls the pressure control mechanism 21 to stabilize the top clearance based on the position signals of the piston 5 and the cylinder 4. However, it is needless to say that similar effects can be obtained even when the feedback control is performed so as to adjust the stroke of the piston 5 by changing the voltage applied to the motor 3 based on the position signals of the piston 5 and the cylinder 4. Fifth Embodiment Fig. 5 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a fifth embodiment of the present invention. In Fig. 5, an auxiliary exhaust pipe 25, slidable in the axial direction, is coupled with the exhaust pipe 10. Operation of the oscillation-type compressor in accordance with the fifth embodiment will be explained hereinafter. When the piston 5 reciprocates in the cylinder 4, the compressor vibrates largely in the axial direction. The caused vibration, transmitted to the stationary element 13 of the compressor, largely vibrates the exhaust pipe 10 connecting the cylinder head 7 to the outside of the tightly closed casing 1. However, according to the fifth embodiment of the present invention, the auxiliary exhaust pipe 25 is coupled with the exhaust pipe 10 and slidable in the axial direction so as to absorb caused vibration. Thus, no vibration is transmitted from the piston 5 to the exhaust pipe 10. Accordingly, as no vibration is transmitted from the reciprocating piston 5 to the exhaust pipe 10, it becomes possible to reduce the repetitive stress applied on the exhaust pipe 10, thereby preventing the reliability from deteriorating due to the damage of the exhaust pipe 10. As described above, the fifth embodiment of the present invention provides the oscillation-type compressor comprising the tightly closed casing 1 having the inside space 1a for storing coolant gas, the block 6 accommodated in the tightly closed casing 1, the motor 3 including the stator 3a and the mover 3b, the piston 5 connected to the mover 3b of the motor 3, the movable element 12 including the mover 3b of the motor 3 and the piston 5, the stationary element 13 including the stator 3a of the motor 3 and the block 6, the elastic element 8 having one portion 8b fixed to the movable element 12 and another portion 8c fixed to the stationary element 13, the cylinder 4 fixed to the block 6 or shiftable in the axial direction with respect the block 6, the cylinder head 7 fixed to the cylinder 4, the auxiliary pipe 25 having one end shiftable in the axial direction with respect to one of the exhaust pipe 10 and the intake pipe 20 and the other end fixed to one of the cylinder 4 and the cylinder head 7. With this arrangement, the exhaust or intake pipe can shift in the axial direction even when large vibration occurs in the axial direction, thereby reducing the large amplitude stress repetitively acting on the exhaust or intake pipe. Thus, it becomes possible to prevent the exhaust or intake pipe from being damaged. Even when the cylinder is shifted, it becomes possible to prevent the exhaust or intake pipe from being damaged. The above-described fifth embodiment discloses the auxiliary exhaust pipe 25 shiftable in the axial direction. However, it is needless to say that similar effects can be obtained even when a similar arrangement is applied to the intake pipe 20. Sixth Embodiment Fig. 6 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a sixth embodiment of the present invention. In Fig. 6, the oscillation-type compressor comprises a tightly closed casing 1 having an inside space serving as a coolant gas space 1a, a main body 2, a motor 3 including a stator 3a and a mover 3b, a cylinder 122, a piston 5, a yoke 106, a cylinder head 7, an intake chamber 7a, an exhaust chamber 7b, and an elastic element 108. The piston 5 has one end inserted in a bore of the cylinder 122 and has the other end held by the yoke 106 so as to reciprocate in the axial direction. A compression chamber 9 is defined by the cylinder 122, the piston 5 and the cylinder head 7. An exhaust pipe 10 extends from the exhaust chamber 7b formed in the cylinder head 7 to an outside cooling system (not shown). The main body 2 is roughly constituted by a movable element 112 and a stationary element 121. The movable element 112 includes the mover 3b of the motor 3 and the piston 5. The stationary element 121 includes the cylinder 122, the stator 3a of the motor 3 and the yoke 106. The main body 2 is elastically supported by a suspension spring (not shown) in the tightly closed casing 1. The elastic element 108 has one end fixed to the movable element 112 and the other end fixed to the stationary element 121. Lubrication oil 11 is stored in the lower portion of the tightly closed casing 1. Next, compression mechanism of the above-described oscillation-type compressor will be explained. First, alternating current of an AC power source is half-wave rectified and supplied to the stator 3a. A magnetic field generated by the stator 3a attracts the mover 3b fixed to the piston 5 based on the principle of magnetic variable resistance. When the mover 3b shifts in the axial direction, the elastic element 108 disposed between the mover 3b and the yoke 106 resiliently deforms in response to the shift movement of the piston 5, storing an elastic force therein. When the elastic force stored in the elastic element 108 is sufficiently increased, the mover 3b is pushed back to the original position. Continuous repetition of this cycle reciprocates the piston 5 in the axial direction. In this reciprocative movement, a position of the piston 5 nearest to the cylinder head 7 is referred to as a top dead center while a position of the piston 5 farthest from the cylinder head 7 is referred to as a bottom dead center. Coolant gas of the cooling system is first introduced into the coolant gas space 1a in the tightly closed casing 1, and then introduced into the intake chamber 7a formed in the cylinder head 7. Subsequently, the coolant gas enters the compression chamber 9 in the cylinder 4 via an intake valve (not shown) provided in the cylinder head 7. The coolant gas introduced in the compression chamber 9 is compressed by the piston 5 which reciprocates in the above-described manner. The compressed coolant gas enters the exhaust chamber 7b of the cylinder head 7 via an exhaust valve (not shown) provided in the cylinder head 7, and is then discharged to the cooling system via the exhaust pipe 10. Part of the elastic element 108 soaks in the lubrication oil 11. The elastic element 108 responsive to the reciprocating piston 5 pumps up the lubrication oil 11. Thus, the lubrication oil 11 is supplied to slide portions of the piston 5 and the yoke 106. The piston 5 receives a force derived from a pressure imbalance between the compression chamber 9 and the back-surface of the piston 5 in addition to a spring force of the elastic element 108 and a driving force of the motor 3. The oscillation center of the piston 5 shifts toward the bottom dead center in response to an increased pressure of the compression chamber. The oscillation amplitude of the piston 5 is increased. In Fig. 6, a block 120, the stator 3a and the yoke 106 cooperatively constitute a stationary element 121. The cylinder 122 is coupled with the block 120 and slidable along an inner wall of the block 120 so as to reciprocate in the axial direction. An enclosed space 123 is formed between the cylinder 122 and the block 120. The piston 5 is coupled with the cylinder 122 and slidably along a bore wall formed in the cylinder 122 so as to reciprocate in the axial direction. A communication passage 124, formed in the cylinder 122, has one end connected to the exhaust chamber 7b and the other end connected to the closed space 123. A spring 125 interposes between the block 120 and the cylinder 122. Operation of the oscillation-type compressor in accordance with the sixth embodiment will be explained hereinafter. High-pressure coolant gas, compressed in the compression chamber 9 during the compressing operation of the compressor, is sent to the exhaust chamber 7b and then discharged to the cooling system via the exhaust pipe 10. At the same time, part of the pressurized coolant gas is introduced into the closed space 123 via the communication passage 124. The cylinder 122 receives a force derived from a pressure imbalance between the closed space 123 and the tightly closed casing 1. The cylinder 122 shifts toward the top dead center and stops at a balanced point where the force caused by the pressure imbalance balances with the spring force of the spring 125. When the ambient temperature is high, the pressure of the closed space 123 increases to a higher level. Thus, the cylinder 122 shifts toward the top dead center than the usual position. By adjusting the motor power, the volume of the compression chamber 9 at the top dead center is maintained at the same value. The top dead center position of the piston 5 shifts away from the neutral position of the elastic element 108. Accordingly, the bottom dead center position shifts in the opposite direction with respect to the neutral position of the elastic element 108. As a result, the piston stroke increases and the exhaust amount of the coolant gas increases. The cooling power increased. Furthermore, the sixth embodiment can reduce an area contacting with high-pressure gas compared with a case where the cylinder shifts in response to the high pressure acting on the entire back surface of the cylinder. This is effective to reduce the thermal loss. Furthermore, under a condition where the cylinder receives a high pressure at its entire back surface, it is impossible to supply low-pressure lubrication oil from the bottom of the tightly closed casing to a high-pressure slide portion. However, according to the sixth embodiment, the high-pressure portion is limited to a smaller space. Thus, the lubrication oil can be pumped up by the movement of the elastic element soaked in the lubrication oil and supplied to the slide portions of the piston and the yoke. As described above, the sixth embodiment of the present invention provides the oscillation-type compressor comprising the block 120 and the piston 5 accommodated in the tightly closed casing 1, the motor 3 including the stator 3a and the mover 3b, the movable element 112 including the mover 3a and the piston 5, the stationary element 121 including the block 120 and the stator 3a, the elastic element 108 having a portion fixed to the movable element 112 and another portion fixed to the stationary element 121, the cylinder 122 accommodating the piston 5 so that the piston 5 is shiftable in the axial direction, the cylinder 122 being inserted in the block 120 so as to reciprocate in the axial direction with the closed space 123 formed between the block 120 and the cylinder 122, the cylinder head 7 comprising the exhaust chamber 7b and attached to the cylinder 122, and the communication passage 124 connecting the closed space 123 and the exhaust chamber 7b. With this arrangement, it becomes possible to increase the piston stroke by causing the cylinder to shift toward the top dead center in response to the increased high pressure of the space when the ambient temperature is high and therefore the required cooling power is high. Thus, the cooling power can be increased. Furthermore, this arrangement can reduce an area contacting with high-pressure gas compared with a case where the cylinder shifts in response to the high pressure acting on the entire back surface of the cylinder. This is effective to reduce the thermal loss. Furthermore, according to this arrangement, the lubrication oil stored in the lower part of the tightly closed casing can be pumped up by the movement of the movable element. Thus, the lubrication oil can be easily supplied to the slide portions, with reduced slide loss and eliminated wear. According to the above-described sixth embodiment, the spring is disposed between the cylinder and the block. However, it is needless to say that the similar effects will be obtained when the spring is replaced by a comparable element, such as a magnet, capable of generating a reaction force for varying the cylinder position in response to the changed pressure of the space. Furthermore, the cylinder 122 is subjected to a variable load in accordance with the changed pressure of the compression chamber 9 during one stroke. This variable load may shift the cylinder 122 widely, reducing the volume of the compression chamber 9 at the bottom dead center and deteriorating the cooling power. Therefore, it is preferable that the cross section of the closed space 123 is sufficiently larger than that of the compression chamber 9. Furthermore, to suppress the shift amount of the cylinder during one stroke, it is preferable to use the spring 125 having a large spring coefficient. Seventh Embodiment Fig. 7 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a seventh embodiment of the present invention. In Fig. 7, an exhaust pipe 126 extends from the closed space 123 to the cooling system located outside the compressor. The seventh embodiment comprises the exhaust pipe 126 in addition to the arrangement of the sixth embodiment. According to the seventh embodiment, the exhaust chamber 7b communicates with the cooling system via the closed space 123. Operation of the oscillation-type compressor in accordance with the seventh embodiment will be explained hereinafter. The high-pressure coolant gas, compressed in the compression chamber 9 during the compressing operation of the compressor, is sent to the exhaust chamber 7b and then discharged to the closed space 123 via the communication passage 124. The closed space 123 acts as a muffler for reducing the flowing speed of the discharged coolant gas. The decelerated coolant gas is then sent to the cooling system via the exhaust pipe 126. The amount of the coolant gas discharged from the compression chamber 9 increases in accordance with an increased ambient temperature. However, the volume of the closed space 123 increases in response to the increased exhaust gas amount so as to suppress the pulsation in the closed space 123, thereby preventing noise and vibration. As described above, the seventh embodiment of the present invention provides the oscillation-type compressor further comprising the exhaust pipe 126 connecting the closed space 123 and the cooling system. With this arrangement, the coolant gas compressed in the compression chamber 9 is once expanded in the closed space 123 and then discharged to the cooling system. Accordingly, when the exhaust gas amount increases in response to an increased stroke, the volume of the closed space 123 increases correspondingly so as to act as a muffler. Thus, the pulsation is surely reduced, while noise and vibration can be suppressed. Eighth Embodiment Fig. 8 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with an eighth embodiment of the present invention. In Fig. 8, a radially extending passage 128 is provided in the block 120. A radially outer end 128a of the passage 128 is connected to the lower part of the closed space 123. A radially inner end 128b is connected to a ring groove 128c extending along the slide surface between the cylinder 122 and the block 120. The eighth embodiment differs from the seventh embodiment in that the passage 128 is additionally provided. Operation of the oscillation-type compressor in accordance with the eighth embodiment will be explained hereinafter. The high-pressure coolant gas, compressed in the compression chamber 9 during the compressing operation of the compressor, is sent into the exhaust chamber 7b and then discharged to the closed space 123 via the communication passage 124. The flowing speed of the coolant gas is reduced in the closed space 123 so that the lubrication oil mist contained in the decelerated coolant gas falls by gravity and gathers at the bottom of the closed space 123. The lubrication oil thus stored in the lower part of the closed space 123 is pumped up via the radially extending passage 128 from the one end 128a to the other end 128b and supplied to the ring groove 128c. The supplied lubrication oil lubricates the entire slide surface between the cylinder 122 and the block 120. Thus, the clearance between the cylinder 122 and the block 120 is completely sealed by the lubrication oil so as to improve airtightness. Thus, it becomes possible to eliminate leaking loss. Furthermore, forming an oil film between the cylinder 122 and the block 120 prevents any wear occurring at the slide surface between the cylinder 122 and the block 120. As described above, the eighth embodiment of the present invention provides the oscillation-type compressor further comprising the passage 128 connecting the slide surface between the cylinder 122 and the block 120 and the bottom of the closed space 123. With this arrangement, it becomes possible to supply lubrication oil from the bottom of the closed space 123 to the slide surface between the cylinder 122 and the block 120 via the passage 128. Thus, the slide surface is airtightly sealed by the supplied lubrication oil. It becomes possible to prevent the coolant gas from leaking from the closed space. Supplying the lubrication oil to the slide surface can prevent the cylinder and the block from wearing. Ninth Embodiment Fig. 9 is a vertical cross-sectional view showing an oscillation-type compressor in accordance with a ninth embodiment of the present invention. Fig. 10 is a vertical cross-sectional view showing an operated condition of the oscillation-type compressor in accordance with the ninth embodiment. In Figs. 9 and 10, a combined groove 130 is provided on a slide surface of the cylinder 122 or the block 120. A groove 130a is provided on the cylinder 122, and another groove 130b is provided on the block 120. A communication passage 131 has one end 131a connected to the exhaust chamber 7b of the cylinder head 7 and another end 131b facing the groove 130b formed on the cylinder 122. The ninth embodiment differs from the sixth embodiment in that the communication passage 124 is omitted and the groove 130 and the communication passage 131 are additionally provided. Operation of the oscillation-type compressor in accordance with the ninth embodiment will be explained hereinafter. The high-pressure coolant gas, compressed in the compression chamber 9 during the compressing operation of the compressor, is sent into the exhaust chamber 7b and then discharged to the cooling system via the exhaust pipe 10. At the same time, part of the pressurized coolant gas is introduced into the closed space 123 via the communication passage 131 and the groove 130b. When the ambient temperature increases, the pressure of the closed space 123 increases to a higher level. The cylinder 122 receives an increased pressure of the closed space 123 and shifts toward the top dead center. The piston 5 has an increased stroke. However, when the system is in an unstable start-up condition or when the ambient temperature is extraordinarily increased, the exhaust pressure may increase extraordinarily to shift the cylinder 122 excessively toward the top dead center. However, according to the ninth embodiment of the present invention, when the cylinder 122 shifts toward the top dead center, the open end 131b of the communication passage 131 is dislocated from the groove 130b so as to disconnect the closed space 123 from the exhaust chamber 7b. Accordingly, introduction of the high-pressure coolant gas into the closed space 123 is stopped. At the same time, the closed space 123 communicates with the inside space of the tightly closed casing 1 via the groove 130a so as to discharge the coolant gas out of the closed space 123. As a result, the pressure level of the closed space 123 is reduced. The movement of the cylinder 122 shifting toward the top dead center is suppressed within a predetermined range. Thus, it becomes possible to prevent the piston stroke from excessively increasing, while causing no problems in the reliability of the elastic element or the like. As described above, the ninth embodiment of the present invention provides the oscillation-type compressor further comprising the combined groove 130 provided on the slide surface of one of the cylinder 122 and the block 120. With this arrangement, when the cylinder 122 widely shifts toward the top dead center, the groove 130 acts as a means for discharging the pressurized gas from the closed space 123 so that the piston stroke can be maintained within a predetermined range. Accordingly, it becomes possible to prevent the piston stroke from excessively increasing, while causing no problems in the reliability of the elastic element or the like.

Claims: An oscillation-type compressor comprising: a tightly closed casing (1) having an inside space (1a) for storing cooling gas; a block (6) accommodated in said tightly closed casing (1); a motor (3) including a stator (3a) fixed to said block and a mover (3b); a piston (5) connected to said mover (3b) of said motor; a movable element (12) including said mover (3b) of said motor and said piston (5); and a stationary element (13) including said stator (3a) of said motor and said block (6); characterised by : an elastic element (8) having a portion (8b) fixed to said movable element (12) and another portion (8c) fixed to said stationary element (13); a cylinder (4) receiving said piston (5) and shiftable in an axial direction with respect to said block (6); and a shifting device (16) for shifting said cylinder in said axial direction. An oscillation-type compressor according to claim 1 further comprising: a cylinder head (7) fixed to said cylinder (4) ; back-pressure chambers (18a, 18b) formed in said coolant gas space (1a) and airtightly partitioned by an integral unit including at least one of said cylinder (4) and said cylinder head (7); and at least one of said back-pressure chambers (18a, 18b) being held at a low pressure level and another one of said back-pressure chambers (18a, 18b) being held at a high pressure level. An oscillation-type compressor in accordance with claim 2, further comprising an elastic member (22) having one end connected to said integral unit including at least one of said cylinder (4) and said cylinder head (7) and the other end connected to said stationary element (13). An oscillation-type compressor in accordance with any one of claims 1 to 3, further comprising a cylinder position detecting sensor (24) fixed to one of said stationary element (13) and said cylinder (14). An oscillation-type compressor according to claim 1 further comprising: a cylinder head (7) fixed to said cylinder (4); and an auxiliary pipe (25) having one end shiftable in said axial direction with respect to one of an exhaust pipe (20) and an intake pipe (10) and the other end fixed to one of said cylinder (4) and said cylinder head (7). An oscillation-type compressor according to claim 1 wherein said cylinder (122) is inserted in said block (120) so as to reciprocate in the axial direction with a closed space (123) formed between said block (120) and said cylinder (122) and constituting said cylinder (122); and further comprising: a cylinder head (7) comprising an exhaust chamber (7b) and attached to said cylinder (122); and a communication passage (124) connected said closed space (123) and said exhaust chamber (7b). An oscillation-type compressor in accordance with claim 6, wherein said closed space (123) is connected to an outside space via an exhaust pipe (126). An oscillation-type compressor in accordance with claim 6 or 7, wherein a slide surface between said cylinder (122) and said block (120) is connected to a lower part of said closed space (123) via a passage. An oscillation-type compressor in accordance with claim 6, wherein a groove (130) is provided on a slide surface of one of said cylinder (122) and said block (120).

Inventors: INAGAKI KOH, KATAYAMA MAKOTO, KOBAYASHI MASANORI, MORITA ICHIRO, INAGAKI, KOH, KATAYAMA, MAKOTO, KOBAYASHI, MASANORI, MORITA, ICHIRO
Applicants: MATSUSHITA REFRIGERATION, MATSUSHITA REFRIGERATION COMPANY
Application year: 1998
Main classification: F04B35
IPC codes: F04B49, H02K1, H02K33, F04B39, F04B35, H02K7