Control device of linear compressor drive system

TECHNICAL FIELD

[0001] The present invention relates to a control apparatus for a linear compressor driving system used for a refrigerator, an air conditioner and the like.

BACKGROUND ART

[0002] In recent years, the necessity of a higher efficiency of a refrigerating apparatus has been increased from the viewpoint of earth environment protection and energy saving. A compressor using a linear motor has been widely used in order to make its efficiency higher and reduce its manufacturing cost, because of its simple mechanical configuration. However, in order to run the linear compressor at a high efficiency, it is necessary to run a piston in a reciprocating manner while keeping a clearance at a top dead center of the piston small. At the same time, the control of the refrigerating performance of the compressor is carried out, correspondingly to the size of the clearance at the top dead center. As mentioned above, this requires the controls that are not carried out in a reciprocating compressor of a conventional connecting rod type.

[0003] As a conventional controlling method of a linear compressor, there is a method described in Japanese Laid Open Patent Application JP-A 2000-121180. FIG. 10 is a sectional view showing a linear compressor that is a main unit in a linear compressor driving system as a control target to be controlled in accordance with the present invention, and FIG. 11 is a block diagram showing the configuration of the conventional control apparatus for controlling the linear compressor driving system.

[0004] In FIGS. 10 and 11, reference numeral 1 denotes a linear compressor, 2 denotes a sealed casing, and 3 denotes a compressor body. Also, reference numeral 4 denotes a linear motor, 5 denotes a cylinder, 6 denotes a piston, and 7 denotes a cylinder head. The motor 4 is provided with: a stator 4a having a coil 4c; and a movable element 4b having a permanent magnet. The movable element 4b is fixed to the piston 6. Also, reference numeral 10 denotes a compression room composed of the cylinder 5 and the piston 6. The compressor body 3 is composed of: a movable device 11 constituted by the movable element 4b of the motor 4 and the piston 6 and the like; and a fixed device 12 constituted by the cylinder 5 and the stator 4a of the motor 4 and the like. Also, reference numeral 14 denotes an elastic device. It is attached to the movable device at its center 14a and attached to the fixed device.

[0005] Also, reference numeral 16 denotes a power supply unit, 17 denotes a voltage determining means, and 18 denotes an ambient temperature detecting means. Reference numeral 19 denotes a heat exchanger constituted by an evaporator 19a and a condenser 19b. 20 denotes an expansion valve. The linear compressor 1, the condenser 19b, the expansion valve 20 and the evaporator 19a are linked through piping, and they form a system 21 in which refrigerant is circulated.

[0006] The operation of the conventional control apparatus for the linear compressor driving system will be described below. The ambient temperature detecting means 18 measures an ambient temperature and outputs a temperature signal based on the temperature. The voltage determining means 17 outputs a voltage target value based on the temperature signal. The power supply unit 16 outputs an alternating current in a shape of a sine wave to the linear compressor 1 at a voltage corresponding to the voltage target value.

[0007] The alternating current outputted from the power supply unit 16 is sent to the coil of the motor 4 in the linear compressor 1 so that a magnetic field is generated by the current flowing through the coil. Thus, the movable element 4b together with the piston 6 is reciprocated by the magnetic force acting between the movable element 4b and the permanent magnet. At this time, the greater the amplitude of the piston 6, the higher the voltage of the power supply unit 16, and the greater the amplitude of the piston, the stronger the refrigerating performance in the system 21.

[0008] By the way, in the case of the refrigerator, the necessary refrigerating performance is different depending on the ambient temperature. That is, if the ambient temperature is high, the thermal load on the refrigerator is high, which requires the strong refrigerating performance. On the other hand, if the ambient temperature is low, the necessary refrigerating performance becomes weak. However, at this time, if the refrigerating performance is excessively strong, a compression ratio is raised to thereby reduce the system efficiency. Hence, the proper refrigerating performance needs to be selected from the viewpoint of the system efficiency.

[0009] Thus, the voltage determining means 17 outputs a high voltage target value if the ambient temperature is high, and outputs a low voltage target value if the transistor is low. Consequently, the power supply unit 16 outputs the voltage necessary for the proper refrigerating performance to the linear compressor 1.

[0010] Also, a frequency of an alternating power supply generated by the power supply unit 16 is given as a resonant frequency mainly determined by a mass of the movable device 11 and a spring constant of the elastic device 14 in the linear compressor 1 and the like. Consequently, the spring force of the elastic device 14 can be effectively used for the reciprocating motion of the movable device 11.

[0011] However, in the case of the above-mentioned conventional configuration, when a tip of the piston 6 gets toward the cylinder head 7, the influence of the action force on the piston and the like brings about the unstable behavior, such as the variation of the position at the top dead center of the piston and the like. There may be a case that the movable member such as the piston and the like collides with the fixed member such as a valve plate and the like. This may be caused by the following influences. That is, the action force on the piston results not only from the spring force through a resonant spring but also from the gas compression force of the compression room. Moreover, this action force has a non-linear property. In addition, even a motor thrust is varied by a compression load.

[0012] The unstable behavior of the piston and the collision between the movable member and the fixed member bring about the problems of noise and vibration, and the strong collision leads to the problem of the drop in the reliability of the valve placed in the cylinder head and the like.

[0013] Even if they do not collide, the severe variation in the behavior of the piston may cause the noise. Moreover, since the circulation amount of the refrigerant is varied, this has the problem that a predetermined performance can not be obtained.

DISCLOSURE OF THE INVENTION

[0014] In view of the above-mentioned problems, it is therefore an object of the present invention to stabilize the behavior of a piston and thereby protect the occurrence of noise vibration and further protect the reduction in the reliability of a compressor and thereby improve the reliability. Also, the object is to stabilize the behavior of the piston and obtain the predetermined refrigerating performance and thereby improve the system efficiency.

[0015] Also, the fear of a collision occurrence is little under the operating condition in which a top clearance is large. Thus, this has the following problem. That is, even if the control for stabilizing the behavior is performed on the slight variation in the top dead center of the piston, there is no effect of the collision protection. Moreover, the electric power for the control is consumed.

[0016] Another object of the present invention is to reduce the occurrence of the circuit loss caused by the execution of the control without executing the control under the operating condition in which the necessity of the control is little.

[0017] Also, in order to keep a top dead center position of the piston constant, when a feedback control is carried out by detecting a position of the piston, a current and a voltage and by changing a supply voltage in accordance with the difference from a target value for each constant cycle, if a cycle of the control and a change amount of the supply voltage are unsuitable, on the contrary, there may be a case that the behavior of the piston becomes unstable.

[0018] Another object of the present invention is to avoid the unstable phenomenon of the piston caused by the unsuitable feedback control and carry out a stable operation.

[0019] The present invention is a control apparatus for a linear compressor driving system, which is used for a linear compressor driving system including: a linear compressor having a linear motor and a piston; and a power supply unit for supplying an electric power to the linear motor, including: an unstableness detecting means for detecting that a behavior of the piston is unstable and outputting an unstableness detection signal; and an unstableness avoiding means that is operated so as to act on the linear compressor driving system in accordance with the unstableness detection signal and thereby avoid the unstable state. This has the effect of protecting the reduction in the reliability and the increase in the noise vibration, which are caused by the collision between the movable member and the fixed member since the behavior of the piston becomes unstable.

[0020] Another embodiment of the present invention is a control apparatus for a linear compressor driving system, which is used for a linear compressor driving system including: a linear compressor having a linear motor and a piston; and a power supply unit for supplying an electric power to the linear motor, including: an operating condition detecting means for detecting at least one of a displacement of the piston, an ambient temperature, a temperature at any part of the linear compressor driving system, and an operating pressure, and then outputting a detection signal; an unstableness detecting means, which if the detection signal of the operating condition detecting means satisfies a predetermined condition, estimates that a behavior of the piston is unstable, and then outputs an unstableness detection signal; and an unstableness avoiding means that is operated so as to act on the linear compressor driving system in accordance with the unstableness detection signal and thereby avoid the unstable state. This has the effect of: protecting the reduction in the reliability and the increase in the noise vibration, which are caused by the collision between the movable member and the fixed member since the behavior of the piston becomes unstable and; and reducing the loss of the control circuit necessary for the control since the unstableness avoiding control is carried out only when it is required.

[0021] Another embodiment of the present invention further includes a displacement detecting means for detecting a displacement of the piston. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with an output of the displacement detecting means. Thus, this has the effect of directly detecting that the behavior is unstable, from the displacement of the piston,

[0022] Another embodiment of the present invention further includes a sound and vibration detecting means for detecting sound or vibration of the compressor. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with an output of the sound and vibration detecting means. Thus, this has the effect of indirectly detecting that the behavior of the piston is unstable, from the sound and the vibration.

[0023] Another embodiment of the present invention further includes a voltage current detecting means for detecting a voltage or a current outputted by the power supply unit. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with an output of the voltage current detecting means. Thus, this has the effect of indirectly detecting that the behavior of the piston is unstable, from the voltage or the current of the power supply unit.

[0024] Another embodiment of the present invention further includes a pressure detecting means for detecting a pressure of the system. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with an output of the pressure detecting means. Thus, this has the effect of indirectly detecting that the behavior of the piston is unstable, from the pressure of the system.

[0025] Another embodiment of the present invention further includes an ambient temperature detecting means for detecting an ambient temperature. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with an output of the ambient temperature detecting means. Thus, this has the effect of indirectly detecting that the behavior of the piston is unstable, from the ambient temperature.

[0026] Another embodiment of the present invention further includes a temperature detecting means for detecting a temperature of the system. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with an output of the temperature detecting means. Thus, this has the effect of indirectly detecting that the behavior of the piston is unstable, from the temperature of a refrigerating system.

[0027] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change a voltage waveform or a current waveform outputted by the power supply unit in accordance with the unstableness detection signal. Thus, this has the effect of reducing the unstable phenomenon of the piston by changing the thrust property of a motor.

[0028] Another embodiment of the present invention further includes a waveform memory for storing waveforms having a plurality of patterns, and the unstableness avoiding means is designed so as to output, from the power supply, the voltage or the current based on the waveform stored in the waveform memory, in accordance with the unstableness detection signal. Thus, the motor thrust property effective for avoiding the unstableness can be selected. Hence, this has the effect of reducing the unstable phenomenon of the piston,

[0029] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change an impedance of the motor in accordance with the unstableness detection signal. Thus, a method of changing the coil of the linear motor from a parallel wiring to a series wiring in accordance with the unstableness detection signal and the like are used to change the impedance of the motor. Thus, the waveform of the current flowing through the motor is changed, and the thrust property of the motor is changed. Consequently, this has the effect of relaxing the unstable behavior of the piston.

[0030] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change an air blowing amount to a heat exchanger in accordance with the unstableness detection signal. Thus, by changing the air blowing amount, the pressure of the system is varied to thereby changing the acting force on the piston. Hence, this has the effect of reducing the unstable behavior.

[0031] Another embodiment of the present invention is such that an air blowing amount changing means is designed so as to change a rotational speed and an air blowing path of an air blower. Thus, the change of them enables the pressure of the system to be changed, and thereby enables the action force on the piston to be changed. Hence, this has the effect of reducing the unstable behavior.

[0032] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change a frequency outputted by the power supply unit in accordance with the unstableness detection signal. Thus, this has the effect of reducing the unstable phenomenon of the piston due to the change of the operating frequency.

[0033] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change the voltage or the current of the power supply unit in accordance with the unstableness detection signal. Thus, this has the effect of increasing the top clearance of the piston to thereby avoid the collision, or selecting the stroke that does not lead to the occurrence of the unstable phenomenon.

[0034] Another embodiment of the present invention includes: a detecting means for detecting a current, a voltage or a piston displacement; a target value setting means for setting a target value of the current or the voltage or the piston displacement in accordance with an operating condition; a timer means for outputting a start signal at a predetermined interval; and a changing means for comparing an output of the detecting means with the target value in accordance with the start signal, and changing the voltage or the current outputted by the power supply unit at a predetermined change amount, correspondingly to the difference from the target value, wherein the unstableness avoiding means is designed so as to change at least one of the change amount of the detecting means and the output interval of the start signal of the timer means, in accordance with the unstableness detection signal. Thus, this has the effect of avoiding the unstable phenomenon of the piston caused by the feedback control at the top dead center position of the piston.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] These and other objects and features will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0036]
FIG. 1 is a block diagram showing a first embodiment of a control apparatus for a linear compressor driving system according to the present invention;

[0037]
FIG. 2 is a waveform view of a current which is detected by a current detecting means in the first embodiment of the present invention and sent from a power supply unit to a linear compressor;

[0038]
FIG. 3 is a flowchart showing an operation of an unstableness detecting means in the first embodiment of the present invention;

[0039]
FIG. 4 is a flowchart showing an operation of an unstableness avoiding means in the first embodiment of the present invention;

[0040]
FIG. 5 is a block diagram showing a second embodiment of a control apparatus for a linear compressor driving system according to the present invention;

[0041]
FIG. 6 is a block diagram showing a third embodiment of a control apparatus for a linear compressor driving system according to the present invention;

[0042]
FIG. 7 is a block diagram showing a fourth embodiment of a control apparatus for a linear compressor driving system according to the present invention;

[0043]
FIG. 8 is a block diagram showing a fifth embodiment of a control apparatus for a linear compressor driving system according to the present invention;

[0044]
FIG. 9 is a block diagram showing a sixth embodiment of a control apparatus for a linear compressor driving system according to the present invention;

[0045]
FIG. 10 is a sectional view showing a conventional linear compressor; and

[0046]
FIG. 11 is a block diagram showing a conventional linear compressor driving system and its control apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0047] Embodiments of a control apparatus for a linear compressor driving system according to the present invention will be described below with reference to FIGS. 1 to 9. By the way, the same symbols are given to the same configurations as the conventional technique, and their detailed explanations are omitted.

First Embodiment

[0048]
FIG. 1 is a block diagram showing a control apparatus for a linear compressor driving system according to a first embodiment of the present invention.

[0049] In FIG. 1, reference numeral 30 denotes a current detecting means for measuring a current of a power supply sent to a linear compressor 1 from a power supply unit 31. Reference numeral 32 denotes an unstableness detecting means for outputting an unstableness detection signal in accordance with an output of the current detecting means 30.

[0050] If the variation in a top dead center of a piston is great, the action force on the piston, such as a compression power and the like, is varied to thereby vary even a current flowing through a motor. Thus, the unstableness detecting means 32 extracts the variation in the peak value of the current measured by the current detecting means. If the variation in the peak value in a certain period is greater than a predetermined value, it estimates and judges that the behavior of the piston becomes unstable, and outputs the unstableness detection signal.

[0051] Here, the unstableness detecting means 32 is described in detail with reference to FIGS. 2 and 3. FIG. 2 is a waveform view of the current, which is detected by the current detecting means 30 in the first embodiment and sent to the linear compressor 1 from the power supply unit 31. FIG. 3 is a flowchart showing the operation of the unstableness detecting means 32 in the first embodiment. In FIG. 2, t indicates a current detection cycle, and n detections are carried out in one detection cycle. Then, the manner when the detection values of n peak currents are obtained is shown, as illustrated by black points in the waveform. The current detection values are represented by I(K-n+1), . . . I(K-2), . . . I(K-1) and I(K).

[0052]
FIG. 3 is the flowchart showing the operation of CPU when the unstableness detecting means 32 is constituted by the CPU (Central Processing Unit) (not shown). At first, at a step S1, an initialization is carried out so as to reset the maximum current Imax and the minimum current value Imin in previous measurement values to zero. Next, J=K-n+1 is calculated at a step S2. Here, K is a predetermined constant, and n is a predetermined number of measurements per cycle, and J is a variable obtained as the calculation result. Next, whether or not the variable J is greater than the constant K is judged at a step S3. Since J<K during the n measurements, the operating flow proceeds to a step S4, and a current value I(J) is detected. Next, if the current value I(J) detected at a step S5 is greater than the Imax, the operating flow proceeds to a step S6, and the I(J) is defined as a new Imax. On the other hand, if the current value I(J) is not greater than the Imax at the step S5, the operating flow proceeds to a step S7, and whether or not the current value I(J) is less than the Imin is judged. If the current value I(J) is less than the Imin, the I(J) is defined as a new Imin at a step S8. If the current value I(J) is not less than the Imin at the step S7, the operating flow proceeds to a step S9. Even if the operations at the steps S6 to S8 have been ended, the operating flow proceeds to the step S9. At the step S9, the variable J is incremented by 1, and the operating flow returns back to the step S3. The n repetitions of the measurements at the steps S3 to S9 lead to J<K, and the operating flow proceeds to a step S10. At the step S10, the difference between the Imax and the Imin is calculated to then judge whether or not this difference (Imax−Imin) is greater than a constant M. If the difference is greater than the constant M, the operating flow proceeds to a step S11. Then, it is judged to be an unstable state, and an unstable flag is set to YES. On the other hand, if the difference is less than the constant M, the operating flow proceeds to a step S12, and it is judged not to be the unstable state, and the unstable flag is set to NO.

[0053] Reference numeral 33 denotes an unstableness avoiding means. When the unstableness detection signal is inputted, it outputs a frequency change signal to the power supply unit 31. When the frequency change signal is inputted to the power supply unit 31, the power supply unit 31 changes the frequency of the power supply sent to the compressor 1. Thus, changing the operating frequency of the linear compressor can avoid the condition that the piston behavior becomes unstable.

[0054] Here, the unstableness avoiding means 33 is described in detail with reference to FIG. 4. FIG. 4 is a flowchart showing the operation when the unstableness avoiding means 33 in the first embodiment is constituted by the CPU. By the way, when it is constituted by the same CPU as the CPU constituting the unstableness detecting means 32, the processes in FIG. 4 can be configured by an interrupting process corresponding to the process of FIG. 3 and the like. At a step S21 in FIG. 4, the unstable flag set at the steps S11, S12 in FIG. 3 is monitored. Then, if the unstable flag is YES, the operating flow proceeds to a step S22, and the frequency of the driving current of the linear compressor is lowered by ΔH1. On the other hand, if the unstable flag is NO, the operating flow proceeds to a step S23. The frequency of the driving current of the linear compressor is kept in its original state.

[0055] By the way, as the consideration result in our company, even if an operating pressure condition is changed in the actual apparatus operation such as a refrigerator or the like to thereby bring about the unstable behavior of a piston, the fact that the unstable behavior is removed by changing the frequency of the power supply by several Hz is experimentally confirmed. Although the obvious reason with regard to this causal relation is not still proved, it may be considered that the motor thrust, the pressure within the compression room, the behavior of the valve and the like contribute to the causal relation.

[0056] As mentioned above, the control apparatus for the linear compressor driving system in this embodiment is provided with: the detecting means for detecting the current of the power supply; the unstableness detecting means for indirectly detecting that the behavior of the piston is unstable, in accordance with the output of the detecting means, and outputting the unstableness detection signal; and the unstableness avoiding means for changing the frequency of the power supply in accordance with the unstableness detection signal. Even if the piston behavior becomes unstable, this control apparatus stabilizes it by adjusting the frequency of the power supply. Thus, this can protect the occurrence of the noise vibration caused by the collision and the reduction in the reliability.

Second Embodiment

[0057]
FIG. 5 is a block diagram showing a control apparatus for a linear compressor driving system according to a second embodiment of the present invention.

[0058] In FIG. 5, reference numeral 40 denotes a sound and vibration detecting means 40 constituted by a vibration pickup, and it is attached to a compressor and detects sound and vibration. Also, reference numeral 41 denotes an unstableness detecting means 41.

[0059] If the behavior of the piston becomes unstable and the movable member of the compressor body 3 (refer to FIG. 10) collides with the fixed member, the collision causes the collisional sound and vibration that are greater than the typical case to be generated in the compressor. When the collision is induced and the output of the sound and vibration detecting means is greater than a predetermined value, the unstableness detecting means 41 judges that the piston is unstable, and outputs the unstableness detection signal.

[0060] Reference numeral 42 denotes an unstableness avoiding means. If the unstableness detection signal is inputted, it outputs a voltage drop signal to a voltage determining means 43. The voltage determining means 43 usually outputs a voltage target value corresponding to an output of the ambient temperature detecting means 18 and controls an output voltage of the power supply unit 16. However, if the voltage drop signal is inputted, the voltage determining means 43 outputs a voltage target value lower than the usual value, which results in the drop in the power supply voltage of the linear compressor 1. Thus, the unstable condition in which the amplitude of the piston is reduced to bring about the collision is removed.

[0061] Also, if the output of the ambient temperature detecting means 18 is less than the predetermined value, the sound and vibration detecting means 40, the unstableness detecting means 41 and the unstableness avoiding means 42 stop their functions.

[0062] The collision between the movable member and the fixed member is easier induced as a top clearance is smaller. When the top clearance is large, the possibility of the collision becomes almost rare. Thus, if the ambient temperature is low and the operation can be carried out at a small refrigerating performance, the top clearance is widely open. Hence, the possibility of the collision is said to be almost zero.

[0063] Thus, in the condition that the ambient temperature is low, the sound and vibration detecting means 40, the unstableness detecting means 41 and the unstableness avoiding means 42 are not required. Hence, the stop of their functions enables the reduction in the electric power consumption.

[0064] As mentioned above, the control apparatus for the linear compressor driving system in this embodiment is provided with: the sound and vibration detecting means for detecting the sound and the vibration of the compressor; the unstableness detecting means for outputting the unstableness detection signal in accordance with the output of the sound and vibration detecting means; the unstableness avoiding means for changing the voltage or the current of the power supply in accordance with the unstableness detection signal; and the detecting means for detecting the ambient temperature. Only if the output of the detecting means satisfies the predetermined condition, the unstableness detecting means and the unstableness avoiding means are actuated. Thus, if the piston behavior becomes unstable to thereby bring about the collision between the movable member and the fixed member in the compressor body, the collision is detected from the vibration, and the voltage sent to the compressor is dropped. Hence, the collision is removed, and the occurrence of the noise and the vibration and the reduction in the reliability are protected. Moreover, the unstableness detecting means and the unstableness avoiding means are stopped in the operating condition that the unstable behavior of the piston is not induced. Hence it is possible to reduce the electric power consumption.

Third Embodiment

[0065]
FIG. 6 is a block diagram showing a control apparatus for a linear compressor driving system according to a third embodiment of the present invention.

[0066] In FIG. 6, reference numeral 50 denotes a displacement detecting means, which is attached to a compressor, for measuring the displacement of a piston.

[0067] Reference numeral 51 denotes an unstableness detecting means, which detects the variation in the top dead center of the piston from the output of the displacement detecting means 50, and outputs the unstableness detection signal if the variation in the top dead center is greater than a predetermined value.

[0068] Reference numeral 52 denotes an unstableness avoiding means, which outputs a constant voltage waveform in a usual case. However, if the unstableness detection signal is inputted, the unstableness avoiding means 52 selects a voltage waveform different from that outputted until this time, from waveforms stored in a waveform memory 53, and outputs it.

[0069] A power supply unit 54 amplifies the voltage waveform outputted from the unstableness avoiding means 52, to the voltage target value outputted from the voltage determining means 17, and then outputs to the compressor 1.

[0070] Thus, when the behavior of the piston becomes unstable, the thrust property of the linear compressor can be changed to thereby change the action force on the piston and further stabilize the behavior of the piston.

[0071] As mentioned above, the control apparatus for the linear compressor driving system in this embodiment is provided with: the displacement detecting means for detecting the displacement of the piston; the unstableness detecting means for outputting the unstableness detection signal in accordance with the output of the displacement detecting means; the waveform memory for storing the waveforms of a plurality of patterns; and the unstableness avoiding means for sequentially outputting from the power supply the voltage waveforms stored in the waveform memory in accordance with the unstableness detection signal. Then, if the behavior of the piston becomes unstable, the waveform of the thrust of the linear motor is changed to thereby stabilize the piston behavior.

Fourth Embodiment

[0072]
FIG. 7 is a block diagram showing a control apparatus for a linear compressor driving system according to a fourth embodiment of the present invention.

[0073] In FIG. 7, reference numeral 60 denotes an unstableness detecting means, which preliminarily stores an ambient temperature at which the behavior of the piston becomes unstable, as a predetermined value, and then outputs the unstableness detection signal at the predetermined ambient temperature to the output of an ambient temperature detecting means. Reference numeral 61 denotes an unstableness avoiding means, which changes an impedance of a motor by using a method of changing a wiring of a linear motor of a compressor from a parallel wiring to a series wiring, in accordance with the unstableness detection signal, and the like. In association with this change, the waveform of the current flowing through the motor is changed, and the thrust property of the motor is also changed. Thus, it is possible to stabilize the behavior of the motor.

[0074] As mentioned above, the control apparatus for the linear compressor driving system in this embodiment is provided with: the ambient temperature detecting means for detecting the ambient temperature; the unstableness detecting means for outputting the unstableness detection signal in accordance with the output of the ambient temperature detecting means; and the unstableness avoiding means for changing the impedance of the motor in accordance with the unstableness detection signal. When the behavior of the piston becomes unstable, the impedance of the motor can be changed to thereby change the waveform of the thrust of the liner motor and further stabilize the piston behavior.

Fifth Embodiment

[0075]
FIG. 8 is a block diagram showing a control apparatus for a linear compressor driving system according to a fifth embodiment of the present invention. In FIG. 8, reference numeral 70 denotes a condenser, 71 denotes an expansion valve, and 72 denotes an evaporator. Including a compressor 1, they generate the refrigerating cycle of the refrigerator. By the way, the condenser 70 and the evaporator 72 are the heat exchangers, respectively, as well known. Also, the combination of them constitutes the heat exchanger. Reference numeral 73 denotes an air blower placed near the evaporator. Cold air generated in the evaporator 72 is sent into the refrigerator by the air blower 73.

[0076] Also, reference numeral 74 is a pressure detecting means attached to the compressor 1. Reference numeral 74A denotes an unstableness detecting means, which judges that the behavior of the piston becomes unstable if an output of the pressure detecting means 74 satisfies a predetermined pressure condition, and outputs the unstableness detection signal.

[0077] Reference numeral 75 denotes an unstableness avoiding means, which when receiving the unstableness detection signal from the unstableness detecting means 74A, increases the air blowing amount of the air blower 73 to thereby raise a temperature of the evaporator 72 and increase a low pressure. Consequently, the operating pressure condition is changed, and the action force on the piston is changed to thereby stabilize the behavior of the piston.

[0078] As mentioned above, the control apparatus for the linear compressor driving system in this embodiment is provided with: the pressure detecting means for detecting the pressure of the system; the unstableness detecting means for outputting the unstableness detection signal in accordance with the output of the pressure detecting means; and the unstableness avoiding means for changing the air blowing amount to the heat exchanger in accordance with the unstableness detection signal. When the behavior of the piston becomes unstable, the air blowing amount to the heat exchanger can be changed to thereby change the pressure condition. Also, the action force on the piston can be changed to thereby stabilize the piston behavior.

[0079] By the way, this embodiment is designed such that the pressure detecting means is defined as the air blower jointly placed in the heat exchanger. However, the similar effect can be attained even by using a different means such as a valve that can change the pressure condition in the refrigerating system.

Sixth Embodiment

[0080]
FIG. 9 is a block diagram showing a control apparatus for a linear compressor driving system according to a sixth embodiment of the present invention.

[0081] In FIG. 9, reference numeral 80 denotes a displacement detecting means, which detects a position of the piston and outputs a top dead center position signal of the piston. Reference numeral 81 denotes a target value setting means, which outputs a standard value of a top dead center position of the piston. Reference numeral 82 denotes a timer means, which outputs a start signal for each constant period. Also, reference numeral 83 denotes a changing means, which when receiving the start signal from the timer means 82, changes a voltage setting value at a predetermined change amount for the difference between the standard value outputted by the target value setting means 81 and the top dead center position signal outputted by the displacement detecting means 80, and outputs the voltage setting value.

[0082] Also, reference numeral 84 denotes an unstableness detecting means, which stores the top dead center position signal outputted by the displacement detecting means 80, and if a value of a variation in a constant temporal width exceeds a predetermined value, judges it to be unstable, and then outputs the unstableness detection signal. Reference numeral 85 denotes an unstableness avoiding means, which when the unstableness detecting means outputs the unstableness detection signal, outputs a cyclic time setting signal to the timer means 82, and changes the cycle of the start signal output of the timer means 82.

[0083] As a result, it is possible to protect the increase in the variation of the top dead center position caused by the unsuitable timing of the control in the feedback control for the top dead center position. Thus, the stable control can be carried out.

[0084] As mentioned above, the control apparatus for the linear compressor driving system in this embodiment is provided with: the target value setting means for setting the predetermined target value on the basis of the operating condition; the detecting means for detecting the displacement of the piston; the unstableness detecting means for detecting that the piston is at the unstable behavior and outputting the unstableness detection signal; the unstableness avoiding means for suppressing or avoiding the unstableness in accordance with the unstableness detection signal; the timer means for outputting the start signal at the predetermined interval; and the changing means for comparing the output of the detecting means with the target value in accordance with the start signal and changing the voltage or the current of the power supply at the predetermined change amount, on the basis of the difference from the target value. Then, the unstableness avoiding means can avoid the unstableness of the piston behavior caused by the feedback control, since the changing means changes the output timing of the start signal of the timer means, for the difference between the output of the detecting means and the target value, and thereby relaxes the unstableness.

INDUSTRIAL APPLICABILITY

[0085] As mentioned above, the present invention include: the unstableness detecting means for directly or indirectly detecting that the behavior of the piston is unstable and outputting the unstableness detection signal; and the unstableness avoiding means to be operated in accordance with the unstableness detection signal. Thus, this can protect the unstable behavior of the piston and protect the reduction in the reliability and the occurrence of the noise vibration, which are caused by the collision.

[0086] Another embodiment of the present invention further includes the detecting means for detecting at least one of the displacement of the piston, the ambient temperature, the system temperature, and the pressure condition. The unstableness detecting means and the unstableness avoiding means are designed so as to act only if the output of the detecting means satisfies the predetermined condition. Hence, the electric power consumption can be reduced by designing that the operations for detecting and avoiding the unstableness are not carried out under the condition in which the collision is not induced.

[0087] Another embodiment of the present invention further includes the displacement detecting means for detecting the displacement of the piston. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with the output of the displacement detecting means. Thus, this can directly detect the unstable behavior, from the displacement of the piston.

[0088] Another embodiment of the present invention further includes the sound and vibration detecting means for detecting the sound and the vibration of the compressor. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with the output of the sound and vibration detecting means. Thus, this can indirectly detect the unstable phenomenon of the piston, from the sound and the vibration.

[0089] Another embodiment of the present invention further includes the detecting means for detecting the voltage or the current of the power supply. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with the output of the detecting means. Thus, this can indirectly detect the unstable phenomenon of the piston, from the voltage or the current.

[0090] Another embodiment of the present invention further includes the pressure detecting means for detecting the pressure of the system. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with the output of the pressure detecting means. Thus, this can indirectly detect the unstable phenomenon of the piston, from the current or the voltage.

[0091] Another embodiment of the present invention further includes the ambient temperature detecting means for detecting the ambient temperature. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with the output of the ambient temperature detecting means. Thus, this can indirectly detect the unstable phenomenon of the piston, from the ambient temperature.

[0092] Another embodiment of the present invention further includes the temperature detecting means for detecting the temperature of the system. The unstableness detecting means is designed so as to output the unstableness detection signal in accordance with the output of the temperature detecting means. Thus, this can indirectly detect the unstable phenomenon of the piston, from the temperature of the refrigerating system.

[0093] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change the voltage waveform or the current waveform of the power supply in accordance with the unstableness detection signal. Thus, the thrust property of the linear motor is changed. It is possible to stabilize the behavior of the piston.

[0094] Another embodiment of the present invention further includes the waveform memory for storing the waveforms having the plurality of patterns. The unstableness avoiding means is designed so as to sequentially output, from the power supply, the voltage or current waveform stored in the waveform memory, in accordance with the unstableness detection signal. Thus, the thrust property of the linear motor is changed. It is possible to stabilize the behavior of the piston.

[0095] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change the impedance of the motor in accordance with the unstableness detection signal. Thus, the thrust property of the linear motor is changed. It is possible to stabilize the behavior of the piston.

[0096] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change amount of the air blowing into the heat exchanger in accordance with the unstableness detection signal. Thus, the acting force by the pressure varies, and it is possible to stabilize the behavior of the piston.

[0097] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to open and close the valve or change the air blowing amount to the heat exchanger in accordance with the unstableness detection signal. Thus, the acting force by the pressure is changed. It is possible to stabilize the behavior of the piston.

[0098] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change the frequency of the power supply in accordance with the unstableness detection signal. Thus, it is possible to stabilize the behavior of the piston.

[0099] Another embodiment of the present invention is such that the unstableness avoiding means is designed so as to change the voltage or the current of the power supply in accordance with the unstableness detection signal. Thus, this can increase the top clearance, protect the reduction in the reliability caused by the collision and protect the occurrence of the noise and the vibration.

[0100] Another embodiment of the present invention is provided with: the detecting means for detecting the current, the voltage or the piston displacement; the target value setting means for setting the target value of the current or the voltage or the piston displacement in accordance with the operating condition; the timer means for outputting the start signal at the predetermined interval; and the changing means for comparing the output of the detecting means with the target value in accordance with the start signal, and changing the voltage or the current of the power supply at the predetermined change amount, correspondingly to the difference from the target value, wherein the unstableness avoiding means is designed so as to change at least one of the change amount of the detecting means and the output interval of the start signal of the timer means, in accordance with the unstableness detection signal. Thus, this can avoid the unstableness caused by the feedback control of the piston position.

Control device of linear compressor drive system

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