Patent Application
20200362842
The present subject matter relates generally to linear compressors, such as linear compressors for refrigerators and other appliances.
Some refrigerators may include sealed systems for cooling chilled chambers of the refrigerators. The sealed systems generally include a compressor that generates compressed refrigerant during operation of the sealed systems. The compressed refrigerant flows to an evaporator where heat exchanges from the chilled chambers, to cool the chilled chambers and food items located therein.
Certain refrigerators have included linear compressors for compressing refrigerant. Linear compressors generally include a piston and a driving coil. The driving coil receives a current that generates a force for oscillating the piston (i.e., sliding the piston forward and backward within a chamber having a cylinder head). An elastic element, such as a spring, may be provided to aid in such oscillation. During motion of the piston within the chamber, the piston compresses refrigerant. Generally, the force of gas compression acts to push the piston away from the chamber and cylinder head.
Motion of the piston within the chamber may be controlled such that the piston does not crash against another component of the linear compressor during motion of the piston within the chamber. The overall motion may be proportional to a stroke length, which may be dependent upon a setpoint of the piston or motor operating the piston. Furthermore, cooling capacity is proportional to the stroke length and setpoint. Generally, the setpoint is a preset physical point determined by the mechanical mounting of the motor to the linear compressor, and therefore is generally not adjustable. Moreover, as stated above, increasing stroke length motion within the chamber may cause undesirable mechanical crashing.
Accordingly, it would be useful to provide a linear compressor and method of operation for addressing one or more of the above-identified issues. In particular, a linear compressor and methods of setpoint and cooling capacity control would be especially advantageous.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In one example aspect of the present disclosure, an appliance is provided. The appliance may include a linear compressor having a reciprocating piston movable in a negative axial direction toward a chamber and positive axial direction away from the chamber. The appliance may further include a motor operatively coupled to linear compressor, the linear motor having a resting setpoint and stroke, an inverter configured to supply a variable frequency waveform to the motor, and a controller configured to control the variable frequency waveform. The controller may be configured to direct a positive DC voltage to the motor to shift the resting setpoint to increase a cooling capacity of the linear compressor.
In another example aspect of the present disclosure, a method of operating a linear compressor is provided. The linear compressor may include a motor and a reciprocating piston movable in a negative axial direction toward a chamber and positive axial direction away from the chamber. The method may include supplying a variable frequency waveform to the motor of the linear compressor to produce a reciprocal motion in the piston at a first cooling capacity, determining that an increase in cooling capacity is required, and directing a positive direct current (DC) voltage to the motor to induce an extension force at the motor in the positive axial direction during at least a portion of the supplying step in response to the determining step.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Within refrigeration system 60, refrigerant flows into compressor 64, which operates to increase the pressure of the refrigerant. This compression of the refrigerant raises its temperature, which is lowered by passing the refrigerant through condenser 66. Within condenser 66, heat exchange with ambient air takes place so as to cool the refrigerant. A fan 72 is used to pull air across condenser 66, as illustrated by arrows AC, so as to provide forced convection for a more rapid and efficient heat exchange between the refrigerant within condenser 66 and the ambient air. Thus, as will be understood by those skilled in the art, increasing air flow across condenser 66 can, e.g., increase the efficiency of condenser 66 by improving cooling of the refrigerant contained therein.
An expansion device (e.g., a valve, capillary tube, or other restriction device) 68 receives refrigerant from condenser 66. From expansion device 68, the refrigerant enters evaporator 70. Upon exiting expansion device 68 and entering evaporator 70, the refrigerant drops in pressure. Due to the pressure drop and/or phase change of the refrigerant, evaporator 70 is cool relative to compartments 14 and 18 of refrigerator appliance 10. As such, cooled air is produced and refrigerates compartments 14 and 18 of refrigerator appliance 10. Thus, evaporator 70 is a type of heat exchanger which transfers heat from air passing over evaporator 70 to refrigerant flowing through evaporator 70.
Collectively, the vapor compression cycle components in a refrigeration circuit, associated fans, and associated compartments are sometimes referred to as a sealed refrigeration system operable to force cold air through compartments 14, 18 (
Turning now to
A piston assembly 114 with a piston head 116 is slidably received within chamber 112 of cylinder assembly 111. In particular, piston assembly 114 is slidable along a first axis A1 within chamber 112. The first axis A1 may include a negative axial direction A(−) and a positive axial direction A(+), and may be substantially parallel to the axial direction A. Thus, piston assembly 114 may alternately slide or oscillate, e.g., the piston head 116, in the negative axial direction A(−) and the positive axial direction A(+). During sliding of piston head 116 within chamber 112, piston head 116 compresses refrigerant within chamber 112. As an example, from a top dead center position (i.e., top dead center point), piston head 116 can slide within chamber 112 towards a bottom dead center position (i.e., bottom dead center point) along the positive axial direction A(+), i.e., an expansion stroke of piston head 116. When piston head 116 reaches the bottom dead center position, piston head 116 changes directions and slides in chamber 112 along the negative axial direction A(−) back towards the top dead center position, i.e., a compression stroke of piston head 116. It should be understood that linear compressor 100 may include an additional piston head and/or additional chamber at an opposite end of linear compressor 100. Thus, linear compressor 100 may have multiple piston heads in alternative example embodiments.
Linear compressor 100 also includes an inner back iron assembly 130. Inner back iron assembly 130 is positioned in the stator of the motor. In particular, outer back iron 150 and/or driving coil 152 may extend about inner back iron assembly 130, e.g., along the circumferential direction C. Inner back iron assembly 130 extends between a first end portion 132 and a second end portion 134, e.g., along the axial direction A.
Inner back iron assembly 130 also has an outer surface 137. At least one driving magnet 140 is mounted to inner back iron assembly 130, e.g., at outer surface 137 of inner back iron assembly 130. Driving magnet 140 may face and/or be exposed to driving coil 152. In particular, driving magnet 140 may be spaced apart from driving coil 152, e.g., along the radial direction R by an air gap AG. Thus, the air gap AG may be defined between opposing surfaces of driving magnet 140 and driving coil 152. Driving magnet 140 may also be mounted or fixed to inner back iron assembly 130 such that an outer surface 142 of driving magnet 140 is substantially flush with outer surface 137 of inner back iron assembly 130. Thus, driving magnet 140 may be inset within inner back iron assembly 130. In such a manner, the magnetic field from driving coil 152 may have to pass through only a single air gap (e.g., air gap AG) between outer back iron 150 and inner back iron assembly 130 during operation of linear compressor 100.
As may be seen in
A piston flex mount 160 is mounted to and extends through inner back iron assembly 130. A coupling 170 extends between piston flex mount 160 and piston assembly 114, e.g., along the axial direction A. Thus, coupling 170 connects inner back iron assembly 130 and piston assembly 114 such that motion of inner back iron assembly 130, e.g., along the axial direction A or the second axis A2, is transferred to piston assembly 114. Piston flex mount 160 defines an input passage 162 that permits refrigerant to flow therethrough.
Linear compressor 100 may include various components for permitting and/or regulating operation of linear compressor 100. In particular, linear compressor 100 includes a controller (not shown) that is configured for regulating operation of linear compressor 100. The controller is in, e.g., operative, communication with the motor, e.g., driving coil 152 of the motor. Thus, the controller may selectively activate driving coil 152, e.g., by supplying current to driving coil 152, in order to compress refrigerant with piston assembly 114 as described above.
The controller includes memory and one or more processing devices such as microprocessors, CPUs or the like, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with operation of linear compressor 100. The memory can represent random access memory such as DRAM, or read only memory such as ROM or FLASH. The processor executes programming instructions stored in the memory. The memory can be a separate component from the processor or can be included onboard within the processor. Alternatively, the controller may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, field programmable gate arrays (FPGA), and the like) to perform control functionality instead of relying upon software.
Linear compressor 100 also includes a spring assembly 120. Spring assembly 120 is positioned in inner back iron assembly 130. In particular, inner back iron assembly 130 may extend about spring assembly 120, e.g., along the circumferential direction C. Spring assembly 120 also extends between first and second end portions 102 and 104 of casing 110, e.g., along the axial direction A. Spring assembly 120 assists with coupling inner back iron assembly 130 to casing 110, e.g., cylinder assembly 111 of casing 110. In particular, inner back iron assembly 130 is fixed to spring assembly 120 at a middle portion 119 of spring assembly 120.
During operation of driving coil 152, spring assembly 120 supports inner back iron assembly 130. In particular, inner back iron assembly 130 is suspended by spring assembly 120 within the stator or the motor of linear compressor 100 such that motion of inner back iron assembly 130 along the radial direction R is hindered or limited while motion along the second axis A2 is relatively unimpeded. Thus, spring assembly 120 may be substantially stiffer along the radial direction R than along the axial direction A. In such a manner, spring assembly 120 can assist with maintaining a uniformity of the air gap AG between driving magnet 140 and driving coil 152, e.g., along the radial direction R, during operation of the motor and movement of inner back iron assembly 130 on the second axis A2. Spring assembly 120 can also assist with hindering side pull forces of the motor from transmitting to piston assembly 114 and being reacted in cylinder assembly 111 as a friction loss.
In contrast, the linear compressor 100 may operate along curve 606. As shown, a basic linear curve portion 608 exists such that there is a conventionally linear relationship between increasing current and cooling capacity until approximately capacity 610. Upon reaching capacity 610, a direct current (DC) voltage can be injected which offsets a resting setpoint (e.g., L0, described more fully below) of the motor, and therefore offers increased cooling capacity with a decrease in efficiency. However, as illustrated, the overall efficiency of the linear compressor 100 is greater than that of a conventional linear compressor. For example, because the resting setpoint L0 of the linear compressor 100 is decreased as compared to a conventional compressor at rest, there is reduced friction when compressing gas, which results in less heating of gases. However, when the resting setpoint L0 of the linear compressor 100 is shifted due to injection of positive DC voltage, cooling capacity is increased while still retaining overall efficiency much higher than the conventional compressor cycle curve 604.
Turning now to
As an example, the mechanical dynamic model for linear compressor 100 may be
F
m
=αi=M{umlaut over (x)}+C{dot over (x)}+K(x−L0)−Fgas
where
Accordingly, a different L0 can be obtained, at least temporarily, by changing DC voltage. Positive DC Voltage will increase the stroke length and further increase cooling capacity at a low clearance. Generally, the control objective of method 700 is to add Vdc to increase L0 and stroke length when higher cooling capacity is needed, required, or selected. For example, a control signal, temperature sensor, temperature selection apparatus, or other suitable control signal may be used to signal that higher cooling capacity is needed.
With respect to
A determination may be made whether an increase in cooling capacity is required by signaling a change in DC voltage. If increased cooling capacity is required, the DC voltage (Vdc) is indexed higher (e.g., from a starting value of 0). In particular, the DC voltage (Vdc) is increased by the index value (ΔVdc). Moreover, the DC voltage (Vdc) is combined as a positive value with the time varying voltage (Vac) to form the voltage function [V(t)]. Additionally, the DC voltage (Vdc) may be repeatedly increased by the index value (ΔVdc). Moreover, the repeated increases may occur at the index rate (TEC) until the DC voltage (Vdc) exceeds the index limit (e.g., upper index limit) or until increased cooling capacity is no longer required. If increased cooling is no longer required, the DC voltage (Vdc) is decreased by the index value (ΔVdc) immediately, or as an indexed value, to zero volts DC.
Generally, the first cooling capacity may be a base capacity related to a resting setpoint L0 of the linear compressor 100. Other first cooling capacities may be chosen, including those already having a small offset of the resting setpoint L0 due to DC voltage injection or other scenarios.
Any suitable time varying voltage waveform may be supplied to the motor of linear compressor 100 at step 802. For example, the time varying voltage may have at least two frequencies components at step 802. Thus, the time varying voltage may be
v
α(t)=v0[sin (2πf1t)+sin(2πf2t)]
where
The first and second frequencies f1, f2 may be about the resonant frequency of linear compressor 100. In particular, the first and second frequencies f1, f2 may be just greater than and just less than the resonant frequency of linear compressor 100, respectively. For example, the first frequency f1 may be within five percent greater than the resonant frequency of linear compressor 100, and the second frequency f2 may be within five percent less than the resonant frequency of linear compressor 100. In alternative example embodiments, the time varying voltage may have a single frequency at step 802.
The method 800 further includes determining that an increase in cooling capacity is required, at block 804. The determining may include receiving a discreet input indicating that a user has requested an increase in cooling capacity. The determining may also include determining that a pull-down event has occurred (such as by leaving a refrigerator door open, initiating an ice maker, or other scenarios). The determining may also include receiving indication from a temperature sensor, a temperature control interface, of other temperature control apparatuses.
The method 800 further includes directing a positive direct current (DC) voltage to the motor to induce an extension force at the motor in the positive axial direction during at least a portion of the supplying step in response to the determining step, at block 806. This extension force positively shifts the resting setpoint L0, as described below.
An example of shifting the resting setpoint L0 is illustrated generally at
In certain example embodiments, the DC voltage of step 806 may be directed continuously or constantly after the determination is made at step 804. Thus, the positive DC voltage may be a constant voltage that is applied during both the positive axial movement and negative axial movement of the piston assembly 114. Moreover, the positive DC voltage may be applied across a plurality of sinusoidal cycles (i.e., strokes) of the piston assembly 114 as it travels between bottom dead center (xBDC) and top dead center (xmc). Notably, directing a constant DC voltage may preserve the existing harmonics for the sinusoidal motion within linear compressor 100.
In additional or alternative example embodiments, the DC voltage of step 806 may be directed intermittently after the determination is made at step 804.
The intermittent DC voltage may be applied according to a set amplitude skew or phase skew.
In particular, the amplitude skew may increase the amplitude of sinusoidal motion for the linear compressor 100 in the positive axial direction A(+). The amplitude skew is applied across a plurality of sinusoidal cycles (i.e., strokes) of the piston assembly 114 as it travels between bottom dead center (xBDC) and top dead center (xTDC). Thus, the amplitude skew may increase half-cycle amplitude in the positive axial direction A(+), e.g., such that half-cycle amplitude in the positive axial direction A(+) 1102 (e.g., amplitude of movement above L0) is greater than half-cycle amplitude in the negative axial direction A(−) 1104 (e.g., amplitude of movement below L0).
As another example, the intermittent DC voltage may be applied according to a set phase skew. In particular, the phase skew may increase the wavelength of sinusoidal motion for the linear compressor 100 in the positive axial direction A(+). The phase skew is applied across a plurality of sinusoidal cycles (i.e., strokes) of the piston assembly 114 as it travels between bottom dead center (xBDC) and top dead center (xTDC). Thus, the phase skew may increase half-cycle wavelength in the positive axial direction A(+), e.g., such that half-cycle wavelength in the positive axial direction A(+) (e.g., wavelength or time of movement above L0) is greater than half-cycle wavelength in the negative axial direction A(−) (e.g., wavelength or time of movement below L0).
Thus, as described above, methods for controlling a resting setpoint and cooling capacity of an appliance have been provided. Technical effects and benefits of the above examples may include higher operational efficiency at low cooling capacity. This may result in better energy savings over the life of an appliance because high cooling capacity is generally used during only a small percentage of the operational life of an appliance. Additionally, due to a lower resting physical setpoint L0, there is lower friction at low cooling capacity (e.g., friction is reduced by about 30% because the stroke length is reduced). This may further increase the longevity of an appliance due to decreased failures related to mechanical wear at the linear compressor 100. Finally, lower recompression losses (e.g., gas at low capacity is not recompressed and therefore the overall cycle is cooler) and higher peak efficiency (e.g., cooler cylinder and suction gas vs high capacity) may also be realized.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
