Patent Description:
In response to the chlorofluorocarbon-free movement in recent years, heat pump apparatuses using natural refrigerant have been actively developed. Among such devices, heat pump apparatuses using carbon dioxide (CO<NUM>) as refrigerant are becoming more popular year by year. Because CO<NUM> has characteristics in which the ozone depletion potential thereof is <NUM> and the global warming potential thereof is <NUM>, CO<NUM> is advantageous in being able to reduce the load on the environment. Moreover, CO<NUM> is also advantageous in terms of a high level of safety due to having no toxicity and no combustibility and in being readily available and relatively inexpensive.

Furthermore, unlike fluorocarbon-based refrigerant, CO<NUM> at the high-pressure side discharged from a compressor has characteristics in which it transitions to a supercritical state. Specifically, when this CO<NUM> in the supercritical state applies heat to another fluid (e.g., water, air, or refrigerant) by exchanging heat therewith, the CO<NUM> does not condense and remains in the supercritical state. Because the loss caused by state transition is small, CO<NUM> having such characteristics is suitable for use in a heat pump apparatus that requires high temperature among various types of heat pump apparatuses. Various heat-pump-type hot water suppliers that use CO<NUM> as the refrigerant and that make full use of the advantages of CO<NUM> to boil water to a high temperature of <NUM> degrees C or higher have been proposed.

A refrigeration cycle apparatus in which refrigerant transitions to a supercritical state at the high-pressure side normally includes a main circuit in which a compressor, a gas cooler, a pressure reducing device, and an evaporator are connected by pipes, and also includes a pressure detection circuit for detecting the refrigerant pressure (high pressure) between the compressor and the gas cooler in the main circuit. The pressure detection circuit has a pressure detection pipe branching off from the main circuit at a branching section provided between the compressor and the gas cooler in the main circuit, and also has a pressure detector (e.g., a pressure sensor, a pressure switch, or other devices) disposed at the terminal end of the pressure detection pipe.

With regard to refrigerant that is not used in the supercritical state, the pressure detection pipe is normally constituted of a pipe with a diameter smaller than the pipe diameter of the main circuit. This is because, in a case where a constant speed compressor driven with a commercial power source is used as the compressor, for example, a capillary pipe is used as the pressure detection pipe for alleviating an increase in detected pressure to prevent the pressure switch from malfunctioning due to a temporary increase in high pressure in the main circuit when the refrigerant circulation amount increases rapidly, such as at the time of activation. The same applies to CO<NUM> refrigerant used in a supercritical state. Moreover, in a case where a compressor driven with an inverter is used, because a temporary increase in high pressure also occurs when the frequency of an inverter power source is increased largely toward the high side (i.e., high frequency side), for example, a capillary pipe is used as the pressure detection pipe for similar reasons. Furthermore, in a case where HFC refrigerant is used, a gas portion with high compressibility always exists due to the characteristics of the refrigerant during normal operation even if the pressure detection pipe has a small diameter section. Thus, high-pressure pulsation is not amplified.

<FIG> is a graph illustrating an example of temporal changes in refrigerant pressure at respective positions in a common refrigeration cycle apparatus in a case where refrigerant, such as CO<NUM> refrigerant, is used in a supercritical state. The abscissa of the graph indicates time (seconds) elapsed from a predetermined reference time point, and the ordinate indicates pressure (MPa). Line a denotes a pressure change at a vicinity of the pressure sensor at the high-pressure side, line b denotes a pressure change at the upstream side of the capillary pipe (i.e., the pressure detection pipe) connected to the pressure switch at the high-pressure side, line c denotes a pressure change at a service port at the high-pressure side, and line d denotes a pressure change at an outlet of a muffler provided at the downstream side of the compressor. The driving frequency of the compressor is decreased from <NUM> to <NUM> at the elapsed time point of <NUM> seconds.

As shown in <FIG>, pressure pulsation occurs at any of the positions of the refrigeration cycle apparatus, and the pulsation cycle is about <NUM>. For example, the pulsation width at the elapsed time point of <NUM> seconds is <NUM> MPa at the vicinity of the pressure sensor (line a), is <NUM> MPa at the upstream side of the capillary pipe (line b), is <NUM> MPa at the service port (line c), and is <NUM> MPa at the outlet of the muffler (line d). The pulsation width at the elapsed time point of <NUM> seconds (i.e., after retardation of the compressor) is <NUM> MPa at the vicinity of the pressure sensor (line a), is <NUM> MPa at the upstream side of the capillary pipe (line b), is <NUM> MPa at the service port (line c), and is <NUM> MPa at the outlet of the muffler (line d). In particular, the pulsation width after the retardation of the compressor increases at the vicinity of the pressure sensor, and the peak pressure at the high-pressure side is higher than that before the retardation of the compressor.

Even in the case of CO<NUM> refrigerant used in a supercritical state, if the difference between a preset value of the pressure switch and the normally-used pressure is large, protection by the pressure switch is not actuated even when high-pressure pulsation occurs. However, if the preset value of the pressure switch is to be reduced and the wall thickness of the pipe is to be reduced for the purpose of cost reduction, it is necessary to accurately detect the refrigerant pressure. Moreover, in a case where a bypass circuit having a pipe diameter smaller than the pipe diameter of the main circuit and larger than the pipe diameter of the pressure detection pipe branches off from the main circuit, the pressure detection pipe may be made to branch off from the bypass circuit so that the costs of processing, such as soldering, can be reduced, thereby achieving cost reduction. Even in this case, pressure pulsation similarly increases.

As described above, the pressure detection circuit in the related art is problematic in that pressure pulsation is amplified in the pressure detection pipe, thus making it difficult to accurately detect the refrigerant pressure by using the pressure detector disposed at the terminal end of the pressure detection pipe.

Document <CIT> discloses a refrigeration cycle apparatus according to the preamble of claim <NUM>.

The present invention has been made to solve the aforementioned problem and an object thereof is to provide a refrigeration cycle apparatus that can detect refrigerant pressure more accurately.

The invention is set out in the appended claim set. A refrigeration cycle apparatus according to the present invention includes a main circuit connecting at least a compressor, a gas cooler, a pressure reducing device, and an evaporator by a pipe and configured to circulate refrigerant transitioning to a supercritical state at a high-pressure side; a pressure detector configured to detect refrigerant pressure in a part of the main circuit between the compressor and the gas cooler; and a pulsation suppression unit configured to suppress pulsation of the refrigerant pressure to be detected by the pressure detector. The pulsation suppression unit includes a pressure detection pipe connecting a branching section, provided at a part of the main circuit between the compressor and the gas cooler, and the pressure detector. The refrigeration cycle apparatus is characterized in that it comprises, as a power source supplied to the compressor, an inverter power source that is capable of changing the driving frequency of the com-pressor within a predetermined range of a driving frequency of the compressor being from <NUM> to <NUM>, wherein a path length of the pressure detection pipe between the branching section and the pressure detector is <NUM>,<NUM> or smaller, wherein the pressure detection pipe has a narrowed pipe section decreasing a flow-path cross-sectional area thereof at an intermediate position from the branching section to the pressure detector, and wherein the pulsation suppression unit further includes a heater configured to heat a part of the pressure detection pipe between the branching section and the narrowed pipe section.

According to the present invention, refrigerant pressure can be detected more accurately.

Among the following Figures, <FIG>, <FIG> and <FIG> do not illustrate embodiments according to the invention, but are helpful to understand certain aspects thereof.

Among the following Embodiments, Embodiments <NUM> to <NUM> and <NUM> do not illustrate embodiments according to the invention, but are helpful to understand certain aspects thereof.

A refrigeration cycle apparatus according to Embodiment <NUM> of the present disclosure will be described. <FIG> is a refrigerant circuit diagram illustrating an example of the configuration of a refrigeration cycle apparatus <NUM> according to Embodiment <NUM>. In Embodiment <NUM>, a refrigeration cycle apparatus (heat pump apparatus) used in a heat-pump-type hot water supplier will be described as an example of the refrigeration cycle apparatus <NUM>. In the following figures including <FIG>, the dimensional relationships among components, the shapes thereof, and other related aspects may differ from the actual aspects.

As shown in <FIG>, the refrigeration cycle apparatus <NUM> has a main circuit <NUM> in which a compressor <NUM>, a gas cooler <NUM>, a pressure reducing device <NUM>, and an evaporator <NUM> are connected by pipes and that circulates refrigerant (e.g., CO<NUM>) that transitions to a supercritical state at the high-pressure side.

The compressor <NUM> is a fluid device that suctions low-temperature low-pressure refrigerant, compresses the suctioned refrigerant to supercritical pressure, and discharges the refrigerant as high-temperature high-pressure refrigerant in a supercritical state. According to the invention, an inverter power source that can change the driving frequency of the compressor <NUM> within a predetermined range from <NUM> to <NUM> is used as a power source supplied to the compressor <NUM>. The gas cooler <NUM> is a water-side heat exchanger that exchanges heat with an external fluid (i.e., circulation water for hot water supply in this example) to cool the refrigerant discharged from the compressor <NUM> and also to heat the external fluid. The refrigerant cooled by the gas cooler <NUM> does not condense to remain in the supercritical state and flows out of the gas cooler <NUM>. The pressure reducing device <NUM> decompresses and expands the refrigerant cooled by the gas cooler <NUM> and causes the refrigerant to flow out as low-temperature low-pressure two-phase gas-liquid refrigerant. In this example, an electronic expansion valve is used as the pressure reducing device <NUM>. The evaporator <NUM> is an air-side heat exchanger that evaporates the two-phase gas-liquid refrigerant flowing out of the pressure reducing device <NUM> by exchanging heat with the external fluid (i.e., air in this example).

The main circuit <NUM> is provided with a high-pressure low-pressure heat exchanger <NUM> that causes the high-temperature high-pressure refrigerant flowing out of the gas cooler <NUM> and the low-temperature low-pressure refrigerant flowing out of the evaporator <NUM> to exchange heat with each other. The high-pressure low-pressure heat exchanger <NUM> is provided with a high-pressure-refrigerant flow path through which the high-temperature high-pressure refrigerant flowing out of the gas cooler <NUM> flows, and a low-pressure-refrigerant flow path through which the low-temperature low-pressure refrigerant flowing out of the evaporator <NUM> flows.

In the main circuit <NUM>, a strainer <NUM> is provided at the downstream side of the high-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger <NUM> and the upstream side of the pressure reducing device <NUM>. A strainer <NUM> is provided at the downstream side of the low-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger <NUM> and the upstream side of the compressor <NUM>.

In the main circuit <NUM>, a muffler <NUM> is provided at the downstream side of the compressor <NUM> and the upstream side of the gas cooler <NUM>. The muffler <NUM> is connected to an oil recovery circuit <NUM> that recovers refrigerating machine oil and returns it to the suction side of the compressor <NUM>. The oil recovery circuit <NUM> connects the muffler <NUM> and a merging section <NUM> provided at the downstream side of the low-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger <NUM> and the upstream side of the compressor <NUM> (i.e., the upstream side of the strainer <NUM>). In the oil recovery circuit <NUM>, a heat exchanger <NUM> that heats water for hot water supply (i.e., circulation water) by causing the water to exchange heat with high-temperature refrigerating machine oil and a bypass circuit <NUM> that bypasses the heat exchanger <NUM> are provided in parallel with each other. The bypass circuit <NUM> is provided with a solenoid valve <NUM> that opens and closes the bypass circuit <NUM>. In the bypass circuit <NUM>, a strainer <NUM> is provided at the upstream side of a branching section where the heat exchanger <NUM> and the bypass circuit <NUM> branch off from each other. A branch pipe <NUM> branches off from the oil recovery circuit <NUM>. The branch pipe <NUM> is provided with a service valve 27a and a service port 27b. A pressure sensor <NUM> that further branches off from the branch pipe <NUM> and that detects the refrigerant pressure at the low-pressure side is provided via a capillary pipe <NUM>.

In the main circuit <NUM>, a branching section <NUM> provided at the downstream side of the muffler <NUM> and the upstream side of the gas cooler <NUM> and a merging section <NUM> provided at the downstream side of the gas cooler <NUM> and the upstream side of the high-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger <NUM> are connected to each other by a bypass circuit <NUM> that bypasses the gas cooler <NUM>. The bypass circuit <NUM> is provided with a solenoid valve <NUM> that opens and closes the bypass circuit <NUM>, and is also provided with a strainer <NUM> at the upstream side of the solenoid valve <NUM>.

In the main circuit <NUM>, a branching section <NUM> provided at the downstream side of the branching section <NUM> and the upstream side of the gas cooler <NUM> and a merging section <NUM> provided at the downstream side of the pressure reducing device <NUM> and the upstream side of the evaporator <NUM> are connected to each other by a bypass circuit <NUM> that bypasses the gas cooler <NUM> and the pressure reducing device <NUM>. The bypass circuit <NUM> is provided with a solenoid valve <NUM> that opens and closes the bypass circuit <NUM>, and is also provided with a strainer <NUM> at the upstream side of the solenoid valve <NUM>.

In the main circuit <NUM>, a branching section <NUM> provided at the downstream side of the high-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger <NUM> (i.e., the downstream side of the strainer <NUM>) and the upstream side of the pressure reducing device <NUM> and a merging section <NUM> provided at the downstream side of the pressure reducing device <NUM> and the upstream side of the evaporator <NUM> (i.e., the upstream side of the merging section <NUM>) are connected to each other by a bypass circuit <NUM> that bypasses the pressure reducing device <NUM>. The bypass circuit <NUM> is provided with an internal heat exchanger <NUM> that exchanges heat with refrigerant flowing in the main circuit <NUM> at the downstream side of the compressor <NUM> and upstream of the gas cooler <NUM>, and is also provided with a solenoid valve <NUM> that opens and closes the bypass circuit <NUM>.

In the main circuit <NUM>, a branching section <NUM> provided at the downstream side of the compressor <NUM> (i.e., the downstream side of the branching section <NUM>) and the upstream side of the gas cooler <NUM> (i.e., the upstream side of the branching section <NUM>) is connected to a pressure detection circuit <NUM>. The pressure detection circuit <NUM> has a pressure switch <NUM> and a pressure detection pipe <NUM> that connects the branching section <NUM> and the pressure switch <NUM>. Furthermore, the pressure detection circuit <NUM> has a pressure sensor <NUM> and a pressure detection pipe <NUM> that branches off from the pressure detection pipe <NUM> at a branching section <NUM> provided in the pressure detection pipe <NUM> and that connects the branching section <NUM> and the pressure sensor <NUM>. The pressure switch <NUM> is provided at the terminal end of the pressure detection pipe <NUM>, and the pressure sensor <NUM> is provided at the terminal end of the pressure detection pipe <NUM>.

The pressure switch <NUM> and the pressure sensor <NUM> both function as pressure detectors that detect the refrigerant pressure (i.e., discharge pressure) between the compressor <NUM> and the gas cooler <NUM> of the main circuit <NUM>. The pressure switch <NUM> cuts off the supply of power to the compressor <NUM> when the refrigerant pressure between the compressor <NUM> and the gas cooler <NUM> reaches an abnormal high pressure. The pressure sensor <NUM> detects the refrigerant pressure between the compressor <NUM> and the gas cooler <NUM> and outputs a detection signal to a controller <NUM>, which will described later.

The pressure detection pipe <NUM> extending from the branching section <NUM> of the main circuit <NUM> to the pressure switch <NUM> has the same inside diameter (e.g., ϕ6. <NUM>) and is not narrowed. Furthermore, the pressure detection pipes <NUM> and <NUM> extending from the branching section <NUM> of the main circuit <NUM> to the pressure sensor <NUM> have the same inside diameter (e.g., ϕ6. <NUM>) and are not narrowed. Specifically, the pressure detection pipes <NUM> and <NUM> have no narrowed pipe sections between the branching section <NUM> and the pressure switch <NUM> or the pressure sensor <NUM>. A narrowed pipe section is a section where the flow-path cross-sectional area of a pipe decreases at an intermediate position thereof when the pipe is traced in one direction along the pipe line (i.e., a direction extending from the branching section <NUM> toward the pressure switch <NUM> or the pressure sensor <NUM> in this example). In Embodiment <NUM>, when the pressure detection pipes <NUM> and <NUM> are traced in the direction extending from the branching section <NUM> toward the pressure switch <NUM> or the pressure sensor <NUM> along the pipe line, the pressure detection pipes <NUM> and <NUM> have no sections where the flow-path cross-sectional areas thereof decrease.

A branch pipe <NUM> branches off from a branching section <NUM> provided in the pressure detection pipe <NUM>. The branch pipe <NUM> is provided with a service valve 121a and a service port 121b.

The refrigeration cycle apparatus <NUM> has various types of temperature sensors. The various types of temperature sensors include a temperature sensor <NUM> that is provided at the downstream side of the compressor <NUM> of the main circuit <NUM> and the upstream side of the muffler <NUM> and that detects the discharge temperature of the compressor <NUM>, a temperature sensor <NUM> that is provided at the downstream side of the gas cooler <NUM> and the upstream side of the high-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger <NUM> (i.e., the upstream side of the merging section <NUM>) and that detects the outlet temperature of the gas cooler <NUM>, a temperature sensor <NUM> that is provided at the downstream side of the pressure reducing device <NUM> (i.e., the downstream side of the merging section <NUM>) and the upstream side of the evaporator <NUM> (i.e., the upstream side of the merging section <NUM>) and that detects the inlet temperature of the evaporator <NUM>, a temperature sensor <NUM> that is provided at the downstream side of the evaporator <NUM> and the upstream side of the low-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger <NUM> and that detects the outlet temperature of the evaporator <NUM>, a temperature sensor <NUM> that is provided at the downstream side of the low-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger <NUM> and the upstream side of the compressor <NUM> (i.e., the upstream side of the merging section <NUM>) and that detects the suction temperature of the compressor <NUM>, and a temperature sensor <NUM> that is provided close to the evaporator <NUM> and that detects the outside air temperature. These temperature sensors output temperature detection signals to the controller <NUM>, which will be described below.

The refrigeration cycle apparatus <NUM> has the controller <NUM>. The controller <NUM> in this example is a microcomputer equipped with, for example, a CPU, a ROM, a RAM, and an I/O port. The controller <NUM> controls the compressor <NUM>, the pressure reducing device <NUM>, and other devices based on detection signals input from the above-described temperature sensors <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, the pressure sensors <NUM> and <NUM>, and other sensors.

The heat-pump-type hot water supplier has a boiler circuit <NUM> that uses the refrigeration cycle apparatus <NUM> to boil water in a hot-water tank (not shown). The boiler circuit <NUM> connects a lower section and an upper section of the hot-water tank. The boiler circuit <NUM> receives low-temperature water from the lower section of the hot-water tank, boils the water by causing it to exchange heat with the refrigerating machine oil at the heat exchanger <NUM> and to exchange heat with the refrigerant at the gas cooler <NUM>, and returns the water as high-temperature water to the upper section of the hot-water tank. In the boiler circuit <NUM>, a circulation pump <NUM> that sends the water in the lower section of the hot-water tank as circulation water to the upper section of the hot-water tank is provided at the upstream side of the heat exchanger <NUM> and the gas cooler <NUM>. In the boiler circuit <NUM>, an electric valve <NUM> that adjusts the flow of the circulation water is provided at the upstream side of the circulation pump <NUM>, a check valve <NUM> is disposed at the downstream side of the electric valve <NUM>, and a pressure reducing valve <NUM> is disposed at the downstream side of the check valve <NUM>. A strainer <NUM> is provided at the downstream side of the electric valve <NUM> and the upstream side of the check valve <NUM>.

In the boiler circuit <NUM>, a merging section <NUM> provided at the downstream side of the pressure reducing valve <NUM> and the upstream side of the circulation pump <NUM> is connected to a water supply circuit <NUM> that supplies tap water to the boiler circuit <NUM>. The water supply circuit <NUM> is provided with an electric valve <NUM> that adjusts the flow of tap water, a check valve <NUM> disposed at the downstream side of the electric valve <NUM>, and a pressure reducing valve <NUM> disposed at the downstream side of the check valve <NUM>. A strainer <NUM> is provided at the downstream side of the electric valve <NUM> and the upstream side of the check valve <NUM>.

In the boiler circuit <NUM>, an electric valve <NUM> that adjusts the flow of the circulation water is provided at the downstream side of the circulation pump <NUM> and the upstream side of the heat exchanger <NUM>. A branch pipe provided with a relief valve <NUM> is connected at the downstream side of the circulation pump <NUM> and the upstream side of the electric valve <NUM>. A flow rate sensor <NUM> that detects the flow rate of the circulation water is provided at the downstream side of the electric valve <NUM> and the upstream side of the heat exchanger <NUM>.

In the boiler circuit <NUM>, a temperature sensor <NUM> that detects the temperature of the pre-boiled circulation water is provided at the downstream side of the circulation pump <NUM> and the upstream side of the heat exchanger <NUM> (i.e., the upstream side of the electric valve <NUM>). Furthermore, in the boiler circuit <NUM>, a temperature sensor <NUM> that detects the temperature of the boiled circulation water is provided at the downstream side of the gas cooler <NUM>.

The above-described temperature sensors <NUM> and <NUM>, the flow rate sensor <NUM>, and other sensors output detection signals to a controller (not shown) of the heat-pump-type hot water supplier or to the controller <NUM> of the refrigeration cycle apparatus <NUM>.

<FIG> illustrates the configuration of the pressure detection circuit <NUM> according to Embodiment <NUM>. In <FIG>, the pressure detection circuit <NUM> shown is simplified in configuration relative to the pressure detection circuit <NUM> shown in <FIG> and is provided with only the pressure sensor <NUM> as a pressure detector. The pressure detection circuit <NUM> shown in <FIG> has the pressure sensor <NUM> that detects the refrigerant pressure at the high-pressure side, and also has the pressure detection pipe <NUM> that connects the branching section <NUM>, which is provided at the downstream side of the compressor <NUM> and the upstream side of the gas cooler <NUM> in the main circuit <NUM>, and the pressure sensor <NUM>. The pressure detection pipe <NUM> branches off at the branching section <NUM> in a direction perpendicular to the main circuit <NUM>. Moreover, the pressure detection pipe <NUM> has a straight-pipe branch-less configuration. The pressure sensor <NUM> is provided at the terminal end of the pressure detection pipe <NUM>. The pressure detection pipe <NUM> extending from the branching section <NUM> to the pressure sensor <NUM> has the same inside diameter and is not narrowed.

<FIG> illustrates the configuration of a pressure detection circuit <NUM> in which the pressure detection pipe <NUM> has a narrowed pipe section <NUM>. Similar to the pressure detection circuit <NUM> shown in <FIG>, the pressure detection circuit <NUM> shown in <FIG> has the pressure sensor <NUM> that detects the refrigerant pressure at the high pressure side and the pressure detection pipe <NUM> that connects the branching section <NUM> and the pressure sensor <NUM>. However, the pressure detection pipe <NUM> in the pressure detection circuit <NUM> differs from the pressure detection pipe <NUM> shown in <FIG> in that a part of the pipe line extending from the branching section <NUM> to the pressure sensor <NUM> has the narrowed pipe section <NUM>. Specifically, the pipe diameter (i.e., the flow-path cross-sectional area) of the pressure detection pipe <NUM> at the terminal end where the pressure sensor <NUM> is provided is smaller than the pipe diameter (i.e., the flow-path cross-sectional area) of the pressure detection pipe <NUM> close to the branching section <NUM>.

The refrigerant used in the refrigeration cycle apparatus <NUM> according to Embodiment <NUM> transitions to a supercritical state at the high-pressure side. Refrigerant in a supercritical state has extremely low compressibility. Consequently, if the narrowed pipe section <NUM> exists in the pressure detection pipe <NUM>, pressure pulsation at the terminal side relative to the narrowed pipe section <NUM> becomes amplified inversely proportional to the rate of change α (<NUM> < α < <NUM>) in the cross-sectional area of the pipe (i.e., flow path) before and after the narrowed pipe section <NUM>. Thus, in the pressure detection circuit <NUM> shown in <FIG>, it may be difficult to accurately detect the refrigerant pressure by using the pressure sensor <NUM> provided at the terminal end of the pressure detection pipe <NUM>.

In contrast, in the pressure detection circuit <NUM> according to Embodiment <NUM> shown in <FIG>, the pressure detection pipe <NUM> is not provided with a narrowed pipe section. Consequently, in the pressure detection pipe <NUM> of the pressure detection circuit <NUM>, the cross-sectional area of the flow path through which the refrigerant flows is fixed and does not change from the branching section <NUM> to the pressure sensor <NUM>. Thus, pressure pulsation can be suppressed at the terminal end of the pressure detection pipe <NUM>. Consequently, in Embodiment <NUM>, the refrigerant pressure (i.e., discharge pressure) can be detected more accurately with the pressure sensor <NUM>.

As described above, the refrigeration cycle apparatus <NUM> according to Embodiment <NUM> has the main circuit <NUM> in which at least the compressor <NUM>, the gas cooler <NUM>, the pressure reducing device <NUM>, and the evaporator <NUM> are connected by pipes and that circulates refrigerant that transitions to a supercritical state at the high-pressure side, the pressure detectors (e.g., the pressure sensor <NUM> and the pressure switch <NUM>) that detect the refrigerant pressure between the compressor <NUM> and the gas cooler <NUM> in the main circuit <NUM>, and a pulsation suppression unit (e.g., the pressure detection pipe <NUM> not provided with a narrowed pipe section) that suppresses pulsation of the refrigerant pressure to be detected by the pressure detectors.

According to this configuration, since pulsation of the refrigerant pressure to be detected by the pressure detectors can be suppressed, the refrigerant pressure between the compressor <NUM> and the gas cooler <NUM> in the main circuit <NUM> can be detected more accurately.

Furthermore, in the refrigeration cycle apparatus <NUM> according to Embodiment <NUM>, the aforementioned pulsation suppression unit connects the branching section <NUM> and the pressure detectors (e.g., the pressure sensor <NUM> and the pressure switch <NUM>) provided between the compressor <NUM> and the gas cooler <NUM> in the main circuit <NUM>. Moreover, the refrigeration cycle apparatus <NUM> according to Embodiment <NUM> includes the pressure detection pipe <NUM> that does not have a narrowed pipe section whose flow-path cross-sectional area decreases at an intermediate position between the branching section <NUM> and the pressure sensors.

According to this configuration, the cross-sectional area of the flow path from the branching section <NUM> to the pressure sensors, through which the refrigerant flows, can be prevented from decreasing. Consequently, pulsation of the refrigerant pressure to be detected by the pressure sensors can be suppressed.

A refrigeration cycle apparatus according to Embodiment <NUM> of the present disclosure will be described. <FIG> illustrates the configuration of the pressure detection circuit <NUM> in the refrigeration cycle apparatus according to Embodiment <NUM>. Components having the same functions and effects as those in the refrigeration cycle apparatus <NUM> and the pressure detection circuit <NUM> according to Embodiment <NUM> will be given the same reference signs, and descriptions thereof will be omitted.

As shown in <FIG>, in the pressure detection pipe <NUM> of the pressure detection circuit <NUM> according to Embodiment <NUM>, a part of the pipe line extending from the branching section <NUM> to the pressure sensor <NUM> has the narrowed pipe section <NUM>. A path length A of the pressure detection pipe <NUM> between the branching section <NUM> and the narrowed pipe section <NUM> is <NUM> or smaller. The reason for setting the path length A to <NUM> or smaller will be described below.

<FIG> is a graph illustrating the correlation between the temperature and the density of CO<NUM> refrigerant in high-pressure states (<NUM> MPa and <NUM> MPa). The abscissa of the graph indicates the temperature (degrees C) of the CO<NUM> refrigerant, and the ordinate indicates the density (kg/m<NUM>) of the CO<NUM> refrigerant. As shown in <FIG>, CO<NUM> refrigerant in a high-pressure state has characteristics in which the density increases with decreasing temperature. The temperature range of the CO<NUM> refrigerant in a pipe (i.e., a main pipe) of the main circuit <NUM> is about <NUM> degrees C to <NUM> degrees C. The pressure detection pipe <NUM> has a pipe diameter smaller than that of the pipe of the main circuit <NUM> and has large heat loss per unit flow-path length. Consequently, the temperature of the refrigerant in the pressure detection pipe <NUM> decreases with increasing distance from the branching section <NUM>. For example, assuming that the refrigerant temperature in the main pipe is <NUM> degrees C, the refrigerant temperature in the pressure detection pipe <NUM> is lower than <NUM> degrees C and decreases monotonously as the distance from the main pipe (i.e., the distance from the branching section <NUM>) increases (see <FIG>). Consequently, when the path length A between the branching section <NUM> and the narrowed pipe section <NUM> exceeds a predetermined value (e.g., <NUM>), the refrigerant between the branching section <NUM> and the narrowed pipe section <NUM> decreases in temperature and increases in density. Thus, pressure pulsation occurs between the branching section <NUM> and the narrowed pipe section <NUM>, causing pressure pulsation at the terminal side relative to the narrowed pipe section <NUM> to be amplified.

In Embodiment <NUM>, the path length A of the pressure detection pipe <NUM> between the branching section <NUM> and the narrowed pipe section <NUM> is set to <NUM> or smaller, so that the density of the refrigerant between the branching section <NUM> and the narrowed pipe section <NUM> can be lower than or equal to a value at which pressure pulsation occurs. Consequently, since amplification of pressure pulsation at the terminal side relative to the narrowed pipe section <NUM> can be suppressed, pulsation of the refrigerant pressure to be detected by the pressure sensor <NUM> can be suppressed.

As described above, in the refrigeration cycle apparatus according to Embodiment <NUM>, the aforementioned pulsation suppression unit includes the pressure detection pipe <NUM> that connects the branching section <NUM>, which is provided between the compressor <NUM> and the gas cooler <NUM> in the main circuit <NUM>, and the pressure detectors (e.g., the pressure sensor <NUM> and the pressure switch <NUM>) and that has the narrowed pipe section <NUM> whose flow-path cross-sectional area decreases at an intermediate position between the branching section <NUM> and the pressure sensors. Moreover, the path length A of the pressure detection pipe <NUM> between the branching section <NUM> and the narrowed pipe section <NUM> is <NUM> or smaller.

According to this configuration, since pulsation of the refrigerant pressure to be detected by the pressure detectors can be suppressed, the refrigerant pressure can be detected more accurately.

As shown in <FIG>, in the pressure detection pipe <NUM> of the pressure detection circuit <NUM> according to Embodiment <NUM>, a part of the pipe line extending from the branching section <NUM> to the pressure sensor <NUM> has the narrowed pipe section <NUM>. The path length A of the pressure detection pipe <NUM> between the branching section <NUM> and the narrowed pipe section <NUM> is, for example, larger than <NUM>. Furthermore, the pressure detection circuit <NUM> is provided with a heater <NUM> that heats a part of the pressure detection pipe <NUM> between the branching section <NUM> and the narrowed pipe section <NUM>. The heater <NUM> heats the part of the pressure detection pipe <NUM> between the branching section <NUM> and the narrowed pipe section <NUM> to a temperature higher than or equal to that of the main circuit <NUM> at the vicinity of the branching section <NUM>.

As mentioned above, when the path length A between the branching section <NUM> and the narrowed pipe section <NUM> exceeds <NUM>, the refrigerant between the branching section <NUM> and the narrowed pipe section <NUM> decreases in temperature and increases in density. Thus, pressure pulsation occurs between the branching section <NUM> and the narrowed pipe section <NUM>, causing pressure pulsation at the terminal side relative to the narrowed pipe section <NUM> to be amplified. In Embodiment <NUM>, the part of the pressure detection pipe <NUM> between the branching section <NUM> and the narrowed pipe section <NUM> is heated by the heater <NUM>. Thus, the refrigerant temperature between the branching section <NUM> and the narrowed pipe section <NUM> can be prevented from decreasing, and the density of the refrigerant between the branching section <NUM> and the narrowed pipe section <NUM> can be lower than or equal to the value at which pressure pulsation occurs, so that amplification of pressure pulsation at the terminal side relative to the narrowed pipe section <NUM> can be suppressed. Consequently, pulsation of the refrigerant pressure to be detected by the pressure sensor <NUM> can be suppressed. Although the pressure detection pipe <NUM> in this example is described as having a path length A larger than <NUM>, the heater <NUM> may be provided at a pressure detection pipe <NUM> with a path length A smaller than or equal to <NUM>.

As described above, in the refrigeration cycle apparatus according to Embodiment <NUM>, the aforementioned pulsation suppression unit includes the pressure detection pipe <NUM> that connects the branching section <NUM>, which is provided between the compressor <NUM> and the gas cooler <NUM> in the main circuit <NUM>, and the pressure detectors (e.g., the pressure sensor <NUM> and the pressure switch <NUM>) and that has the narrowed pipe section <NUM> whose flow-path cross-sectional area decreases at an intermediate position between the branching section <NUM> and the pressure sensors, and the heater <NUM> that heats the part of the pressure detection pipe <NUM> between the branching section <NUM> and the narrowed pipe section <NUM>.

A refrigeration cycle apparatus according to Embodiment <NUM> of the present invention will be described. <FIG> illustrates the configuration of the pressure detection circuit <NUM> in the refrigeration cycle apparatus according to a version of Embodiment <NUM> which is not according to the present invention. Components having the same functions and effects as those in the refrigeration cycle apparatus <NUM> and the pressure detection circuit <NUM> according to Embodiment <NUM> will be given the same reference signs, and descriptions thereof will be omitted.

As shown in <FIG>, the pressure detection pipe <NUM> of the pressure detection circuit <NUM> according to Embodiment <NUM> has no narrowed pipe section between the branching section <NUM> and the pressure sensor <NUM>. Embodiment <NUM> is also applicable to a pressure detection pipe <NUM> having a narrowed pipe section and said version of Embodiment <NUM> is according to the present invention. A path length B of the pressure detection pipe <NUM> between the branching section <NUM> and the pressure sensor <NUM> (i.e., the overall length of the pressure detection pipe <NUM>) is <NUM>,<NUM> or smaller. The reason for setting the path length B to <NUM>,<NUM> or smaller will be described below.

Assuming that the pressure wavelength in the pressure detection pipe <NUM> is defined as λ, when the path length B between the branching section <NUM> and the pressure sensor <NUM> is equal to ((2n - <NUM>)/<NUM>)λ (n = <NUM>, <NUM>, <NUM>,. ), such as <NUM>/4λ and <NUM>/4λ, amplification of pressure pulsation at a vicinity of the pressure sensor <NUM> becomes maximum. Consequently, amplification of pressure pulsation at the vicinity of the pressure sensor <NUM> can be suppressed by preventing the path length B from being equal to ((2n - <NUM>)/<NUM>)λ. A pressure wavelength λ is obtained from the driving frequency of the compressor <NUM> and the speed of sound in the refrigerant.

<FIG> is a graph illustrating the relationship between the driving frequency of the compressor <NUM> and the pressure wavelength. The abscissa of the graph indicates the frequency (Hz) of the compressor <NUM>, and the ordinate indicates the length (mm) of the pressure wavelength. As shown in <FIG>, assuming that the range of the driving frequency (i.e., operating range) of the compressor <NUM> is about <NUM> to <NUM>, ((2n - <NUM>)/<NUM>)λ (only <NUM>/4λ and <NUM>/4λ are shown in <FIG>) may be all values larger than about <NUM>,<NUM> at frequencies in the operating range of the compressor <NUM>. In other words, in a case where the path length B is larger than about <NUM>,<NUM>, the path length B is always equal to ((2n - <NUM>)/<NUM>)λ with respect to at least some of the frequencies in the operating range of the compressor <NUM>. In contrast, if the path length B is smaller than or equal to <NUM>,<NUM>, the path length B will not be equal to ((2n - <NUM>)/<NUM>)λ at frequencies in the operating range of the compressor <NUM>. Consequently, by setting the path length B smaller than or equal to <NUM>,<NUM>, amplification of pressure pulsation at the vicinity of the pressure sensor <NUM> can be prevented from being the maximum, thereby suppressing pulsation of the refrigerant pressure to be detected by the pressure sensor <NUM>. Although the pressure detection pipe <NUM> in this example is described as not having a narrowed pipe section, Embodiment <NUM> is also applicable to a pressure detection pipe <NUM> having a narrowed pipe section and said version of Embodiment <NUM> is according to the present invention.

As described above, in the refrigeration cycle apparatus according to Embodiment <NUM>, the aforementioned pulsation suppression unit includes the pressure detection pipe <NUM> that connects the branching section <NUM>, which is provided between the compressor <NUM> and the gas cooler <NUM> in the main circuit <NUM>, and the pressure detectors (e.g., the pressure sensor <NUM> and the pressure switch <NUM>). Moreover, the path length B of the pressure detection pipe <NUM> between the branching section <NUM> and the pressure detectors is <NUM>,<NUM> or smaller.

A refrigeration cycle apparatus according to Embodiment <NUM> of the present disclosure will be described. As mentioned above, the pulsation cycle of the refrigerant pressure in the refrigeration cycle apparatus is about <NUM>. Thus, with the sampling cycle of <NUM> commonly used in the pressure detection algorithm in the related art, pressure pulsation (e.g., a peak pressure value) cannot be detected, thus making it not possible to control the compressor <NUM> based on an accurate refrigerant pressure. In Embodiment <NUM>, it is assumed that the waveform of pressure pulsation is a sine wave, and the pressure detection algorithm in the controller <NUM> is defined as follows to allow for more accurate detection of the refrigerant pressure.

<FIG> illustrates a pressure detection algorithm of the refrigeration cycle apparatus according to Embodiment <NUM>. The abscissa in <FIG> indicates time (ms) elapsed after the power is turned on. In Embodiment <NUM>, a sampling cycle for acquiring a detection value of the refrigerant pressure detected by the pressure sensor <NUM> (i.e., an output signal of the pressure sensor <NUM>) is set to <NUM>/<NUM> or smaller of one cycle of the frequency (i.e., minimum driving frequency) of the compressor <NUM>. For example, in a case of a compressor whose driving frequency is controlled in a range of about <NUM> to <NUM>, the sampling cycle is set to <NUM> or smaller, which is <NUM>/<NUM> or smaller of one cycle (<NUM>) of the minimum driving frequency (<NUM>). In this example, the sampling cycle is set to <NUM>. Specifically, a detection value Hpt of the refrigerant pressure is acquired in a <NUM>-ms cycle.

Subsequently, an average value Hpa and a half amplitude value Hpb are determined for every predetermined period, which is N times of the sampling cycle (N is an integer larger than or equal to <NUM>) (i.e., every <NUM>, which is <NUM> times of the sampling cycle), with reference to a time when the power is turned on. The average value Hpa is an average value of N units (<NUM> in this example) of detection values Hpt acquired within the aforementioned predetermined period. The half amplitude value Hpb is an average of absolute values of deviation from the average value Hpa of the N units of detection values Hpt. For example, assuming that a detection value acquired after T (ms) (T = <NUM>, <NUM>, <NUM>,. , <NUM>) elapsed after the power is turned on is defined as HptT, the half amplitude value Hpb is expressed by (|Hpa - Hpt5| + |Hpa - Hpt10| + |Hpa - Hpt15| +. + |Hpa - Hpt100|)/<NUM>.

Subsequently, an effective amplitude value Hpc, a peak amplitude value Hpd, and a peak pressure value Hpmpeak are calculated for every predetermined period mentioned above. The effective amplitude value Hpc is an average (moving average) of M units of half amplitude values Hpb (M is an integer larger than or equal to <NUM>) calculated for M times of previous predetermined periods (five previous predetermined periods in this example). The peak amplitude value Hpd is √<NUM> times of the effective amplitude value Hpc. The peak pressure value Hpmpeak is the sum of the peak amplitude value Hpd and the average value Hpa. The peak pressure value Hpmpeak may alternatively be the sum of the peak amplitude value Hpd and an average (moving average) of M units of average values Hpa calculated for M times of previous predetermined periods. If <NUM> have not elapsed after the power is turned on (i.e., if the time elapsed after the power is turned on is <NUM>, <NUM>, <NUM>, or <NUM>), the effective amplitude value Hpc is set as an average value of one to four determined half amplitude values Hpb. Specifically, the effective amplitude value Hpc, the peak amplitude value Hpd, and the peak pressure value Hpmpeak are all calculated for every predetermined period (i.e., <NUM>) elapsed after the power is turned on. Because the effective amplitude value Hpc, the peak amplitude value Hpd, and the peak pressure value Hpmpeak in a case where <NUM> have not elapsed after the power is turned on are calculated based on a method different from that used when <NUM> have elapsed after the power is turned on, these values are denoted by Hpc (*), Hpd (*), and Hpmpeak (*) in <FIG>.

Based on the peak pressure value Hpmpeak calculated for every predetermined period, the controller <NUM> performs control, such as increasing and decreasing the driving frequency of the compressor <NUM> and stopping the compressor <NUM> if abnormal pressure is detected. The pressure detection algorithm described above may also be applied to the configuration of the refrigeration cycle apparatus according to any of Embodiment <NUM> to Embodiment <NUM> described above and may also be applied to the configuration of a refrigeration cycle apparatus in the related art.

As described above, the refrigeration cycle apparatus according to Embodiment <NUM> has the main circuit <NUM> in which at least the compressor <NUM>, the gas cooler <NUM>, the pressure reducing device <NUM>, and the evaporator <NUM> are connected by pipes and that circulates refrigerant that transitions to a supercritical state at the high-pressure side, the pressure sensor <NUM> that detects the refrigerant pressure between the compressor <NUM> and the gas cooler <NUM> in the main circuit <NUM>, and the controller <NUM> that controls the compressor <NUM> based on the refrigerant pressure. The controller <NUM> sets a sampling cycle for acquiring a detection value Hpt of the refrigerant pressure detected by the pressure sensor <NUM> to <NUM>/<NUM> or smaller of one cycle of the minimum frequency of the compressor <NUM>, calculates an average value Hpa of N units of detection values Hpt and a half amplitude value Hpb, which is an average of absolute values of deviation from the average value Hpa of the N units of detection values Hpt, for every predetermined period, which is N times of the sampling cycle (N is an integer larger than or equal to <NUM>), calculates a peak pressure value Hpmpeak, which is the sum of a peak amplitude value Hpd, which is √<NUM> times of the moving average (i.e., an effective amplitude value Hpc) of M units of half amplitude values Hpb (M is an integer larger than or equal to <NUM>) calculated for M times of previous predetermined periods, and the average value Hpa, and controls the compressor <NUM> based on the peak pressure value Hpmpeak.

According to this configuration, the refrigerant pressure can be detected more accurately, and the compressor <NUM> can be controlled based on the more accurate refrigerant pressure.

The advantageous effects of Embodiment <NUM> will be described with reference to <FIG> is a graph illustrating an example of a pressure value (i.e., a peak pressure value Hpmpeak) calculated in Embodiment <NUM>. In the graph, each solid diamond symbol denotes a pre-input pressure value, each void triangle symbol denotes an average value Hpa, and each void square symbol denotes a peak pressure value Hpmpeak. <FIG> is a graph illustrating an example of detected pressure values in the related art. In the graph, each solid diamond symbol denotes a pre-input pressure value and each solid square symbol denotes a detected pressure value in the related art. In both <FIG>, the waveform of pressure pulsation is a sine wave, the pulsation frequency is <NUM>, the pulsation amplitude is <NUM> MPa, and the increasing rate of average pressure is <NUM> MPa/s. As shown in <FIG>, pressure pulsation cannot be detected with the detected pressure values in the related art. In contrast, as shown in <FIG>, the peak pressure value Hpmpeak calculated in accordance with Embodiment <NUM> is substantially equal to a high-pressure-side peak value of pressure pulsation. Consequently, a high-pressure-side peak of pressure pulsation can be detected in accordance with Embodiment <NUM>.

The present invention is not limited to Embodiment <NUM> described above and may be variously modified.

For example, although the pressure detection pipes <NUM> and <NUM> having the same inside diameter (i.e., the same flow-path cross-sectional area) from the branching section <NUM> to the pressure switch <NUM> or the pressure sensor <NUM> are used as examples of pressure detection pipes not having narrowed pipe sections in Embodiment <NUM>, the present disclosure is not limited to this configuration. The pressure detection pipes <NUM> and <NUM> may be expanded between the branching section <NUM> and the pressure switch <NUM> or the pressure sensor <NUM>.

Furthermore, the pressure detection pipes <NUM> and <NUM> may each have an expanded pipe section whose flow-path cross-sectional area increases at an intermediate position within a range so that the flow-path cross-sectional area immediately before the pressure switch <NUM> or the pressure sensor <NUM> is not smaller than the flow-path cross-sectional area immediately after the branching section <NUM>. Alternatively, the pressure detection pipes <NUM> and <NUM> may each have an expanded pipe section and a narrowed pipe section within a range so that the flow-path cross-sectional area immediately before the pressure switch <NUM> or the pressure sensor <NUM> is not smaller than the flow-path cross-sectional area immediately after the branching section <NUM>.

Furthermore, Embodiment <NUM> to Embodiment <NUM> described above and the modifications thereof may be combined with one another.

Claim 1:
A refrigeration cycle apparatus comprising:
a main circuit (<NUM>) connecting at least a compressor (<NUM>), a gas cooler (<NUM>), a pressure reducing device (<NUM>), and an evaporator (<NUM>) by a pipe and configured to circulate refrigerant transitioning to a supercritical state at a high-pressure side;
a pressure detector (<NUM>, <NUM>) configured to detect refrigerant pressure in a part of the main circuit between the compressor and the gas cooler; and
a pulsation suppression unit configured to suppress pulsation of the refrigerant pressure to be detected by the pressure detector,
the pulsation suppression unit including a pressure detection pipe (<NUM>) connecting a branching section (<NUM>), provided at a part of the main circuit between the compressor and the gas cooler, and the pressure detector,
characterized in that
the refrigeration cycle apparatus comprises, as a power source supplied to the compressor (<NUM>), an inverter power source that is capable of changing the driving frequency of the compressor (<NUM>) within a predetermined range from <NUM> to <NUM>,
wherein the pressure detection pipe has a narrowed pipe section (<NUM>) decreasing a flow-path cross-sectional area thereof at an intermediate position from the branching section to the pressure detector, and
wherein the pulsation suppression unit further includes a heater (<NUM>) configured to heat a part of the pressure detection pipe between the branching section and the narrowed pipe section.