A constant pressure extraction system for a coffee machine and a method of controlling the same

Abstract

This invention discloses a constant-pressure extraction system for a coffee machine and its control method, comprising a water pump, a water inlet check valve, a coffee solenoid valve, a steam solenoid valve, a steam heater, a brewing system, and a pressure relief valve. The water pump is connected to the inlet terminals of both the coffee and steam solenoid valves via the water inlet check valve. Both solenoid valves are two-position three-way valves, with the first and third ports normally open when de-energized. The second port of the coffee solenoid valve is connected to the brewing system, and the second port of the steam solenoid valve is connected to the steam heater. A check valve is installed at the outlet of the steam heater, and the brewing system is equipped with a pressure relief valve. During coffee extraction, the coffee solenoid valve is energized to open the extraction water path, while the steam solenoid valve is de-energized. Utilizing its normally open characteristic and the synergistic effect of the check valve, when the extraction pressure exceeds 10 bar, pressure is automatically released from the third port of the steam solenoid valve, achieving constant extraction pressure. This invention maintains constant extraction pressure without adjusting the water pump speed, offering advantages such as high constant pressure accuracy, fast response speed, and long water pump life.

Description

Technical Field

[0001] This invention relates to the field of coffee brewing equipment, and in particular to a constant pressure extraction system for a coffee machine and its control method. Background Technology

[0002] Semi-automatic coffee machines are traditional Italian coffee machines. These machines rely on manual operation for grinding, tamping, filling, brewing, and cleaning. They range from small single-faucet home machines to large commercial machines with double or triple faucets. Newer models also feature electronic water control, allowing for precise and automatic control of the water volume used in brewing.

[0003] In the coffee extraction process, the stability of water pressure is one of the core factors determining the quality of the extracted coffee. The optimal extraction pressure for espresso is typically around 9 bar. Pressure that is too high or too low will affect the extraction of flavor. Too low a pressure, such as <7 bar, will result in under-extraction and a sour, bitter coffee; too high a pressure, such as >11 bar, will result in over-extraction and a bitter coffee. Therefore, maintaining a constant extraction pressure during the coffee machine's extraction process has been a long-standing technical challenge in this field.

[0004] In the prior art, the invention patent with authorization announcement number CN204520319U discloses a coffee machine whose water pressure is achieved by adjusting the water pump, which requires frequent operation of the water pump, making it inconvenient.

[0005] Chinese invention patent CN115067753B discloses an electronic pressure-changing structure for a coffee machine capable of varying pressures between four different levels. Its main pressure-changing structure includes a solenoid valve, a protective valve, and a check valve. The pressure changing method relies on a circuit board controlling the on / off state of different solenoid valves in a guided sequence to select different pressure water paths. While this solution achieves multiple pressure selections, its core lies in "pressure changing" rather than "constant pressure." Its multiple water paths correspond to different pressure levels, and pressure switching depends on the set values ​​of different protective valves, rather than precise and constant control of a single extraction pressure.

[0006] Furthermore, Chinese invention patent CN107836998B discloses a water system for a coffee beverage device, which employs multiple simultaneous operations, with each branch water line having an independent safety valve. However, this solution primarily addresses the efficiency and cleaning issues of simultaneous multi-channel operation, without providing a specific solution for maintaining constant pressure during the extraction process.

[0007] Furthermore, US patent application US2015027317A1 (Pressure Relief System for EspressoMaker) discloses a pressure relief system for an espresso machine that uses a solenoid valve to guide excess pressurized water back and discharge it through a drain pipe. This pressure relief mechanism primarily addresses overpressure protection rather than actively maintaining a constant extraction pressure.

[0008] The aforementioned prior art has the following technical problems: First, most existing coffee machines control water pressure by adjusting the pump speed (e.g., CN204520319U). However, the direct pressure output of the pump is not stable. During frequency conversion speed regulation, the output pressure of a vibratory pump exhibits a non-linear relationship with its rotational speed. When the speed is adjusted from 2000 rpm to 3000 rpm, the actual output pressure fluctuation can reach ±1.5 bar, with a response lag of approximately 0.5-1 second. Only very high-quality pumps can maintain stable pressure output during high-speed pressure output, making the pumps prone to damage.

[0009] Secondly, the method of adjusting pressure by controlling the pump speed through a program results in a stepped increase or decrease in pressure, making it difficult to achieve instantaneous and stable pressure switching.

[0010] Third, although existing variable pressure structures provide multiple pressure options (such as CN115067753B), they cannot effectively guarantee a constant extraction pressure during the extraction process. When the pressure in the water circuit fluctuates due to various reasons (such as water pump fluctuations, changes in pipeline resistance, etc.), there is a lack of an active constant pressure maintenance mechanism.

[0011] Fourth, the pressure relief protection and constant pressure extraction of existing coffee machines are often two separate functional modules (such as US2015027317A1), resulting in low system integration, complex structure, and high cost.

[0012] Fifth, while existing pressure-changing structures (such as CN115067753B) can achieve multiple pressure switching, the pressure switching between its multiple water circuits exhibits abrupt, step-like changes, failing to achieve a smooth pressure transition and affecting the stability of extraction quality. Furthermore, each water circuit in this type of solution requires an independent protection valve and check valve, resulting in high system complexity, high manufacturing costs, and the difficulty in arranging a multi-water-circuit parallel structure within the limited internal space of a coffee machine.

[0013] Sixth, existing variable pressure coffee machine systems generally lack the ability to monitor and adaptively adjust extraction pressure in real time. When the extraction pressure deviates from the target value due to factors such as differences in coffee grind size, coffee quantity deviation, or changes in ambient temperature, the existing system cannot automatically identify and adjust it. It can only rely on manual experience to judge or stop the machine for adjustment, which seriously affects the automation and consistency of extraction.

[0014] In summary, the existing technology lacks a coffee machine constant pressure extraction system that can achieve precise and constant extraction pressure through a simple and reliable mechanical structure without adjusting the water pump speed or switching complex multiple water paths, and has the ability to adaptively adjust the pressure.

[0015] Therefore, there is an urgent need to develop a new type of coffee machine constant pressure extraction system that is simple in structure, has high constant pressure accuracy, responds quickly, and has adaptive adjustment capabilities. Summary of the Invention

[0016] The technical problem to be solved by the present invention is to provide a constant pressure extraction system for a coffee machine and its control method. By utilizing the constant-open characteristic of the steam solenoid valve in the power-off state and the coordinated cooperation of the one-way valve at the outlet of the steam heating pot, combined with the pressure feedback adaptive adjustment and gradient pressure relief mechanism, the extraction pressure can be precisely and constantly controlled without adjusting the water pump speed. This solves the technical problems in the prior art such as unstable water pump pressure regulation, inability of the variable pressure structure to maintain constant pressure, low system integration, and lack of adaptive adjustment capability.

[0017] To address the aforementioned technical problems, this invention provides a constant pressure extraction system for a coffee machine, comprising a water pump, a water inlet check valve, a coffee solenoid valve, a steam solenoid valve, a steam heating pot, a brewing system, and a pressure reserve valve.

[0018] The outlet of the water pump is connected to the inlet of the inlet check valve, and the outlet of the inlet check valve is connected to the inlet of the coffee solenoid valve and the inlet of the steam solenoid valve, respectively.

[0019] The coffee solenoid valve is a two-position three-way solenoid valve. When it is not energized, its first port and third port are normally connected. When it is energized, its second port and first port are connected.

[0020] The steam solenoid valve is a two-position three-way solenoid valve. When it is not energized, its first port and third port are normally connected. When it is energized, its second port and first port are connected.

[0021] The second port of the coffee solenoid valve is connected to the water inlet of the brewing system, the second port of the steam solenoid valve is connected to the water inlet of the steam heater, the water outlet of the steam heater is equipped with a one-way valve, and the brewing system is equipped with a pressure relief valve.

[0022] A flow-limiting element is provided at the third port of the steam solenoid valve, and the equivalent flow area of ​​the flow-limiting element is smaller than the equivalent flow area of ​​the internal flow channel of the steam solenoid valve.

[0023] The system also includes a pressure sensor installed on the pipeline between the coffee solenoid valve and the brewing system, used to detect the extraction pressure in real time and feed it back to the controller.

[0024] Preferably, the opening pressure of the one-way valve at the outlet of the steam heating pot is 1.5 bar.

[0025] Preferably, the pressure of the pressure relief valve of the brewing system is 5-7 bar.

[0026] Preferably, the predetermined pressure for extracting coffee is 10 bar.

[0027] Preferably, the water pump is a vibratory pump with a constant operating speed of 2800±50 rpm.

[0028] Preferably, the flow-limiting element is a flow-limiting orifice plate or a capillary tube.

[0029] Furthermore, the present invention also provides a control method for a constant pressure extraction system of a coffee machine, comprising the following steps: Pre-infusion step: The controller energizes the coffee solenoid valve while keeping the steam solenoid valve de-energized; the water pump runs at a first speed for a first predetermined time, and water flows into the brewing system at a first pressure to pre-infuse the coffee grounds. The pre-infusion step ensures the coffee grounds are fully wetted under low pressure, expelling air from the grounds and preventing channeling during high-pressure extraction. Simultaneously, it causes the coffee grounds to initially expand under low pressure, forming a uniform puck structure, laying the foundation for subsequent high-pressure extraction.

[0030] Coffee extraction steps: The water pump switches to the second speed, and the water flows through the coffee solenoid valve into the brewing system for coffee extraction; the steam solenoid valve remains de-energized. Utilizing the characteristic that the first and third ports of the steam solenoid valve are always open when de-energized, and the opening pressure of the one-way valve at the outlet of the steam heater, when the extraction water pressure exceeds the predetermined pressure relief pressure, the excess pressure is released through the always-open channel between the first and third ports of the steam solenoid valve, so that the extraction pressure remains constant and does not exceed the predetermined pressure relief pressure.

[0031] The flow-limiting element makes the discharge flow rate at the third port of the steam solenoid valve exhibit a non-linear characteristic: when the extraction pressure is within the first pressure range, the discharge flow rate is the first flow rate Q1, i.e., a small discharge, which only offsets the pressure spikes caused by pump pulsation, making the pressure curve smoother and avoiding frequent pressure oscillations; when the extraction pressure exceeds the predetermined pressure relief pressure, the discharge flow rate is the second flow rate Q2, which is a rapid discharge, and Q2 > Q1. The flow-limiting element achieves the above-mentioned non-linear discharge characteristics through its physical structure, which is smaller than the equivalent flow area of ​​the internal flow channel of the steam solenoid valve. Under low pressure differential conditions, flow resistance dominates, and the discharge flow rate is limited; under high pressure differential conditions, the fluid kinetic energy increases, which can overcome the flow resistance to achieve rapid discharge. This mechanism avoids the pressure oscillations caused by the binary mode of "fully open / fully closed" of traditional pressure relief valves, and achieves smooth pressure regulation.

[0032] Pressure adaptive adjustment steps: The pressure sensor detects the extraction pressure in real time and feeds it back to the controller; when the extraction pressure is consistently lower than the first pressure threshold, this situation may be caused by reasons such as coarsely ground coffee powder, insufficient powder quantity, or aging water pump. The controller controls the coffee solenoid valve to de-energize, and then uses the characteristic that its first and third ports are always open to perform an active pressure relief pulse before re-energizing, so that the water pressure is rebuilt to the target pressure range.

[0033] The technical principle behind this step is as follows: When the coffee solenoid valve is de-energized, its first and third ports connect, causing pressurized water in the brewing system to rapidly leak from the third port, resulting in a sharp drop in system pressure. Subsequently, the controller re-energizes the coffee solenoid valve, reconnecting the first and second ports. The water pump supplies water to the brewing system at a constant speed. Because the system pressure has decreased, the pump's supply capacity exceeds the system's leakage capacity, causing the pressure to quickly recover and surpass the previously low level, rebuilding to the target pressure range. This "active pressure relief-rapid reconstruction" pulse process utilizes the water supply characteristics of the constant pump speed in conjunction with the on / off switching of the solenoid valve, rather than adjusting the pump speed. The duration of the active pressure relief pulse is precisely controlled by the controller. If it is controlled within 0.5-1.0 seconds, it can effectively reset the pressure state without causing extraction interruption or backflow of coffee liquid due to excessively long pressure relief time.

[0034] Depressurization after extraction: After coffee extraction is complete, the controller de-energizes the coffee solenoid valve. The first and third ports of the coffee solenoid valve remain open, and the residual pressure in the brewing system is released through the third port of the coffee solenoid valve.

[0035] Boiler overpressure protection procedure: When the pressure of the steam boiler or coffee boiler is too high, the steam solenoid valve releases pressure by connecting the first port and the third port normally when the power is off.

[0036] Steam generation steps: When generating steam, the controller energizes the steam solenoid valve, and the second port of the steam solenoid valve is connected to the first port. After being heated by the steam heater, the steam is output through the one-way valve at the outlet.

[0037] Preferably, the first pressure range is 9-10 bar, the predetermined pressure relief pressure is 10 bar, the first pressure threshold is 9 bar, and the target pressure range is 9-10 bar.

[0038] Preferably, the first rotational speed is 1800 rpm, the first predetermined time is 3-5 seconds, and the first pressure is 3-5 bar; the second rotational speed is 2800 rpm.

[0039] Preferably, the duration of the active pressure relief pulse is 0.5-1.0 seconds.

[0040] Compared with the prior art, the present invention has the following beneficial effects: First, this invention utilizes the coordinated operation of a coffee solenoid valve and a steam solenoid valve. During coffee extraction, the coffee solenoid valve is energized, allowing water to flow into the brewing system, while the steam solenoid valve remains de-energized. By leveraging the characteristic that the first and third ports of the steam solenoid valve are always open when de-energized, and the one-way valve at the outlet of the steam boiler, precise and constant control of the extraction pressure is achieved. When the extraction pressure exceeds 10 bar, the excess pressure is automatically released from the third port of the steam solenoid valve, ensuring that the extraction pressure never exceeds 10 bar, thus reaching the optimal extraction pressure range.

[0041] Secondly, the present invention sets a flow-limiting element at the third port of the steam solenoid valve, so that the discharge flow has a non-linear characteristic, with only a small amount of discharge in the 9-10 bar range, and rapid discharge when it exceeds 10 bar. This avoids the pressure oscillation caused by the binary mode of "fully open / fully closed" of the traditional pressure relief valve, realizes smooth pressure regulation, and further improves the constant pressure accuracy.

[0042] Third, this invention achieves closed-loop control of extraction pressure through a pressure sensor and adaptive adjustment logic. When the extraction pressure remains below 9 bar, the controller uses an active pressure relief pulse to quickly rebuild the pressure to the 9-10 bar range, effectively compensating for pressure deviations caused by objective factors such as differences in coffee powder grind size and powder quantity deviations, and significantly improving the automation and consistency of extraction.

[0043] Fourth, this invention achieves constant pressure without adjusting the pump speed. The pump only needs to maintain a constant, stable speed (e.g., 2800±50 rpm), eliminating the need for frequent speed changes. Compared to traditional variable frequency speed control schemes (where the pump changes speed approximately 200-300 times per day), this invention's pump requires no speed changes. Durability tests show that the pump's service life under continuous operating conditions is extended by approximately three times.

[0044] Fifth, this invention uses a solenoid valve for control, achieving a pressure relief response time in the millisecond range when the pressure exceeds the limit. The measured pressure relief response time is ≤50 ms, while the response time of traditional water pump pressure regulation schemes is in the second range. That is, the response time of traditional schemes is usually about 0.5-1s, achieving instantaneous and stable pressure switching. The addition of a flow-limiting element further smooths the pressure curve, reducing the standard deviation of pressure fluctuation to below ±0.25 bar.

[0045] Sixth, the present invention adds a pre-infusion step before coffee extraction, pre-infusing the coffee powder for 3-5 seconds at a lower pressure, such as 3-5 bar and a lower rotation speed, such as 1800 rpm, so that the coffee powder is fully wetted and expanded, forming a uniform cake structure, effectively avoiding the channel effect during high-pressure extraction, and improving the uniformity of extraction and the quality of the finished product.

[0046] Seventh, after coffee extraction is complete, the coffee solenoid valve is de-energized, immediately releasing residual pressure in the brewing system to prevent excessive pressure from causing the system to fail to reset. When the pressure in the steam boiler or coffee boiler is too high, the first and third ports of the steam solenoid valve remain open when de-energized, automatically releasing pressure and protecting the pipeline. Simultaneously, because both the coffee and steam solenoid valves have a normally open pressure-relieving characteristic when de-energized, the system achieves a passive fault-tolerant safety mode of "pressure relief upon power failure," significantly superior to traditional solutions relying on active control.

[0047] Eighth, when producing steam, the steam solenoid valve is energized, and the steam is heated by the steam heater and then output through the 1.5 bar check valve to ensure that the steam pressure is stable at 1.5 bar, thus ensuring the stability of steam quality. In extraction mode, the check valve also acts as a back pressure element to help maintain the system pressure, and in steam mode, it ensures that the steam output pressure is not lower than 1.5 bar, realizing the three-in-one function of preventing backflow, pressure isolation, and steam pressure maintenance. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of a constant pressure extraction system for a coffee machine according to the present invention; Figure 2 This is a schematic diagram of the water circuit structure of one embodiment of the constant pressure extraction system for a coffee machine according to the present invention; Figure 3This is a control logic state transition diagram for one embodiment of a constant pressure extraction system for a coffee machine according to the present invention; Figure 4 This is a comparison diagram of the extraction pressure curves of a constant pressure extraction system for a coffee machine according to the present invention; Figure 5 This is a schematic diagram of the overall system structure of another embodiment of the constant pressure extraction system for a coffee machine according to the present invention; Figure 6 This is a schematic diagram of the water circuit structure of another embodiment of the constant pressure extraction system for a coffee machine according to the present invention; Figure 7 This is a control logic state transition diagram for another embodiment of a constant pressure extraction system for a coffee machine according to the present invention. Detailed Implementation

[0049] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0050] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0052] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0053] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0054] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation. Example 1

[0055] Please refer to the following: Figures 1 to 7 A constant pressure extraction system for a coffee machine includes a water pump 1, a water inlet check valve 2, a coffee solenoid valve 3, a steam solenoid valve 4, a steam heating pot 5, a check valve 6, a brewing system 7, a pressure reserve valve 8, a pressure sensor 9, and a flow limiting element 10.

[0056] The outlet of water pump 1 is connected to the inlet of inlet check valve 2 via a copper pipe. The outlet of inlet check valve 2 is connected to the inlet of coffee solenoid valve 3 (i.e., first port 31) and steam solenoid valve 4 (i.e., first port 41) via copper pipes.

[0057] The coffee solenoid valve 3 is a two-position three-way solenoid valve, having a first port 31, a second port 32, and a third port 33. In the de-energized state, the first port 31 and the third port 33 are normally connected; in the energized state, the second port 32 is connected to the first port 31. The second port 32 of the coffee solenoid valve 3 is connected to the water inlet of the brewing system 7. The brewing system 7 is equipped with a pressure reserve valve 8, with a pressure range of 5-7 bar.

[0058] The steam solenoid valve 4 is a two-position three-way solenoid valve, having a first port 41, a second port 42, and a third port 43. In the de-energized state, the first port 41 and the third port 43 are normally connected; in the energized state, the second port 42 is connected to the first port 41. The second port 42 of the steam solenoid valve 4 is connected to the water inlet of the steam heater 5. The water outlet of the steam heater 5 is equipped with a one-way valve 6, with an opening pressure of 1.5 bar.

[0059] Pressure sensor 9 is installed on the pipeline between coffee solenoid valve 3 and brewing system 7 to detect extraction pressure in real time and feed it back to controller (not shown in the figure).

[0060] A flow-limiting element 10 is provided at the third port 43 of the steam solenoid valve 4. The equivalent flow area of ​​the flow-limiting element 10 is smaller than the equivalent flow area of ​​the internal flow channel of the steam solenoid valve 4. The flow-limiting element 10 is a flow-limiting orifice plate, and in this embodiment, a flow-limiting orifice plate with an orifice diameter of 0.8 mm is used.

[0061] The system also includes a controller (not shown in the figure), which is electrically connected to the coffee solenoid valve 3 and the steam solenoid valve 4, and is used to control the on / off state of the coffee solenoid valve 3 and the steam solenoid valve 4. The controller also receives detection signals from the pressure sensor 9. The water pump 1 is a vibratory pump, and its operating speed is constant at 2800±50 rpm.

[0062] Technical explanation of the functions and connections of each component: Inlet check valve 2: Prevents water from flowing back into the water circuit after the water pump stops, maintains the initial pressure of the system water circuit, and prevents air from entering the water circuit system.

[0063] Coffee solenoid valve 3: As a switching element of the extraction water circuit, its two-position three-way structure enables it to automatically depressurize when the power is off, that is, when the first port 31 and the third port 33 are normally open, without the need to set up an additional depressurization pipeline.

[0064] Steam solenoid valve 4: As a core component for constant pressure, when power is off, i.e. when the first port 41 and the third port 43 are normally open, it forms a precise pressure relief channel. It works in conjunction with the one-way valve 6 at the outlet of the steam heating pot 5 at an opening pressure of 1.5 bar. When the system pressure exceeds 10 bar, the excess pressure is released through the normally open channel between the first port 41 and the third port 43 of the steam solenoid valve 4, thus achieving precise constant pressure.

[0065] Flow limiting element 10: Located at the third port 43 of the steam solenoid valve 4, its equivalent flow area is smaller than the equivalent flow area of ​​the internal flow channel of the steam solenoid valve 4. When the extraction pressure is in the range of 9-10 bar, the flow limiting element 10 restricts the discharge flow to the first flow rate Q1, i.e., a small discharge, which only offsets the pressure spikes caused by pump pulsation. When the extraction pressure exceeds 10 bar, the fluid kinetic energy increases, and the discharge flow automatically increases to the second flow rate Q2 (Q2>Q1), achieving rapid pressure relief. The flow limiting element 10 achieves the above-mentioned nonlinear discharge characteristics through its physical structure, avoiding the pressure oscillations caused by the binary mode of "fully open / fully closed" of traditional pressure relief valves, and making the pressure curve smoother.

[0066] Pressure sensor 9: Real-time detection of extraction pressure and feedback to the controller, providing a data basis for adaptive adjustment. When the extraction pressure remains below 9 bar, the controller triggers an active pressure relief pulse to restore the pressure to the 9-10 bar range.

[0067] Steam cooker 5 and one-way valve 6: The 1.5 bar opening pressure of one-way valve 6 ensures the minimum pressure threshold for steam output, and also acts as a back pressure element in extraction mode to help maintain system pressure. One-way valve 6 also has an anti-backflow function, which prevents hot water in steam cooker 5 from flowing back into steam solenoid valve 4 in extraction mode; moreover, it also has a pressure isolation function, which ensures that the normally open channel of steam solenoid valve 4 will not accidentally release extracted water due to siphon effect when the pressure is below 10 bar.

[0068] Backup pressure valve 8: Provides a base back pressure of 5-7 bar as the first guarantee for constant pressure, forming a two-stage pressure control with the 10 bar pressure relief of steam solenoid valve 4.

[0069] The working principle of this embodiment is as follows: (a) Pre-soaking mode Before coffee extraction, the controller first performs a pre-infusion step. The controller energizes the coffee solenoid valve 3, connecting its second port 32 to its first port 31; the steam solenoid valve 4 remains de-energized. The water pump 1 runs at a first speed, such as 1800 rpm, for a first predetermined time, such as 3-5 seconds, and the water flows at a first pressure, such as 3-5 bar, through the coffee solenoid valve 3 into the brewing system 7, performing low-pressure wetting and pre-infusion of the coffee grounds.

[0070] Pre-infusion allows the coffee grounds to be fully wetted under low pressure, expelling air from the grounds and preventing the channeling effect during high-pressure extraction, where water flows quickly through the grounds along the path of least resistance, resulting in some coffee grounds not being fully extracted. At the same time, it allows the coffee grounds to initially expand under low pressure, forming a uniform puck structure, laying the foundation for subsequent high-pressure extraction.

[0071] (ii) Coffee extraction mode After pre-infusion, water pump 1 switches to the second speed, such as 2800 rpm, to enter the high-pressure extraction stage. The controller keeps the coffee solenoid valve 3 energized and the steam solenoid valve 4 de-energized.

[0072] The water pump 1 operates at a constant speed of 2800 rpm. After the water flows through the inlet check valve 2, it flows into the brewing system 7 through the first port 31 and the second port 32 of the coffee solenoid valve 3 for coffee extraction.

[0073] During this process, the steam solenoid valve 4 remains de-energized. Since the first port 41 and the third port 43 of the steam solenoid valve 4 are normally open when de-energized, and the outlet of the steam cooker 5 is equipped with a 1.5 bar one-way valve 6, the entire water circuit is open. When the water pressure for coffee extraction exceeds 10 bar, the excess water flows out through the normally open channel between the first port 41 and the third port 43 of the steam solenoid valve 4. Because the opening pressure of the one-way valve 6 at the outlet of the steam cooker 5 is 1.5 bar, the water pressure needs to reach at least 1.5 bar to pass through. Therefore, excess water will leak out from the third port 43 of the steam solenoid valve 4 through the flow-limiting element 10, thus ensuring that the extraction pressure does not exceed 10 bar.

[0074] The function of the flow-limiting element 10 is as follows: When the extraction pressure is in the 9-10 bar range, i.e., before exceeding 10 bar, a brief pressure spike may occur due to pump pulsation or other reasons. The flow-limiting element 10 allows a small release, i.e., the first flow rate Q1, to offset the pressure spike and make the pressure curve smoother. When the extraction pressure exceeds 10 bar, the flow-limiting element 10 allows rapid release, i.e., the second flow rate Q2, where Q2 > Q1, quickly pulling the pressure back below 10 bar. This non-linear release characteristic avoids the pressure oscillations caused by the binary "fully open / fully closed" mode of traditional pressure relief valves.

[0075] The pressure relief valve 8 (5-7 bar) in the brewing system 7 provides basic back pressure, further ensuring pressure stability during the extraction process.

[0076] (III) Pressure Adaptive Adjustment Mode During the extraction process, pressure sensor 9 detects the extraction pressure in real time and feeds it back to the controller.

[0077] When the extraction pressure remains below 9 bar, this may be caused by factors such as coarsely ground coffee, insufficient coffee powder, or an aging water pump. In this case, the controller will trigger adaptive adjustment. First, the controller de-energizes the coffee solenoid valve 3. Since the first port 31 and the third port 33 of the coffee solenoid valve 3 are normally open when the power is off, the pressurized water in the brewing system 7 is rapidly released from the third port 33, causing a sudden drop in system pressure and an active pressure relief pulse that lasts for 0.5-1.0 seconds.

[0078] Subsequently, the controller re-energizes the coffee solenoid valve 3, reconnecting the first port 31 and the second port 32. The water pump 1 supplies water to the brewing system 7 at a constant speed of 2800 rpm. Since the system pressure has decreased, the water pump's supply capacity exceeds the system's discharge capacity, causing the pressure to rise rapidly and surpass the previous low state, rebuilding to the target pressure range of 9-10 bar.

[0079] The aforementioned active pressure relief-rapid reconstruction pulse process utilizes the water supply characteristics of a constant pump speed in conjunction with the on / off switching of a solenoid valve, rather than adjusting the pump speed. A single active pressure relief pulse can effectively reset the pressure state, preventing extraction interruption or backflow of coffee liquid due to excessively long pressure relief time.

[0080] When the extraction pressure is in the range of 9-10 bar, the controller does not intervene and relies entirely on the passive pressure relief of the steam solenoid valve 4 and the nonlinear discharge characteristics of the flow limiting element 10 to maintain constant pressure.

[0081] (iv) Decompression mode after extraction After coffee extraction is complete, the controller de-energizes the coffee solenoid valve 3. The first port 31 and the third port 33 of the coffee solenoid valve 3 are normally open, and the residual pressure in the brewing system 7 is released through the third port 33 of the coffee solenoid valve 3.

[0082] (v) Boiler overpressure protection mode When the pressure in the steam boiler or coffee boiler is too high, since the first port 41 and the third port 43 of the steam solenoid valve 4 are always connected when the power is off, the pressure will automatically be released from the third port 43 through the flow limiting element 10.

[0083] (vi) Creating a steam mode When generating steam, the controller energizes the steam solenoid valve 4, connecting its second port 42 to its first port 41. The water pump 1 starts, and water flows through the steam heater 5 for heating. Steam is then output through the one-way valve 6 at the outlet of the steam heater 5. Because the steam heater has a 1.5 bar one-way valve 6 at its front end, steam must reach a pressure of 1.5 bar before being output, ensuring the steam pressure remains stable at 1.5 bar.

[0084] When steam production is finished, the steam solenoid valve 4 is de-energized, and excess pressure is discharged from the third port 43 through the flow limiting element 10.

[0085] To verify the constant pressure extraction effect of the present invention, the following describes the comparative experimental process of the system.

[0086] Experimental conditions: The same batch of Italian-roasted coffee beans was used, roasted within 30 days of the date of roasting. The grind size was standard Italian fineness, such as 200-250μm. The amount of coffee grounds was 18g, the target extraction amount was 36g (double espresso), and the target extraction time was 25-30 seconds. The ambient temperature was 25±2℃, and the relative humidity was 50±5%.

[0087] Experimental Groups:

[0088] Experimental results:

[0089] Control group 3 represents the test scheme of the present invention without a flow-limiting element, i.e., a version that relies solely on direct pressure relief through the normally open channel of the steam solenoid valve, without pressure feedback and adaptive adjustment. Experimental data show that: (1) The addition of the current limiting element further reduced the standard deviation of pressure fluctuation from ±0.35 bar to ±0.25 bar, a decrease of about 29%; the smoothness of the pressure curve (measured by peak count) decreased from ≤8 times / minute to ≤2 times / minute, a decrease of about 75%, indicating that the current limiting element significantly suppressed pressure oscillation.

[0090] (2) The addition of the adaptive adjustment mechanism enables the system to automatically recover to the target pressure range within 3 seconds when the low pressure deviates (<9 bar), while the solution of the infinite flow element requires manual intervention or a longer recovery time, which significantly improves the automation and consistency of extraction.

[0091] (3) The mean TDS increased from 9.6% to 10.0%, and the standard deviation of TDS decreased from ±0.35% to ±0.25%, indicating that the extraction was more thorough, uniform and stable.

[0092] Experimental conclusion: Constant pressure accuracy: The standard deviation of pressure fluctuation (±0.25 bar) of this invention is reduced by 72% compared with control group 1, by 64% compared with control group 2, and by 29% compared with control group 3 (without flow limiting element), demonstrating a significant advantage in constant pressure. The addition of the flow limiting element further improves the constant pressure accuracy.

[0093] Response speed: The response time of this invention is ≤50 ms, which is much faster than that of control group 1 (0.5-1s) and control group 2 (0.3-0.6s), and can achieve instantaneous pressure stabilization.

[0094] Pressure smoothness: The peak count of the pressure curve of the present invention is ≤2 times / minute, which is significantly better than the control group 3 (≤8 times / minute), indicating that the nonlinear discharge characteristics of the current limiting element effectively suppress pressure oscillation.

[0095] Adaptive capability: When the extraction pressure deviates from the target value, the present invention can automatically recover within 3 seconds, while control group 1 and control group 2 require manual intervention. The adaptive adjustment mechanism of the present invention significantly improves the level of automation of extraction.

[0096] Extraction quality: The mean TDS (10.0%) of this invention is higher than that of all control groups, and the standard deviation of TDS is the smallest, indicating that the extraction is more thorough, uniform and stable.

[0097] Pump lifespan: The pump of this invention does not require speed change, has an average of 0 speed change times per day, and its continuous service life is 3.3 times that of control group 1 and 1.3 times that of control group 2.

[0098] Overall results: This invention outperforms existing technologies in six dimensions: constant pressure accuracy, response speed, pressure smoothness, adaptability, extraction quality, and equipment lifespan, demonstrating outstanding substantive features and significant progress.

[0099] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0100] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A constant pressure extraction system for a coffee machine, characterized in that, include: Water pump (1), inlet check valve (2), coffee solenoid valve (3), steam solenoid valve (4), steam heating pot (5), brewing system (7) and pressure reserve valve (8); The outlet of the water pump (1) is connected to the inlet of the inlet check valve (2), and the outlet of the inlet check valve (2) is connected to the inlet of the coffee solenoid valve (3) and the inlet of the steam solenoid valve (4), respectively. The coffee solenoid valve (3) is a two-position three-way solenoid valve. When it is not energized, its first port (31) and third port (33) are normally connected. When it is energized, its second port (32) is connected to its first port (31). The steam solenoid valve (4) is a two-position three-way solenoid valve. When it is not energized, its first port (41) and third port (43) are normally connected. When it is energized, its second port (42) is connected to its first port (41). The second port (32) of the coffee solenoid valve (3) is connected to the water inlet of the brewing system (7), the second port (42) of the steam solenoid valve (4) is connected to the water inlet of the steam heating pot (5), the water outlet of the steam heating pot (5) is provided with a one-way valve (6), and the brewing system (7) is provided with a pressure reserve valve (8). A flow limiting element (10) is provided at the third port (43) of the steam solenoid valve (4), and the equivalent flow area of ​​the flow limiting element (10) is smaller than the equivalent flow area of ​​the internal flow channel of the steam solenoid valve (4). The system also includes a pressure sensor (9) installed on the pipeline between the coffee solenoid valve (3) and the brewing system (7) to detect the extraction pressure in real time and feed it back to the controller.

2. The constant pressure extraction system for a coffee machine according to claim 1, characterized in that, The opening pressure of the one-way valve (6) at the outlet of the steam heating pot (5) is 1.5 bar.

3. The constant pressure extraction system for a coffee machine according to claim 1, characterized in that, The pressure of the pressure valve (8) of the brewing system (7) is 5-7 bar.

4. The constant pressure extraction system for a coffee machine according to claim 1, characterized in that, The predetermined depressurization pressure for coffee extraction is 10 bar.

5. The constant pressure extraction system for a coffee machine according to claim 1, characterized in that, The water pump (1) is a vibratory pump with a constant operating speed of 2800±50 rpm.

6. The constant pressure extraction system for a coffee machine according to claim 1, characterized in that, The current limiting element (10) is a current limiting orifice plate or a capillary tube.

7. A control method for a constant pressure extraction system for a coffee machine, employing the constant pressure extraction system for a coffee machine as described in any one of claims 1-6, characterized in that, Includes the following steps: Pre-infusion step: The controller controls the coffee solenoid valve (3) to be energized, while the steam solenoid valve (4) remains de-energized; the water pump (1) runs at a first speed for a first predetermined time, and the water flows into the brewing system (7) at a first pressure to pre-infuse the coffee powder; Coffee extraction steps: The water pump (1) is switched to the second speed, and the water flows through the coffee solenoid valve (3) into the brewing system (7) for coffee extraction; the steam solenoid valve (4) is kept in the de-energized state. Utilizing the characteristic that the first port (41) and the third port (43) of the steam solenoid valve (4) are always open in the de-energized state, and the opening pressure of the one-way valve (6) at the outlet of the steam heater (5), when the extraction water pressure exceeds the predetermined pressure relief pressure, the excess pressure is discharged through the normally open channel between the first port (41) and the third port (43) of the steam solenoid valve (4), so that the extraction pressure is constant and does not exceed the predetermined pressure relief pressure; The flow limiting element (10) makes the discharge flow at the third port (43) of the steam solenoid valve (4) have a non-linear characteristic: when the extraction pressure is in the first pressure range, the discharge flow is the first flow Q1; when the extraction pressure exceeds the predetermined pressure relief pressure, the discharge flow is the second flow Q2, and Q2 > Q1; Pressure adaptive adjustment steps: The pressure sensor (9) detects the extraction pressure in real time and feeds it back to the controller; when the extraction pressure is continuously lower than the first pressure threshold, the controller controls the coffee solenoid valve (3) to be de-energized, and uses the characteristic that its first port (31) and third port (33) are always open to perform an active pressure relief pulse and then re-energizes it so that the water pressure is rebuilt to the target pressure range; Depressurization step after extraction: After coffee extraction is completed, the controller controls the coffee solenoid valve (3) to be de-energized. The first port (31) and the third port (33) of the coffee solenoid valve (3) are normally open, and the residual pressure in the brewing system (7) is released through the third port (33) of the coffee solenoid valve (3). Boiler overpressure protection steps: When the pressure of the steam boiler or coffee boiler is too high, the steam solenoid valve (4) releases pressure through the first port (41) and the third port (43) in the de-energized state; Steam making steps: When making steam, the controller controls the steam solenoid valve (4) to be energized. The second port (42) of the steam solenoid valve (4) is connected to the first port (41). After the steam is heated by the steam heating pot (5), it is output through the one-way valve (6) at the outlet.

8. The control method for the constant pressure extraction system of a coffee machine according to claim 7, characterized in that, The first pressure range is 9-10 bar, the predetermined pressure relief is 10 bar, the first pressure threshold is 9 bar, and the target pressure range is 9-10 bar.

9. The control method for the constant pressure extraction system of a coffee machine according to claim 7, characterized in that, The first rotational speed is 1800 rpm, the first predetermined time is 3-5 seconds, and the first pressure is 3-5 bar; the second rotational speed is 2800 rpm.

10. The control method for the constant pressure extraction system of a coffee machine according to claim 7, characterized in that, The duration of the active pressure relief pulse is 0.5-1.0 seconds.

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