Supercooling degree control type expansion valve

Abstract: In a supercooling degree control type expansion valve a differential pressure regulating valve (4, 5 6) is provided upstream of a restriction passage 8. Valve element 5 contains or defines an oil passage 11 even when the differential pressure regulating valve is closed during low load operation of the compressor, to allow refrigerant to flow at a minimum flow rate and to return oil contained in the refrigerant to the compressor, whereby the seizure of the compressor can be prevented.

Description: This invention relates to a supercooling degree control type expansion valve, particularly for use in a refrigeration cycle of an air conditioning system for an automotive vehicle. As the refrigeration cycle of an air conditioning system for an automotive vehicle, there has been widely employed one using a receiver/dryer arranged at an outlet side of a condenser for storing a superfluous refrigerant and subjecting the stored refrigerant to air-liquid separation, a thermal expansion valve for controlling the flow rate of the refrigerant flowing into the evaporator according to the pressure and temperature of a low-pressure refrigerant delivered from the evaporator. On the other hand, another refrigeration cycle is also known which uses an accumulator arranged at an outlet side of an evaporator, for storing a superfluous refrigerant and subjecting the stored refrigerant to air-liquid separation, and a supercooling degree control type expansion valve comprised of a restriction passage (orifice) for control of the flow rate of the refrigerant according to the degree of supercooling and dryness of a high-pressure refrigerant delivered from a condenser, and a differential pressure regulating valve for carrying out control such that the refrigerant is cooled to a predetermined supercooling degree (EP 987 505 A). FIG. 7 is a cross-sectional view showing the structure of another conventional supercooling degree control type expansion valve (prior art). A body 2 of the conventional supercooling degree control type expansion valve 1 is connected at its left side to the upstream side of a refrigeration cycle. Inside of a large opening a strainer 3 is fitted. The body 2 defines a refrigerant passage formed with a valve seat 4. A valve element 5 is axially movably opposed to the valve seat 4 from the downstream side. Valve element 5 is urged in valve-closing direction by a spring 6 arranged on a downstream side thereof. A lower end of body 2 receives a spring-receiving member 7 containing an annular orifice 8. Body 2 carries O-rings 9 for sealing purposes. When the refrigeration cycle is operating at a low load condition or the compressor is rotating at a low rotational speed, the refrigeration cycle is at a low pressure condition, so that the valve element 5 is held by spring 6 in a closed state against valve seat 4. This inhibits the refrigerant from flowing therethrough. When the refrigeration cycle is operating at a normal load condition, high-pressure refrigerant from a condenser, not shown, filtered by strainer 3, reaches the upstream side of valve element 5. As soon as the pressure of the refrigerant overcomes the force of spring 6, valve element 5 leaves valve seat 4. The refrigerant flows downstream, passes through annular orifice 8, where it undergoes thermal expansion, and flows to an evaporator, not shown. Valve element 5 controls the flow rate of the refrigerant depending on the balance between the differential pressure between the upstream side and downstream side of valve seat 4, and the urging force of spring 6. When the temperature of the outside air is low e.g. during winter, or when the rotational speed of the engine is low e.g. during idling operation of the engine, the pressure in the whole refrigeration cycle is low. This may cause a situation in which valve element 5 remains closed and inhibits any flow of the refrigerant. The refrigerant, however, contains oil for the lubrication of the compressor. If the refrigerant ceases to flow, the amount of oil returning to the compressor decreases, which in worst cases causes seizure of the compressor due to oil shortage. Further, when the vehicle is running at a high speed, the compressor too increases the pressure within the refrigeration cycle. Therefore, it is necessary to configure the supercooling degree control type expansion valve such that it withstands high pressure from the viewpoint of safety. Further, the power of the compressor is increased to a larger degree than required for cooling, which degrades the coefficient of performance of the refrigeration cycle as well as fuel economy. An expansion valve according to the preamble part of claim 1 is known from EP 0 279 622 A. The expansion valve contains a bypass hole upstream of the restriction passage. The bypass hole ensures a remaining refigerant flow into the compressor in order to delay seizure of the compressor. The bypass hole either is defined by a bore in a separation wall and deviates the valve bore. The cross-section of the bypass hole is smaller than the cross-section of the valve bore. In another embodiment, the valve seat is formed with a slit. The slit keeps the bypass open if the valve element is seated on the valve seat. It is an object of the present invention to provide a supercooling degree control type expansion valve which is capable of preventing seizure of a compressor, at a low load condition, but avoids a back flow of refrigerant. Another object of the present invention is to provide a supercooling degree control type expansion valve which is capable to suppress an undesirable pressure rise when the vehicle or its engine is running at a high speed. The present invention provides a supercooling degree control type expansion valve including a restriction passage arranged in a refrigerant passage through which a refrigerant flows, for subjecting the refrigerant introduced to adiabatic expansion, and a differential pressure regulating valve arranged on an upstream side of the restriction passage, for carrying out control such that the refrigerant introduced has a predetermined cooling degree, and equips the valve with a differential pressure regulating valve bypass means allowing refrigerant to flow at a minimum refrigerant flow rate required for e.g. compressor lubrication even when the differential pressure regulating valve is closed. Although the differential pressure regulating valve is closed when the rotational speed of the engine is low and the compressor is at a low load condition, still a part of the introduced refrigerant is allowed to flow via the differential pressure regulating valve bypass means. Oil contained in the refrigerant is returned to the compressor, to prevent seizure of the compressor. However, when the pressure at the outlet side of the restriction passage becomes high, e.g. caused by switching of the refrigerant flow path, the check valve will close and will prevent a back flow of refrigerant. According to another aspect, the restriction passage may include passage area-varying means for increasing a passage area thereof in response to received pressure higher than a predetermined pressure. When the refrigerant is introduced at high pressure due to high rotational speed of the compressor (e.g. when the vehicle is running at high speed) the passage area-varying means increases the passage area of the restriction passage to increase the flow rate of a refrigerant flowing through the restriction passage. This prevents an undesired pressure rise and damages, and improves performance and fuel economy of the engine. The present invention will now be described in detail with reference to drawings showing preferred embodiments thereof. In the drawings is: Fig. 1 (A) a cross-sectional view of a supercooling degree control type expansion valve according to a first embodiment, Fig. 1 (B) an enlarged cross-sectional view taken on line b-b of Fig. 1 (A), Fig. 2 an exploded perspective view of a valve element of the supercooling degree control type expansion valve of Figs 1(A) and 1(B), Fig. 3 a cross-sectional view of a supercooling degree control type expansion valve according to another embodiment in a state in which a refrigerant is flowing in a normal direction, Fig. 4(A) a cross-sectional view of the valve of Fig. 3 in which the refrigerant is flowing in a reverse direction, Fig. 4(B) an enlarged cross-sectional view of the valve taken on line d-d of Fig. 4(A), Fig. 5(A) a cross-sectional view of a supercooling degree control type expansion valve according to another embodiment in a state in which the pressure is normal, Fig. 5(B) a cross-sectional view of the valve taken on line e-e of Fig. 5(A), Fig. 6 a cross-sectional view of the valve of Figs 5(A) and 5(B) in a state in which the high pressure is avoided, and Fig. 7 a cross-sectional view of a conventional supercooling degree control type expansion valve (prior art). It should be noted that further on in the description component parts identical to those of the Fig. 10 valve are designated by identical numerals. The supercooling degree control type expansion valve 1 in Figs 1 (A) and 1 (B) has a body 2, and a strainer 3 fitted in a portion of the body 2 where a high-pressure refrigerant is introduced from the upstream side of a refrigeration cycle. A refrigerant passage extends through a central portion of the body 2 into which the refrigerant is introduced via the strainer 3, and is formed with a stepped portion constituting a valve seat 4. A valve element 5 is axially movably arranged in the refrigerant passage in a manner opposed to the valve seat 4 from the downstream side of the refrigerant passage. The valve element 5 has three legs 10 formed on an upstream side thereof such that the legs 10 protrude via an opening of the valve seat 4 into a portion of the refrigerant passage upstream of the valve seat 4, whereby the legs 10 guide the axial movement of the valve element 5. Legs similar to the legs 10 are also formed on a downstream side of the valve element 5, such that they protrude into a portion of the refrigerant passage downstream of the valve seat 4, whereby the legs guide the axial movement of the valve element 5. Further, the valve element 5 has an oil passage 11 formed therethrough (a bypass means M of the differential pressure regulating valve) which extends along the axis thereof with a very small cross-sectional area. Further, at a location downstream of the valve seat 4, a spring 6 is arranged in a manner urging the valve element 5 in a valve-opening direction. The spring 6 is supported by a valve-receiving member 7 fitted in a downstream end of the body 2. The valve seat 4, the valve element 5, and the spring 6 constitute a differential pressure regulating valve. The spring-receiving member 7 is formed therethrough with a restriction passage which forms an orifice for restricting the flow of a refrigerant. The restriction passage 8 is annularly formed such that no hole is formed from outside, while a recess is formed in a refrigerant passage-side surface of the spring-receiving member 7 such that the recess communicates with part of the restriction passage 8. This causes the refrigerant within the refrigerant passage accommodating the spring 6 to be discharged in an annular form in cross-section via the restriction passage 8, thereby reducing the sound generated by passing of the refrigerant therethrough. The body 2 has an O-ring 9 fitted on the outer periphery thereof. In the supercooling degree control type expansion valve 1 designed as described above, when the refrigeration cycle is operating at a low load condition, or when the compressor is rotating a low rotational speed, the pressure of the refrigerant introduced into the supercooling degree control type expansion valve 1 is low, so that the valve element 5 is urged by the spring 6 against the valve seat 4, whereby the valve 1 is held in a closed state. However, the low-pressure refrigerant flows through the oil passage 110 formed through the valve element 5, and further through the restriction passage 8 toward the evaporator. This makes it possible to secure the return of oil at a minimum flow rate required when the compressor is operating at the low rotational speed. During a normal load operation, the high-pressure refrigerant from the condenser is first filtered by the strainer 3, and then introduced into the upstream side of the valve element 5. At this time, depending on the balance between the differential pressure between the upstream side and the downstream side of the valve seat 4, and the urging force of the spring 6, the valve element 5 is moved to leave the valve seat 4, thereby controlling the flow rate of the introduced refrigerant passing therethrough. The refrigerant having passed through this differential pressure regulating valve passes through the annular restriction passage 8 of the spring-receiving member 7, and is supplied to the evaporator. In the shown embodiment of Figs 1(A), 1(B) and Fig. 2 valve element 5 has a plug 12 loosely fitted therein to thereby form the oil passage 11a (bypass means M) in the form of an annulus. More specifically, the valve element 5 has a small-diameter hole 13 and a large-diameter hole 14 formed therethrough along an axis thereof. The plug 12 has an outer diameter slightly smaller than the inner diameter of the small-diameter hole 13, and three protrusions 15 formed along the circumference thereof which have respective ends thereof brought into pressure contact with the inner wall of the large-diameter hole 14. By press-fitting the protrusions 15 into the large-diameter hole 14 of the valve element 5, the plug 12 is positioned in the center of the small-diameter hole 13, whereby the oil passage 11 a in the form of an annulus is formed between the inner peripheral surface of the small-diameter hole 13 and the outer peripheral surface of the plug 12. In the embodiment of Figs 3, 4(A), 4(B) a check valve is arranged in an oil passage 11 (bypass means M), whereby a backflow of the refrigerant is prevented. Valve element 5 has an oil passage formed along the axis thereof with a ball 16 being axially movably arranged therein in a loosely fitted manner. A portion of the oil passage on the upstream side of the ball 16 provides a valve seat for receiving the ball 16, while in a portion of the same on the downstream side of the ball 16, a plug 17 is fitted. The plug 17 has through holes 18 axially formed therethrough. The through holes 18 are arranged in three on a concentric circle at equal intervals, as shown. in FIG. 4(B), and three protrusions 19 protruding toward the upstream side are formed respectively between the three through holes 18. The protrusions 19 prevent the through holes from being closed by the ball 16 when the ball 16 is brought into contact with the plug 17 by the flow of the refrigerant in the normal direction. When a high-pressure refrigerant is introduced into a portion of the supercooling degree control type expansion valve 1 on the side where the strainer 3 is arranged, the ball 16 is in contact with the protrusions 19 of the plug 17, as shown in FIG. 3, whereby an oil passage is formed. Even if the valve element 5 is seated onto the valve seat 4 to close the valve due to a decrease in pressure of the refrigerant, when the refrigeration cycle is operating at a low load condition, or when the compressor is rotating at a low rotational speed, the oil passage makes it possible to secure the flow of refrigerant at the minimum flow rate required and thereby return oil to the compressor. On the other hand, when the pressure at the outlet side of the restriction passage 8 of the supercooling degree control type expansion valve 1 becomes high, the high-pressure refrigerant causes the ball 16 to be seated on its seat to close the valve. This closes the oil passage whereby the backflow of refrigerant can be prevented. The supercooling degree control type expansion valve 1 comprised of a differential pressure regulating valve with a check valve is useful for cases in which the pressure at the outlet side of the restriction passage 8 can become high e.g. by switching of the flow path of refrigerant, depending on a configuration of the piping forming components of the refrigeration cycle. The embodiment of Figs 5(A), 5(B) and Fig. 6 includes a mechanism arranged on a downstream side of a differential pressure regulating valve thereof, for varying an orifice area of the already mentioned restriction passage 8 in response to a high pressure received thereat. More specifically, a spring-receiving member 7a fitted in a refrigerant outlet side end of the supercooling degree control type expansion valve 1 is formed by a hollow cylindrical portion, and a ring portion integrally formed with the hollow cylindrical portion and having an opening extending through a central portion thereof. A portion of a shaft 20 is inserted into the opening to thereby form the restriction passage 8 in the form of an annulus. The shaft 20 has guide members 21 integrally formed therewith along its circumference, for axially movably guiding the shaft 20 while positioning the shaft 20 on the axis of the spring-receiving member 7a. Between the guide members 21, there are formed passages 22 through which the refrigerant having passed through the restriction passage 8 in the form of an annulus passes. Further, the shaft 20 is urged in an upstream direction by a spring 24 interposed between the shaft 20 and a spring-receiving member 23 fitted in an end of the spring receiving member 7a, and at the same time, restricted in position in an axial direction by a stopper 25 such that the restriction passage 8 having a predetermined orifice area is formed between the shaft 20 and the opening of the ring portion. When the pressure of the refrigerant within the refrigeration cycle is normal, the shaft 20 is held by the urging force of the spring 24 in a position shown in FIG. 5(A). Further, if the rotational speed of the compressor becomes high and the pressure within the refrigeration cycle as a whole becomes high, e.g. when the vehicle is running at a high speed, the pressure of the refrigerant introduced into the supercooling degree control type expansion valve 1 and having passed through the differential pressure regulating valve also becomes high. The pressure of the refrigerant having passed the differential pressure regulating valve is received by the upstream-side end face of the shaft 20 defining the restriction passage 8, and when the pressure exceeds a predetermined value, the shaft 20 overcomes the urging force of the spring 24 to move in a downstream direction, as shown in FIG. 6. This increases the orifice area of the restriction passage 8 to thereby increase the flow rate of refrigerant flowing though the restriction passage 8 and the passages 22, so that the pressure of the refrigerant decreases. This makes it possible to prevent a further increase in the pressure of the refrigerant. Although the supercooling degree control type expansion valve according to the invention is assumed to be employed in a refrigeration cycle using chlorofluorocarbon HFC-134a as the refrigerant, this is not limitative, but it can be similarly applied to refrigeration cycles using carbon dioxide (CO 2 ), a hydrocarbon (HC), ammonia (NH 3 ), etc. Further, provision of the check valve in the oil passage makes it possible to close the oil passage e.g. when the pressure at the outlet side of the supercooling degree control type expansion valve becomes high, whereby the backflow of the refrigerant can be prevented. Further, owing to provision of means for varying the orifice area of a restriction passage in response to received pressure which is higher than a predetermined pressure, the pressure of refrigerant, which may be increased e.g. when the vehicle is running at a high speed, is prevented from becoming higher than a predetermined value by increasing the orifice area. This enhances the safety of the apparatus from high pressure, and further prevents degradation of the coefficient of performance, and fuel economy. The differential pressure regulating valve bypass means M is provided either in the valve element 5 or between the valve element 5 and its associated valve seat 4.

Claims: A supercooling degree control type expansion valve (1) including a restriction passage (8) arranged in a refrigerant passage through which a refrigerant flows, for subjecting the refrigerant introduced to adiabatic expansion, a differential pressure regulating valve (4, 5, 6) arranged on an upstream side of the restriction passage, for carrying out control such that the refrigerant introduced has a predetermined cooling degree, and differential pressure regulating valve bypass means (M) for allowing the refrigerant to flow therethrough at a minimum refrigerant flow rate required for a compressor even when the differential pressure regulating valve (4, 5, 6) is closed characterized in that said differential pressure regulating valve bypass means (M) includes a check valve (16, 19) for closing the bypass means (M) when pressure on a downstream side of the differential pressure regulating valve becomes higher than pressure on an upstream side of the differential pressure regulating valve. Supercooling degree control type expansion valve according to claim 1, characterized in that said differential pressure regulating valve bypass means (M) is a passage (11a) in the form of an annulus formed by positioning, in a through passage formed through a valve element (5) of the differential pressure regulating valve, a plug member (12) having a profile smaller than a profile of the through passage, on an identical axis. Supercooling degree control type expansion valve according to claim 1, characterized in that the restriction passage (8) includes passage area-varying means (20) for increasing a passage area thereof in response to received pressure which is higher than a predetermined pressure.

Inventors: HISATOSHI HIROTA, YUUSUKE INOUE, YUUSUKE, INOUE, Hisatoshi Hirota, c/o TGK Co.,Ltd., Yuusuke, Inoue, c/o TGK Co.,Ltd.
Applicants: TGK CO LTD, TGK CO., LTD.
Application year: 2001
Main classification: F25B41
IPC codes: F16K1, F16K17, F25B31, G05D16, F25B41, F16K15, B60H1