Abstract:
An expansion valve adapted to achieve a stable operation in case of variations of the pressure of a high-pressure refrigerant is actuated by a power element transmitting an opening force to a valve body via a rod located between the power element and the power body by applying couple forces to the rod and generating a retarding force for the rod while the rod is guided in the direction of its shaft line

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention refrigerant by controlling the flow rate of the refrigerant supplied to an evaporator in a refrigerating cycle, and according to the preamble part of claims  1  and  11 . 
     In known expansion valves a valve body is arranged opposite to a valve seat formed by a thin contraction in the high-pressure refrigerant duct. Said valve body is moved in relation to said valve seat to open and close said valve seat corresponding to the temperature and the pressure of low-pressure refrigerant exiting the evaporator. The valve body is moved by an axially retractable rod which is guided along its shaft line in a penetration bore of the valve casing. Said rod is actuated by a power element operating corresponding to the temperature and the pressure of low-pressure refrigerant. In operation it may occur that due to some reasons the pressure of the high-pressure refrigerant supplied into the expansion valve significantly varies at the upstream side of the valve body. Said pressure variations are transmitted to the expansion valve body by means of the refrigerant medium. In case the pressure raises upstream the valve body due to a pressure variation, a pressure depending force acts on the valve body in its closing direction and consequently pushes said rod repeatedly. As a result, due to the closing or increasing throttling effect of the valve body the pressure of the refrigerants on the upstream side also is increasing and the occurring pressure variation even is multiplied. This might lead to an extremely unstable operation of the expansion valve. 
     2. Description of the Related Art 
     As disclosed in JP H 9-222 268 the operation of a known expansion valve was made stable by applying energy in lateral direction to the rod axially retractably disposed between the power element and the valve body, e.g. by a spring or the like. As a result, the valve body cannot respond as sensitively anymore to a variation of the pressure. However, the spring laterally pressing against the rod had to be made passive during a stable operation of the expansion valve and only should be set into action to stabilise the operation behaviour in case of pressure variations of the high-pressure refrigerant. As a result, the structure of the expansion valve became complicated as well as the assembling work, and the costs for manufacturing and assembling the expansion valve were high. 
     It is an object of the invention to provide an expansion valve performing a stabilised operation even in case of variations of the pressure of the high-pressure refrigerant and having an extremely simple and low cost design. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Said object is achieved by the features of claim  1  and an independent claim  11 . Since the forces originating from the power element and applied to the rod held between the power element and valve body as well as for the valve body closing spring and even forces resulting from a pressure rise upstream of the valve body now are applied as couple forces, as a result, said forces applied to the rod from both its ends act to rotate or to bend the rod. Thus, a large frictional resistance occurs when the rod tends to slide axially. The valve body is disabled to respond too sensitively to a pressure change of the high-pressure refrigerant. Furthermore, it is possible to achieve said stable operational behaviour of the expansion valve by an extremely simple and cheap structure. During normal and stable operation of the expansion valve said couple forces may not gain significant influence. In other words, only in case that both ends of the rod are loaded by oppositely directed, significant forces said couple forces increase the sliding resistance of the rod temporarily in order to stabilise the operation. This is the consequential effect of the couple forces tending to rotate or bend or displace the rod sidewardly in firmer contact with the wall of said penetrating bore guiding the rod. The structure is simple and cheap, because the structural measures for the generation of the couple forces can easily be realised in the design of the expansion valve without complicating its design or the work necessary to assemble the expansion valve. 
     Preferred embodiments are disclosed in the depending claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-section of the first embodiment of an expansion valve, 
     FIG. 2 is a longitudinal section of a second embodiment of an expansion valve, 
     FIG. 3 is a longitudinal section of a third embodiment of an expansion valve, 
     FIG. 4 is a longitudinal section of a fourth embodiment, 
     FIG. 5 is a longitudinal section of a fifth embodiment, 
     FIG. 6 is a partial cross-section of a variation of the fifth embodiment, 
     FIG. 7 is a partial cross-section of a second variation of the fifth embodiment, 
     FIG. 8 is a perspective view of a detail of the fifth embodiment, 
     FIG. 9 is a longitudinal section of a further variation of the fifth embodiment, 
     FIG. 10 is a longitudinal section of a further variation of the fifth embodiment, 
     FIG. 11 is a perspective view of a variation of a detail of the fifth embodiment, 
     FIG. 12 is a longitudinal section of a further variation of a detail of the fifth embodiment, 
     FIG. 13 is a perspective view of the further variation of the detail of the fifth embodiment, 
     FIG. 14 is a longitudinal section showing a further variation of details of the fifth embodiment, 
     FIG. 15 is a longitudinal section showing a further variation of a detail of the fifth embodiment, 
     FIG. 16 is a longitudinal section of a sixth embodiment, 
     FIG. 17 is a longitudinal section of a seventh embodiment, and 
     FIG. 18 is a longitudinal section of an eighth embodiment of an expansion valve. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 a refrigerant cycle, e.g. an air conditioning system for an automotive vehicle, comprises an evaporator  1 , a compressor  2 , a condenser  3 , an accumulator  4  connected to the outlet of the condenser  3  and an expansion valve  10 . 
     A valve casing  11  of the expansion valve  10  contains a low-pressure refrigerant duct  12  for passing low-temperature and low-pressure refrigerant gas as supplied from the evaporator  1  into the compressor  2  and a separate high-pressure refrigerant duct  13  for adiabatically expanding high-temperature and high-pressure refrigerant fluid supplied to the evaporator  1 . 
     Ducts  12  and  13  are approximately parallel to another. Perpendicular to both ducts  12 ,  13  a penetrating bore  14  extends between both ducts  12 ,  13  in valve casing  11 . Aligned with the penetrating bore  14  a power element  30  is installed into an opening of the valve casing  11 . Said opening extends from duct  12  to the outer side of the valve casing  11 . 
     Duct  13  is formed with a contraction in its middle portion so that a valve seat bore  15  is defined. In flow direction through duct  13  upstream of valve seat bore  15  a valve body  16  e.g. a spherical valve body, is associated to valve seat bore  15 . Valve body  16  is pre-loaded in closing direction against valve seat bore  15  by a compression coil spring  17  held in place by a spring receiver  18 . 
     Penetrating bore  14  receives rod  20  so that rod  20  is axially slidably guided in the direction of its shaft line. An upper end part of rod  20  reaches to the lower surface of power element  30 . A middle part of rod  20  crosses duct  12  and is in engagement With penetrating bore  14 . The lower end of rod  20  passes through valve seat bore  15  and contacts valve body  16 . The diameter of rod  20  in its portion penetrating valve seat bore  15  is smaller than the inner diameter of valve seat bore  15 . 
     Power element  30  is hermetically encapsulated by a housing  31  made of a thick metallic plate. Power element  30  contains a diaphragm  32 , e.g. made of a flexible and thin metallic plate, e.g. of stainless steel with a thickness of e.g. 0.1 mm. 
     In an upper chamber of power element  30  a saturated vapour gas is contained which might be the same gas as is used as the refrigerant flowing through ducts  12  and  13 . A plug  34  blocks a filling bore of power element  30 . 
     Against the lower surface of diaphragm  32  a large diaphragm receiver  33 , e.g. in the form of a plate, is disposed. The upper end part of rod  20  is contacting the lower surface of diaphragm receiver  33 . 
     In order to transmit the actuating force of power element  30  to rod  20  by couple forces or by a momentum or bending momentum an upper end part  21  of rod  20  is slightly bent sidewardly, e.g. with an angle of about 60° in relation to the shaft line of rod  20 . The, e.g. rounded end of end part  21  is contacting the lower surface of diaphragm receiver  33 . As long as valve body  16  is not seated on valve seat bore  15  rod  20  is loaded from both ends by the force of power element  30  and force of valve closure spring  17 . In the embodiment of FIG. 1 the central axis of diaphragm receiver  33  is aligned with an extension line of the shaft line of rod  20 . A point where the force of power element  30  is applied onto rod  20  or its end parts  21  is laterally offset with respect to the central axis of diaphragm receiver  33 . 
     Diaphragm receiver  33  has at least a refrigerant bore  40  controlling the transmission of low-pressure refrigerant to the lower surface of diaphragm  32  so that power element  30  is not affected by sudden temperature changes of the low-pressure refrigerant. If the temperature of the low-pressure refrigerant in duct  12  decreases, also the temperature of diaphragm  32  drops. The saturated vapour gas in power element  30  starts to condense on diaphragm  32 . Consequently, the pressure in power element  30  drops and diaphragm  32  is displaced upwardly. Rod  20 , loaded by compression coil spring  17 , follows the motions of diaphragm  32 . Valve body  16  moves towards valve seat bore  15  and reduces the cross-section for the high-pressure refrigerant flow. The flow rate of the refrigerant supplied to the evaporator  1  decreases. To the contrary, with raising temperature in duct  12  power element  30  presses down rod  20  moving valve body  16  away from valve seat bore  15 . The flow rate of the high-pressure refrigerant supplied to the evaporator increases. Due to the bent end part  21  of rod  20  the forces applied from power element  30  and compression coil  17  to rod  20  act as couple forces tending to rotate or bend rod  20  in a direction changing the direction of the shaft line. Since rod  20  is guided by the inner wall of penetrating bore  14  while  17  moves in the direction of its shaft line, as a result, extreme or temporarily increased frictional resistance occurs between rod  20  and penetrating bore  14 . In case that the pressure of the high-pressure refrigerant in duct  13  is varied, rod  20  due to the retarding sliding resistance does not sensitively respond. The switching operation of valve body  16  is stabilised. 
     In the second embodiment of the expansion valve  10  in FIG. 2 the diaphragm receiver  33  contacted by end part  21  of rod  20  is made of thick plastic material with low thermal conductivity. 
     In the third embodiment of the expansion valve  10  of FIG. 3 slightly bent end part  21  of rod  20  contacts diaphragm receiver  33  at the position of its central axis. However, the shaft line of rod  20  as well as penetrating bore  14  are laterally offset with respect to the central axis of power element  30 . At the centre of the lower surface of diaphragm receiver  33  a circular concave part  35  is formed receiving the tip of bent end part  21 . Between the opening of valve casing  11  containing housing  31  of power element  30  and duct  12  a guiding projection  11 ′ is formed for additionally guiding and laterally supporting rod  20 . 
     In the fourth embodiment of expansion valve  10  in FIG. 4 rod  20  is straight such that its upper end part is in line with its shaft line. The central axis of power element  30  is aligned with the shaft line of rod  20  as well. However, a misalignment between the central axis of power element  30  and shaft line of rod  20  also would be tolerable. Diaphragm receiver  33  is formed with a slanted abutment surface  36  contacting the upper, in this case rounded, tip of rod  20 . Said tip can be smoothly rounded or may have another shape like the shape of a cone or other kinds of shapes. Due to the slanted or inclined abutment surface  36  the force applied by power element  30  to rod  20  is forming couple forces. 
     In the fifth embodiment of expansion valve  10  of FIG. 5 further improvements are provided. Valve body  16  can be made of metal, and is, e.g. a stainless steel balls. The mouth of valve seat bore  15  can be conical. Compression coil spring  17  has a tapering shape such that its winding diameter is gradually decreasing towards valve body  16 . Spring  17  is made of metal like stainless steel. Valve body  16  may be directly fixed to the end winding of spring  17  by welding or the like. Due to this, valve body  16  cannot be lost from spring  17  during assembling. Furthermore, valve body  16  and spring  17  are easy to recycle in case that both their materials have the same quality. Spring receiver  18  of spring  17  is housed in a bore  19  the axis of which is aligned with the axis of valve seat bore  15 . Spring receiver  18  is press-fitted in bore  19 . Preparation of the fixation of spring receiver  18  does not create chips, because a threaded connection is avoided. Spring receiver  18  is of cylindrical form and has an inner closed end surface. The fixing position of spring receiver  18  is adjusted when assembling the expansion valve such that the spring force of compression coil spring  17  has a proper value. In order to secure airtightness for spring receiver  18  without using a seal means like an O-ring, a screw-lock or welding or the like can be used instead. The airtight fixation also could be achieved by a spring back effect when using a spring material for the spring receiver  18 . 
     The lower end of rod  20  has a V-shaped or similarly shaped concave depression  22  where rod  20  is contacting valve body  16 . As a result, valve body  16  does not lose contact with rod  20  and does not create vibration sound. Concave depression  22  can be, e.g. as shown in FIGS. 6 and 7, with a U-shape or a V-shape and a smaller diameter than the outer diameter of rod  20 . 
     In FIG. 5 the engagement length between rod  20  and penetrating bore  14  may be about 10 to 15 mm or more. The clearance of rod  20  in penetrating bore  14  is about 0.01 to 0.12 mm so that rod  20  is controlled to be loose. Said slide fit also controls or suppresses vibration sounds generated by valve body  16 . 
     Rod  20  is provided with a projecting part  23  higher up than an opening part  14   a  of penetrating bore  14  in duct  12 . Projecting part  23  can be formed by crushing or squeezing rod  20  laterally. Projecting part  23  hinders that rod  20  can slide down through penetrating bore  14 . This holds rod  20  stably during assembly. Opening part  14   a  can be shaped conically. 
     All parts of power element  30  can be made, e.g. of the same metallic material like stainless steel. When disassembling expansion valve  10  it is possible to recycle removed power element  30 . 
     As a variation of the fifth embodiment in FIG. 8 diaphragm receiver  33  is a plate having three leg parts  33   a  formed by bending. Diaphragm receiver  33  can be produced by pressing a board material. Slanted or inclined abutment surface or slope  36  is formed at the central portion of diaphragm receiver  33 . The angle of surface  36  in relation to the plane of diaphragm  32  lies within a range of about 5° to 25° 0 . If said angle would be larger or too large, the sliding force is increased and hysteresis might occur. A too small angle would lead to a negative effect. Leg parts  33   a  have to stabilise the posture of or have to guide diaphragm receiver  33  along an inner surface of housing  31  of power element  30 . Furthermore, by bending leg parts  33   a  downwardly from the plane of diaphragm receiver  33  notches are created serving as refrigerant ducts  40 . As shown in FIG. 9 the lower tips of leg parts  33   a  can be bent inwardly. Said measure avoids that leg parts  33   a  can be caught at the inner guiding surface of housing  31 . The movement of diaphragm receiver  33  in the direction of the shaft line of rod  20  becomes smoother. 
     In FIGS. 10 and 11 diaphragm receiver  33  is formed as a cap. Refrigerant duct  40  is formed as a small diameter bore. 
     In FIGS. 12 and 13 diaphragm receiver  33  is formed as the head of a rivet by forging or the like. The refrigerant duct  40  is formed as a groove in the lower surface of said rivet head and a flattened portion in the collar of diaphragm receiver  33  used to guide the linear motion of diaphragm receiver  33 . FIG. 12 shows that housing  31  of power element  30  has a bottom defining a guiding bore or guiding collar for the upper end part of rod  20  engaging at rod  20  distant from slanted or inclined surface  36  in the direction of the shaft line. Additional bores  38  allow the entrance of low-pressure refrigerant into housing  31  and further along duct  40  to the lower side of diaphragm  32 . A similar design is shown in FIG. 5, already. 
     In FIG. 5 housing  31  is formed with an engaging part  25  for engagement with the inner wall of the opening in valve casing  11 . Engaging part  25  forms a guiding collar  37  for the upper end part of rod  20  spaced apart in the direction of shaft line of rod  20  from inclined surface  36 . A sealing means  26  below housing  31  and in a groove of valve casing  11  can be used as well. Guiding collar or rod receiver  37  slidably engages rod  20  in order to control the slide fit of rod  20  and to avoid the generation of noise. Bores  38  in the bottom of housing  31  are provided for passing refrigerant with a small flow rate to the diaphragm  32  of power element  30 . Due to these variations of temperature and pressure of the refrigerant are transmitted slowly to diaphragm  32 . Therefore, the operation of expansion valve  10  does not change suddenly. 
     In FIG. 14 a bushing  131 , e.g. made of plastic or the like, is held between power element  30  and valve casing  11 . Bushing  131  is provided with bore  38 . 
     In FIG. 15 a symmetrical bushing  131  is provided as a middle part between power element  30  and the bottom of the opening receiving housing  31  of power element  30 . Due to the symmetrical shape of bushing  131  it can be assembled in any position facilitating assembling. 
     In the embodiment of FIG. 16 rod  20  is formed as a thickened pole in its portion extending through penetrating bore  14  and further upward to inclined surface  36 . Spring receiver  18  in this case is installed by a threaded connection in valve casing  11 . 
     In the embodiment of FIG. 17 rod  20  is short and extends only slightly into an upper widened portion of penetrating bore  14 . A thicker pole-shaped straight part  133  the shaft line of which is aligned with the shaft line of rod  20  or is in parallel line with it, extends through said widened portion and between the upper end of rod  20  and diaphragm receiver  33 . In FIG. 17 part  133  is unitary with diaphragm receiver  33 . The lower end surface of part  133  contacting the upper end of rod  20  is formed as a slope or inclined surface  36 ′. Forces transmitted between rod  20  and part  133  generate respective laterally directed forces due to inclined surface  36 ′. Said forces increase the sliding resistance of rod  20  and/or part  133  in penetrating bore  14 . 
     In the embodiment of FIG. 18 thicker pole-shaped part  133  is made of a material different from the material of diaphragm receiver  33 . Part  133  can be connected with diaphragm receiver  33  via a socket provided at the lower surface of diaphragm receiver  33 . 
     According to the invention the forces acting on both ends of rod  20  cause a longitudinal compression of said rod  20 . Due to the lateral offset between the point where the force of the power element is transmitted to the upper end of rod  20  and the shaft line where the rod is guided in penetrating bore  14  or in the guiding collar  37  and where the force of valve body  16  is applied, the sliding resistance of said rod at least temporarily is increased due to intentionally created lateral retarding forces. Temporarily means that this effect mainly takes place when the upwardly directed force of valve body  16  increases due to a pressure variation upstream of valve body  16  to then stabilise the operation behaviour of the expansion valve  10 . During normal operation said retarding forces need not necessary affect the operation. However, even during normal operation the stabilising effect can be used.