Abstract:
A solenoid valve, in particular for a fluid-regulated heating and/or cooling system, including a valve housing having at least one feed channel and at least one discharge channel and an electromagnetically switched valve member which establishes the connection between the feed channel and the discharge channel in one switch position and blocks it in the other switch position. The valve member is rigidly connected to an armature which may be moved by displacing fluid in a guide bushing of a magnet coil, the guide bushing being inserted into an expanded part of an opening of the magnet coil which is delimited by an annular shoulder. A damping disk surrounding the armature is situated between the annular shoulder and an adjacent face end of the guide bushing.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a solenoid valve. 
   BACKGROUND INFORMATION 
   Solenoid valves of this type are used in motor vehicles in particular, for example, in fluid-regulated heat exchangers of their heating and/or air conditioning systems or as switching valves that short-circuit a coolant stream from an internal combustion engine of the motor vehicles in one of the two switch settings and in the other guide it across a heat exchanger. The solenoid valves may be activated by clock pulses as a function of the particular temperature in the heating and/or air conditioning system or in a passenger compartment of the motor vehicle, the flow rate being essentially determined by the mean time area. The valve member is opened by the fluid pressure and/or a valve spring acting on a valve shaft and is closed by excitation of the magnet coil acting on the armature. The space in which the armature is situated is not hermetically sealed but is instead filled with fluid. This fluid is intended to dampen the movement of the armature hydraulically in order to prevent the valve from opening or closing abruptly, thus reducing the noise associated with this. Due to the relatively large play required between the armature and the guide bushing for equalizing the tolerance between the components of the entire valve, the hydraulic damping produced by the fluid and accordingly the noise-reducing effect is, however, relatively low. 
   To reduce the noise produced when closing the valve, the applicant in European Published Patent Application No. 0 958 155 already described providing means on the side of the valve shaft facing the valve member which decelerate the speed of the valve shaft when the valve member is closed. Such means may be, among other things, formed by a damping disk which is attached to the valve shaft and is guided with low play in a fluid-filled chamber of the valve housing. Each time the valve member moves, the fluid must flow through a narrow annular gap between an outer circumference of the damping disk and an adjacent wall part of the valve housing, which slows the movement of the valve shaft. However, the provision of the damping disk and the chamber result in increased expense in manufacturing the solenoid valve. In addition, relatively close tolerances must be adhered to, which is difficult if low-priced components are used due to the temperature differences of the fluid when operating the valve in heating and/or air conditioning systems. 
   SUMMARY OF THE INVENTION 
   In the solenoid valve a very low play in the annular gap between the armature and its guidance is achieved using the simplest structural means and without limiting the movability of the armature in the area of the damping disk. The damping disk thus increases the hydraulic damping considerably and consequently reduces the production of noise. In this connection, the damping disk performs a function similar to that of a piston ring of a piston-cylinder array by providing a stronger seal for the annular gap and accordingly increasing the flow resistance when displacing fluid past the armature without negatively influencing the forces needed for moving the armature. 
   In a preferred embodiment of the present invention, an annular gap is provided between an inner circumference of the damping disk and the armature, forming the only flow path for the displaced fluid in the area of the damping disk, the annular gap having a clearance of less than 0.04 mm and preferably less than 0.025 mm at least over a part of and expediently over the entire length of the displacement path of the armature. 
   Another advantageous embodiment of the present invention provides that the damping disk is to a limited degree axially movable between the annular shoulder and the adjacent face end of the guide bushing. This has the result that the outer circumference of the damping disk, which is advantageously situated in the radial of the inner wall of the expanded part of the opening, is pressed against the face end of the guide bushing or the annular shoulder by the fluid displaced by the armature over at least a part of the displacement path of the armature, thus preventing the fluid from flowing around the damping disk. 
   The damping disk may be slotted or unslotted and is preferably made of bronze; however, in principle it may be manufactured from a suitable synthetic material, polypropylene sulfide, for example. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a cross section of a solenoid valve in its energized closed position. 
       FIG. 2  shows a cross section of the solenoid valve in its de-energized open position. 
       FIG. 3  shows an enlarged detail view of section III from  FIG. 1 . 
       FIG. 4  shows an enlarged detail view of section IV from  FIG. 2 . 
   

   DETAILED DESCRIPTION 
   Solenoid valve  2  shown in the drawing situated between a heating and/or cooling circuit of an internal combustion engine and a heater core of a motor vehicle (not shown) has a valve housing  4  having a feed channel  6  connected to the cooling circuit of the internal combustion engine and a discharge channel  8  connected to the heater core. Within valve housing  4  is located a movable valve member  10  which has a valve cone  12 , which in the closed position of valve  2  shown in  FIG. 1  interacts with a valve seat  14  in housing  4  and blocks the connection between feed channel  6  and discharge channel  8 . 
   Valve member  10  is attached to an elongated hollow valve shaft  16  which projects from valve housing  4  into a pot magnet  18  fastened onto valve housing  4  with sealing effect. Pot magnet  18  encloses a cylindrical magnet coil  20  which is wound on a coil former  22  manufactured from plastic by injection molding. Coil former  22  has an axial opening  24  for valve shaft  16 , to the upper end of which an armature  26  is attached. Armature  26  interacts with magnet coil  20  and with an armature core  28  mounted in a lower part of opening  24 , thus forming an electromagnetic actuator for the axial displacement of valve member  10 . 
   As long as no power for excitation is fed to magnet coil  20 , the fluid pressure prevailing in the heating and/or cooling circuit of the motor vehicle and accordingly also in feed channel  6  presses valve member  10  into the open position shown in  FIG. 2 . In the open position, in which the upper face end of valve shaft  16  is in contact with a stop  30  placed above opening  24  in pot magnet  18 , valve cone  12  is lifted off from valve seat  14  and the connection between feed channel  6  and discharge channel  8  is opened. As soon as magnet coil  20  is excited by current feed, armature core  28  pulls armature  26  downward into the closed position shown in  FIG. 1  against the fluid pressure in feed channel  6  and against the force of a valve spring  34  inserted between armature  26  and armature core  28 . 
   In addition to magnet coil  20 , armature core  28 , valve spring  34  and valve shaft  16  including armature  26 , pot magnet  18  further encloses a guide bushing  36  for armature  26  situated in opening  24  of coil former  22 . The open space remaining between components  16 ,  20 ,  26 ,  28 ,  34  and  36  in the interior of pot magnet  18  is filled with fluid from the heating and/or cooling circuit during the operation of solenoid valve  2 , the fluid being drawn up through a narrow annular gap between valve stem  16  and the inside wall of a valve stem bore  38  in armature  28  by the application of a partial vacuum, i.e., as a consequence of a pumping action of armature  26  moved up and down while displacing air into the open space. 
   Cylindrical guide bushing  36  used for guiding armature  26  is inserted from above into an expanded upper part  40  of stepped opening  24  of coil former  22  and in the open position surrounds an upper cylindrical part of armature  26  at a radial distance, which may not be reduced as desired due to the manufacturing and assembly tolerances of components  12 ,  14 ,  16 ,  28 ,  26 ,  36 . As shown best in  FIGS. 3 and 4 , its lower face end  42  is situated at an axial distance of approximately 0.5 to 1.5 mm above an annular shoulder  44 , which limits expanded part  40  of opening  24  of coil former  22  toward the bottom. Annular shoulder  44  is adjoined toward the bottom by a narrowed part  46  of opening  24 , into the lower end of which armature core  28  is fitted. The upper end of narrowed part  46  of opening  24  accommodates the part of armature  26  projecting from guide bushing  36 , the tapering lower end of which has a conical outside circumference. In the open position of valve  2  ( FIG. 4 ), transition  48  between the cylindrical circumferential surface of the upper part and the conical circumferential surface of the lower end of armature  26  is located at a small axial distance below lower face end  42  of guide bushing  36 . 
   Due to the relatively large radial play present between guide bushing  36  and armature  26  for tolerance equalization, the hydraulic damping of armature  26  is relatively low in its axial movement in guide bushing  36 . In order, however, to avoid abrupt opening or closing of valve  2  and accordingly to minimize noise caused by opening or closing, a damping disk  50  surrounding armature  26  is situated between annular shoulder  44  and adjacent face end  42  of guide bushing  36 . At this point, damping disk  50  should provide a reduction of the cross-sectional dimensions of an annular gap  52  between armature  26  and its guidance, as a result of which a portion of the fluid enclosed in pot magnet  18  is displaced past armature  26  each time it is moved axially. 
   As is also best shown in  FIGS. 3 and 4 , damping disk  50  has a circular bore for armature  26 , the inside diameter of which above the stroke of armature  26  is adapted to the outside diameter of its upper cylindrical part, so that an annular gap  54  formed between the inner circumference of damping disk  50  and the outer circumferential surface of armature  26  has a very small clearance of approximately 0.02 mm. In contrast, an annular gap  56  formed between the outer circumference of disk  50  and the inner circumference of the expanded part of opening  24  has relatively large dimensions so that disk  50  is axially movable in the fluid in the intermediate space between annular shoulder  44  and lower face end  42  of guide bushing  36 . 
   Damping disk  50  has two flat broad surfaces which are diametrically opposed to a complementary flat lower face of guide bushing  36  or a complementary flat annular surface of annular shoulder  44 . Furthermore, damping disk  50  may be radially or obliquely slotted at a point along its circumference similar to a piston ring of a piston of an internal combustion engine in order to avoid tolerance problems. 
   Damping disk  50  is preferably made of bronze; however, it is in principle also possible to use other metals or plastics, such as polypropylene sulfide (PPS), for example. 
   When armature  26  is moved downward into the closed position, the fluid displaced by armature  26  presses damping disk  50  upward so that its upper broad surface is in contact with the adjacent lower face of guide bushing  36  with sealing effect and the displaced fluid is only able to pass through narrow annular gap  54  between the inner circumference of damping disk  50  and the outer circumference of armature  26 , which produces a strong hydraulic damping of armature  26 . When armature  26  is moved upward into the open position, damping disk  50  is pressed downward against annular shoulder  44  in the opposite direction by the fluid displaced by armature  26 , so that its lower broad surface is in contact with annular shoulder  44  with sealing effect and forces the displaced fluid through annular gap  54 , as a result of which this movement of armature  26  is subject to strong hydraulic damping. 
   In comparative tests in which the production of noise was measured when closing a solenoid valve  2  without or with a damping disk  50 , it was therefore possible as expected to detect a considerable noise reduction when damping disk  50  was used. 
   The characteristic curve of the hydraulic damping of armature  26  and accordingly of valve member  10  may be changed as desired by changing the internal diameter of damping disk  50  or the shape of the outer circumferential surface of armature  26 , which moves past damping disk  50  between the closed position and the open position. For example, a narrowing situated in the center of this area and extending over a part of the displacement path of armature  26  would provide greater play between damping disk  50  and armature  26  over the height of the narrowing and accordingly a less severely decelerated movement of armature  26  over a middle portion of the distance between the closed position and open position.