Abstract:
In a needle valve ( 1 ) for a high-pressure gas conduit system consisting of two units ( 2, 3 ) which are joined and one of which encloses a stepping motor ( 8 ) and the other includes gas flow passages and a gas flow control bore ( 17 ), a valve needle ( 10 ) is supported in the housing unit so as to be movable by the stepping motor and extends into the gas flow control bore ( 17 ) in the other housing unit through a guide passage ( 18 ) provided with seals to prevent gas from flowing to the housing unit including the stepping motor ( 8 ) between a region of the guide bore ( 18 ) and a low pressure region of the needle valve ( 1 ) a compensation connection is provided for relief of pressure at the sealing region ( 43 ) of the guide bore ( 18 ). The needle valve is particularly suitable as an expansion valve in an automotive CO 2  air conditioning system.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a needle valve for a high pressure gas line including a housing with a stepping motor to which a needle is connected to be operated thereby for controlling the gas flow through a control passage extending through the housing. 
   For controlling the expansion valve of air-conditioning systems, it is known from EP 0 607 953 and WO 00/70276 to arrange the valve drive or a part of the latter, which is connected mechanically to the valve needle, in a housing part, which is connected to the housing including the valve in a gas-tight manner. This method of sealing off the inner region of the housing relative to the outside presumes that the parts of the valve drive, such as, for example, the armature winding of the latter, are not attacked by the medium flowing through the expansion valve. Moreover, a high pressure-resistant design of the drive housing requires a housing of appropriate strength. 
   It is known, furthermore, from U.S. Pat. No. 3,464,227 and U.S. Pat. No. 4,556,193, to connect the shank of the valve needle or of the closing body of an expansion valve of an air-conditioning system to the housing in a gas-tight manner via a bellows. A bellows-type seal however is suitable only for relatively low gas pressures and, to be arranged in the housing block of the needle valve, requires a relatively large space. 
   It is the object of the invention to provide a valve which is as small as possible, that is, a valve which is suitable for high pressures and has flow connections in two opposite directions and which can be used as an expansion valve of an air-conditioning system operated with carbon dioxide, that is to say for pressures up to 150 bar. Moreover, it should be simple in design, easy to manufacture, and easy to mount in the conduit system of a vehicle air-conditioning system. 
   SUMMARY OF THE INVENTION 
   In a needle valve ( 1 ) for a high-pressure gas conduit system consisting of two units ( 2 ,  3 ) which are joined and one of which encloses a stepping motor ( 8 ) and the other includes gas flow passages and a gas flow control bore ( 17 ), a valve needle ( 10 ) is supported in the housing unit which includes the stepping motor so as to be movable by the stepping motor and extends into the gas flow control bore ( 17 ) in the other housing unit through a guide passage ( 18 ) provided with sealing means to prevent gas from flowing to the housing unit including the stepping motor ( 18 ). The needle valve is particularly suitable as an expansion valve in an automotive CO 2  air conditioning system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective illustration of the housing of a stepping-motor drive, including a valve needle, 
       FIG. 2  is a perspective illustration of the housing of the needle valve, for mounting to the stepping motor drive housing, 
       FIG. 3  is an overall perspective illustration of the needle valve with its mounting units according to  FIGS. 1 and 2  mounted together, 
       FIG. 4  is a cross sectional view of the needle valve according to  FIG. 3 , 
       FIG. 5  is a cross sectional view of another embodiment of the needle valve, 
       FIG. 6  is an enlarged partial illustration showing the area VI of the cross-sectional illustration of  FIG. 4 , with the valve needle in the uppermost position, 
       FIG. 7  is an illustration corresponding to that of  FIG. 6 , but with a modified version of the housing block and with the valve needle in the closing position, 
       FIG. 8  shows a side view of an exemplary embodiment of a valve needle differing from the valve needle shown in  FIGS. 6 and 7 , and 
       FIG. 9  shows a further exemplary embodiment of a valve needle. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   The needle valve  1  consists of two removably interconnected housing units  2  and  3 , the first of which consists of a valve housing  4  having a plurality of bores and is formed, for example, from a an extrusion molded member and is provided for the connection of pipe portions  5 ,  6  of a high-pressure gas conduit system. The second housing unit  3  is a drive housing  7  including a stepping motor  8  with a drive mechanism  9  for the valve needle  10  which is known per se. A drive nut, not illustrated, capable of being rotated by the motor  8 , engages an external thread  11  of the valve needle  10 . The valve needle is secured against rotation at its profiled upper end  12  and therefore is moved by the rotation of the nut in its longitudinal direction for valve actuation. The valve needle  10  is an integral part of the second mounting unit  3 . The two mounting units  2  and  3  can be assembled in a simple way to produce the ready-to-use needle valve  1 , as it will be described in more detail below. 
   The ends of the pipe portions  5 ,  6  are held in a gas-tight manner in pipe connection bores  13 ,  14  of the housing  4  by soldering according to the exemplary embodiment shown in  FIG. 5 . The connecting bores  13 ,  14  may also form a spigot receptacle for a releasably insertable pipe spigot of a pipe coupling with sealing rings, such as is described in detail in patent application DE 101 63 931.7. The connection bores  13 ,  14  merge into short valve conduits  15 ,  16  in the form of blind holes. These have a substantially smaller diameter and are transversely offset relative to one another, so that they overlap one another that is extend parallel to each other. A valve bore  17  forms a right-angled cross connection between these valve conduits. However, instead, the valve bore  17  may extend at an inclination to the valve conduits  15 ,  16 , for example in order to eliminate noise caused by the right-angled change in the direction of the flow. 
   In the exemplary embodiment according to  FIG. 4 , the transverse offset with coaxial connecting bores  13 ,  14  is achieved in that the valve conduits are disposed eccentrically to connecting bores  13 ,  14 , that is, they are axially offset. In the exemplary embodiment according to  FIG. 5 , the valve conduits  15 ,  16  extend coaxially with the connecting bores  13 ,  14  provided for the pipe portions  5 ,  6 , but the connecting bores are axially offset relative to one another. The capacity for the simpler production of coaxial bores  13 ,  16 ;  14 ,  15  has the disadvantage, however, that the housing  4 ′ cannot be mounted in different angular positions in relation to the axes of the pipe portions  5 ,  6 . 
   The valve needle  10 , which is drive-connected to the stepping motor  8 , extends into the housing  4  through a guide bore  18  extending co-axially with the valve bore  17 . The stepping motor makes it possible to adjust the valve needle continuously in the guide bore  18 , so that the free opening cross-section of the valve bore  17  can be changed continuously between a minimum and a maximum value. 
   The inner region of the housing  4  formed by the bores  15 ,  16  and the central guide bore  18  are sealed relative to the outside in the region of the guide bore  18  by providing at least one sealing ring  19 ,  20 . 
   In order to achieve good sealing with respect to carbon dioxide, which is under high pressure, at a relatively low outlay in structural terms without excessive frictional resistances occurring during the adjusting movement of the valve needle, two O-rings  19 ,  20  are provided at a distance from one another and are preferably held in peripheral grooves  21 ,  22  of the valve needle  10 . 
   In the exemplary embodiment according to  FIG. 7 , the receiving grooves  23 ,  24  for two O-rings  25 ,  26  are provided in the guide bore  18 , but this leads to higher expenses for the machining of the valve housing  4  and to a somewhat larger diameter of the O-rings  25 ,  26 . 
   The sealing in the region of the guide bore  18  by means of O-rings  19 ,  20 ;  25 ,  26  also has the advantage of a substantially easier mounting of the needle valve  1  in a gas conduit system for example in the engine compartment of a motor vehicle, in that, during the mounting of the gas conduit system, first only the valve housing  4  has to be inserted between two pipe portions  5 ,  6  and the needle valve  1  can then be completed by mounting the drive housing  7  already connected to an electrical lead  28  in place and, at the same time, inserting the valve needle  10  into the guide bore  18 . Finally, a firm connection is established by four screws  29  which extend through corner regions of the drive housing  7  into correspondingly arranged threaded holes of the housing  4 , so that the flange surfaces  30 ,  31  of the two housings  4 ,  7  come to bear firmly against one another. 
   The guide bore  18  may extend up to the flange surface  31  facing the drive housing  7 , which thus supports and guides the valve needle  10 . As shown in the exemplary embodiment, the valve housing  4  may be provided with a socket  32  of larger diameter for receiving a cylindrical housing extension  33  of the drive housing  7 , the housing extension containing part of the drive mechanism  9  of the stepping motor  8 . The latter version is preferred, since the drive housing  7  can thereby be smaller. Sufficient space for a correspondingly larger socket  32  is available in the valve housing  4  if engagement bores  34 ,  35  are provided in the valve housing  4  for the fastening of the side flange of a pipe coupling adjoining the pipe portions, according to patent application DE 101 63 931.7. 
   In order to provide for a small sealing surface area, that is a small area along which frictional sealing contact is necessary, so that the stepping motor, together with its housing  7  surrounding the drive system, can also be made small, the valve needle  10  and consequently also the guide bore  18  are provided with as small a diameter as possible. If there is no need for a completely leak-tight closing of the needle valve  1 , for example when it is used as a controllable expansion valve of a CO 2  air-conditioning system, the guide bore  18  preferably also has as small a diameter as possible like the valve bore  17 . For providing a sealing seat by means of a conical end region  36  of the valve needle  10 , the guide bore  18  may only be larger in diameter by 15 to 20% than a corresponding diameter of the cylindrical head part of the valve needle  10 . 
   Since there is no need for a complete closing of the expansion valve if a needle valve  1  is used as an expansion valve of an air-conditioning system, the diameter of the valve bore  17  and consequently also of the guide bore can be as shown in the exemplary embodiment of  FIG. 7  where a part-flow is conducted past the valve bore  17  through a bypass passage  37 . In this connection, for example, the bore of the valve conduit  16  located at the low-pressure side extends co-axially with a substantially smaller diameter, into the bottom area  38  of the opposite connecting bore  14  ( FIG. 4 ). 
   Furthermore, a bypass connection  42  may also serve for relieving the sealing region of the guide bore  18 , in that, within the guide bore  18  ( FIG. 7 ) and/or at a corresponding location an the valve needle  10 ″, a peripheral groove  40  or  41  which is in communication via a bore  42  with the end area  43  of the low pressure connection bore  13 . Instead, or in addition, a bypass passage  39  may also extend through the valve needle  10 ′, as shown in the cross-sectional illustration of  FIG. 9 . 
   The diameter of the valve bore  17  and consequently also that of the guide bore  18  can further be made as small as possible if the valve needle  10  can be moved with its tapered front end  36  fully out of the valve bore  17 , so that the latter can be completely opened. 
   Finally, the through-flow of the valve bore  17  can be improved by a conical or curved design of its orifice edges  27 ,  27 ′, so that a better utilization of the cross-sectional size of the valve bore  17  is obtained. Also, as a result, noises caused by the throttling of the flow in the region of the valve duct  17  can be reduced or eliminated in this way. 
   For pipe systems which, together with their electrical connections  28 , may be damaged, for example, due to a crash, so that the out-flowing medium could cause damage, the housing  7  of the stepping motor  8  may include an emergency power-generating system  44  with an electrical energy storage and with control electronics, which are programmed, in the event of an interruption in a main power supply for the stepping motor  8 , to energize the motor for closing the needle valve  1 .