Patent Abstract:
A control valve for installation in a wobbleplate compressor with a changeable working volume is provided with an inlet for a connection to a pressure chamber, a first outlet for connection to a crank chamber, and a second outlet for connection to a suction chamber. A closing element cooperates with the second outlet and is acted upon by a device for controlling the gas mass flow.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of German Application No. 101 35 727.3, filed Jul. 21, 2001. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a control valve for installation in a wobbleplate compressor with a changeable working volume, and that has an inlet for connecting it to a pressure chamber of the compressor. A first outlet is connectable to a crank chamber of the compressor. A closing element and means for acting upon the closing element are provided. The present invention is also directed to a wobbleplate compressor with a changeable working volume, in particular for use in a motor vehicle air conditioning system. 
     Wobbleplate compressors are used a great deal in vehicle air conditioning systems where they compress the cooling agent from the evaporator before it is supplied to a heat exchanger. Among other things, these rugged compressors have the advantage that they can also be used for compressing CO 2 , which for environmental reasons has mostly replaced the fluorinated hydrocarbons used in the past as cooling agents. 
     Different types of cooling agents, such as CO 2 , will in the future replace the cooling agents used so far, for example R134a, for environmental reasons. Since CO 2  must be compressed considerably more as compared to the cooling agents used so far, for example by a factor of 10, to obtain a comparable cooling output, the requirements with respect to the seal between the compressor housing and the environment, for example, and the control requirements, will also increase considerably. 
     Modern automobiles for the most part use wobbleplate compressors with a changeable working volume. For this usage, the wobbleplate is pivotally attached to a drive shaft, so that the angle of the wobbleplate with respect to the drive axis is changeable. By changing this angle, the working volume and—with a given revolutionary speed—the compressor output is changed. As a rule, the change in the angle is achieved by changing the inside pressure of the crankshaft housing, i.e., the crank chamber. 
     A wobbleplate compressor and a control valve for controlling and regulating the crank chamber pressure is known from reference EP 0 748 937 A2. The valve of this publication is an electromagnetic two-way valve, which connects a pressure chamber to the crank chamber through bores. The pressure of the crank chamber pressure is changed by opening and closing this valve. In principle, the known device can be used for controlling the crank chamber pressure, but a high control speed cannot be achieved with this device. A high control speed, however, is of considerable importance for many application cases. 
     SUMMARY OF THE INVENTION 
     Starting with this prior art, it is an object of the invention to modify a control valve for a wobbleplate compressor in such a way that it is possible to achieve a high control speed. This object is solved with a control valve having a second outlet for connecting it to a suction chamber of the compressor. A closing element cooperates with the second outlet. The object is also achieved with a wobbleplate compressor having such a control valve. 
     According to the invention, a three-way control valve is used, which has an additional outlet that is connected to the suction chamber. This additional outlet only is acted upon by a closing element, which means that the passage between the pressure chamber and the crank chamber is continuously opened. By opening and closing the output leading to the suction chamber, low pressure is “added to” the existing high pressure. A quick control is possible because the pressure differences in that case are very high. 
     Means for acting upon the closing element can include a coil and an armature that can move inside the coil. Thus, the closing element is indirectly acted upon by electromagnetic forces, which also contributes to a high control speed. 
     With a control valve having a coil that is supplied with an alternating voltage having a frequency above 100 Hz, and preferably approximately 500 Hz, a type of swimming control state can be obtained. Thus, the outlet connected to the suction chamber will never be quite open and never be quite closed. This contributes to a further increase in the control speed. 
     The wobbleplate compressor may have a safety valve, which connects the crank chamber to the suction chamber if the differential pressure between the crank chamber and the suction chamber exceeds a predetermined value. This configuration provides for particularly high operational safety. 
     The wobbleplate compressor may have piston rings arranged on the pistons. Further, the piston stroke may be larger than the piston diameter. Moreover, a pressure above 100 bar, preferably approximately 140 bar, may be generated on the high-pressure side. Further, the wobbleplate compressor may have a working volume of approximately 25-30 cm 3 . Such a compressor is particularly suitable for use with a CO 2  air conditioning system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view through a wobbleplate compressor, wherein the valve according to the invention is shown schematically. 
     FIG. 2 is a schematic representation of a three-way valve according to the present invention. 
     FIG. 3 is a schematic representation of a safety valve according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a wobbleplate compressor, used in particular in a motor vehicle. A housing  10  includes a crank housing  12 , a cylinder block  14  and a cylinder head  16 . Inside the crank housing  12  is a crank chamber  22 , in which a wobbleplate  32  is arranged such that it can swivel on the shaft  32 A. The wobbleplate  32  is connected via sliding blocks to a piston  34  to drive the piston. Although not shown, there may be a plurality of pistons  34 . By changing the angle of inclination of the wobbleplate  32 , the working volume and thus—with a given rotational speed—the output of the wobbleplate compressor is changed. For example, if the wobbleplate  32  is positioned perpendicular to the shaft  32 A, the working volume is zero. 
     The suction chamber  26  is located inside the cylinder head  16  and is connected to a cooling agent evaporator, which is not shown herein. The decompressed gas travels via inlet valve  42  from the suction chamber  26  into the cylinder  24 . From there, the gas is pushed with a corresponding piston movement through outlet valve  44  and into the pressure chamber  27 , which in turn is connected to a heat exchanger that is not shown herein. 
     The piston  34  is provided with a circumferential groove or grooves for accommodating piston rings  35 . The respective piston rings  35  are preferably made from gray cast iron. The piston rings generate the pressures needed for a CO 2  air conditioning system. 
     The wobbleplate compressor may be configured for use in a CO 2  air conditioning system, by providing the piston stroke to be larger than the piston diameter. For example, the piston stroke can be 21 mm while the piston diameter is 16 mm. When six cylinders are provided, the total working volume of the six cylinders thus amounts to approximately 25 cm 3 . During the operation, a pressure of approximately 140 bar exists on the high-pressure side, while a pressure of approximately 40 bar exists on the suction side. The tilting of the wobbleplate  32  (and thus also the working volume) is controlled via the pressure in the crank chamber  22 . In this case, it is true that the larger the working volume, the lower the pressure inside the crank chamber  22  and vice versa. 
     The control valve  60  is used to control the crank chamber pressure. This valve is a three-way valve with the following connections: an inlet  63 , a first outlet  61  and a second outlet  62 . The inlet  63  is connected via a pressure line  53  of a passage to the pressure chamber  27 . The first outlet  61  is connected via the control line  51  of the passage to the crank chamber  22 . The second outlet  62  is connected via the suction line  52  to the suction chamber  26 . 
     As shown in FIG. 2, the effective diameter of the second outlet  62  is controlled with the first ball  67 . As a result of the pressure conditions, the first ball  67  is pushed onto the valve seat  68 , so that the second outlet  62  is closed if no counter force is acting upon the ball. 
     The first ball  67  can be pushed away from the second outlet  62  by means of a tappet  66 . The tappet  66  is connected to an armature  65 , which in turn is enclosed by a coil  64 , so that a change in the coil current results in a linear movement of the armature  65  and thus also the tappet  66 . By controlling the coil current, the effective diameter of the second outlet  62  can thus be controlled. The coil is preferably actuated with a frequency of approximately 500 Hz, so that a so-called “swimming control condition” results. In this case, the second outlet  62  is never quite fully opened and never quite fully closed. The average effective opening is controlled via the amount of coil current. This high-frequency operation further increases the control speed that can be achieved. 
     The pressure chamber  27  and the crank chamber  22  are constantly connected, i.e. in constant fluid communication, with the aid of the 3-way valve. The crank chamber pressure is controlled in that a portion of the gas mass flow, flowing from the pressure chamber  27  to the crank chamber  22 , may be branched off into the suction chamber  26 . If the valve is opened wide, a great deal of gaseous cooling agent flows off into the suction chamber  26 , thus causing the pressure inside the crank chamber  22  to sink. Due to the high pressure difference between pressure chamber  27  and suction chamber  26 , correspondingly high flow speeds for the gas are generated, which leads to a correspondingly fast pressure drop inside the crank chamber  22  and thus to a high control speed. 
     A safety valve  70  is preferably arranged between the suction line  52  and the control line  51 , or directly between the suction chamber  26  and the crank chamber  22 . This safety valve  70  has a purely mechanical design, so that even if there is a failure in the electronic system, any excess pressure is prevented from accumulating inside the crank chamber  22 , which could lead to damage to the compressor. 
     FIG. 3 shows one exemplary embodiment of the safety valve  70 . A second ball  76  is pushed by means of a pressure spring  74  onto a saddle  72 . The pressure spring  74  in this case counteracts the pressure drop between crank chamber  22  and suction chamber  26 . If the pressure difference exceeds a predetermined value, then the pressure spring  74  is compressed and the second ball  76  is thus lifted off the saddle  72 . Excess pressure in the crank chamber  22  is discharged to the suction chamber  26  until the level falls below the predetermined pressure difference value and the safety valve closes again. 
     The lines and valves are shown only schematically in FIG.  1 . However, the lines may be formed as bores in the housing  10  and the valves may be arranged inside the housing. 
     It should be understood, however, that the invention is not necessarily limited to the specific process, arrangement, materials and components shown and described above, but may be susceptible to numerous variations within the scope of the invention. 
     It will be apparent to one skilled in the art that the manner of making and using the claimed invention has been adequately disclosed in the above-written description of the preferred embodiments taken together with the drawings. 
     It will be understood that the above description of the preferred embodiments of the present invention are susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

Technology Classification (CPC): 5