Abstract:
A valve has a chamber ( 11 ) in a housing ( 10 ), in which the valve seat ( 17 ) is closed by a valve body ( 19 ). The valve seat ( 17 ) is supported by an actuator ( 15 ) which is capable of axially expanding and contracting. In response to an actuating signal the actuator ( 15 ) contracts which causes the valve seat ( 17 ) to move away from the valve body ( 19 ) so rapidly that the valve body ( 19 ) is not capable of following, which produces a flow passing through the valve seat ( 17 ). The flow pushes the valve body ( 19 ) back into the closed position. The valve allows short switching times and a high repetition rate to be achieved.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a quick-acting valve having a chamber which comprises an inlet opening, an outlet opening and a valve seat which can be closed with a movable valve body. 
     For certain applications quick-acting valves are required which are capable of permitting a fluid flow to pass abruptly through them as well as allowing a high switching rate. Applications for such valves are for example spectrometers where gas samples of precisely measured volumes are subjected to a spectrographic examination, the energizing of the control nozzles of satellites and the field of microsystem technology. For such applications valves with extremely short switching times and high repetition rate are required. 
     DE 38 35 788 A1 describes a quick-acting ball valve comprising a ball seated in a valve seat. An actuator device acting transversely to the valve seat allows the ball to be removed from the valve seat by a lateral impact. The resultant flow pushes the ball back to the valve seat. This quick-acting valve has turned out to be successful in practical application. 
     In the journal O+P “Ölhydraulik und Pneumatik” 38 (1994), no. 9, pages 554-562, employment of piezoelectric actuators for quick-acting actuating drives are described. Piezoelectric actuators are used for example in dosing units for fluids with the actuator being attached to a nozzle tube which injects the fluid into an air jet. In this way quick-acting dosing devices suitable for various viscosities and droplet rates can be realized. 
     In the journal VDI-Z 119 (1977), no. 11-June (1), pages 569-570 a valve for fuel injection is described where a piezoelectric rod expands and contracts to control the valve opening process according to the pulse duration/modulation principle. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to provide a quick-acting valve which is improved with regard to short switching times, high repetition rate and numbers of cycles limiting the service life. 
     According to the invention this object is solved in accordance with the features stated in claim  1 . 
     In the valve of the invention the valve seat is connected with an actuator which, when being operated, moves the valve seat and removes it from the valve body at such a high acceleration rate that the valve body is not capable of following and is lifted off the valve seat. The passage of the valve seat is opened for a short defined period until the valve body returns to the valve seat under the force exerted by the flowing medium and closes it. Then the actuator sets the valves seat which is closed by the valve body back to its initial position so that the next cycle can be carried out. 
     The quick-acting valve of the invention may be configured in such a way that short switching times in the order of max. 100 μs are realized. In the practice repetition rates of 400 to 1000 Hz have been attained. The response rate and the repetition rate depend, of course, on the overall size of the valve and in particular on the mass of the valve body. The valve body should have a low density which results in a small mass. The valve body may for example be executed as a hollow body. 
     The valve of the invention is in particular provided for controlling gases. It may however also be used for controlling fluids. For example, the valve is suited for fuel injection in internal combustion engines. 
     The actuator supporting the valve body is preferably executed as piezoelectric contraction body which contracts in response to an actuating signal. Alternatively, the actuator may for example also operated as an electromagnetic unit. It is essential that a high acceleration of the valve seat is achieved for a short period, which is higher than the acceleration of the valve body subjected to the medium pressure. 
     A particular advantage of the valve according to the invention is the low wear rate of valve body and valve seat. Since the valve seat moves away from the valve body in axial direction and subsequently takes up the valve body also moving ing axial direction, the impact forces are distributed annularly onto the valve seat and the valve body. For further wear reduction the actuator is controlled in such a way according to the invention that, in response to an actuating signal, it moves the valve seat quickly and then more and more slowly in order to smoothly catch the ball lifted off the valve seat. 
     A ball may be used as valve body. However, the invention is not limited to this configuration, it is rather also possible to use a conical or similarly shaped valve body. 
     In the following embodiments of the invention are explained in detail with reference to the drawings in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic longitudinal section of a quickacting valve of the invention, 
     FIG. 2 shows a section of the actuator, 
     FIG. 3 shows a time diagram of the movement of the valve seat in response to an actuating signal, 
     FIG. 4 shows a second embodiment of the chamber containing the valve body, 
     FIG. 5 shows another embodiment of the valve of the invention and 
     FIG. 6 shows an embodiment where the actuator acts in the plane of the valve seat. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to FIG. 1 the valve comprises a housing  10  encircling a chamber  11  which is closed towards the environment. The chamber  11  comprises an inlet opening  12  and an outlet opening  13  which are arranged along a common axis. The inlet opening  12  is connected to a pressure source (not shown) for the medium to be controlled, while the outlet opening  13  is connected with the consumer. 
     On the housing  10  the bottom wall  14  surrounding the outlet opening  13  an actuator  15  is arranged through which an outlet duct  16  passes which is connected with the outlet opening  13 . To the actuator  15  a valve seat  17  is attached, said valve seat comprising a disk, preferably made of metal, provided with a central porthole  18 . On said porthole  18  the valve body  19  is seated which is configured here as a ball sealingly closing the porthole. The valve seat  17  and the actuator  15  form a unit sealingly connected with the housing  10 . The valve body  19  is arranged coaxially to the inlet duct  12  and is located in an extension of the chamber  11  which the extension serving as receiving chamber  11   a  for the valve body  19 . The diameter of the receiving chamber  11   a  is at maximum 5 times the diameter of the valve body  19 . This ensures that a flow passing through the receiving chamber  11   a  centers the valve  19  relatively to the porthole  18  from any position so that the valve body is moved by the fluid flow into its closing position. 
     FIG. 2 shows a schematic section of the actuator  15 . Said actuator is a piezoelectric contraction body made up of a plurality of piezoelectric layer  20  arranged in parallel between which thin metal sheets  21  are located. Every second sheet  21  is connected with a first electrical line  22  and the intermediate sheets are connected with a second electrical line  23 . In this way a plurality of capacitors with piezoelectric material as dielectric material are formed. When a voltage is applied to lines  22  and  23 , the piezoelectric layers  20  expand. When the voltage is reduced or cut off, these layer contract. 
     The valve shown in FIG. 1 operates as follows: In the idle state a voltage is applied to the lines  22 ,  23  of the actuator  15 , which causes the actuator to assume the expanded condition. Owing to this the valve seat  17  is maintained at a given level in the chamber  11 . The valve body  19  obturates the porthole  18  of the valve seat so that the pressurized medium at the inlet opening  12  cannot flow to the outlet opening  13 . In response to an actuating signal the voltage at the actuator  15  is reduced so that the actuator  15  contracts in axial direction. This causes the valve seat  17  to move away from the valve body  19  in axial direction. The valve body  19  remains in the previously assumed position due to its mass inertia. This causes the porthole  18  of the valve seat  17  to be opened and the fluid to flow around the valve body  19  and passing via the porthole  18  through the valve. Due to the effect of said flow the valve body  19  is moved towards the valve seat  17  and then closes the porthole  18  again. When the valve body  19  has reached the valve seat  17 , the actuator  15  expands again so that the valve seat and the valve body return into the initial position shown in FIG.  1 . 
     The valve does not only operate in the vertical position shown in FIG. 1 but also in any other orientation. The reason for this is that the forces exerted by the flow which push the valve body  19  back to the valve seat  17  are considerably larger than the gravity given a sufficient pressure difference prevails between the inlet  12  and the outlet  13 . 
     Contrary to the embodiment shown in FIG. 1 it is also possible to arrange the actuator  15  at the upper side of the housing wall and the valve seat  17  at the lower side of the actuator. In this case the actuator is temporarily expanded for the purpose of moving the valve seat  17  away from the valve body  19 . 
     Control of the actuator  15  is effected by a control unit (not shown) to which the actuating signal is fed. FIG. 3 shows the position x along the ordinate, which is assumed by the valve seat  17  in axial direction in the housing  10 . Along the abcissa time t is plotted. At time to the actuating signal is generated. This causes the actuator  15  to contract rapidly until time t 1  has been reached. The interval between t 0  and t 1  is the valve opening time. Then the actuator  15  is further contracted duing a catching period which continues up to time t 2 , but this contraction takes place at a considerably lower velocity. During the catching period extending from t 1  to t 2  the valve body  19  is smoothly taken up by the valve seat  17  so that a heavy impact is prevented and the wear rate reduced. At time t 3  the return phase begins in which the actuator  15  slowly expands again and it reaches its initial position at time t 4 . Then the valve is ready for performing a new opening cycle. 
     FIG. 4 shows another embodiment of the valve where the shape of the receiving chamber  11   a  containing the valve body  19  differs from that shown in FIG.  1 . In this case the receiving chamber  11   a  is executed as a sphere or a semisphere whose central point is located approximately at the central point of the valve ball when the latter is seated on seat  17 . In the wall of the receiving chamber uniformly distributed openings  25  are arranged through which the medium can flow towards the ball. 
     First the inlet opening  11  leads into a distribution chamber  26  out of which the medium flows through the openings  25 . The spherical configuration of the receiving chamber  11   a  offers the advantage of improved centering of the valve body  19  relatively to the porthole  18  of the valve seat. The valve chamber  11   a  limits the movement of the valve body  19  and ensures by its shape and size that a flow passing through the porthole  18  pushes the valve body  19  back into the closing position. 
     In the embodiment of FIG. 5 the actuator  15  is arranged outside the housing  10 . The housing  10  is attached to the actuator  15  which in turn is fixed to a stationary holding fixture  30 . In the housing  10  the valve seat  17  is arranged which in this case is permanently fixed to the housing. 
     The inlet opening  12  is connected with a flexible line  31  since in this embodiment the complete housing  10  is movably attached to the actuator  15 . When the actuator  15  is operated, the housing  10  and the valve seat  17  contained therein are moved in the direction indicated by the bidirectional arrow  32 . 
     In the embodiment of FIG. 6 the actuator  15  is also attached to a stationary holding fixture  30  and moves the housing  10  in vertical direction. In the housing  10  the valve seat  17  is arranged in such a way that its seat extends in parallel in the moving direction  32  of the actator  15 . When the actuator  15  is operated, the valve seat  17  is displaced in parallel to its plane without the ball  19  being capable of following this rapid displacement. Only by the subsequently occurring flow through the outlet opening  13  is the ball  19  moved back into the closing position on seat  17 . As shown in FIG. 6, said valve operates even with vertically oriented seat. Of course, seat  17  may also be horizontally oriented. 
     Although a preferred embodiment of the invention has been specifically illustrated and described herein, it is to be understood that minor variations may be made in the apparatus without departing from the spirit and scope of the invention, as defined the appended claims.