Abstract:
A valve in a breathing device has a housing with an inlet and an outlet, a valve housing having an inlet and an outlet, a valve seat arranged in the housing, a valve body arranged in the housing to be freely moveable with respect to the valve seat between a closed position where the valve body completely covers the valve seat and an open position where the valve body is distanced from the valve seat. The valve body comprising a rigid central portion and a circumferential wrinkled and flexible portion devised for friction-free movement of the rigid central portion, and an actuator for controlling a force applied on the valve body in response to a control signal. The actuator includes an actuator body, a shaft having an end contactable with the valve body, and an electromagnetic displacement coil.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a valve of the type suitable for use in a breathing device. 
   2. Description of the Prior Art 
   Breathing devices such as medical ventilators and anesthetic apparatuses normally include an inspiratory side for supplying breathing gas toward a subject and an expiratory side for removing breathing gas from the subject. 
   In the inspiratory side, an inspiration valve is situated to control flow of gas and/or pressure in the inspiratory side. In the expiratory side, an expiration valve is situated to control flow of gas and/or pressure in the expiratory side. 
   Such valves can be controlled pneumatically, mechanically or electromechanically. Electromechanical actuators such as solenoids or voice coil motors have been used 
   SUMMARY OF THE INVENTION 
   An object of the invention is to provide a valve of the above type which is highly accurate, stable and reliable as well as practical, easy to maintain and support, and economical. 
   In a preferred embodiment of the invention, this object is achieved in a valve in a breathing device having a housing with an inlet and an outlet, a valve seat arranged in the housing, a valve body arranged in the housing that is freely moveable with respect to the valve seat between a closed position where the valve body completely covers the valve seat and an open position where the valve body is spaced from the valve seat. The valve body has a rigid central portion, a circumferential wrinkled and highly flexible portion which allows friction-free movement of the rigid central portion, and a soft portion on the rigid central portion facing the valve seat. An actuator is provided for controlling the force operating on the valve body relative to the valve seat in response to a control signal. The actuator includes a shaft attached to an electromagnetic displacement coil and having an enc contactable with the valve body. 
   The highly flexible portion of the valve body will not exercise any unwanted forces within its moving range. Ideally, the movement of the valve body will take place completely without friction or spring force action. In reality, a very small and almost constant spring force action will persist over the operational stroke. The highly flexible portion is made to ensure this. Structures similar to roll membranes can be employed. 
   Another important function of the highly flexible portion is to provide a highly effective gas seal against leakage from the gas flow path. 
   The overall construction of the valve is made to minimize or exclude friction forces from interfering with the operation of the valve. Basically, a linear correlation between the driving current and force exercised by the shaft on the valve body is present with the valve according to the invention. A given current I to the coil results in a force F=k*I (where k is a constant) which is practically independent of the position of the shaft. Since the relationship F=P*A (where P is pressure operating on the area A of the valve body) also exists, the valve opening will automatically adjust itself until the desired pressure P is achieved (linear relationship between current I and pressure P) independent of the magnitude of the gas flow through the valve. This results in a very accurate control over the pressure upstream of the valve body. When used as an expiration valve, the valve can exercise a precise control over the expiration pressure, etc. 
   This control also is enhanced by the fact that the valve body in all open positions will hover or float with respect to the valve seat. This effect is caused by allowing the valve body to freely tilt on the shaft end. In other words, the valve body strives to attain a fully equidistant position from the valve seat due to aerodynamic principles. When open, gas will flow out along the entire perimeter of the valve opening. No physical contact force between valve body and valve seat will therefore upset the desired balance (F=k*I=P*A). This promotes the accuracy and predictability of the valve control. 
   The separation of the actuator and valve body (or rather the entire housing) facilitates cleaning and selection of material. The separation also makes it easy to replace parts due to wear. Only the interior of the housing is exposed to the breathing gases and therefore requires proper disinfecting through autoclaving, washing etc. The actuator therefore can be designed entirely for its actuating purposes without requirements of being able to be autoclaved etc. The actuator may for instance be constructed to have a lifetime ten times longer than the valve body or more. Basically, this means that the actuator can remain the same and a number of housings are used (more or less) consecutively. 
   The two modular parts of housing and actuator can be separated and reassembled (in particular with different housings being exchanged on a regular basis). During normal exchanges (when the breathing device is not in use) the parts can be physically completely separated, which means there is no risk during separation and reassembly to interfere with alignment of shaft with respect of the valve body. In use however, there is a slight risk for a minute lateral displacement between the two modular parts. This could cause unwanted friction in the shaft movement when a standard bearing construction is used. This mainly is due to the presence of play within given tolerances between the parts. 
   To avoid this risk, the shaft can have a rounded end and be arranged in the actuator in a manner allowing the rounded end to be moved slightly in a lateral manner in addition to the axial movement. This can be achieved by using rounded or spherical bearings for the shaft or having part of the shaft display a slightly rounded area in contact with a sliding bearing. 
   At the same time the valve body can have a hole or recess in the rigid central portion, arranged so that the rounded end of the shaft will interact with the hole or recess. If a hole is used, it should be smaller than the diameter of the rounded end and if a recess is used it should have a radius larger that the radius of the rounded end of the shaft. This will ascertain a self-centering effect for the shaft-valve body arrangement that can accommodate any problems mentioned above. 
   The lateral deviation obtained will, due to the special bearing, not cause any friction so the control of the valve is not interfered with. 
   When the housing containing the valve body is removed for cleaning etc, the actuator will be completely exposed. Liquid or other material, however, is prevented from entering into the actuator body by means of a dome-shaped sealing between the rounded end and the actuator body interacting with a lip on the surface of the actuator body. This dome-shaped sealing is preferably free moving above the actuator body when the valve is activated, but seals around the lip when the shaft is maximally retracted (when the valve is inactivated, i.e. at zero current). The dome-shaped sealing diverts anything falling on it away from the shaft entrance of the valve body and the lip prevents any liquid persisting on the actuator body from entering same when the valve is activated and the dome-shaped sealing is raised from is sealing position. The placement of course carries the extra advantage that no friction is added during control of the valve since the dome-shaped sealing is not in physical contact with any other parts when the shaft is moving. (A similar sealing effect can be obtained by using bellows, but a bellows would always cause frictional hysteresis, so the innovative dome-shaped sealing is much more advantageous.) 
   Choice of materials is in some sense important. Both the shaft and the rigid portion (of the valve body) should be made of hard materials. However, the shaft preferably is harder than the rigid central portion of the valve body to ascertain that the shaft attains a higher durability. At the same time, the difference in hardness, as well as contact area (roundness of rounded end) must be chosen so the rigid central portion does not become indented by the contact pressure from the (rounded) end. A high surface finish also is important to reduce friction and facilitate movements between the shaft and the rigid portion when the shaft centers itself. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically illustrates an example of a breathing apparatus in which an expiration valve according to the invention can be used. 
       FIG. 2  shows an embodiment of the inventive expiration valve. 
       FIG. 3  shows in more detail how a valve body and actuator of the expiration valve in  FIG. 2  are designed. 
       FIG. 4  is an enlargement of a section of the valve body in FIG.  3 . 
       FIG. 5  shows a detail of how the shaft and valve body can be constructed for proper interaction in accordance with the invention. 
       FIGS. 6A and 6B  shows further examples of how shaft and valve body can be constructed for proper interaction. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A general overview of a breathing apparatus  2  connected to a patient  4  is depicted in FIG.  1 . Gas can be supplied to the breathing apparatus  2  via gas inlets  6 . From the breathing apparatus  2  breathing gas is transferred to the patient  4  via an inspiration tube  8  and from the patient  4  via an expiration tube  10 . 
   The breathing apparatus  2  is controlled by a control unit  12 . One example of a parameter that can be controlled is the positive end expiratory pressure, PEEP. A pressure meter  14  can measure pressure in the expiration tube  10  and forward a pressure signal to the control unit  12 , which in turn sends a control signal to an expiration valve  16 . 
   The present invention more particularly relates to the design of the expiration valve  16 . The shown breathing machine  2  is thus only given as an example of working environment for the expiration valve  16 . The breathing apparatus could be any known breathing apparatus, in particular any medical ventilator or anesthetic apparatus. 
   A preferred embodiment of the expiration valve  16  is shown in FIG.  2 . The expiration valve  16  has a housing  18  with an inlet  20  and an outlet  22  for breathing gas. 
   A valve seat  24  and a valve body  26  are arranged in the housing  18  to interact with each other for control of a valve opening, i.e. distance between valve seat  24  and valve body  26 . 
   An actuator  28  controls the force exercised on the valve body  26  toward the valve seat  24  depending on the control signal from the control unit  12  (FIG.  1 ). The pressure from the gas upstream the valve body (i.e. pressure in the expiration tube  10  in  FIG. 1 ) constitutes a force in the opening direction of the valve  16 . The balance between the two forces thus determines the opening of the valve in such way that the pressure is determined solely by the applied force and independent on the flow through the valve  16 . By altering the force from the actuator  28 , the pressure in the expiration tube can be controlled. 
   The actuator  28  has a shaft  30  attached to a displacement coil  52  inside an actuator body  32  and contactable with the valve body  26  for controlling the force with which the shaft  30  shall press on the valve body  26 . 
   Since the shaft  30  is not attached to the valve body  26 , only contactable therewith, the actuator  28  and the housing  18  can be completely separable. This has the distinct advantage that the parts exposed to breathing gas exhaled by the patient (housing  18 ) can be removed to be thoroughly cleaned and disinfected, whereas the more sensitive control parts of the actuator  28  such as the moving coil  52  and bearing  34  (that remain unexposed to contamination at all times) need not be exposed to such harsh treatment. Washing with a disinfecting cloth is normally sufficient for the actuator  28 . 
   This further facilitates the possibility of having the housing  18  form an integral part of an expiratory cassette of the breathing machine. Such an expiratory cassette contains all expiratory components that require cleaning after each use or after a certain time. Such an expiratory cassette therefore can be removed easily and readily from the breathing machine for cleaning. The same or a new cassette then can be placed in the breathing apparatus. 
   The bearing  34  in the actuator body  32  preferably is rounded or spherical to make it possible for a first end  36  of the shaft  30  to move slightly in a lateral manner apart from the axial movements. More specifically in the preferred embodiment, the bearing  34  represents an interaction between a slight bulge (exaggerated in the figure) on the shaft  30  and a sliding bearing. 
   The lateral movement helps the expiration valve  16  to take up vibrations and jolts without affecting the operation of the valve. It also facilitates alignment of shaft  30  and valve body  26  when the shaft  30  is activated. The function of this is explained in more detail in connection with  FIG. 3  below. 
   Also present on the shaft is a dome-shaped seal  38 , which prevents water and other liquids or solids from entering the interior of the actuator body  32 . This occurs in particular when the housing  18  with valve body  26  is removed for cleaning or replacement, which exposes the actuator  28 . This will also be discussed in more detail with reference to  FIG. 3  below. 
   Certain parts of the preferred embodiment of the expiration valve  16  are shown in more detail in FIG.  3 . 
   Here, it can be seen that the valve body  26  has a rigid central portion  40 , facing the shaft  30 , a soft portion  42  on the rigid central portion  40 , facing the valve seat, and a circumferential wrinkled and highly flexible portion  44 . The circumferential wrinkled and highly flexible portion  44  preferably would provide no additional axial force, but any force added is practically constant over the range of movement for the circumferential wrinkled and highly flexible portion  44 . No force added means that the force from the actuator via shaft  30  will be directly correlatable with the desired pressure upstream the valve (F=P*A, where F is the force from the shaft, P is the desired pressure and A is the valve area exposed to the pressure). With a constant force added, compensation has to be done for the additional force (i.e. the above relation becomes F-c=P*A, where c represents the additional constant force). The flexible portion  44  also strives to maintain the central portion  40  (i.e. valve body  26 ) centered over the valve seat. The flexible portion also seals a part of the housing, providing a gas tight seal which ascertains that gas will only flow out through the outlet. A further advantageous effect of the flexible portion  44  is the provision of friction-free movement. 
   The friction-free movement is important because it creates an essentially linear relationship with no, or very low hysteresis between control current to the moving coil and closing pressure of the valve (F=k*I, where F is the force acting on the valve body, I is the control current and k is a constant. This enhances and facilitates control of the valve and allows for very high accuracy and performance. (With the force c above being close to zero F=P*A=k*I, which means a practically direct relationship between control current I and pressure P.) 
   In this specific embodiment, the soft portion  42  and the circumferential wrinkled and flexible portion  44  are formed by one single membrane. They may, however, also be formed by two or more separate components. 
   Another advantageous detail is indicated at IV and shown more clearly in FIG.  4 . Here it can be seen that the soft portion  42  has a cutout  46 . This cutout  46  is annular and situated in the contact area with the valve seat  24  (although having a width noticeably larger than the valve seat  24 ). The cutout  46  faces the portion  40 , thereby forming a much thinner membrane facing the valve seat  24 . This thinner membrane has several important implications. The valve can be closed completely with considerably lower force (without risk for leakage), the requirements for flatness of the valve seat  24  and tolerances for membrane surface on valve body  26  become much lower and there will be no physical contact between the membrane and the valve seat  24  even at very small openings (low flows) due to combination of membrane resilience, rounded end  36  of shaft  30  and aerodynamic physical principles and thus the force balance will not be disturbed. 
   A hole  48  (which could be a multitude of holes situated equidistantly from the center) is disposed in the central portion  40 . This hole  48  (or holes) provide a major advantage. The hole  48  serves to release gas from the cutout  46  whenever the pressure changes within the cutout  48  (in relation to surrounding pressure). This can occur when the volume of the cutout  46  decreases as it engages the valve seat. This can also occur when exposed to higher temperatures or vacuum during disinfecting processes (autoclaving etc). The hole  48  (or holes) also will reduce the weight of the central portion  40 , without altering its rigidity. 
   Returning to  FIG. 3 , the interaction between the shaft  30  and valve body  26  will now be explained in detail. When the shaft  30  is in its lowest position (at zero current—not shown) it will not be in contact with the valve body  26 . The valve body  26  will be suspended by the flexible portion  44 . As the actuator  28  is activated, the shaft  30  moves to make contact with the valve body  26 . For an exact force balance F=P*A, it is essential that the shaft  30  contacts the valve body  26  very close to it center and that the valve body  26  freely can tilt around the shaft. The shaft  30  therefore is rounded at the end  36  and a recess  50  is made in the center of the valve body  26 . The recess  50  has a radius that is larger than the radius of the rounded end  36 , which is evident from FIG.  5 . This causes the shaft  30  and rigid portion  40  to make contact at a point, around which the valve body  26  can tilt. 
   As the shaft  30  makes contact with the valve body  26 , the rounded end  36  will be guided into the recess  50 . As explained previously, the end  36  can move in a lateral manner so the shaft  30  will assume a position with a small contact area in the center of the valve body  26 . This also functions as a type of bearing, preventing any risk that the shaft will laterally move so much that it comes in contact with any other part of the actuator body  32  that the bearing described in connection with  FIG. 2  above. There will thus be no additional friction forces present. 
   As mentioned, the dimensioning radius of the shaft&#39;s  30  rounded end  36  is important. Some of the purposes or functions it fulfils are to guide the shaft  30  to the center of the valve body, to minimize sliding and rolling friction between shaft  30  and valve body  26 , to allow the valve body  26  to roll or tilt sufficiently to attain its floating position in relation to the valve seat, and to stabilize the valve body  26  in such floating position and not cause any mechanical damage on the valve seat  26 . 
   The floating of the valve body  26  in relation to the valve seat is due aerodynamic effects as well as to geometric effects. The aerodynamic effects are basically such that as the pressure of the gas acts on the valve seat  26 , any slant of the valve body in relation to the valve seat  26  will result in returning moment due to static and dynamic pressure relations, bringing the valve body  26  back to a planar position. 
   The geometric effects are basically such that should the valve body  26  roll slightly on the tip of the shaft  30  and become slanted, the new contact point will be off center. Thus a uniform pressure acting on the valve body  26  will cause a restoring moment, tending to stabilize the valve body  26  in a position where the moment is zero, i.e. where the contact point is exactly centered. 
   It is therefore beneficial to have contact surfaces made with a high smoothness, so that rolling and movements in the contact area between the shaft  30  and the valve body  26  results in a minimum of friction. 
   The recess  50  can be replaced by a hole (of less diameter than the shaft) in the central portion  40  without altering the effect or functionality. Further alternatives will be presented below. 
   The recess  50  (or hole) also serves as a mass reducer for the rigid central portion  40 , without effecting the rigidity of it (similar to the hole or holes  48  mentioned in connection with FIG.  4 ). 
   The dome-shaped seal  38  also is shown in FIG.  3 . Here it can be seen that the dome-shaped seal  38  can interact with a circular lip  64  at the central part of the actuator body  32 . When the shaft  30  is completely retracted into the actuator body  32 , the dome-shaped seal  38  will completely cover the lip  64 , thereby completely sealing the interior of the actuator body  32 . When the shaft  30  is raised (valve active), the lip  64  prevents any remaining or collecting amount of liquid to flow into the interior of the actuator body  32 . 
   Further in  FIG. 3 , it can be seen that the shaft  30  has a tapered portion  60  that interacts with a correspondingly shaped recess  62  in the actuator body  32  as the shaft  30  is retracted into the actuator body  32 . This assures that the shaft  30  is always properly centered when the valve is activated (at start up of the breathing machine, after change of expiration cassette (including valve body  26 ), etc.). 
   Another feature of the expiration valve  16  is evident from FIG.  2 . The actuator body  32  has a moving part  52  with a winding  54  (the shaft  30  is also attached to, connected to or formed as an integral part of the moving part  52 ) and magnetically coupled to a core  56  with a permanent magnet  58 , magnetized in the direction of the shaft  30 . 
   The winding  54  and interior part  66  of the core  56  should be arranged to face each other. All parts of the core  56  except the permanent magnet  58  preferably are made of a ferromagnetically soft material, e.g. soft iron. The permanent magnet  58  preferably is placed in connection with the interior part  66  of the core  56  so that the magnetic field will be able to attain an essentially radial orientation across the winding  34  and bobbin part. 
   If the bobbin part of the moving part  52  is made of a highly conductive material such as Cu, Al, Ag, etc., eddy currents will be induced in the bobbin when it moves in the radial magnetic field resulting in a viscous damping, i.e. a damping force proportional to the velocity of the moving part  52 . This is highly desirable in many applications. 
   This overall design thus creates damping, it has a linear relationship between current and force, it exhibits very little magnetic hysteresis since it operates at a constant magnetic working point and friction is kept low since there are only very small lateral forces involved. Therefore, the shaft  30  will move easily and predictably in the actuator body  32  and the entire actuator  28  is controllable through current only to provide a desired force, linear in current and with a desired damping characteristic. 
   Alternate embodiments can readily be arrived at by those skilled in the art. A few variations of possible alternatives in arranging the contact between the shaft and valve body are shown in  FIGS. 6A and 6B . 
   As shown in  FIG. 6A , the valve body  26 A may have a rounded part  70 A which can interact with a flat surface on a shaft  30 A. This provides the same effects for tilting and providing geometric and aerodynamic effects striving to maintain a floating position for the valve body  26 A in relation to the valve seat. 
   Likewise, in  FIG. 6B  the valve body  26 B has a rounded part  70 B interacting with a bore  72  in the shaft  30 B for producing the same effect. 
   Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.