Abstract:
A leveling valve for discharging and supplying air from and to a plurality of utilization elements comprises a valve disc arrangement configured to direct air between a source of pressurized air, an exhaust port, and the utilization elements. The valve disc arrangement comprises a first and a second valve disc, which are rotatable with respect to each other such that the valve is switchable between multiple switching positions, and, in some switching positions, either the source of pressurized air or the exhaust port are in fluid communication with the utilization elements. The valve discs provide a stepped increase in flow cross-section in a respective flow path to or from the utilization elements. The stepped increase is dependent on the angle of rotation between the valve discs.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of EP 13168528 filed on May 21, 2013, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention generally relates to a leveling valve for discharging and supplying air from and to a plurality of utilization elements, such as pneumatic suspension bellows, the valve comprising a valve disc arrangement for directing air between a source of pressurized fluid, an exhaust port, and the utilization elements. 
     BACKGROUND OF THE INVENTION 
     A leveling valve of the general type under consideration is described in WO 2010/089089, Leveling valves are commonly used to regulate the vertical clearance of a vehicle such as a truck or other utility vehicle with respect to ground level. Depending on the load situation of the vehicle or depending upon dynamic forces acting on the utilization elements such as pneumatic suspension bellows of a vehicle, it is, in certain situations, necessary to increase or decrease the suspension level of the utilization elements. This is achieved by switching the leveling valve, in particular the valve disc arrangement, from its neutral position to either an “exhaust” switching position or an “air supply” switching position. Depending on the switching position, air will be exhausted from the utilization elements into the atmosphere, or will be supplied to the utilization elements from a source of pressurized air. 
     The known leveling valve described in WO 2010/089089 focuses on possible ways of decreasing the number of sealing elements used inside a valve by making a non-rotatable valve disc axially movable inside a valve housing, wherein the two valve discs are pressed against each other by pressure prevailing in either a line connected to the source of pressurized air or in a line connected to the utilization elements. 
     In practice, it is often necessary to regulate the level of the utilization elements very quickly. As a consequence, air has to be moved with high flow rates from the utilization elements towards the atmosphere or from the source of pressurized air into the utilization elements through the leveling valve. In order to achieve this, the flow paths inside the valve need to be dimensioned accordingly. There are, however, limits to the dimensioning of the flow paths as the entire leveling valve must not exceed. predetermined total dimensions in order to be practically usable on vehicles. In conventional valve systems, very small flow cross-sections inside the valve flow paths can lead to insufficient and slow reactivity when switching the valve and pushing air through the valve. 
     A further problem commonly found with pneumatic valves is the acoustic noise emitted when switching and pushing large amounts of air at high pressures through the valve. 
     SUMMARY OF THE INVENTION 
     Generally speaking, it is an object of the present invention to provide a leveling valve with improved functionality that overcomes drawbacks of conventional constructions. In particular, it is an object of the invention to provide a leveling valve with improved reactivity when switched. Furthermore, it is an object of the invention to provide a leveling valve that provides improved functionality while at the same time emitting as little acoustic noise as possible. 
     The present invention includes a valve disc arrangement for directing air between a source of pressurized fluid, an exhaust port, and the utilization elements comprising a first and second valve disc. The first and second valve discs are substantially concentric to each other, contacting each other along respective contact surfaces, and are rotatable with respect to each other such that the valve disc arrangement is switchable between multiple switching positions. At least one of the switching positions is a neutral position wherein fluid communication between the utilization elements and both the source of pressurized fluid and the exhaust port is blocked. In the other switching positions, either the source of pressurized air or the exhaust port is in fluid communication with the utilization elements. 
     According to one embodiment, in the leveling valve, the valve discs—when switched away from the neutral position—are adapted to provide a stepped increase in flow cross-section in a respective flow path between either the source of pressurized air or the exhaust port and the utilization elements. The stepped increase is dependent on the angle of rotation between the valve discs. 
     Preferably, the increase in flow cross-section is linked to the increasing angle of rotation between the valve discs such that an increased angle of rotation also leads to an increased flow cross-section in the respective flow path between either the source of pressurized fluid and the utilization elements, or between the exhaust port and the utilization elements, depending on the switching position of the valve disc arrangement. 
     The stepped increase can be achieved by providing a sudden and steep increase in flow cross-section at very low rotation angles away from the neutral position, followed by a comparatively shallow increase at higher rotation angles. A combination of these two features is salutary. Namely, the steep increase at very low rotation angles provides good reactivity of the valve because immediately upon switching from the neutral position to one of the flow positions, significant amounts of pressurized fluid are allowed to pass by a flow cross-section such that the level of the utilization element can quickly be regulated. The comparatively shallow increase after the first few degrees of rotation achieves the additional salutary effect of limiting acoustic noise. 
     In one embodiment, the stepped increase in flow cross-section comprises a first section (A) corresponding to a first increase ratio, and a second section (B) corresponding to a second increase ratio different from the first ratio, preferably lower than the first increase ratio. The stepped increase in flow cross-section can also comprise a third section (C) corresponding to a third increase ratio different from the second ratio, preferably higher than the second increase ratio. 
     Preferably, the neutral position of the valve disc arrangement encompasses only a small angular range of the leveling valve. The neutral position can extend for about ±1°-3° about a zero line, preferably about ±1.5° about the zero line. Outside of this so-called “dead band” for the neutral position, it is preferred that the first section (A), which features the steep increase of flow cross-section, is allocated an angular range of about ±4°-10° about the zero line. 
     In a further embodiment, a progressive increase in flow cross-section is provided from the second section (B) towards the third section (C) along with a substantially linear increase in flow cross-section in section (C) towards a full opening of the flow cross-section (section D). Preferably, the full channel opening is achieved at about +20° from the zero line or at greater angles. 
     The aforementioned angular ranges are mentioned with “±” in order to indicate that, in one direction from the zero line, there will be one or more switching positions for exhausting air from the utilization elements, whereas in the respective other direction from the zero line, there will be one or more switching positions for supplying air to the utilization elements. 
     According to another embodiment, at least one of the flow paths comprises a throttle, the throttle being integrated in the valve disc arrangement, or alternatively being integrated into a housing of the leveling valve. According to this embodiment featuring an integrated throttle inside the valve disc arrangement, there is provided a leveling valve for discharging and supplying air from and to one or more utilization elements, in particular a plurality of pneumatic suspension bellows, comprising a valve disc arrangement for directing air between a source of pressurized air, an exhaust port, and the utilization elements. The valve disc arrangement comprises a first and second valve disc contacting each other along respective contact surfaces, the first and second valve discs being rotatable with respect to each other such that the valve is switchable between multiple switching positions, wherein each switching position corresponds to a distinct flow path, characterized in that at least one of the flow paths comprises a throttle, the throttle being integrated in the valve disc arrangement. 
     A particular advantage of the throttle according to this embodiment is that no extra part is required externally to the leveling valve for providing a throttle function. This increases the versatility of the valve and lowers the cost of implementing throttled leveling in vehicles. 
     The integrated throttle affords, the opportunity to conduct pressure equalization between the utilization elements controlled with the leveling valve according to the invention. The throttle at the same time enables air flow between the utilization elements and also limits the maximum flow rate due to the small throttle diameter. Accordingly, pressure equalization happens slowly such that the vehicle dynamic, whenever utilization elements such as pneumatic suspension bellows are concerned, is not negatively impacted. The pressure equalization should beneficially be minimized in driving situations where one utilization element is subjected to higher load for an extended period of time, such as is the case in long curves at higher speeds for trucks. 
     In yet another embodiment, the first valve disc comprises a first air passage for connection to a source of pressurized air, a second air passage for connection to a first utilization element, a third air passage for connection to a second utilization element, and a fourth air passage for connection to an air exhaust. 
     Preferably, the throttle is formed as an air channel connecting the second and third air passages. The throttle can be formed as a recess in the contact surface face of the first valve disc facing the second valve disc. Alternatively, the throttle can be formed as a recess in the contact surface of the second valve disc facing the first valve disc. As a further alternative, the throttle can be formed as a recess in a surface of the first valve disc opposite, i.e., facing away, from the contact surface with the second valve disc. By providing the throttle in this manner, it is possible to create the throttle element along with the creation of the air passages in the first valve disc. This may be achieved by conventional manufacturing techniques, which depend on the material of the valve being employed. In a preferred embodiment, the first and second valve discs are made from a ceramic material. 
     In yet another alternative embodiment, the throttle can be formed as a flow passage, e.g., a bore, inside the housing of the leveling valve. 
     According to a further embodiment, the first air passage and the fourth air passage comprise arcuate, in particular circular, first and second flow portions. Preferably, the first and second flow portions are respectively formed as a recess in the contact surface of the first valve disc facing the second valve disc. Ideally, both the first and second arcuate flow portions are located on the same radius with respect to the center of rotation of the valve discs. Advantageously, for both air flow modes (exhaust mode and supply mode), the same angle of rotation of the valve discs relative to each other, i.e., the same lever movement in cases where a lever is used for rotating the valve discs, will lead to the exact same flow channel opening, i.e., flow resistance for both air flow modes. The increased symmetry of operation makes it possible to design the leveling valve and, in particular, the valve discs to be even more compact since both channels may be made equally small/large. If the flow portions were not located on the same radius but instead on different radii, the flow cross-section for one of the two flow portions would have to be enlarged asymmetrically, which, in turn, would lead to a larger outer diameter of the valve disc. 
     According to another embodiment, the second valve disc comprises a manifold. That manifold is preferably formed as a recess on the contact surface of the second valve disc facing the first valve disc. Ideally, depending on the switching position the manifold is in fluid communication with none or at least one of the first, second, third and fourth air passage, which are respectively preferably provided in the first valve disc. The advantage of forming the manifold in the way described hereinabove is the same as with respect to the flow portions and air passages in the first valve disc. Therefore, reference is made to the comments hereinabove. 
     Preferably, in a first switching position the manifold connects the first air passage to the second and third air passages, in a second switching position the manifold connects the fourth air passage to the second and third air passage, and in a third switching position, the manifold is in the neutral position, connecting neither first nor fourth air passages to the second and third air passages. 
     In one embodiment, the manifold comprises a first and a second arcuate, in particular circular, manifold flow portion, the first and second manifold flow portions respectively being formed as a recess on the contact surface of the second valve disc facing the first valve disc, and the first and second manifold flow portions being arranged—depending on the switching position—for communication with the second and third air passages, which preferably are provided on the first valve disc. 
     Also, the first and second arcuate flow portions of the manifold can be arranged on the same radius in order to provide for symmetrical flow behavior regardless of the chosen flow mode (exhaust or supply). 
     Preferably, the manifold comprises at least one of: (i) an outer inlet/outlet flow portion in fluid communication with the first and second manifold flow portions, the outer inlet/outlet flow portion being formed as a recess in the contact surface of the second valve disc facing the first valve disc; and arranged—depending on the switching position—for communication with the first air passage or with the fourth air passage; and (ii) a first and second inner inlet/outlet flow portion located on each end of the first and second manifold flow portions, the first and second inlet/outlet flow portion being formed as a recess in the contact surface of the second valve disc facing the first valve disc, and arranged—depending on the switching position—for communication with the second and third air passages. 
     In a further embodiment of the leveling valve, the outer inlet/outlet flow portion has across-sectional shape that is congruent with a corresponding cross-sectional shape of the first and second end portion provided on bath ends of the flow portions of the first and fourth air passages. Also, alternatively or additionally, each of the first and second inner inlet/outlet flow portion preferably has a cross-sectional shape that is congruent with a corresponding cross-sectional shape of the second and third air passages. Here, congruency can mean that the width of the respective flow portions in a radial direction is identical in both respective flow portions. The edges of the outer and inner flow portions and, correspondingly, the edges of the first and second flow portions of the first and fourth air passages, and the first and second manifold flow portions are each shaped and oriented such that, upon rotation of the valve discs relative to each other, the respective flow portions are brought into fluid communication over their entire width immediately, leading to a steep first increase in flow cross-section. 
     According to another embodiment of the leveling valve, at least one, preferably each, of the end portions of the outer inlet/outlet flow portion comprises a step, rounded edge, or chamfer. The element is preferably oriented to provide a retarded increase in flow cross-section as a transition from the first section (A) to the second section (B) when switching the valve. By partially reducing the depth of the respective flow portion over the length of the chamfer, the initial steep increase is “slowed,” leading to the shallower second section increase. 
     Preferably, in a fourth switching position, the manifold connects the first air passage to the second and third air passages, wherein the flow cross-section established between the outer inlet/outlet flow portion of the manifold and the first flow portion (of the first air passage) is smaller than in the first switching position, and in a fifth switching position, the manifold connects the fourth air passage to the second and third air passage wherein the flow cross-section established between the outer inlet/outlet flow portion and the second flow portion (of the fourth air passage) is smaller than in the second switching position. When switching from the neutral position in either the exhaust or supply direction, there are now more switching positions; throttled and a non-throttled switching positions. All this is possible without providing external parts. 
     In a further embodiment of the leveling valve, the first valve disc and the second valve disc are arranged concentrically with respect to each other. Preferably, the second valve disc is rotatably mounted in a valve housing, and rotatable between the plurality of switching positions, wherein the first valve is fixedly mounted in the housing, or vice-versa. If only one of the two valve discs is rotatable, overall construction of the leveling valve can be simplified and made more reliable. 
     In another embodiment of the leveling valve, the manifold is formed and arranged in the second valve disc, and the first, second, third, and fourth air passages are formed and arranged in the first valve discs such that an identical number of switching positions is provided by the valve when rotating the second valve disc by 180° with respect to the first valve disc. Preferably, this is achieved by arranging the first and fourth, and the second and third air passages, respectively, around a rotational center axis of the first valve disc. Ideally, the first and fourth, and the second and third air passages are arranged point-symmetrically around the rotational center axis of the first valve disc, wherein the rotational center axis is perpendicular to the contact surface of the first valve disc. Further, the arcuate manifold flow portions are preferably arranged symmetrically around a rotational center axis of the second valve disc. Still further, the crosslink flow portion is preferably arranged radially with respect to the rotational center axis of the second valve disc. 
     According to yet another embodiment of the leveling valve, at least one, preferably each, of the first and second valve discs comprises one or more support ridges abutting against the contact surface of the respective other valve disc when the valve is assembled, wherein the support ridges are located in a radially peripheral region of the respective valve discs surface. The one or more support ridges have a beneficial effect insofar as the two valve discs are supported against each other in more stable fashion. Due to a maximized (radial) distance between the support ridges and the rotational center axis of the valve discs, any normal force or level force can be better absorbed by the valve discs with respect to the valve housing. Accordingly, higher force can be imposed on the valve discs, leading to improved sealing between the valve discs. 
     Another object of the present invention is to provide an air suspension system for use in a vehicle comprising a plurality of utilization elements, in particular suspension bellows, a leveling valve for discharging and supplying air from and to the utilization elements, and a source of pressurized air connected to a first air passage of the leveling valve, wherein the leveling valve is a leveling valve according to any one of the embodiments described herein. 
     A further object of the invention is to provide a vehicle, e.g., a truck, comprising a plurality of tires mounted on a vehicle axle, a superstructure, and an air suspension system coupling the axle to the superstructure, wherein the air suspension system is an inventive air suspension system as described herein. 
     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
     The present invention accordingly comprises the features of construction, combination of elements, and arrangement of parts, all as exemplified in the constructions herein set forth, and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the invention, the invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view of a leveling valve according to an exemplary embodiment of the present invention; 
         FIG. 1 a    is an alternative cross-sectional view of the leveling valve shown in  FIG. 1 ; 
         FIG. 2  is a side view of a valve disc arrangement of the leveling valve shown in  FIG. 1 ; 
         FIGS. 2 a , 2 b    show different cross-sectional views of the valve disc arrangement shown in  FIG. 2 ; 
         FIG. 3  is a detailed side view of the valve disc arrangement shown in  FIGS. 2, 2   a ,  2   b;    
         FIGS. 3 a , 3 b    are further side views of the valve disc arrangement shown in  FIG. 3 ; 
         FIG. 4  is a further detailed side view of the valve disc arrangement shown in  FIG. 2 ; 
         FIGS. 4 a , 4 b    are further side views of the valve disc arrangement shown in  FIG. 4 ; 
         FIG. 5  is a schematic representation of a vehicle comprising the leveling valve according to  FIGS. 1 to 4 ; and 
         FIG. 6  is a schematic diagrammatic presentation of the characteristic flow curve of the leveling valve according to  FIGS. 1 to 5 . 
     
    
    
     LIST OF REFERENCE CHARACTERS 
     
         
           1  fluid (air) supply port 
           21  first fluid (air) channel 
           22  second fluid (air) channel 
           3  fluid (air) exhaust port 
           101  leveling valve 
           103  disc valve arrangement 
           105   a - e  switching positions 
           105   a  second switching position (exhaust) 
           105   b  fifth switching position (exhaust “throttled”) 
           105   c  neutral (third) switching position 
           105   d  fourth switching position (supply “throttled”) 
           105   e  first switching position (supply) 
           107  first valve disc 
           109  second valve disc 
           111  contact surface of first valve disc 
           113  contact surface of second valve disc 
           115   a - c  throttle 
           117  first air passage (for connection to source of pressurized air) 
           119  second air passage (for connection to first utilization element) 
           121  third air passage (for connection to second utilization element) 
           123  fourth air passage (for connection to air exhaust) 
           125  first flow portion (of first air passage) 
           126   a,b  first end portion (of flow portion of first air passage) 
           127  second flow portion (of fourth air passage) 
           128   a,b  second end portion (of flow portion of fourth air passage) 
           130   a - d  step, rounded edge or chamfer 
           131  first manifold flow portion 
           132   a,b  first inner inlet/outlet flow portion 
           133  second manifold flow portion 
           134   a,b  second inner inlet/outlet flow portion 
           135  outer inlet/outlet flow portion 
           136   a  rotational center axis of first valve disc 
           136   b  rotational center axis of second valve disc 
           137  crosslink flow portion 
           138   a - d  first support ridge 
           139   a - e  second support ridge 
           140  housing 
           141  base body 
           142   a,b,c  connection ports 
           143  lever 
           145  rotatable housing portion 
           147  spring 
           148  housing lid 
           150  coupler 
           152  dirt seal 
           154  first air plenum 
           156  second air plenum 
           158  air flap 
           200  air suspension system 
           205   a,b  utilization elements 
           207  source of pressurized air 
           300  vehicle 
           301  vehicle axle 
           303  tire 
           305  superstructure 
         S supply side 
         E exhaust side 
         N neutral section 
         A first flow section 
         B second flow section 
         C third flow section 
         D full flow channel opening 
       
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A leveling valve  101  in accordance with a preferred embodiment of the invention is depicted in  FIG. 1  and in  FIG. 1 a   . The leveling valve  101  comprises a valve disc arrangement  103  for directing air between a plurality of utilization elements  205   a,b  and either a source  207  of pressurized air or an exhaust port  3 . The valve disc arrangement  103  comprises a first valve disc  107  and a second valve disc  109 . The first and second valve discs  107 ,  109  of the valve disc arrangement  103  comprise respective flow portions forming flow paths for guiding the air through the valve. This will be discussed in greater detail hereinafter in connection with  FIGS. 2-5 . 
     The first and second valve discs  107 ,  109  are rotatable with respect to each other. In the embodiment of  FIG. 1 , the first valve disc  107  is mounted to be stationary inside a housing  140  of the leveling valve  101 . The second valve disc  109  is mounted to be rotatable inside the housing  140 . The housing  140  of the leveling valve  101  comprises a base body  141 . The first valve disc  107  is mounted non-rotatably inside the base body  141 . The housing  140  further comprises a rotatable housing part  145  fastened to the base body  141  by way of a housing lid  148  and extending into the base body  141 . Inside a first air plenum  154  formed between the rotatable housing part  145  and the base, body  141 , a resilient element, for example in the form of a spring  147 , is located and effective to push the second valve disc  109  towards the first valve disc  107  in order to establish a sealing, preferably air-tight, relationship between the valve discs  107 ,  109  of the valve disc arrangement  103  and the housing, in particular with respect to the base body  141  of the housing  140 . 
     The base body  141  of the housing  140  comprises a first fluid channel  21  at the end of which is located a connection port  142   a  for connecting the leveling valve  101  and, in particular, the first fluid channel  21 , to a utilization element  205   a  of a vehicle ( FIG. 6 ). Further, the base body  141  comprises a second fluid channel  22 . At the end of the second fluid channel  22  there is a connection port  142   b  for connecting the leveling valve  101  to a second utilization element  205   b . Utilization elements  205   a,b  may be, for example, pneumatic suspension bellows of a truck, where the first utilization element  205   a  might be a right side suspension bellow of the vehicle and the second utilization element  205   b  might be the left side suspension bellow, or vice-versa. 
     The fluid channels  21 ,  22  are connected to respective flow portions in the first valve disc  107  of the valve disc arrangement  103 . The location and function of the flow portions inside the valve disc arrangement will be discussed hereinafter in connection with  FIGS. 2-5 . 
     The rotating portion  145  of the housing  140  comprises an external mounting section, which in  FIG. 1  receives a lever  143  for operating the valve  101 . The lever comprises at its (in  FIG. 1 ) rightmost end portion a coupler  150  that engages a portion of the vehicle. Mechanical elements for translating a control motion from the vehicle to the valve  101  may be rollers, steering rods, etc. Upon actuation of the lever  143 , the rotatable housing portion  145  is rotated relative to the base body  141  of the housing  140 . The second valve disc  109  of the valve disc arrangement  103  is mounted non-rotatably with respect to the rotatable housing portion  145 . Thus, upon actuation of the lever  143 , the second valve disc  109  is rotated relative to the first valve disc  107  in this embodiment. 
     The base body  141  and the rotatable housing part  145 , as well as the rotatable housing part  145  and the housing lid  148 , are sealed against dirt ingress with one or more dirt seals  152 . The first air plenum  154  is thus exposed to atmospheric pressure (cf.  FIGS. 1 a    and  5 ). 
     The leveling valve  101  may optionally comprise a throttle  115   a ,  115   b  or  115   c .  FIG. 1  shows throttle  115   a , which is formed as a flow passage in the shape of a conical bore in the base body  141 , connecting the first and second fluid channels  21 , 22  with each other. Alternative locations for throttles are shown as well. There may be a throttle  115   b  formed in a contact surface between the first and second valve discs  107 , 109  (cf. throttle  115   b  in  FIG. 2 a , 2 b   ). Alternatively, there may be a throttle  115   c  formed in a surface  108  of the first valve disc  107 , the surface  108  being opposite the contact surface  111 . 
     The fluid flow into and out of the leveling valve  101  of  FIG. 1  are best seen from  FIG. 1 a   . Most of the reference signs shown in  FIG. 1 a    are also in  FIG. 1 , which is why in regard to these reference signs, explicit reference is made to  FIG. 1 . 
     The cross-section shown in  FIG. 1 a    is a 90° rotation. The air flow into and out of leveling valve  101  is accomplished as explained hereinafter. The leveling valve  101  comprises in its base body  141  a fluid supply port  1 . The fluid supply port  1  is in air-tight sealing contact with the first valve disc  107  and in fluid communication the first air passage  117  in the first valve disc  107 . The fluid supply port  1  also comprises a connection port  142   c  similar to connection ports  142   a,b  shown in  FIG. 1  leading to the utilization elements  205   a,b . Connection port  142   c  is adapted for connection to a source  207  of pressurized air. 
     Through fluid supply port  1 , pressurized air can be supplied through the first air passage  117  into the first flow portion  125  of the first valve disc  107  ( FIG. 1 ). Depending on the angle of rotation of the second valve disc  109  relative to the first valve disc  107 , air will be transported in fluid communication through the crosslink portion  137  of the second valve disc  109  to the second and third air passages  119 ,  121  in the first valve disc, and from there to the first and second fluid channels  21 ,  22 , which lead towards the utilization elements  205   a,b.    
     In the other switching scenario, air is being transported through the fluid channels  21 ,  22  and the second and third air passages  119 ,  121  of the first valve disc  107  into the second valve disc  109 , through the second flow portion  127  in the second valve disc  109 , and from there to the fourth air passage  123  in the first valve disc  107 . The fourth air passage  123  in the first valve disc  107  is in fluid communication with a second air plenum  156 . Also in fluid communication to the second air plenum  156  is an exhaust port  3  provided in the base body  141  of leveling valve  101 . The exhaust port  3  is sealed against entry of air with an air flap  158 , which opens if the pressure inside the second air plenum  156  is greater than the atmospheric pressure outside of valve  101 . 
     The alternative throttle positions  115   b,c  shown in  FIG. 1  have been omitted from  FIG. 1 a    for an improved overview. The location of the alternative throttle position  115   b,c  can better be seen in  FIGS. 2 a,b    and  3  and  3   a.    
     The above disc arrangement  103  show  FIGS. 1 and 1   a  is explained in more detail with reference to  FIGS. 2, 2   a  and  2   b . The valve disc arrangement  103  comprises the first valve disc  107  and the second valve disc  109 . The orientation and arrangement shown in  FIGS. 2, 2   a  and  2   b  corresponds to the arrangement of the valve discs  107 ,  109  when mounted inside the housing  140  of the valve  101 . The First and second valve disc  107 ,  109  are arranged concentrically with respect to each other. The first valve disc  107  and the second valve disc  109  abut against each other with respective contact surfaces  111 ,  113 , cf.  FIGS. 3, 3   a ,  3   b  and  4 ,  4   a ,  4   b.    
     As can best be seen from  FIGS. 2, 2   a  and  b  and  3 ,  3   a ,  3   b , the first valve disc  107  has a substantially cylindrical shape and is substantially rotationally symmetric with respect to rotational center axis  136   a . A number of recesses are formed in the periphery of the valve disc  107  to provide means for securing valve disc  107  to the housing  140  of valve  101 . The first valve disc  107  comprises in its contact surface  111  a first air passage  117  for connection to the source  207  of pressurized air ( FIG. 5 ). Further, the first valve disc  107  comprises a second air passage  119  for connection to a first utilization element  205   a . Still further, the first valve disc  107  comprises a third air passage  123  for connection to a second utilization element  205   b . The second and third air passages  119 ,  121  extend completely through the axial length of the valve disc  107 . The first valve disc  107  further comprises a fourth air passage for connection to an air exhaust port  3 . The first and fourth air passages  117 ,  123  extend completely through the axial length of the valve disc  107 . 
     The first valve disc  107  may optionally comprise a number of first support ridges  138   a - d  (cf,  FIG. 3 b   ). Alternatively or additionally, the second valve disc may comprise a number of second support ridges  139   a - e  (cf.  FIG. 4, 4   b ). The function of these first and/or second support ridges  138   a - d ,  139   a - e  is to enhance the stability of the abutment of the first and second valve discs  107 , 109  against each other such that higher forces and leverage can be absorbed and air-tight sealing can be improved between the contact surfaces  111 , 113  of the first and second valve discs  107 , 109 . 
     As an extension of the first and fourth air passages  117 ,  123 , the first valve disc  107  comprises in its contact surface  111  a first flow portion  125  connected to the first air passage  117 , and a second flow portion  127  connected to the fourth air passage  123 . These first and second flow portions  125 ,  127  are arcuate in shape, in particular circular, and arranged on the same radius with respect to each other and with respect to the rotational center axis of the valve disc. The flow portions are formed as recesses in the contact surface  111  and do not extend entirely through the axial length of the valve disc. The first and second flow portions  125 ,  127  are arranged to cooperate with the second valve disc for providing a given flow cross-section for each rotational alignment (switching position) of the first valve disc relative to the second valve disc. 
     The first flow portion  125  comprises on opposite ends first end portions  126   a ,  126   b . These first end portions  126   a,b  are adapted and dimensioned to cooperate with an outer inlet/outlet portion  135  provided in the second valve disc  109  (cf.  FIGS. 4, 4   a ,  4   b ). 
     In similar fashion to the first flow portion  125 , the second flow portion  127  comprises on opposite ends second end portions  128   a,b . Just like the first end portions  126   a,b , the second end portions  128   a,b  are adapted and dimensioned to cooperate with the outer inlet/outlet portion  135  of the second valve disc (cf.  FIGS. 4, 4   a ,  4   b ). 
     Within the area delimited by the air passages  117 ,  123  and first/second flow portions  125 ,  127 , the second and third air passages  119 ,  121  are arranged. The second and third air passages  119 ,  121  are optionally linked in fluid communication by throttle  115   b  or throttle  115   c . The throttle  115   b  is optionally formed as a small recess in the contact surface  111 . The throttle  115   c  is optionally formed as a small recess in a surface  108  opposite the contact surface  111  of the first valve disc  107 . 
     The depth of the throttle  115   b/c  as well as its width are significantly smaller than the depth and width of the first/second flow portions  125 ,  127  such that there is only very little mass flow between the second and third air passages  119 ,  121 . 
     On opposing face sides of each first and second flow portion  125 ,  127 , there is located a step  130   a - d . The step  130   a - d  provides a retarded increase in flow cross-section. 
     The function of throttle  115   a - c  is to constantly allow-limited air exchange between the utilization elements  205   a,b  connected to the second and third air passages  119 ,  121 . On the one hand, this serves to provide for pressure equilibrium in the plurality of utilization elements  205   a,b . On the other hand, the limited cross-section of the throttle  115   a - c  prevents the utilization elements from over-expanding/over-compressing with regard to the respective other utilization element. This might, for example, be the case when one utilization element is aloft suspension bellow of a truck and the other utilization element is a right suspension bellow, and the truck drives at elevated speeds through long curves. 
     Between the first and second flow portions  125 ,  127  there is a respective dead space in the contact surface  111 . This dead space is adapted to accommodate entirely an outer inlet/outlet flow portion  135  of a manifold  129  shown in  FIGS. 4, 4   a ,  4   b . This is discussed in more detail hereinafter. 
     The second valve disc  109  of the valve disc arrangement  103  is shown in  FIGS. 4, 4   a  and  4   b . The second valve disc  109  comprises a contact surface  113 , which, when mounted inside the valve  101 , faces and abuts against the contact surface  111  of the first valve disc  107 . The second valve disc  109  is substantially rotationally symmetrical and cylindrical in shape with respect to rotational center axis  136   b . In the periphery of the second valve disc  109 , a number of recesses are formed to ensure securing and positioning of the second valve disc relative to the rotating housing portion  145  of the valve  101 . In the contact surface, there is formed a manifold  129 . The manifold comprises two arcuate manifold flow portions  131 ,  133 . The arcuate manifold flow portions  131 ,  133  are preferably arranged on the same radius with respect to the rotational center axis  136   b , and are circular in shape. The manifold flow portions  131 ,  133  are connected in fluid communication through a crosslink flow portion  137 , which extends radially between the two flow portions  131 ,  133 . As an extension to the crosslink flow portion  137  and extending outwards of the radius of the flow portions  131 ,  133 , the manifold  129  comprises the outer inlet/outlet flow portion  135 . From comparing  FIG. 3  and  FIG. 4 , it becomes clear that the outer contour of the outer inlet/outlet flow portion  135  is congruently shaped with respect to the opposing face edges and outer contour of the first and second flow portions  125 ,  127  connected to the first air passage  117  and fourth air passage  123 , respectively. 
     The crosslink flow portion  137  functions to constantly put manifold flow portions  131 ,  133  in fluid communication with each other. Thus, when the outer inlet/outlet flow portion  135  is in fluid communication with either the first air passage  117  or the fourth air passage  123  through either one of the first or second flow portions  125 ,  127  of the first valve disc  107 , air will flow either from both the second and third air passages  119 ,  121  towards an exhaust port of the valve  101 , or air will be supplied from the source of pressurized air through both the second and third air passages  119 ,  121  simultaneously. 
     Provided on opposite ends of the first arcuate manifold flow portion  131 , there are formed respective end portions  132   a,b . The end portions  132   a,b  are preferably dimensioned and adapted to respond with the shape of the second and third air passages  119 ,  121 . 
     Similarly, the second arcuate manifold flow portion  133  comprises on its opposite end portions  134   a,b , which are shaped in the same manner as the end portions  132   a,b.    
     Between the end portions  132   b ,  134   a  and  132   a ,  134   b , there is a dead space in the contact surface  113  of the second valve disc. The dead space is adapted to accommodate entirely the cross-section of the second and third air passages  119 ,  121  when the valve discs are in the neutral position  105   c  (cf.  FIG. 2 ). The end portions as inner inlet/outlet flow portions  134   a,b  and  132   a,b  are located on each end of the arcuate manifold flow portions  131 ,  133 . If the valve discs  107 ,  109  are rotated with respect to each other, the second and third air passages  119 ,  121  and the first and second manifold flow portions  131 ,  133  are brought into fluid communication with each other. 
     In a preferred embodiment, the dead space between the manifold flow portions  131 ,  133  in the second valve discs contact surface  113  are matched to the dead spaces between the first and second flow portions  125 ,  127  in the contact surface  111  of the first valve disc  107  such that, upon switching the valve, i.e., rotating the valve discs  107 ,  109  relative to each other, both the outer inlet/outlet flow portion  135  and the inner inlet/outlet flow portion  132 ,  134  are brought into fluid communication with the respective air passages. 
     As can best be seen from  FIG. 4 b   , the contact surface  113  preferably comprises in its periphery a number of second support ridges  139   a,b,c,d,e . Preferably, the height of the second support ridges  139   a - e  is flush with the inner portion of the contact surface  113  accommodating the manifold  129 . This may, for example, be achieved by creating a planar surface  113  and then removing a centrally circular recess in between the inner portion of the contact surface and the peripheral region accommodating the second support ridges  139   a - e.    
     With continued reference to  FIGS. 3 and 4 , and looking back at  FIGS. 2, 2   a  and  2   b , the different switching positions of the valve disc arrangement  103  are explained in more detail. In  FIG. 2 , the orientation of the valve discs  107 ,  109  in the neutral position is given reference sign  105   c . In this position, the outer inlet/outlet flow portion  135  is in the dead space between the first and second flow portions  125 ,  127  of the first valve disc  107 . Similarly, the second and third air passages  119 ,  121  are in the dead space between the flow portions  131 ,  133  of the manifold  129  in the second valve disc  109 . 
     If switched away from the neutral position  105   c , e.g., by moving lever  143  shown in  FIG. 1 , the valve discs can be brought into an arrangement as indicated by reference sign  105   b . In this switching position  105   b  (fifth switching position), the outer inlet/outlet flow portion  135  is in fluid communication with the second flow portion  127  and connected to air passage  123 . The flow cross-section between the valve discs  107 , 109  is however not yet maximized. If the rotation is continued from (fifth) switching position  105   b  onwards in the same direction, the next position reached, e.g., by further rotating the lever  143 , will be (second) switching position  105   a . In this position, the outer inlet/outlet flow portion  135  is in fluid communication with air passage  123  through second flow portion  127 . Now, however, the cross-section established between the two valve discs  107 , 109  is maximized and larger than in the “throttled” fifth switching position  105   b.    
     Alternatively, the valve may be switched away from the (third switching position) neutral position  105   c  shown in  FIG. 2  in the other direction. If switched from the (third) neutral switching position  105   c  to a position  105   d  (fourth switching position), the outer inlet/outlet flow portion  135  is brought into throttled fluid communication with the first air passage  117  and the corresponding first flow portion  125 . If the switching movement is continued until a (first) switching position  105   e  is reached, the throttle effect will again be minimized or deactivated. Because of the arcuate, preferably point-symmetric, design of the respective first and second flow portions  125 , 127  and first and second manifold flow portions  131  and  133 , and the radially oriented crosslink portion  137  spanning this constellation, it also becomes clear that operation of the valve is also possible if the first and second valve disc are placed next to each other rotated by 180° clockwise or counterclockwise. This enables more flexible selection of the place of mounting the valve  101 . 
       FIG. 5  shows an exemplary use of the valve  101  according to the embodiment of  FIGS. 1 to 4 . In particular,  FIG. 5  schematically shows a vehicle  300 . The vehicle  300  comprises an axle  301  supporting a number of tires  303 . The tires  303  and the axle  301  are linked through an air suspension system  200  to a superstructure  305 . 
     The air suspension system  200  comprises a plurality of utilization elements  205   a,b  such as pneumatic suspension bellows. The utilization elements  205   a,b  are functionally linked to the axle  301  and/or optionally directly to a single-tire support. 
     The utilization elements  205   a,b  are connected through a first fluid channel  21  and a second fluid channel  22  to the valve disc arrangement  103  of valve  101 . Upon rotation of a lever, such as lever  143  of  FIG. 1 , the valve  101  can be brought into one of five switching positions  105   a - e  as explained hereinabove with respect to  FIGS. 2 to 4 . Depending on the switching position, air is transported from the utilization elements through the valve  101  to an exhaust port  3  (switching positions  105   b  “with throttle” or  105   a  “without throttle”). Alternatively, air can be supplied from a source  207  of pressurized air through fluid supply port  1  to the valve  101  and from thereon to the utilization elements  205   a,b  (position  105   d  “with throttle” and position  105   e  “without throttle”). 
     In the diagrammatic representation of  FIG. 6 , the flow rate of air streaming through the valve is plotted against the angular rotation in degrees of the valve discs with respect to each other. Starting from a rotational angle of 0°, there is a first section N in which the valve remains in the neutral position. Upon exceeding the neutral position range, there is a first section A with comparatively steep increase in flow rate. In this section A, the respective inner and outer flow portions  132 ,  134 ,  135  of the manifold  129  are brought along their entire width in fluid communication with the congruently shaped and correspondingly aligned first and second flow portions  125 ,  127  and first and second manifold flow portions  131 ,  133 . Next, due to the provision of steps  130   a - d , or alternatively rounded edges or chamfers, the increase in flow rate becomes more shallow compared to the first section A in a section B. Towards higher degrees of rotation, the flow rate increase becomes steeper again and, in section C, the flow rate increase is substantially linear until approaching full opening of the flow cross-section, which is denominated by section D. 
     The part of the diagram to the right of  FIG. 6 , denominated S, is the flow characteristic of the “supply” switching positions. The left side of the diagram in  FIG. 6 , denominated E, is the “exhaust” switching position flow characteristic. Section N substantially corresponds to the neutral position  105   c  in  FIG. 2 . 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.