Abstract:
A ventilation arrangement for the head space of the fuel tank of a vehicle comprises a switchable main valve intended for adjusting an arbitrary pressure in the head space of the tank. By way of the opening position of the main valve, a connection between a connection ( 5 ) intended for connection to the head space and a connection ( 6 ) intended for connection to the surrounding atmosphere is established, wherein the main valve is assigned a pilot valve, which opens during a first path element of a switching movement, wherein the main valve only opens following this first path element. Because of the small cross section of the pilot valve and the pressure relief that materialized through its opening, the switching power can be reduced and a smaller size drive can be employed.

Description:
BACKGROUND 
     The invention relates to a ventilation arrangement for a fuel tank of a vehicle. 
     During the course of the drive development of motor vehicles, vehicles are being developed which, besides the classic combustion engine, also include a drive that is electromotorically fed by a battery. These vehicles are also called hybrid vehicles and make possible locomotion for a certain time solely with the help of an electric motor. 
     The fuel required for operating the combustion engine is stored in a fuel tank, from which with the engine stationary, vapors escape because of vapor pressure differentials relative to the surrounding atmosphere, which are conducted through an activated charcoal filter inserted in a ventilation line, which is intended to adsorptively bind hydrocarbon components. With the engine running, by contrast, these retained hydrocarbon components are absorbed by inflowing air and fed to the combustion engine process of the engine, so that their escape into the environment is likewise prevented. 
     Since in the time of an exclusively electric operation of the vehicle, no ambient air flows through the activated charcoal filter, a regenerating of stored hydrocarbon components is not required during this time. In order to achieve an at least approximately regeneration despite the thus reduced operating time of the combustion engine, a pressure that is increased compared with the surrounding atmosphere is demanded in the head space of the fuel tank in order to reduce the amount of hydrocarbon components that have to be adsorbed in the activated charcoal filter. 
     It is generally known, to limit the pressure in the head space of the fuel tank by means of a pressure relief valve for safety reasons. This pressure relief valve establishes a continuous connection between the head space and the surrounding atmosphere when an overpressure or a maximum pressure occurs. 
     It is known, furthermore, to limit the pressure drop within the tank during the operation of the combustion engine as a result of a continuous removal of fuel through a valve, which on undershooting a minimum pressure, establishes a connection to the surrounding atmosphere and thus a pressure balance. 
     While refueling the vehicle, the gas volume displaced by the inflowing, liquid fuel plus fuel evaporations have to be conducted out of the tank. In the process, a pressure balance with the surroundings has to be established through a complete ventilation, since otherwise fuel is discharged from the filler tube of the tank. 
     However, this demand opposes the desire for an increased pressure in the fuel tank. 
     For operating a fuel tank in which an increased internal pressure has to be maintained, there is thus the necessity of three valves. These have to have an adequate tightness, since otherwise the pressure forming in the tank would be removed with prolonged stoppage and the conditions mentioned at the outset of a quantatively balanced adsorption and desorption of hydrocarbon components in the activated charcoal filter could not be satisfied. 
     From the associated main application 10 2010 044 336.0, a ventilation arrangement for a fuel tank of a vehicle is known, wherein in a housing the functions of a pressure relief valve, of a valve for ventilation for the purpose of limiting a negative pressure during the operation of the motor and that of an electromagnetically switchable valve, which is intended for producing a pressure balance with the surroundings during refueling, are combined. 
     For establishing preferably low flow resistances, the line cross sections, via which the ventilation arrangement is in connection with an activated charcoal filter and the head space of the tank, is dimensioned relatively large. However, this in turn results in high actuating forces even with low pressure gradients, which have to be created via the drive of the electromagnetically switchable valve. Usually, a magnetic drive or an electric motor is employed at this point, which however in view of the switching forces to be created, have to be dimensioned relatively large. The dimensioning is accompanied by a correspondingly large volume. 
     SUMMARY OF THE INVENTION 
     In view of this background it is the object of the invention to improve a ventilation arrangement for the fuel tank of a vehicle with its valves assigned to the head space for realizing a maximun non-exceeding pressure, a minimum, not undershootable, pressure, and an arbitrarily adjustable pressure in particular intended for fueling, in that a drive for the electromagnetically switchable valve integrated in the ventilation arrangement can be dimensioned weaker in terms of power and in an installation space saving manner. With such a ventilation arrangement, this object is solved through the features of the invention as described below. 
     It is substantial for the invention that the switching movement of the drive, starting out from the closing position of the valve to the realization of an arbitrary pressure, in the following partly also called main valve, up to its opening position, is divided into two path elements, wherein during the first path element merely a pilot valve is opened. Compared to the flow cross sections of the two mentioned connections, this is merely characterized by a small cross section, so that the energy expenditure for its opening is correspondingly low. Opening of the pilot valve however results in a reduction of the pressure gradient acting on the sealing plate of the main valve, so that altogether the switching power to be provided via the drive is correspondingly reduced. This brings with it the advantage, that a drive with a smaller installation volume can be employed. 
     The features of another embodiment are directed at a possible design concretization of the ventilation arrangement, in particular of the pilot valve. This is characterized by a blocking element, which interacts with a seat surface arranged on the one end of a bore of a shaft, wherein the blocking element is in connection with an armature part, the movement of which can be generated by means of an ring coil of the drive. On the one end of the shaft, a sealing head is molded on which engages behind a sealing plate, which forms an element of the main valve. For realizing the pilot valve, use insofar is made of design elements of the ventilation arrangement which are present anyhow. Thus, said ventilation arrangement can thus be made available altogether as a highly compact unit. 
     The features of yet another embodiment are directed at further details relating to the design realization of the two path elements. During the first path element, the main valve remains functionless and is only opened during the course of the second path element. 
     In further embodiments of the invention, the features are each directed at realizing the closing position of the pilot valve and of the main valve. These are brought about in the currentless state of the drive by springs in each case. 
     The features of additional embodiments are directed at the realization of the first path element, in particular at the actuation of the pilot valve and the main valve which commences one after the other during the switching movement of the drive starting out from the closing position. 
     Above, the drive was described as magnetic drive consisting of a ring coil and a plunger armature. Similarly, an electric motor can also be employed at this point. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING  
       In the following, the invention is described in more detail making reference to the exemplary embodiment shown according to  FIG. 1  in the drawing which shows an axial section of a valve assembly. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a valve assembly according to the invention in an axial section, consisting of a first housing part  2  receiving an ring coil  1 , which at the bottom is fitted via a collar  3  to a facing section  4  of a connection  5  intended for connection to the head space of a fuel tank and to a connection  6  intended for connection to the ambient atmosphere. Both housing parts  2 ,  7  in the assembled state form the housing  30  that receives all components of the valve assembly. 
     Within the ring coil  1 , extending in direction of its axis, there is located a bar-shaped armature path  8 , the movement of which in the direction of a top side  9  is limited by a magnetically active stop part  10  that is arranged in a fixed manner. A coupling piece  11  that is in connection with the armature  8  protrudes out of the housing part  2  at the bottom and into the housing part  7 . The housing part  2  thus mainly serves to receive the coil body of the ring coil  1 . 
     An attachment part molded onto the top of the housing  2  is designated  12 , which attachment part serves for receiving an electrical connection  13  for the ring coil  1 . 
     The coupling piece  11  extends through an opening  20  of the housing part  7  and stands at its lower end, guided in a sliding manner via a backing disk  14  along a cage  15 , which in turn is fastened to a support plate  16 . The support plate  16  is designed as carrier of a sealing plate  17  preferentially consisting of a rubber-elastic material, which bears against a ring-like sealing surface  18  forming the inlet opening  26  of the connection  6 . The backing disk  14  in each case is connected in a fixed manner to the coupling piece  11 . 
     A spring, the one end of which is axially supported on the side of the support plate  16  facing away from the sealing surface and its other end on the coil element of the ring coil  1  or the housing part  2 . The sealing plate  17  thus bears against the sealing surface  18  under a preload, which is defined by the spring  19 , wherein through axial displacement of the mentioned coil element or the housing part  2  an adjustment of this preload is possible. For example, a screw connection can exist between the housing parts  2 ,  7 , which in axial direction of the ring coil  1  makes possible an adjustment of the position of these housing parts relative to each other. 
     A shaft, which extends coaxially to the armature part  8 , within which a continuous bore  28  runs likewise coaxially to the armature part  8 , the end of which facing the coupling piece  11  forms a conically expanding seat surface  31  for a blocking element  32  formed complementarily to said seat surface and molded onto the facing side of the backing disk  14 , is designated  21 . A ring-like sealing disc preferentially consisting of an elastomer material surrounding the blocking element  32  and held on the side of the backing disk  14  facing the shaft  21 , is designated  33 . 
     A yoke, which is displaceably arranged along the cage  15  and which is in connection with the shaft  21  on its one end facing the armature part  8  is designated  22 . The other end of the shaft  21  extends through a central, ring-like opening  23  of the support plate  16  and of the sealing plate  17  and is in connection on the side facing the connection  6  with a plate-like sealing head  24  bearing against the rim of the opening  23  in a sealing manner. 
     A further spring, the one end of which bears against the side of the yoke  22  facing the support plate  16  and the other end of which bears against the side of the support plate  16  facing the yoke  22 . This spring  25  determines the preload, under which the sealing head  24  bears against the rim of the opening  23 . It is evident that with the valve assembly according to the invention, three valve functions that act independently of one another are realized. 
     The shaft  21  in conjunction with the sealing head  24  bearing against the rim of the opening  23  under the preload of the spring  25  forms a pressure relieve valve, which in the opening position makes possible a flowing-out of gases from the head space of the fuel tank via the connection  5  and an opening  23  in the manner of a circular ring between the shaft  21  and the inner surfaces facing the latter towards the atmospheric connection  6 . The overpressure within the head space, which leads for opening this pressure relief valve, is defined by the spring  25  and can be adjusted in that the shaft  21  via its screw connection with the yoke  22  can be axially moved to a greater or lesser degree. For this purpose, the sealing head  24  is equipped with an internal square profile  27  or a comparable profile determined for interaction with a screwing tool. 
     The system consisting of the support plate  16 , of the sealing plate  17  bearing against the sealing surface  18 , the cage  15  and the spring  19  forms a vacuum valve, which in the opening position makes possible the inflow of gases via the atmospheric connection  6 , the inlet opening  26  and the connection  5  in the head space of the fuel tank. The vacuum within the head space, which leads to the opening of this vacuum valve, is defined by the preload of the spring  19 , which is adjustable through the axial displacement of the coil element of the ring coil  1  or of the housing part  2 . In the event of a screw connection between the housing parts  7 ,  2 , this adjustment can be carried out in a particularly easy manner. 
     The system consisting of the ring coil  1 , the armature part  8 , the coupling piece  11 , the backing disk  14 , the cage  15 , the support plate  16  and the sealing plate  17  bearing against the sealing surface  18  form an electromagnetically switchable valve, which in the opening position makes possible a continuous connection between the connections  5 ,  6  via the inlet opening  26 . A switching position of the valve, namely the opening position, is established in the case of electrification of the ring coil  1 , whereas the closing position materializes in the currentless state of the ring coil  1  under the action of the spring  19 . This valve is used in order to prevent the development of an increased pressure in the head space of the fuel tank during fueling. 
     A spring, which is active between the stop part  10  that is arranged in a fixed manner and the armature part  8  that by contrast is movably arranged, is designated  29 . The purpose of this spring consists of the following: 
     The system consisting of the seat surface  31 , the blocking element  32  and the coupling piece  11  forms a pilot valve within the scope of the electromagnetically switchable valve, also called main valve, mentioned above, which in the non-electrified stage of the ring coil  1  is held in the closing position under the resetting force of the spring  29 , in which the blocking element  32  bears against the seat surface  31  in a sealing manner, thereby closing the bore  28 . 
     Upon an electrification of the ring coil  1 , the armature part  8  is initially moved against the resetting force of the spring  29  by a first path element in the direction of the stop part  10 , so that the mentioned pilot valve is transferred into its opening position, in which between the connection  6  via the bore  28  and the cage  15  a continuous connection with the connection  5  is established. Between the seat surface  31  on the one hand and the outer surface of the blocking element  32  on the other hand, there is a ring-shaped through-flow surface in this opening position of the pilot valve, which is increasingly enlarged during the opening movement along the first path element. 
     A through-flow of the pilot valve results in a pressure relief of the support plate  16 , so that the energy expenditure for opening the inlet opening  26  is correspondingly less. Only at the end of the first path element will the backing disk  14  exert a driving action on the cage  15 , namely along a second following path element up to the complete opening of the inlet opening  26 . 
     During the opening movement along the two path elements, the pilot valve and the main valve are thus opened one after the other. 
     Within the cage  15 , which is in a fixed connection with the support plate  16 , the backing disk  14 , which is in fixed connection with the coupling piece  11  and in this manner with the armature part  8 , is movably arranged in a limited manner in axial direction of the coupling piece  11 , namely corresponding to the dimensioning of the mentioned first path element. 
     As soon as an electrification of the ring coil  1  is absent, the spring  29  supported by the spring  19  exerts a resetting force on the support plate  16 , which transfer the pilot valve and the main valve in the closing position. 
     It is evident that because of the pilot valve having a comparatively small flow cross section despite the relatively large cross sections of the connections  5 ,  6 , the main valve, as explained above, can be actuated with a relatively low energy expenditure, so that a correspondingly small size drive is adequate. 
     LIST OF REFERENCE NUMBERS 
     
         
         
           
               1 . Ring coil 
               2 . Housing part 
               3 . Collar 
               4 . Section 
               5 . Connection 
               6 . Connection 
               7 . Housing part 
               8 . Armature part 
               9 . Top 
               10 . Stop part 
               11 . Coupling piece 
               12 . Attachment part 
               13 . Connection 
               14 . Backing disk 
               15 . Cage 
               16 . Support plate 
               17 . Sealing plate 
               18 . Sealing surface 
               19 . Spring 
               20 . Opening 
               21 . Shaft 
               22 . Yoke 
               23 . Opening 
               24 . Sealing head 
               25 . Spring 
               26 . Inlet opening 
               27 . Internal square profile 
               28 . Bore 
               29 . Spring 
               30 . Housing 
               31 . Seat surface 
               32 . Blocking element 
               33 . Sealing disk