Flow limiting element for a fuel vapor switching and ventilation valve of an internal combustion engine

Abstract

Flow limiting element (94) for a fuel vapor switching and ventilation valve (10) of an internal combustion engine (26), comprising a control body (100) having a radially inner flow-around body (102) that is movable into a flow channel (107) with a nozzle-shaped section (104) that is formed in a second flow housing part (108), a spring (122) by means of which the control body (100) is loaded in a direction pointing out of the nozzle-shaped section (104), a cylindrical housing wall (136) that lies opposite a radial boundary wall (132) of the control body (100), wherein a plurality of knobs (138) distributed over the circumference are formed on the radial boundary wall (132) of the control body (100), with which knobs the control body (100) contacts the housing wall (136).

Description

The invention relates to a flow limiting element for a fuel vapor switching and venting valve of an internal combustion engine, having a regulating body which has a radially inner flow-around body which is movable into a flow duct having a nozzle-shaped section which is formed in a flow housing part, a spring via which the regulating body is loaded in a direction pointing out of the nozzle-shaped section, and a cylindrical housing wall which is opposite a radial limiting wall of the regulating body.Such flow restriction members are used, for example, in fuel vapor switching and venting valves serving as cut-off and relief valves for the fuel tank. They are arranged fluidically between the fuel tank of the vehicle and an activated carbon filter which serves for absorbing fuel vapors and are intended to compensate pressure fluctuations in the fuel tank. In the case of an overpressure or underpressure which arises in the tank, the pressure is intended to be reduced by a mechanical bypass function in the case of the overpressure by venting to the activated carbon filter and, in the case of the underpressure, by venting, the underpressure in the tank is intended to be limited or compensated.In addition, for safety reasons, it must be made possible to actively actuate the valve in order to be able to open the path between the fuel tank and the activated carbon container in the event of faults in the region of the tank pressure regulation in order to avoid implode or explode the tank.Thus, the fuel vapor switching and venting valve must be opened, for example, directly before and during the refueling process, in order to ensure, on the one hand, that no fuel vapors get to the user as a result of overpressure when the fuel cap is opened and, on the other hand, that no increased pressure build-up takes place during refueling in the tank.The flow limiting elements of these valves serve to avoid overloading of the activated carbon filter. In order not to have to build the activated carbon filters too large, the maximum flow rate to the activated carbon filter is limited by means of the flow limiting elements to a flow rate which allows the activated carbon filter to completely filter the fuel vapor in order to prevent fuel vapors from getting into the open air.Various valves have become known which combine one or more of these functions. Thus, DE 10 2010 044 336 A1 describes a valve arrangement in which a switching valve can be actuated by means of an electromagnet in order to establish a connection between the tank and the activated carbon filter. The valve body of this valve has a second bearing surface with which the valve body bears against the regulating body of a pressure relief valve which bears spring-loaded against the valve body and thus closes a central passage in the valve body as long as there is no overpressure in the tank. Furthermore, in the event of a negative pressure in the tank, the valve body can be moved from the seat against a second spring element, with the result that the tank is ventilated. Accordingly, with only one valve, an active connection and disconnection of a fluidic connection between the tank and the activated carbon filter can be produced and, in addition, at defined switching points, venting or venting can be produced in the event of excess or suppression being too high. However, it is not possible with this valve to limit the flow rate to a specific value, since the opening cross section at the pressure relief valve also increases as the pressure difference increases.Accordingly, a flow limiting element must be provided which responds even in the event of small pressure differences occurring and permits a sufficient flow, and can thus be flowed through with as little pressure loss as possible.Thus, DE 103 13 662 A1 proposes a flow limiting valve in which a regulating body is displaceable into a nozzle-shaped section counter to the force of a spring if a certain pressure difference is exceeded. Depending on the spring design, however, either the switching point of the valve is too late, with a sufficient flow rate being present, or the switching point is shifted in the direction of a lower pressure difference, which, however, leads to low flow rates. The long guide surface of the valve results in increased friction, which leads to undesired increased necessary opening forces.DE 11 2012 003 664 T5 discloses a double-acting nonreturn valve, the inner part of which is loaded in the opposite direction to the outer part by a spring in each case. The inner part of this valve has radially outer projections on which the one spring is supported.U.S. Pat. No. 6,353,955 B2 likewise describes a double-acting nonreturn valve in which the outer part slides along guide ribs of the housing.Accordingly, there is the problem of ensuring a sufficient flow rate by reducing the pressure losses in the valve even in the case of small applied pressure differences and nevertheless providing a sufficient force for switching the flow restrictor in order thus to limit the flow rate to a maximum. Furthermore, the problem arises that, in order to generate a sufficient opening force over the entire stroke, on the one hand, a force compensation via the flow-limiting valve must be delayed and, on the other hand, an increased frictional resistance, which would lead to the flow-limiting element being difficult, must be prevented. In addition, a guide must be provided with which tilting or tilting of the flow limiting element is reliably prevented.The object therefore is to provide a flow limiting element for a fuel vapor switching and venting valve of an internal combustion engine, with which, on the one hand, an actuation for limiting the maximum flow rate is made possible and, on the other hand, in the case of very small pressure differences, a sufficient flow rate is ensured due to low pressure losses in the valve in order to be able to reduce an overpressure sufficiently quickly. Accordingly, with the smallest possible pressure losses and thus small pressure differences occurring, the smallest possible necessary flow rate should be able to be realized, which corresponds to a maximum permissible flow rate. In particular, a timely and reliable switching is to be ensured in that the friction on the flow-limiting element is reduced and thus as large an opening force as possible acts on the body of the flow-limiting element due to the pressure difference. In addition, tilting or tilting of the flow limiting element is to be prevented.This object is achieved by a flow limiting element for a fuel vapor switching and venting valve of an internal combustion engine having the features of main claim 1.The flow limiting element has a regulating body with a radially inner flow around body, which is arranged in a flow channel of a second flow housing part. It projects into a nozzle-shaped section of the flow channel and is moved out of the nozzle-shaped section or into the latter on account of an applied pressure difference and a spring force. The spring force is applied by a spring, by means of which the control body is loaded in a direction pointing out of the nozzle-shaped section. By using the nozzle shape in the flow channel, the surface available for the flow is changed depending on the applied pressure difference, so that with a larger pressure difference, a smaller flow surface is available, whereby the volume flow reaching the activated carbon filter is limited even with high pressure differences. The flow limiting element has a radial limiting wall which lies opposite a cylindrical housing wall. Because a plurality of knobs distributed over the circumference are formed on the boundary wall of the control body, with which knobs the control body touches the housing wall, a guidance of the control body in the flow housing is produced, by means of which guidance a ready-to-move action is achieved on account of the small contact surfaces, as a result of which the actuating forces can be lower. Thus, on the one hand, a sealing narrow gap can be produced on the flow limiting element, by means of which a pressure equalization between the front side and the rear side is delayed, and in spite of the small gap, a difficulty is avoided. The housing wall accordingly serves as a guide wall and can either protrude into the regulating body or radially surround it. If the housing wall projects into the flow-limiting element, it can be arranged both radially inside and radially outside the limiting wall of the flow-limiting element on which the knobs are formed, as long as these two walls are situated opposite one another in contact. Furthermore, by distributing the knobs over the circumference, tilting of the flow limiting element in a first flow housing part is also avoided.Preferably, however, the boundary wall of the control body is a radial outer wall on which the knobs are formed with which the control body touches the housing wall, which is an inner wall surface of the first flow housing part. The housing wall thus completely surrounds the regulating body, so that the gap between the housing wall and the boundary wall simultaneously serves as a gap seal, which delays a pressure equalization between the inflow side and the outflow side of the throughflow boundary element. The sealing effect is further enhanced by the knobs, since the flow resistance is additionally increased.It is particularly preferred if the knobs touch the housing wall in punctiform fashion. Such minimal contact provides minimal friction, so that the static pressure difference can be almost completely used as the pressure force displacing the flow limiting element. However, this point contact also requires a very precise production.In a particular embodiment, the knobs are designed as ball segments. These are simple to produce and make it possible that even with small tolerance deviations and resultant small oblique positions, a line contact with the housing wall is maintained.In a preferred embodiment, three to five knobs are arranged on the boundary wall of the regulating body so as to be distributed uniformly over the circumference. By means of three segments, even guidance over the circumference can already be achieved, wherein the production effort is minimized.The control body preferably has a radially outer ring, on the radially outer boundary wall of which the knobs are formed, as a result of which the pressure loss via the throughflow limiting element is kept low and at the same time a larger force application surface is provided by the ring for actuation, which makes possible an earlier switching of the throughflow limiting element. For this purpose, the wall of the first flow housing part surrounding the ring is arranged very close to the ring, so that only a narrow gap is left free, which offers a flow resistance and thus forms a gap seal. This embodiment prevents pressure equalization from occurring between the inflow side of the ring, i.e. the side which is directed toward the actuator, and the downstream side. Accordingly, the pressure difference on the ring is maintained even as the opening of the flow limiting element progresses, as a result of which the opening force is also maintained over the entire stroke of the flow limiting element. The studs are very simple to form in this embodiment.A particularly simple embodiment using little installation space results if the spring bears against the outer ring, wherein one or more passage openings are formed radially between the ring and the flow-around body. In this way, the spring is also arranged outside the region through which flow takes place and thus does not cause any additional pressure losses.The knobs are correspondingly arranged in a gap which is formed between an inner surface of the housing wall of a first flow housing part and the radially outer ring and increase the flow resistance produced by the gap seal. This ensures reliable guidance over the entire stroke of the flow limiting element.Preferably, the flow body has a spherically or conically shaped flow surface which is arranged opposite an inner surface of the nozzle-shaped section, wherein the radially outer ring is arranged radially outside the smallest flow cross section of the nozzle-shaped section of the flow channel and has a base from which the radially outer boundary wall extends axially in a direction pointing away from the nozzle-shaped section. The spherical shape of the flow-around body in conjunction with the nozzle-shaped section brings about a uniform flow to the activated carbon filter, so that an almost constant flow can be achieved for different pressure differences. By the arrangement of the passage openings, the pressure loss via the flow limiting element is kept low. The ring does serve as an application surface for an applied pressure difference or the static pressure that arises, but it is located outside the main flow through the flow channel, so that it causes a pressure loss only to a small extent. When the flow-limiting element is displaced to the maximum extent against the spring force, the flow-limiting element still bears with the ring against the axial end of the nozzle-shaped section, which serves as a stop. The bottom of the outer ring serves to enhance the function of the radially outer ring as a force application surface because ram pressure surfaces form on the bottom because the pressure on the bottom is maintained longer because outflow radially outward through the boundary wall is reduced. Furthermore, this wall serves as a stop on the first flow housing part in the end position. In addition, this wall enhances the effect of a clearance seal because it extends the clearance between the radially outer ring and the surrounding wall of the first flow housing portion, thereby increasing the flow resistance.It is also advantageous if a radially inner boundary wall extends axially from the bottom of the radially outer ring in a direction pointing away from the nozzle-shaped section and webs are formed in the circumferential direction between the passage openings on the control body, via which webs the radially outer ring is fastened to the flow-around body, wherein the radially inner boundary wall has opening slots which are arranged in a radial extension of the webs. This arrangement further reinforces the effect of the bottom as a force application surface, since a radially inward outflow is also prevented. A particularly strong ram effect and thus a particularly high actuating force is also achieved, since the webs are formed on the control body in the circumferential direction between the passage openings, and the opening slots are arranged in the radially inner boundary wall in a radial extension of the webs. The opening slots do not of course have to have the same width as the webs. The webs act as dynamic pressure points, from which the flow produced by the dynamic pressure is conducted via the opening slots to the bottom of the radially outer ring and there again generates a force acting against the spring. Accordingly, the switching point is shifted toward smaller pressure differences.A flow limiting element for a fuel vapor switching and venting valve is thus provided, with which the fuel vapor can be passively discharged to the activated carbon filter in the event of an excessively high overpressure with respect to atmosphere in the tank. In addition, an excessively rapid outflow of the fuel vapor from the tank and to the activated carbon filter is prevented by the flow limiting element according to the invention, which limits the flow rate for all pressures to a maximum flow rate, which corresponds to a fuel vapor flow rate to be absorbed or stored by the activated carbon filter. This flow is achieved even at low pressure differences due to the low pressure losses and the high force application surfaces provided. Also, a frictional force acting in the opposite direction is minimized, so that the flow limiting element can be moved even at relatively low actuating forces due to the simple and effective sliding guide. Due to the exact guidance over the circumference, tilting or an oblique position increasing the friction is also avoided.An embodiment of a fuel vapor switching and venting valve with a flow limiting element according to the invention for an internal combustion engine, in particular for use in a hybrid drive, is illustrated in the figures and is described below. FIG. 1 shows a side view of a fuel vapor switching and venting valve with schematically depicted connected components. FIG. 2 shows a side view of the fuel vapor switching and venting valve from FIG. 1 with a flow limiting element according to the invention in a sectioned representation.FIG. 3 shows a side view of the control body of the flow limiting element according to the invention in a sectional illustration.As shown in FIG. 1, the fuel vapor switching and venting valve 10 has a first port 12 that protrudes laterally from a housing 14 of the fuel vapor switching and venting valve 10 and a second axial port 16. The first, lateral port 12 is connected to a fuel tank 18, while the second axial port 16 is connected to an activated carbon filter 20. From activated carbon filter 20, a line leads via a fuel vapor outlet valve 22 to the atmosphere or via a second line, in which a purge valve 24 is arranged, to an internal combustion engine 26, where the fuel vapors can be supplied to the combustion.The construction of the fuel vapor switching and venting valve 10 can be seen in FIG. 2. It consists of an electromagnet 28, which serves as an actuator and has a coil 32, wound onto a coil carrier 30, an inner core 34, an axially displaceable armature 36 and a yoke 38 radially surrounding the coil 32, and a flux return plate 40 arranged at the axial ends of the coil carrier 30, each of which forms an electromagnetic circuit. This electromagnet 28 and in particular the yoke 38 is injection-molded with a plastic to form an actuator housing part 42 of the housing 14, which plastic also forms a plug 44 and fastening eyes 46 and has an axial opening 48 at the end opposite the core 34, into which a sliding socket 50 is inserted, which guides the armature 36. This sliding bushing 50 is made of a non-magnetizable material and is cup-shaped, with the bottom 52 resting against the core 34. The main guide region of the sliding bushing 50 is surrounded by a soft magnetic bushing 54 which is pressed into the return plate 40 and the coil carrier 30. The sliding bushing 50 has a radial extension 55, from which an extended region 56 extends at its open end, which is arranged opposite the wall surfaces of the actuator housing part 42 delimiting the opening 48, wherein a sealing ring 58 is arranged between the extended region 56 of the sliding bushing 50 and the wall surface delimiting the opening 48, by means of which sealing ring penetration of fuel vapor in the direction of the coil 32 is prevented.A first flow housing part 60 is fastened to the actuator housing part 42 and forms the first connection 12 and in which a valve body 62 is movable, which is coupled to the armature 36 by a valve rod 64 being fastened to the armature 36, to which valve body 62 is gimbal-mounted. The valve rod 64 is fastened to the armature 36 by the valve rod 64 being pushed through a through bore 66 in the armature 36 until the valve rod 64 bears with an extension 68 axially against the end of the armature 36 pointing toward the valve body 62. In this state, the valve rod 64 protrudes at the opposite end from the armature 36 and can be deformed there, so that a type of rivet head 70 bears in an annular recess 72 on the side of the armature 36 facing the core 34. On the opposite side, the valve rod 64 likewise has a type of rivet head 74 which projects into the valve body 62, with the result that the valve body 62 bears on the armature side against the flat end of the rivet head 74, for which purpose an opening 76 is formed on the valve body 62, the diameter of which opening substantially corresponds to the diameter of the valve rod 64. The round side of the rivet head 74 is arranged opposite a projection 78 projecting radially into the interior of the valve body 62, so that the valve body 62 is only slightly movable axially relative to the valve rod 64.A first spring 80 biases the valve body 62 against the flat side of the rivet head 74 on the one hand and the valve body 62 with the armature 36 against a first valve seat 82 formed on the first flow housing part 60 by clamping the spring 80 between the valve body 62 and the extension 55 of the slide bush 50.In the closed state, the valve body 62 bears with a first, radially outer bearing surface 84, which is designed as a sealing lip of a sealing element 86, against the first valve seat 82, which surrounds a through-flow opening 87. The sealing element 86 consists of an elastic material, in particular an elastomer, and is fastened to a carrier element 88, via which the connection to the valve rod 64 also exists, so that the projection 78 and the opening 76 are formed on the carrier element 88. The carrier element 88 covers the sealing element 86 as far as possible in the direction of the armature 36 and also surrounds it at least partially radially. In addition to the first bearing surface 84, the sealing element 86 has a further, second bearing surface 90 which is placed radially inside the first bearing surface 84 and is likewise designed as a sealing lip and is arranged axially closer to the armature 36 than the first bearing surface 84 and with which the sealing element 86 can be lowered onto a second valve seat 92.This second valve seat 92 is axially movable and is formed on a flow limiting element 94 according to the invention, which, when resting on the second bearing surface 90, closes a passage opening 96 formed radially inside the second bearing surface 90 on the sealing element 86 and on the valve body 62.The flow limiting element 94 is embodied in two parts in the present exemplary embodiment and consists of a valve seat body 98 which consists of a fastening pin 97 and a bearing surface 99 extending perpendicular to the central axis, on which bearing surface the second valve seat 92 is formed, and a regulating body 100 having a central blind hole 101 into which the fastening pin 97 of the valve seat body 98 extends for fastening the regulating body 100 to the valve seat body 98.The control body 100 has a radially inner flow-around body 102 with a spherically shaped flow-around surface 103, which corresponds to a nozzle-shaped section 104 formed on an inner surface 106 of a second flow housing part 108, which is fastened to the first flow housing part 60 and forms a flow channel 107 opening out at the second, axial connection 16.The control body 100 has webs 110 which extend radially outwards from the flow-around body 102 and connect the flow-around body 102 to a radially outer ring 112. Correspondingly, viewed in the circumferential direction, a plurality of passage openings 114 are formed between the webs 110 and between the flow-around surface 103 and the ring 112.The second flow housing part 108 has a radially inner, annular projection 116, on the inside of which the nozzle-shaped section 104 is formed and the axial end of which serves as a stop 118 for the movement of the flow limiting element 94, which, when the ring 112 bears against the stop 118, only opens up a narrow gap 120 between the flow-around surface 103 and the inner surface 106 of the nozzle-shaped section 104. The flow limiting element 94 is loaded by means of a second spring 122, which is clamped between an axial groove 124 of the ring 112 and a bearing surface 126 on the second flow housing part 108, in the direction of the valve body 62 and pointing away from the stop 118, so that the spring 122 presses the second valve seat 92 against the valve body 62 and loads the flow-around body 102 out of the smallest cross section of the nozzle-shaped section 104.On the side of the ring 112 axially opposite the axial groove 124, the latter has a base 128, from which a radially inner limiting wall 130 extends radially on the inside and a radially outer limiting wall 132 extends radially on the outside in the direction of the actuator or the valve seat 92. Opening slots are formed in the inner boundary wall 130, opposite the webs 110, via which the base 128 of the ring is directly connected fluidically to the surface of the webs 110. The radially outer boundary wall 132 is arranged radially directly opposite a cylindrical housing wall 136 of the surrounding flow housing part 60, so that only a narrow gap remains between the radially outer boundary wall 132 and the flow housing part 60, which gap acts as a gap seal.Furthermore, the limiting wall 132 serves as a stop, by means of which the end position of the flow limiting element 94 is fixed.According to the invention, three knobs 138, which are distributed uniformly over the circumference and by means of which the regulating body 100 bears in each case in punctiform manner against the surrounding cylindrical housing wall 136, are formed on the radially outer boundary wall 132. These knobs 138 serve correspondingly to guide the flow-limiting element 94 in the flow housing part 60 in a uniform manner, as a result of which frictional forces which occur are minimized and tilting of the flow-limiting element 94 is prevented.The function of the valve is now such that, in the normal state, the valve body 62 rests on the first valve seat 82 and the second valve seat 92 and there is therefore no flow through between the connections 12, 16.If, for example, the pressure in the fuel tank 18 and thus at the first connection 12 now rises to, for example, above 0.3 bar overpressure with respect to atmosphere, the second valve seat 92 is lifted off the second bearing surface 90 of the valve body 62, since at this pressure the forces acting on the flow limiting element 94 due to the pressure difference are greater than the spring force of the second spring 122. Correspondingly, fuel vapor flows from the first connection 12 via the passage opening 96 on the valve body 62 and the passage opening 87 in the interior of the first valve seat 82, and through the passage openings 114 between the webs 110 and the gap 120 to the second connection 16 and thus in the direction of the activated carbon filter 20, so that the pressure in the fuel tank 18 is reduced. The volume flow which arises in this case is influenced by the position of the flow-around body 102 in the nozzle-shaped section 104.At very high pressures, which would lead to volume flows that can no longer be absorbed by the activated carbon filter 20, the function of the flow limiting element 94 is activated. This is displaced against the stop 118 in the event of very high pressure differences. In this position, only a minimum gap 120 is released between the flow-around body 102 and the nozzle-shaped section 104, which allows a maximum flow rate corresponding to the maximum permissible flow rate of the activated carbon filter 20 of, for example, approximately 220 l / min. This is achieved by utilizing the bottom 128 of the radially outer ring 112 completely as an additional force application surface against which the flow from the first port 12 impinges. The boundary wall 132 prevents the fuel vapor from easily flowing out from the ring 112, serves as a stop to the flow housing part 60 in the other end position and forms an obstacle to flowing out over the radially outer surface over the entire stroke of the flow-limiting element 94. The force applied in this way can also be used almost completely for displacement, since the friction due to the knobs 138 is minimized. The boundary wall 130 ensures a flow settling with the aim of generating a high static pressure and can likewise be used as a stop or part of a labyrinth seal. Instead, the ring 112 thus forms an additional ram surface. This effect is further enhanced by the existing opening slots, since the flow striking the webs 110 is likewise directed via the opening slots onto the base 128 of the ring 112, as a result of which the static pressures which are produced have an even greater force effect on the flow limiting element 94. Accordingly, a sufficiently large activation force can be provided even without generating excessively large pressure losses. Notably, the static pressure differential acting on the radially outer ring 112 may be maintained by the narrow gap acting as a gap seal between the radially outer boundary wall 132 and the surrounding flow housing portion 60.In the other states, the flow through the gap 120 is changed as a function of the applied pressure difference, that is to say a larger flow cross section is made available as the pressure falls. However, it should be noted that the shape of the flow-around body 102 keeps the pressure loss very low, so that a relatively high volume flow can be conveyed even with relatively low pressure differences.If, for example, due to the tank emptying, the pressure in the fuel tank 18 and thus at the first connection 12 now drops to a negative pressure with respect to atmosphere of, for example, less than -0.1 bar, the valve body 62 is lifted off from the first valve seat 82, since at this pressure the forces acting on the valve body 62 due to the pressure difference are greater than the spring force of the first spring 80. Accordingly, air flows from the second connection 16 through the gap 120 between the regulating body 100 and the nozzle-shaped section 104 and through the through-flow opening 87 and radially between the valve body 62 and the first valve seat 82 to the first connection 12, so that a pressure equalization takes place in the tank. In this state, the flow limiting element 94 bears further against the second bearing surface 90 of the valve body 62, i.e. is moved by the second spring 122 in the direction of the electromagnet 28.Furthermore, by energizing the solenoid 28, it is possible to actively operate the fuel vapor switching and venting valve 10. This takes place, for example, before the initiation of the tank process in order to ensure that no overpressures or underpressures are present in the tank 18 at this time. In this case, by lifting off, the same state of the valve 10 is produced, as in the case of a high vacuum in the tank 18.A flow of air from the second port 16 to the first port 12 is also possible, as is a flow of fuel vapor in the opposite direction, while the function of the flow limiting element 94 is retained in this case.During the refueling process, it must be ensured that the pressure in the tank 18 arising from refueling can be reduced rapidly enough. For this purpose, a sufficient flow through the flow limiting element 94 is to be ensured, which is achieved by the shape of the flow-around body 102, which causes very low pressure losses. In addition, the dynamic pressure surface of the ring 112 is arranged radially outside the flow cross section of the nozzle-shaped section 104 of the flow channel 107, while the passage openings 114 are arranged radially inside this cross section.Accordingly, a flow limiting element for a fuel vapor switching and venting valve 10 is provided which ensures a sufficiently high flow at low differential pressures in operation in the event of very low pressure losses in order to be able to reduce excess pressures in the tank quickly, as arise, for example, during the refueling process, and nevertheless brings about a reliable limitation of the maximum permissible flow rate in order to avoid overloading of the activated carbon filter. Due to the reduced friction, the deflections of the flow limiting element become more reproducible, since the fluctuation width of the frictional force becomes smaller. Emission values can thus be better complied with. The knobs 138 are also simple and cost-effective to produce and to integrate them into the mold during the injection molding of the control body 100.It should be clear that various modifications are possible in comparison with the embodiment without departing from the scope of the main claim. In addition to a different embodiment of the components of the fuel vapor switching and venting valve, the flow restriction element can also be changed in its shape or its structure. For example, the shape of the flow-around body can be changed. The switching point can be individually adjusted with the spring and the additional dynamic pressure surface provided, depending on the application. The same applies to the maximum permissible flow rate, which can also be adapted by changing the design of the nozzle-shaped section. Instead of the radial gap seal, a labyrinth seal can also be provided through the narrow gap between the flow housing and the radially outer ring of the flow limiting element. This can be effected, for example, by an annular projection which extends from the first flow housing part axially between the boundary walls of the radially outer ring and thus forms the labyrinth seal with the latter. The knobs can also be shaped differently, for example pyramidal. Furthermore, it is conceivable to arrange the knobs on another outer wall of the flow limiting element. Thus, the knobs can be formed, for example, on the radially inner wall which delimits the groove on which the tongue bears. Accordingly, this would be a radially inner outer wall which would be guided over the knobs on the outer wall of the housing connecting piece forming the nozzle-shaped section. Other arrangements of the knobs, which are situated opposite a cylindrical housing wall, which serves as a guide surface, are of course likewise conceivable.

Claims

Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26), having a regulating body (100) which has a radially inner flow around body (102) which can be moved into a flow duct (107) having a nozzle-shaped section (104) which is formed in a second flow housing part (108), a spring (122) via which the regulating body (100) is loaded in a direction pointing out of the nozzle-shaped section (104), a cylindrical housing wall (136) which is opposite a radial limiting wall (132) of the regulating body (100), wherein a plurality of knobs (138) distributed over the circumference are formed on the radial limiting wall (132) of the regulating body (100), with which knobs the regulating body (100) contacts the housing wall (136).Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to Claim 1, characterized in that the limiting wall (132) of the regulating body (100) is a radial outer wall on which the knobs (138) are formed, with which the regulating body (100) touches the housing wall (136), which is an inner wall surface of a first flow housing part (60).Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to Claim 1 or 2, characterized in that the knobs (138) touch the housing wall (136) in punctiform fashion.Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to one of the preceding claims, characterized in that the knobs (138) are designed as ball segments.Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to one of the preceding claims, characterized in that three to five knobs (138) are arranged on the limiting wall (132) of the regulating body (100) distributed uniformly over the circumference.Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to one of the preceding claims, characterized in that the regulating body (100) has a radially outer ring (112), on the radially outer limiting wall (132) of which the knobs (138) are formed.Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to Claim 6, characterized in that the spring (122) bears against the outer ring (112), wherein one or more passage openings (114) are formed radially between the outer ring (112) and the flow body (102).Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to Claims 2 and 7, characterized in that the knobs (138) are arranged in a gap which is formed between an inner surface of the housing wall (136) of the first flow housing part (60) and the radially outer ring (112).Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to one of Claims 6 to 8, characterized in that the flow body (102) has a spherical or conical-shaped flow surface (103) which is arranged opposite an inner surface (106) of the nozzle-shaped section (104), wherein the radially outer ring (112) is arranged radially outside the smallest flow cross section of the nozzle-shaped section (104) of the flow duct (107) and has a base (128) from which the radially outer limiting wall (132) extends axially in a direction pointing away from the nozzle-shaped section (104).Flow limiting element (94) for a fuel vapor switching and venting valve (10) of an internal combustion engine (26) according to Claims 7 and 9, characterized in that a radially inner limiting wall (130) extends axially from the base (128) of the radially outer ring (112) in a direction pointing away from the nozzle-shaped section (104), and webs (110) are formed on the control body (100) in the circumferential direction between the passage openings (114), via which webs the radially outer ring (112) is fastened to the bypass body (102), wherein the radially inner limiting wall (130) has opening slots which are arranged in a radial extension of the webs (110).

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