DE10259894A1 - Pump used as a vane cell pump/roller cell pump comprises a lower vane groove divided into two so that the groove assigned to the suction region of the pump half is connected to the lower vane groove assigned to the pressure region - Google Patents

Abstract

Pump, especially a vane cell pump or roller cell pump, comprises a two-stroke contour ring (1), a rotor (3), vanes (5), side plates, a casing, a casing cover, and lower vane grooves (25, 27, 31, 33) for supplying the lower vane surfaces with pressure. The lower vane groove is made in two parts. Each part extends below a suction region and at least one subsequent pressure region. The lower vane groove is divided into two so that the lower vane groove assigned to the suction region (11) of the pump half is connected to the lower vane groove assigned to the pressure region (9) of the same pump half. No connections exist to the lower vane grooves of the other pump half.

Description

The invention relates to a pump, in particular a vane pump or Roller cell pump, with a two-stroke contour ring, with a rotor, with vanes, with side plates, with a housing and a housing cover, with Lower wing grooves to supply the lower wing surfaces with pressure, the wing are arranged radially displaceably in the rotor and by the pressure under the Extend wings and press against the contour ring. such Vane pumps are known, they are used in particular for the supply of Power steering systems or similar hydraulic systems in motor vehicles used. The two pressure chambers of the vane cells are over one Pressure collection chamber connected to each other within the pump, which in a common pressure line leads to the consumer. The two are the same Suction chambers of the vane cells connected to each other and lead to Intake area of the pump, in which the steering or a tank back-flowing oil is fed back to the pump.

The invention has for its object a double-stroke vane pump to create, in which the assigned suction and pressure areas each one Form the pump half and thus as two separately available feed pumps are usable.

The task is performed by a pump, in particular a vane pump or Roller cell pump, with a two-stroke contour ring, with a rotor with Wings, with side plates and a housing and a housing cover, with Under wing grooves to supply the lower wing surfaces with pressure, the Radially displaceable blades in the rotor due to the pressure in the lower wing groove are pressed against the contour ring by loosening the under wing groove is divided into two and each is a part, viewed in the direction of rotation, under one Suction kidney and at least one subsequent pressure kidney extends so that the lower wing groove, which is assigned to the suction area of one pump half, with the corresponding under wing groove, which corresponds to the pressure area of the same Pump half is assigned, is connected and no connection to the There are under-wing grooves in the other half of the pump. As a result, the Under-wing supply is designed such that the channels in the Side plates no direct short circuits occur and the wings always with that necessary pressure to be pressed against the contour to prevent unwanted lifting and thus prevent short circuits.

A preferred embodiment of the invention is characterized in that that the part of the lower wing groove under the pressure kidney, in the direction of rotation seen, essentially by the angular amount of a leading cell is extended.

Furthermore, a pump is preferred in which the extension of the Under wing groove is designed so that the leading wing of the leading cell only with a maximum of one wing thickness in the next, if necessary unpressurized under wing groove stands when the trailing wing of the leading cell just the connection to the one positioned above the lower wing groove Pressure kidney has left. That means that the leading wing is just leaving Lower wing groove if the trailing wing is the pressure kidney positioned above leaves.

Another embodiment according to the invention is characterized in that that the under wing groove on the opposite pressure plate or if necessary, the same division on the same in the housing or housing cover Point has like the first pressure plate.

Another pump according to the invention is characterized in that the Pressure plate and / or the counter plate two delimited pressure-tight Has high pressure fields, between which there is a suction pressure field. At a Pump according to the invention, the pressure fields through sealing devices sealed.

In the case of a pump, each pressure field is preferably the respective one Under wing groove or under wing kidney supplied with high pressure or circulating pressure, especially via channels within the respective pressure field.

This means that the pump halves are hydraulically separated internally. The correspondingly assigned lower wing areas and upper wing areas Cut. There is a common suction line and two separate ones Pressure lines. A pressure field is assigned to each vane pressure output the realization of the printing plate compensation is required. Within this Pressure field are channels that are used to supply the under-wing of the respective Serve half of the pump.

As already mentioned, the under-wing groove is made in two parts. The division has on the opposite side plate, for example a total of 4 Lower wing kidneys can contain to take place on the same slope, only the Under wing kidneys of the same pump half may be connected.

The leading wing of the cell that is just finishing the squeezing process may only then, with its slotted surface under the wing, the lower wing kidney, which the corresponding pressure range is assigned to the associated pump half, leave when the trailing wing is no longer connected to the pressure kidney Has. This is the only way to ensure that the leading wing always is pressed against the contour with sufficient pressure and it closes no wing lift-off or short circuits.

The invention will now be described with reference to the figures.

Fig. 1 shows schematically the structure of a two-stroke, double-flow vane pump.

Fig. 2 shows a rotating group of the present invention with an inventive Unterflügelnut.

Fig. 3 also shows a rotating group with an under wing groove according to the invention.

Fig. 4 shows a side plate.

Fig. 5 shows an opposite side plate.

Fig. 6 shows the outside of a side plate with two separate pressure fields.

Fig. 7 shows the hydraulic circuit diagram of a double-flow pump.

Fig. 8 shows an external view of a pump according to the invention.

FIG. 9 shows the cross section KK of FIG. 8.

FIG. 10 shows the cross section LL from FIG. 8.

FIG. 11 shows a further cross section from FIG. 8.

Fig. 12 shows check valves in cross section.

Fig. 13 shows different Konturhübe.

In Fig. 1, the structure of a two-stroke, two-flow vane pump is shown schematically. A rotor 3 with retractable blades 5 is shown within a double-stroke cam ring 1 . The rotor 3 is driven in rotation by a shaft 7 . The double-stroke vane pump contains two pressure areas 9 and two suction areas 11 , which are represented by corresponding pressure and suction kidneys and correspondingly enlarging or reducing cells within the lifting ring. The function of such vane pumps is known. The direction of rotation is represented by an arrow 13 . When the rotor 3 rotates, the cells between two vanes in the suction space 11 enlarge and thus suck fluid into the rotating group. In the pressure area 9 , the cell volumes between two wings decrease and thus press the fluid out of the pressure areas 9 .

The special circuit of a double-flow pump will now be discussed below. The two suction areas 11 are connected to a reservoir 17 via suction lines 15 and suck in the fluid from this common reservoir. The upper pressure area 9 leads to a pressure line 19 , while the lower pressure area 9 leads to a pressure line 21 . The two pressure ranges are therefore hydraulically separated. Furthermore, the upper pressure area 9 has a connection 23 to a lower wing groove 25 , in which pressure medium from the pressure area presses the wings from below out of the rotor 3 against the contour ring 1 . The lower wing groove 25 in the suction area is connected to the lower wing groove 27 in the pressure area, which is not shown in this FIG. 1. The upper pressure area 9 and the right suction area 11 represent one half of the double-flow vane pump.

The second half of the double-flow vane pump is represented by the lower pressure area 9 and the left suction area 11 . The lower pressure area 9 is connected by a connection 29 to a lower wing groove 31 in the left suction area 11 . This underfloor groove 31 is in turn connected to the underwing groove 33 in the lower pressure region 9 of this pump half. This means that for each half of the double-flow vane pump, the respective pressure range supplies the under-wing grooves with pressure and thus presses the vanes hydraulically against the contour ring 1 . If one of the two vane cell pump halves is now depressurized because a corresponding consumer does not need the pressure, the lower vane area is also depressurized, so that the vanes can continue to move in a substantially pressure-balanced manner in the respective pump area. In the depressurized state, there is a minimum circulating pressure of up to 3 bar, which, in addition to the centrifugal force, also supports the removal of the wings.

Fig. 2 shows the inventive design of the rotation group of a double flow vane pump. The same parts as in Fig. 1 are given the same reference numerals and are not explained again separately here.

It is important that the lower vane groove 25 in the suction area 11 and the lower vane groove 27 in the pressure area 9 are connected to each other for the upper vane pump half. It can also be seen that the lower wing groove 27 is extended by an area 35 . This area 35 extends essentially over a complete cell width between the wings 37 and 39 . It can be seen that the wing 37 just leaves the pressure area 9 , ie the upper pressure kidney, when the leading wing 39 leaves the lower wing groove 35 . This means that the wing 39 must be supplied with high pressure from the lower wing groove 35 or 27 , since there is still high pressure in the cell between the wings 37 and 39 , which acts on the wing head of the wing 39 from above, which is not may cause the wing to be pressed down. When moving on to the suction area 41 of the next vane pump half, the wing head is depressurized from above, and thus the lower vane area of this wing may also be depressurized if the lower vane pump area is switched to unpressurized circulation in this double-flow pump. Likewise, a leading cell between the vanes 43 and 45 in this part of the vane pump which is switched off under pressure is supplied with an unpressurized underfloor medium by an extension 47 of the lower wing groove, so that the wings 43 and 45 are also in pressure equilibrium. When the vane cell pump continues to rotate, this cell will then be immersed again in the pressurized part of the double-flow vane cell pump and supplied with pressure again by the lower vane groove 25 .

Fig. 3 is a somewhat differently configured shows the extension Unterflügelnut 35th When the wing 37 just leaves the upper pressure kidney 9 , the wing 39 is with half its wing thickness in the subsequent lower wing groove 51 of the depressurized vane pump half. The groove 35 ends at a distance 49 in front of the wing 39 of the leading wing cell.

In FIG. 4, the inside of a printing plate 57 is shown. The high-pressure kidney 9 and the suction kidney 11 can be seen in the pressure plate. Furthermore, the lower wing groove of the upper pump half is represented by the lower wing groove part 25 in the suction area, by the lower wing groove part 27 in the pressure area and by the inventive extension of the lower wing groove 35 in the pressure area. The separating regions 53 and 55 to the lower under-wing groove, which are essential to the invention, can also be clearly seen and thus separate the under-wing supply of the two pump halves from one another.

In FIG. 5, the back plate 59, which covers the rotating group on the other side of the vane pump shown. Below the suction grille 11 is the lower wing groove area 25 , which is separated here from the lower wing area 27 of the pressure area 9 by a separation point 63 . The extension of the lower wing groove 27 by the part 35 is arranged here as a mirror image of the plate in FIG. 4. It is again possible to see the separating areas 53 and 55 which are essential to the invention in this position for the double-flow pump. The lower lower wing area is divided by the separating point 61 into two lower wing groove areas. This separation point is provided for appropriate cold start behavior and for pressing out the wings during cold starts by forming certain resistances and pumping processes in the lower wing grooves. In addition, FIG. 5 shows plate openings 65 and 67 , which can lead from the outside of the high-pressure oil or low-pressure oil pressure area, depending on the pump circuit, to this lower wing area.

In Fig. 6 these apertures 65 and 67 are recognizable. In FIG. 6, the pressure plate 59 is now shown from the outside. Two pressure fields 69 and 71 can be seen , into each of which the pressure kidneys 9 introduce the pressure oil expelled from the pump and thus press this pressure plate from the outside with pressure against the contour ring and the rotating group by means of these pressure fields 69 and 71 . The pressure fields 69 and 71 are sealed at their boundaries by seals against the rest of the pressure plate surface 73 , which is acted upon by suction pressure. Thus, the oil expressed from the pressure kidneys 9 of the vane pump, which, according to FIG. 1, is passed on to the pressure lines 19 or 21 , is supplied to the corresponding half-wing groove halves via channels 75 and 77 and the openings 65 and 67 which are embedded in the pressure plate here. The two pressure plates 59 and 57 and the contour ring 1 are connected to one another in a rotationally fixed manner by means of through openings 79 and 81 and positioning bolts located therein and are fixed in their alignment.

Fig. 7 shows a circuit diagram in which the function of a double-flow vane pump is shown schematically. The two pump halves of the double-flow vane pump are symbolically represented here by the pump symbols 101 and 103 , which draw the corresponding fluid from the reservoir 15 together from a reservoir 17 . Separate pressure outputs 19 and 21 can supply the pressure oil from the respective pump half, depending on the circuit of the respective consumer. In this circuit diagram, only one consumer connection 113 and an unpressurized circulation circuit for the pump half 101 are provided. A changeover valve 105 connects the pressure outlet 19 of the pump half 101 to a connection 107 which is connected to a connection point 111 via a check valve 109 . The pressure line 21 of the second pump half 103 also opens into the connection point 111 . In the switching position of the valve 105 shown here, a consumer at the consumer port 113 can thus be supplied with the oil flow from both pump halves 101 and 103 . To secure the hydraulic circuit, a pressure limiting valve 115 is also provided, which opens when the maximum pressure is exceeded and allows excess oil flow to flow back into the reservoir 17 via a connection 117 , so that the pressure cannot rise further. Is now ready for the supply to the load at the actuator port 113 of the total oil flow of the pump halves 101 and 103 is not necessary, the oil flow of the pump half 101 may be the reservoir 17 and the Ansaugbereichen be supplied 15 of the pump again via a line 119 by switching the valve 105th The pump half 101 is therefore in the unpressurized circulation at a circulation pressure of approx. 1 to 3 bar, depending on the resistances of the partial circuit.

Fig. 8 shows an external view of a pump according to the invention. The end of a shaft 202 protrudes from a pump housing 200 . FIG. 8 serves to orient two cuts, of which the section KK through the rotating group is shown in FIG. 9 and the section LL in FIG. 10 through adjacent pressure channels with integrated check valves.

The pump itself must not run empty when the vehicle is parked, even if the pressure side loses due to valve spool leakage in the transmission control 01 and the suction channel also runs empty due to the principle of the communicating tubes. The internal channels of the pump are therefore arranged in such a way that even under these conditions the rotation group remains filled with oil at least over the middle of the shaft. An illustration of this internal oil channel guide can be seen in FIG. 9. As already described in FIG. 1, the rotation group consists, among other things, of the contour ring 1 , of the rotor 3 , of the vanes 5 , of the shaft 7 and contains the two pressure areas 9 and the two suction areas 11 . An intake duct 206 is formed by forming an intermediate wall 208 in such a way that its inlet region 210 is arranged above the center of the shaft 7 and thus the rotation group remains filled with oil up to the height of the intermediate wall 208 , even if the intake duct 206 should otherwise run empty. Via an arcuate extension 212 of the inner pump housing, the suction area 11 on the right side is also connected to the suction side 210 and thus to the suction channel 206 .

FIG. 10 shows the design of the pressure channels in the pump according to the invention in section LL from FIG. 8. A first pressure channel 214 and a second pressure channel 216 are formed in the pump housing 200 . The first pressure channel 214 is assigned to the upper pressure range and closed by a check valve 218 , the function of which will be explained later. The lower pressure range of the vane pump is also closed by a check valve 220 . While the upper pressure range with the check valve 218 lies above the shaft center 7 , the lower pressure range with the check valve 220 is designed by a siphon-like design of the pressure channel 216 such that the oil definitely remains above the shaft center within this oil channel if the right one Part of the pressure channel 216 should run empty. This is made possible by the raised duct wall 224 .

In Fig. 11, the pump of the invention is shown in a further cross-sectional so that the check valves 218 and 220 are visible in cross section. They protrude partially into the pressure plate 59 from FIG. 6 in such a way that they close the upper pressure field 69 and the lower pressure field 71 against the pressure outlets 214 from FIGS. 10 and 216 from FIG. 10. The upper check valve consists of a valve seat 224 , into which the sealing body 226 is pressed by means of a spring 228 . The valve seat 224 is additionally sealed off from the housing by a seal 230 . The seals of the pressure fields can also be recognized by the seal 232 . The lower check valve 220 is constructed identically and will not be described again here. The function of the check valves is that when the pump is at a standstill, the pressure areas are closed and the respective pressure areas are only connected to their lower wing grooves, as described in FIGS. 2 to 6. After the start of the delivery, a pressure builds up within the rotation group, which allows the check valve body 226 to be lifted from its seats and thus enables the delivery of the pressure oil to the outside into the two pressure channels 214 and 216 and thus to corresponding consumers. The check valves are thus arranged at the transition between the pressure field volumes of the plate 59 and the pressure channels. These check valves are primarily intended to be resistance elements, which do not necessarily have to be 100% tight. The check valves also connect the volume of the pressure fields of the plate 59 to the pressure channels leading to the consumer. The check valves are designed as simple plate valves. Any other variants are possible. The seat of this spring-loaded plate 226 is an automatic turned part, which, sealed with an O-ring, is installed in the pump housing and is positively fixed by shoulders in the pump housing and corresponding design of the pressure plates. Of course, it is also possible to omit the O-ring and press fit the seat with a transition or press fit. Since the rotation group itself must not run empty, the shaft is sealed to the outside with a shaft sealing ring 234 .

If the internal pump leakage collects in the middle of the shaft, from one certain pressure open the shaft seal, and the leak oil can in the Escape gearbox. The exact function of this special shaft seal, that can work as a check valve is already in another registration described in detail.

A check valve is shown enlarged in the open state in FIG. 12.1 and in the closed state in FIG. 12.2. It can be seen that the plate valve body 226 in FIG. 12.1 is opened by the valve seat 224 by the opening stroke X, so that the pressure oil can flow into the corresponding pressure channel. In FIG. 12.2, the plate valve body 226 is pressed against the valve seat 224 by the force of the spring 228 .

The suction process of the pump according to the invention now works as follows: In the worst case, e.g. B. after an aborted cold start when parking a rotating diesel engine, all wings are in the slot base of the rotor near the small circle diameter of the cam ring. Now the turns Rotor when starting, the wings extend minimally due to the centrifugal force. this The wings on the pressure side of the stroke contour also move back into the Rotor into it. The volume that the wing has when entering the Feeding under wing groove is almost without loss under one on the suction side sliding out of the wing. This wing is now at least perishing the amount that the retracting wing is retracted. Work in addition centrifugal forces on the wing. With more and more wings extending creates a kind of centrifugal pump effect. The resulting flow and delivery pressure is completely due to the check valve elements brought the under-wing supply to the associated pump half. Through the special design of the under wing channels and through the non-return elements there is a self-reinforcing effect that ensures the safe suction of the pump leads. For this initial kick, oil is necessary, which is formed by the formation of the siphon-like channels is provided. If the pump now pumps oil, open the Check valves, and the pump splashes empty but remains in function, even if it now pumps air due to an empty suction pipe. The pressure built up by the check valves is sufficient to ensure the function of the Keep the pump upright. Now the pump sucks until oil from z. B. is sucked in a filter. The oil in the siphons is used for the initial kick needed to break loose the wings sticking strongly in the slots and the Get the self-reinforcement mechanism going.

FIG. 13 shows a special configuration of the rotation group, in which asymmetrical pump divisions can also be achieved by different contour strokes. The known components contour ring 1 , rotor 3 , wing 5 and the shaft 7 and the two pressure areas 9 and the two suction areas 11 have already been described in their function. The representation of the small circle areas 236 and 238 of the cam ring contour is different in FIG. 13. While the right small circle area 236 , as is normally designed for vane pumps, corresponds approximately to the outer diameter of the rotor 3 , the small circle area 238 on the left side is provided with a larger radius than the outer radius of the rotor 3 , so that a considerable gap is created here. The two large circle areas 240 above the rotor 3 and 242 below the rotor 3 within the cam ring 1 should be of the same size in this example. The following function is conceivable for moving from a small circle radius 236 to a large large circle radius 242 , which corresponds, for example, to 60% suction based on the total delivery volume of the pump. When moving from the large circle area 242 to a larger small circle radius 238 , the cell volume reduction means that only 40% of the stroke volume, based on the total delivery volume of the pump, is expressed. If you move from this larger small circle radius 238 to the large circle radius 240 , this also means only a 40% suction, based on the total delivery volume of the pump. If this large circle radius 240 is then used again for the smaller small circle radius 236 , this means that the oil is squeezed out 60%. In this variant, the aspirated cell volumes differ from the expressed cell volumes. This solution can have advantages if, for reasons of installation space, less installation space is available on one side than for suction or pressure channels on the other. In the simplest case, the small circle remains at the same level and the large circles are of different sizes. It is important that both the small circle radius and the large circle radius or both radii can be varied together independently of one another.

All of the solutions described in this application can be used with Vane pumps with a double-stroke contour ring, each of which Half of the pump can pump oil at different pressure levels separately and either different pressure circuits can be supplied with oil or one of which Half of the pump is switched into circulation without pressure to save energy.

The pump halves are hydraulically separated internally. That is, the corresponding assigned lower wing areas and upper wing areas are separated. There are a common suction line and two separate pressure lines. Each Rotation group pressure output is assigned a pressure field that for the Realization of the pressure plate compensation is required. Within this Ducts are implemented to supply the under-wing of the respective Serve half of the pump.

The claims filed with the application are Proposed wording without prejudice for obtaining further patent protection. The The applicant reserves the right to do so, so far only in the description and / or combinations of features disclosed in the drawings claim.

Relationships used in subclaims point to the others Training the subject of the main claim by the features of respective subclaim; they are not a waiver of attainment an independent, objective protection for the combinations of features to understand the related subclaims.

Since the subjects of the subclaims with regard to the prior art reserves the right to make its own and independent inventions on the priority day Applicant before becoming the subject of independent claims or To make divisional declarations. You can continue to work independently Inventions contain one of the objects of the previous Have independent claims independent design.

The exemplary embodiments are not intended to limit the invention understand. Rather, there are numerous within the scope of the present disclosure Changes and modifications possible, especially such variants, elements and combinations and / or materials, for example by combination or modification of individual in connection with that in general Description and embodiments and the claims described and features or elements contained in the drawings or Process steps for the person skilled in the art with a view to solving the problem are and through combinable features to a new item or lead to new process steps or process step sequences, also as far as they Manufacturing, testing and working procedures concern.

Claims (16)

1. Pump, in particular a vane pump or a roller cell pump, with a two-stroke contour ring, with a rotor, with vanes, with side plates, with a housing and with a housing cover, with under-wing grooves for supplying the lower wing surfaces with pressure, the vanes being radially displaceably mounted in the rotor are pressed against the contour ring by the pressure to the outside, characterized in that the lower wing groove is divided into two and a part, viewed in the direction of rotation, extends under a suction grille and at least one subsequent pressure grille, the lower wing groove being divided in two such that the lower wing groove, which is assigned to the suction area of one pump half, is connected to the associated lower wing groove, which is assigned to the pressure area of the same pump half, and there are no connections to the lower wing grooves of the other pump half. 2. Pump, in particular according to claim 1, characterized in that the Part of the lower wing groove under the pressure grille, in the direction of rotation seen, essentially by the angular amount of a leading cell is extended. 3. Pump, in particular according to claim 2, characterized in that the Extension of the lower wing groove is designed so that the leading wing the leading cell with a maximum of one wing thickness in the next, possibly unpressurized under wing groove is when the trailing wing of the leading cell just above the Left wing groove positioned pressure kidney. 4. Pump, in particular according to one of the preceding claims, characterized characterized that the under wing groove on the opposite side of the Rotating group, d. H. on the other plate or in the housing if necessary or in the housing cover, the same division in the same place as the first Plate. 5. Pump, in particular according to one of the preceding claims, characterized characterized in that the pressure plate and / or the counter plate two has high-pressure fields delimited in a pressure-tight manner, between which there is a Suction pressure field is located. 6. Pump, in particular according to claim 5, characterized in that the Pressure fields are sealed by sealing devices. 7. Pump, in particular according to one of the preceding claims, characterized characterized that the respective under wing groove or Under-wing kidney is supplied with high pressure or circulating pressure, especially via channels within the respective pressure field. 8. Pump, in particular according to one of the preceding claims, characterized characterized that the internal suction and pressure channels of the pump so are arranged so that the rotation group at least over the The center of the shaft remains filled with oil. 9. Pump, in particular according to one of the preceding claims; thereby characterized in that the two pressure channels each by a Check valve be closed. 10. Pump, in particular according to one of the preceding claims, characterized characterized that the check valves when the pump is at a standstill Seal the pressure areas to the outside and thus the respective ones Pressure areas are only connected to their lower wing grooves. 11. Pump, in particular according to one of the preceding claims, characterized characterized that the shaft with a shaft seal to the outside is sealed, which from a certain pressure as a check valve works and allows leak oil to escape into the gearbox. 12. Pump, in particular according to one of the preceding claims, characterized characterized that asymmetrical by different contour strokes Pump divisions are realizable. 13. Pump, in particular according to one of the preceding claims, characterized characterized that a small circle area with a larger radius than the outer radius of the rotor. 14. Pump, in particular according to one of the preceding claims, characterized characterized that the two great circle areas are different sizes are. 15. Pump, in particular according to one of the preceding claims, characterized characterized that both the small circle radii and the Great circle radii as well as both radii together arbitrarily independently of each other are variable. 16. Pump, in particular vane pump or roller cell pump, with a two-stroke contour ring, with a rotor, with blades, with side plates, with one housing and with one housing cover, with under wing grooves for Supply of the lower wing surfaces with pressure, the radial in the rotor sliding wing by the pressure to the outside against the Contour ring are pressed, characterized by at least one in the Filing documents disclosed inventive feature.