US20250017429A1

US20250017429A1 - Portable work apparatus

Info

Publication number: US20250017429A1
Application number: US18/772,128
Authority: US
Inventors: Benjamin Rutschke; Sebastian Piekarek; Thilo Stützel; Mathias Schmitz
Original assignee: Andreas Stihl AG and Co KG
Current assignee: Andreas Stihl AG and Co KG
Priority date: 2023-07-14
Filing date: 2024-07-13
Publication date: 2025-01-16
Also published as: DE102023118780A1; DE102023118780B4

Abstract

A portable work apparatus is designed as a vacuum and/or blower. It includes a housing (2) and a drive motor (3) arranged in the housing (2). A fan (4) has a spiral housing (5) and a fan wheel (6) arranged in the spiral housing (5). The spiral housing (5) has a housing section (8) which forms a first intake opening (9) of the fan (4). The fan wheel (6) has a first wall section (10) which forms a second intake opening (12) of the fan wheel (6). A gap seal (15) is formed between the housing section (8) of the spiral housing (5) and the first wall section (10) of the fan wheel (6). At least one air guide element (16) for generating a swirl zone (30) is formed in the gap seal (15).

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of German Patent Application DE 10 2023 118 780.5, filed on Jul. 14, 2023, the content of which is incorporated by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to a portable work apparatus, and more specifically to a blower, vacuum, or blower-vacuum combination tool.

BACKGROUND

Vacuums, blowers, or 2-in-1 combination devices which have both a vacuum function and a blower function are generally known. Such devices are used to suck up or blow away yard waste such as leaves, etc. If the devices have a suction function, this can also be combined with a shredder, and may be referred to as a shredder vacuum. The shredder further chops up the yard waste as it is sucked in.
Such a vacuum and/or blower comprises a housing and a drive motor arranged in the housing. The drive motor drives a fan wheel that is housed in a spiral housing. The fan wheel and the spiral housing together form a fan. During operation of the work apparatus, an air flow is generated by the fan wheel driven by the drive motor. The air flow is sucked in through an intake of the fan, flows through the fan wheel and exits again through an outlet opening of the spiral housing. If the work apparatus is designed as a vacuum, a suction tube is connected to the negative pressure side of the fan, i.e. to the intake. The yard waste can so be sucked up via the suction tube. If the work apparatus is designed as a blower, a blower tube is connected to the pressure side of the fan, i.e. to the outlet opening of the spiral housing. The yard waste can be blown away with air emerging from the blower tube.
When the fan is in operation, in addition to the air flow for sucking in or blowing out air, a leakage flow is also generated. Such a leakage flow reduces the efficiency of the work apparatus. It is disadvantageous that the performance of the work apparatus decreases as a result and in turn the energy consumption of the work apparatus increases.

SUMMARY

The present application presents a work apparatus, in particular a blower, vacuum, or blower-vacuum combination, which operates more efficiently than known apparatuses.
The improvement is based on the finding that a particularly high leakage flow occurs at the gap seal between the spiral housing and the fan wheel. The fan wheel creates a negative pressure in the intake area, i.e. in the area of the first intake opening and the second intake opening. On the other hand, an overpressure arises in the spiral housing during operation of the work apparatus. The overpressure zone and the negative pressure zone are connected to each other via a gap seal. If pressure is equalized between the two zones across the gap seal, a leakage flow occurs. In the portable work apparatus as disclosed herein, this leakage flow is minimized.
The portable work apparatus is designed as a vacuum and/or blower. It includes a housing and a drive motor arranged in the housing. A fan includes a spiral housing and a fan wheel arranged in the spiral housing. The fan wheel can be driven by the drive motor so as to rotate about an axis of rotation in order to generate an air flow. The spiral housing has a housing section which forms a first intake opening of the fan. The fan wheel has a first wall section which forms a second intake opening of the fan wheel. A gap seal is formed between the housing section of the spiral housing and the first wall section of the fan wheel. At least one air guide element is formed in the gap seal for generating a swirl zone.
When the work apparatus is in operation, the air guide element creates a turbulence in the gap flow in the gap seal. This creates a swirl zone in the gap seal. The swirl zone impedes flow through the gap seal and thus increases the sealing effect of the gap seal between the overpressure zone and the negative pressure zone. The leakage flow through the gap seal is reduced, which enables efficient operation of the work apparatus.
It is advantageously provided that the at least one air guide element is arranged on the housing section of the spiral housing. The at least one air guide element is preferably fixedly connected to the spiral housing, in particular formed on the spiral housing. The gap flow is swirled around the axis of rotation of the fan wheel by the fan wheel, which rotates relative to the spiral housing. The gap flow flows against the air guide element of the spiral housing and is swirled. The swirl zone is created. The air guide element is particularly advantageously designed in such a way that the gap flow through the air guide element undergoes a flow reversal. As a result, the gap flow is deflected by the air guide element back in the direction of the spiral housing, in particular back in the direction of the high-pressure zone. In an alternative embodiment of the work apparatus, the air guide element is firmly connected to the fan wheel.
The at least one air guide element is formed in particular as a rib with a longitudinal plane. The fan wheel is driven to rotate around the axis of rotation in one direction of rotation, with the rib being arranged with its longitudinal plane running transversely to the direction of rotation. Due to this arrangement of the rib, the gap flow, which has a swirl around the axis of rotation due to the rotation of the fan wheel, flows against the rib. The gap flow is redirected, which creates turbulence in the gap flow.
It is preferably provided that the housing section of the spiral housing has a bulge which delimits the first intake opening. The bulge of the spiral housing preferably overlaps the fan wheel in the region of the second intake opening in the direction of the axis of rotation. This creates the longest possible gap seal. The bulge of the spiral housing overlaps the fan wheel in the area of the second intake opening, particularly radially to the axis of rotation of the fan wheel. Thus, any gap flow in the bulge undergoes a change in direction, which in turn increases the flow resistance of the gap flow. In this way, an increased sealing effect of the gap seal can be achieved.
It is in particular provided that the at least one air guide element, in particular the rib, is formed in the bulge. This creates the swirl zone in the bulge itself, which prevents the gap flow from flowing through the bulge.
The rib is preferably arranged on the inner side of the housing section of the spiral housing. The rib preferably extends from the inner side of the housing section to the outer side of the housing section of the spiral housing. This stiffens the fan wheel. In such an embodiment of the work apparatus, the rib has a dual function, namely, on the one hand, to generate a swirl zone as an air guide element and, on the other hand, to increase the stiffness of the fan wheel.
It is particularly advantageously provided that a plurality of ribs are formed on the spiral housing, adjacent ribs being arranged in particular at uniform angular distances from one another with respect to the axis of rotation of the fan wheel. This ensures sufficient turbulence with a corresponding sealing effect and sufficient rigidity of the fan housing.
Further features of the invention will become apparent from the drawing, in which an embodiment of the invention is described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of the work apparatus as a blower.

FIG. 2 shows a perspective view of the work apparatus according to FIG. 1 without an intake grille.

FIG. 3 shows a perspective sectional view of the fan of the work apparatus according to FIG. 1 with air guide elements.

FIG. 4 shows a perspective, partial sectional view of the fan of the work apparatus according to FIG. 1 .

FIG. 5 shows a lateral sectional view of the fan of the work apparatus according to FIG. 1 .

FIG. 6 shows a perspective view of the spiral housing of the work apparatus according to FIG. 1 with air guide elements.

DETAILED DESCRIPTION

In FIG. 1 , a portable work apparatus 1 is shown. In the exemplary embodiment, the work apparatus 1 is designed as a blower. In an alternative embodiment, the work apparatus 1 is designed as a vacuum. Alternatively, the work apparatus can also be designed as a 2-in-1 blower and vacuum device. In such an embodiment, the work apparatus 1 can be operated in two working modes, namely a vacuum mode and a blower mode. The term “portable” is to be understood in such a way that the work apparatus is carried by the operator and is hand-guided during its intended use.
As shown in FIG. 1 , the work apparatus 1 comprises a housing 2. In addition, the work apparatus 1 comprises a drive motor 3, which is arranged in the housing 2. The work apparatus 1 comprises a fan 4. The fan 4 comprises a spiral housing 5 and a fan wheel 6. The fan wheel 6 can be driven to rotate about an axis of rotation 7 by means of the drive motor 3 (FIG. 3 ). The fan wheel 6 is mounted so as to be rotatable relative to the housing 2. In the exemplary embodiment, the drive motor 3 is designed as an electric motor. The electric motor is supplied with electrical energy in particular by at least one first battery pack 41, preferably by a first battery pack 41 and by a second battery pack 41′. The two battery packs 41, 41′ are each guided in a battery compartment 42 that is open towards the outside of the housing, so that the battery packs 41, 41′ can be replaced without opening the housing 2. Alternatively, the electric motor can also be supplied with energy via an electrical cable. Alternatively, it can also be provided that the drive motor 3 is designed as an internal combustion engine, in particular as a two-stroke engine or as a fuel-oil mix-lubricated four-stroke engine.
As shown in FIGS. 1 and 2 , the work apparatus 1 includes a handle 36. At least one actuating element 37 is assigned to the handle 36 in order to control the drive motor 3. In the present embodiment of the work apparatus 1, the actuating element 37 is arranged on the handle 36. The actuating element 37 is designed as an operating lever. The handle 36 comprises further actuating elements 38, 38′ which serve, for example, to release the drive motor 3, to set continuous throttle, corresponding operating modes for adjusting the power, the speed, etc. Furthermore, the handle 36 comprises a display for transmitting information to the operator.
As shown in FIGS. 1 and 2 , the work apparatus 1 includes a carrying device 50. The carrying device 50 comprises a carrying frame 51 and a carrying strap system (not shown in detail). In the exemplary embodiment, padding for the shoulder straps and the hip straps as well as a back pad are provided on the carrying frame 51. In an alternative embodiment, further padding can be provided. Alternatively, some or all of the padding can be omitted. The work apparatus 1 is attached to the carrying frame 51.
As shown in FIG. 2 , during operation of the work apparatus 1, the fan 4 sucks in air via an intake 20 and blows it out via an outlet opening 21. Here, an air flow 31 passes the intake 20 in a first flow direction 32. The air flow 31 flows from an external environment 34 of the work apparatus 1 into an interior space 35 of the housing 2 to the fan 4. In the exemplary embodiment, the fan 4 is designed as a radial fan. The air flow 31 is therefore deflected by the fan 4 from the intake 20 via the spiral housing 5 to the outlet opening 21. The air flow 31 leaves the interior space 35 of the housing 2 via the outlet opening 21 in a second flow direction 33. The first flow direction 32 of the air flow 31 at the intake 20 and the second flow direction 33 of the air flow 31 at the outlet opening 21 are aligned transversely to each other.
As shown in FIGS. 1 and 2 , the work apparatus 1 includes a blower tube 22. The blower tube 22 is connected to the outlet opening 21 of the housing 2, in particular of the spiral housing 5. The blower tube 22 comprises a connecting piece 23, an elastic tube section 24, an intermediate piece 25, and an end piece 26. The connecting piece 23 is arranged at, in particular fastened to, the outlet opening 21 of the housing 2, in particular of the spiral housing 5. The connecting piece 23 is curved in such a way that the remaining blower tube 22 is oriented forwards, starting from an operator (not shown) who carries the work apparatus 1. The tube section 24 connected to the connecting piece 23 is designed to be elastic, so that the operator of the work apparatus I can easily pivot the blower tube 22 in order to be able to direct the air flow 31 specifically onto the material to be blown. In the exemplary embodiment, the elastic tube section 24 is designed as a bellows. An intermediate piece 25 is connected downstream to the elastic tube section 24. The intermediate piece is preferably designed to be rigid. The handle 36 is preferably attached to the blower tube 22. The blower tube 22 may be pivoted via the handle 36. For this purpose, the handle 36 is particularly preferably attached to the rigid intermediate piece 25. The end piece 26 is mounted on the intermediate piece 25. The end piece 26 tapers conically. Accordingly, the end piece 26 is designed in the form of a nozzle. The individual components of the blower tube 22 are connected to one another via clamps, plug connections and/or screw connections.
As shown in FIG. 3 , the drive motor 3 is disposed in a motor housing 43. The motor housing 43 is part of the housing 2. The drive motor 3 comprises a drive shaft 44. In the exemplary embodiment, the drive shaft 44 is designed as a rotor 45 of the electric motor. The electric motor also comprises a stator 46, which is firmly connected to the motor housing 43. The electric motor is designed as an outrunner. In an alternative design, the electric motor can also be designed as an inrunner. The fan wheel 6 is attached to one end of the drive shaft 44. The drive shaft 44 has an axis of rotation that corresponds to the axis of rotation 7 of the fan wheel 6. The fan wheel 6 is held clamped on the drive shaft 44 of the drive motor 3 by a central screw 47. The fan wheel 6 is fastened to the drive shaft 3 only by the one central screw 47. Additional fasteners are not required, and therefore a simple and fast fastening of the fan wheel 6 to the drive shaft 3 is ensured.
As shown in FIG. 3 , the fan wheel 6 is surrounded by a spiral 48 radially to the axis of rotation 7. The spiral 48 is formed from the motor housing 43 and the spiral housing 5. A plurality of fan blades 49 are formed on the fan wheel 6. When the work apparatus 1 is in operation, air is sucked in through the intake 20 by the fan wheel 6 as the fan wheel 6 rotates. The air is conveyed radially outward into the spiral 48 by the fan blades 49. This results in the already described air flow 31, which flows from the intake 20 via the fan wheel 6 into the spiral 48. The air flow 31 then flows via the outlet opening 21 into the blower tube 22 and via the end piece 26 of the blower tube 22 back into the external environment 34.
As shown in FIGS. 3 and 5 , the spiral housing 5 comprises a housing section 8. A first intake opening 9 is provided on the housing section 8. The air flow 31 can flow from the external environment 34 to the fan wheel 6 via the first intake opening 9 of the housing section 8 (FIG. 3 ). The first intake opening 9 is preferably formed coaxially with the axis of rotation 7 of the fan wheel 6.
As shown in FIGS. 3 and 5 , the fan wheel 6 comprises a first wall section 10 and a second wall section 11. The first wall section 10 and the second wall section 11 are spaced apart from each other. The fan blades 49 are arranged between the first wall section 10 and the second wall section 11 of the fan wheel 6. The first wall section 10 of the fan wheel 6 faces away from the drive shaft 44 of the drive motor 3. The second wall section 11 of the fan wheel 6 faces the drive shaft 44 of the drive motor 3. The fan wheel 6 has a second intake opening 12. The second intake opening 12 is formed on the first wall section 10 of the fan wheel 6. The second intake opening 12 is preferably formed coaxially with the axis of rotation 7 of the fan wheel 6. The air flow 31 flows from the second intake opening 12 of the fan wheel 6 via the fan blades 49 into the spiral 48 (FIG. 3 ). The first intake opening 9 and the second intake opening 12 are preferably arranged coaxially with one another. The intake 20 of the fan 4 is formed by the first intake opening 9 of the spiral housing 5 and by the second intake opening 12 of the fan wheel 6.
As shown in FIG. 5 , a negative pressure is generated in the intake area, i.e. in the region of the intake 20, during operation of the work apparatus 1 due to the rotation of the fan wheel 6. On the other hand, an overpressure is created in the spiral 48. Accordingly, during operation of the work apparatus 1, a negative pressure zone 28 is created in the region of the intake 20 and an overpressure zone 29 is created in the spiral 48. The overpressure created in the spiral 48 should be used as fully as possible to blow air out of the blower tube 22. The overpressure zone 29 should be sealed off as well as possible from the negative pressure zone 28, so that leakage flows can be minimized or even completely avoided. A seal is therefore provided between the spiral housing 5 and the fan wheel 6. Since the fan wheel 6 is movable relative to the spiral housing 5, a non-contact seal is required. Therefore, in the present embodiment, the fan 4 comprises a gap seal 15. The gap seal 15 is formed between the spiral housing 5 and the fan wheel 6.
As shown in FIG. 4 , the gap seal 15 is formed between the housing section 8 of the spiral housing 5 and the first wall section 10 of the fan wheel 6. The housing section 8 of the spiral housing 5 extends from the spiral 48 to the first intake opening 9 of the spiral housing 5. The housing section 8 of the spiral housing 5 has an inner side 17 facing the fan wheel 6 and an outer side 18 facing away from the fan wheel 6. The first wall section 10 of the fan wheel 6 faces the inner side 17 of the spiral housing 5. The first wall section 10 extends from an inner end 52 to an outer end 53. The distance of the outer end 53 from the axis of rotation 7 of the fan wheel 6 is greater than the distance of the inner end 52 from the axis of rotation 7 of the fan wheel 6. The second intake opening 12 of the fan 4 is formed at the inner end 52 of the wall section 10. The outer end 53 of the fan wheel 6 is arranged adjacent to the spiral 48. The overpressure zone 29 is flow-connected to the negative pressure zone 28 via the gap seal 15.
As shown in FIGS. 3 to 5 , at least one air guide element 16 is arranged in the gap seal 15. In the preferred embodiment, a plurality of air guide elements 16 are arranged in the gap seal 15. The air guide element 16 is preferably arranged on the spiral housing 5. In an alternative embodiment of the work apparatus 1, however, it can also be provided that the air guide element 16 is provided on the fan wheel 6. The air guide element 16 is formed on the spiral housing 5, in particular in one piece. The spiral housing 5 is preferably a molded part, in particular an injection-molded part. The spiral housing 5 is in particular made of plastic, preferably completely made of plastic. As a result of the design of the air guide element 16 in the gap seal 15, the air flowing out of the overpressure zone 29 is swirled in such a way that a swirl zone 30 is formed in the gap seal 15. The swirl zone 30 blocks the air flowing out of the overpressure zone 29, as a result of which it can no longer flow into the negative pressure zone 28. As a result of the generation of the swirl zone 30 in the gap seal 15, the sealing effect between the overpressure zone and the negative pressure zone is improved, as a result of which any leakage flows are reduced.
As shown in FIG. 4 , the housing section 8 of the spiral housing 5 comprises a bulge 14. In the exemplary embodiment, the bulge 14 of the housing section 8 engages around the inner end 52 of the first wall section 10 of the fan wheel 6. Thus, the gap seal 15 has the shape of a loop in the area of the bulge 14 of the housing section 8. This can also increase the sealing effect of the gap seal. The bulge 14 of the housing section 8 delimits the first intake opening 9 of the fan 4. As also shown in particular in FIG. 5 , the bulge 14 of the spiral housing 5 overlaps the fan wheel 6 in the region of the second intake opening 12, i.e. the inner end 52 of the first wall section 10, in the direction of the axis of rotation 7 towards the second wall section 11 of the fan wheel 6. Furthermore, the bulge 14 of the spiral housing 5 overlaps the inner end 52 of the first wall section 10 of the fan wheel 6 radially towards the axis of rotation 7 of the fan wheel 6. In the exemplary embodiment, the at least one air guide element 16 is arranged in the bulge 14. As a result, at least part of the swirl zone 30 is formed in the bulge 14.
As shown in FIGS. 4 and 5 , the at least one air guide element 16 is designed as a rib. The rib has a longitudinal plane 27. The rib is flat. The longitudinal plane 27 is spanned by the two main directions of extension of the rib. The ribs are arranged in the gap seal 15 in such a way that they are arranged with their longitudinal plane 27 transversely to the direction of rotation 13 of the fan wheel 6. The ribs are particularly preferably arranged with their longitudinal plane 27 perpendicular to the direction of rotation 13 of the fan wheel 6. The longitudinal plane 27 of the rib is preferably aligned parallel to the axis of rotation 7 of the fan wheel 6.
As shown in FIG. 4 , the bulge 14 extends from an outer end section 55 to an inner end section 54. The distance between the inner end section 54 and the axis of rotation 7 of the fan wheel 6 is smaller than the distance between the outer end section 55 and the axis of rotation 7 of the fan wheel 6. The inner end section 54 of the bulge 14 forms the end of the housing section 8 of the spiral housing 5, which delimits the first intake opening 9. The inner end section 54 of the bulge 14 is connected to the outer end section 55 of the bulge 14 via an intermediate section 56 of the bulge 14.
The inner end section 54 of the bulge 14 preferably extends substantially in the direction of the axis of rotation 7 of the fan wheel 6. The inner end section 54 of the bulge 14 is preferably formed coaxially with the axis of rotation 7 of the fan wheel 6. The inner end section 54 of the bulge 14 overlaps in particular the inner end 52 of the wall section 10 of the fan wheel 6 in the direction of the axis of rotation 7 of the fan wheel 6. The outer end section 55 of the bulge 14 preferably extends substantially in the direction of the axis of rotation 7 of the fan wheel 6. The outer end section 55 of the bulge 14 is preferably formed coaxially with the axis of rotation 7 of the fan wheel 6. The outer end section 55 of the bulge 14 overlaps in particular the inner end 52 of the wall section 10 of the fan wheel 6 in the direction of the axis of rotation 7 of the fan wheel 6. The inner end 52 of the wall section 10 of the fan wheel 6 projects into the bulge 14 and is arranged between the outer end section 55 of the bulge 14 and the inner end section 54 of the bulge 14. The intermediate section 56 of the bulge 14 preferably extends substantially radially to the axis of rotation 7 of the fan wheel 6. The intermediate section 56 of the bulge 14 preferably overlaps the inner end 52 of the wall section 10 of the fan wheel 6 radially to the axis of rotation 7 of the fan wheel 6.
In the preferred embodiment of the work apparatuses 1, the air guide element 16 extends from the inner end section 54 of the bulge 14 along the intermediate section 56 of the bulge 14 to the outer end section 55 of the bulge 14. The air guide element 16 is of course arranged at a distance from the fan wheel 6, in particular from the inner end 52 of the wall section 10 of the fan wheel 6.
As shown in FIGS. 2 and 4 , the at least one air guide element 16, in particular the at least one rib, extends from the inner side 17 of the housing section 8 to the outer side 18 of the housing section 8 of the spiral housing 5. Because the ribs are located on both the inner side 17 and the outer side 18 of the housing section 8, the mechanical structure of the spiral housing 5 is strengthened. As shown in FIG. 2 , the ribs on the outer side 18 of the spiral housing 5 extend over the entire housing section 8. As shown in FIGS. 2 and 6 , the ribs are distributed on the spiral housing 5 at uniform angular distances with respect to the axis of rotation 7 of the fan wheel 6.

Claims

What is claimed is:

1. A portable work apparatus being a vacuum, a blower, or a vacuum-blower combination, comprising:

a housing (2);

a drive motor (3) arranged in the housing (2); and

a fan (4) with

a spiral housing (5) and

a fan wheel (6) arranged in the spiral housing (5),

wherein the fan wheel (6) can be driven by the drive motor (3) to rotate about an axis of rotation (7) to generate an air flow (31),

wherein the spiral housing (5) has a housing section (8) which forms a first intake opening (9) of the fan (4),

wherein the fan wheel (6) has a first wall section (10) which forms a second intake opening (12) of the fan wheel (6),

wherein a gap seal (15) is formed between the housing section (8) of the spiral housing (5) and the first wall section (10) of the fan wheel (6), and

wherein at least one air guide element (16) for generating a swirl zone (30) is formed in the gap seal (15).

2. The portable work apparatus according to claim 1,

wherein the at least one air guide element (16) is arranged on the housing section (8) of the spiral housing (5).

3. The portable work apparatus according to claim 1,

wherein the at least one air guide element (16) is formed as a rib with a longitudinal plane.

4. The portable work apparatus according to claim 3,

wherein the fan wheel (6) is driven to rotate around the axis of rotation (7) in a direction of rotation (13), and

wherein the rib is arranged with the longitudinal plane running transversely to the direction of rotation (13).

5. The portable work apparatus according to claim 1,

wherein the housing section (8) of the spiral housing (5) has a bulge (14) which delimits the first intake opening (9).

6. The portable work apparatus according to claim 5,

wherein the bulge (14) of the spiral housing (5) overlaps the fan wheel (6) in an area of the second intake opening (12) radially to the axis of rotation (7).

7. The portable work apparatus according to claim 5,

wherein the at least one air guide element (16) is formed as a rib with a longitudinal plane in the bulge (14).

8. The portable work apparatus according to claim 3,

wherein the rib is arranged on an inner side (17) of the housing section (8) of the spiral housing (5).

9. The portable work apparatus according to claim 8,

wherein the rib extends from the inner side (17) of the housing section (8) to an outer side (18) of the housing section (8) of the spiral housing (5).

10. The portable work apparatus according to claim 3,

wherein a plurality of ribs are formed on the spiral housing (5), adjacent ribs being arranged at uniform angular distances from one another with respect to the axis of rotation (7) of the fan wheel (6).