Mixture Formation Apparatus, Method of Manufacturing a Mixture Formation Apparatus and Working Device or Internal Combustion Engine

Abstract

A mixture formation apparatus, especially for an internal combustion engine of a working device, has a mixture formation apparatus housing, where a surface of the mixture formation apparatus housing is provided at least partly with a layer structure for protection from corrosion and/or deposits. The layer structure has at least one aluminium oxide layer having a layer thickness of at least 10 m. A method of manufacturing the mixture formation apparatus, and a working device or an internal combustion engine having the mixture formation apparatus, are disclosed.

Claims

1. A mixture formation apparatus, comprising: a mixture formation apparatus housing; and a layer structure provided at least partly on a surface of the mixture formation apparatus housing for protection from corrosion and/or deposits, wherein the layer structure comprises at least one aluminium oxide layer having a layer thickness of at least 10 m.

2. The mixture formation apparatus according to claim 1, wherein the at least one aluminium oxide layer has a constant layer thickness and/or a layer thickness of 10 m to 40 m.

3. The mixture formation apparatus according to claim 1, wherein the at least one aluminium oxide layer is formed on the surface of the mixture formation apparatus housing.

4. The mixture formation apparatus according to claim 1, wherein the layer structure further comprises at least one pore-sealing layer selected from the group consisting of: at least one nickel acetate layer, at least one aluminium hydroxide layer, and a combination of at least one nickel acetate layer and at least one aluminium hydroxide layer.

5. The mixture formation apparatus according to claim 4, wherein the at least one pore-sealing layer has a layer thickness of 5 m.

6. The mixture formation apparatus according to claim 4, wherein the at least one pore-sealing layer is formed on the at least one aluminium oxide layer and/or as at least one layer that concludes the layer structure exteriorly.

7. The mixture formation apparatus according to claim 1, wherein the surface of the mixture formation apparatus housing is an outer surface, an inner surface or both an outer surface and an inner surface of the mixture formation apparatus housing.

8. The mixture formation apparatus according to claim 1, wherein the surface of the mixture formation apparatus housing has an inner surface that bounds, at least in regions, a hollow volume of the mixture formation apparatus housing.

9. The mixture formation apparatus according to claim 8, wherein the hollow volume of the mixture formation apparatus housing is: (i) a hollow volume of a duct selected from the group consisting of: an intake duct, a mixture duct, an air feed duct, a fuel feed duct, and combinations thereof, of the mixture formation apparatus housing, and/or (ii) a hollow volume of a control chamber and/or a compensation chamber of the mixture formation apparatus housing.

10. The mixture formation apparatus according to claim 1, wherein the surface of the mixture formation apparatus housing has a surface of an inner wall and/or of a base of at least one depression in the mixture formation apparatus housing, and/or a surface of an inner wall of at least one opening in the mixture formation apparatus housing.

11. The mixture formation apparatus according to claim 10, wherein the at least one depression takes the form of at least one hole and/or the at least one opening takes the form of at least one hole.

12. The mixture formation apparatus according to claim 1, wherein the mixture formation apparatus is a carburetor, and the mixture formation apparatus housing is a carburetor housing.

13. A method of manufacturing a mixture formation apparatus having a mixture formation apparatus housing and a layer structure provided at least partly on a surface of the mixture formation apparatus housing for protection from corrosion and/or deposits, the method comprising the steps of: a) degreasing and/or pickling the surface of the mixture formation apparatus housing; and b) subsequently, at least partly providing the surface of the mixture formation apparatus housing with the layer structure comprising at least one aluminium oxide layer having a layer thickness of at least 10 m.

14. The method according to claim 13, wherein step b) is conducted by anodizing.

15. The method according to claim 13, wherein step b) is conducted by eloxing.

16. The method according to claim 13, wherein the method further comprises, after step b), the step of: c) treating the surface of the mixture formation apparatus housing with a pore-sealing material, namely nickel acetate and/or water, to form at least one pore-sealing layer.

17. The method according to claim 13, wherein step b) is conducted only once.

18. An apparatus, comprising: a mixture formation apparatus according to claim 1; and a working device or an internal combustion engine having the mixture formation apparatus.

19. The apparatus according to claim 18, wherein the working device is a hand-guided, hand-held or motor-driven working device.

20. The apparatus according to claim 18, wherein the working device is an outdoor and/or autonomous mobile processing robot, a motor saw, a cutting grinder, a brush cutter, a hedge shears, a blower or a lawn mower.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] FIG. 1: a schematic diagram of a two-stroke engine with a mixture formation apparatus according to an embodiment of the invention,

[0102] FIG. 2: an enlarged schematic diagram of a mixture formation apparatus in longitudinal section and

[0103] FIG. 3: an embodiment of a method of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0104] FIG. 1 shows a schematic of an internal combustion engine, namely a two-stroke engine 1. The two-stroke engine 1 is designed as a cylinder two-stroke engine. The two-stroke engine 1 serves in particular to drive a tool of a hand-guided or hand-held working device, for example a cutting grinder, a motor saw, a brush cutter or the like. The two-stroke engine 1 has a cylinder 2 in which a combustion chamber 3 is formed. The combustion chamber 3 is bounded by a piston 5 mounted so as to move back and forth within the cylinder 2. The piston 5, via a piston rod 6, drives a crankshaft 7 mounted so as to be rotatable within a crankcase 4.

[0105] The two-stroke engine 1 has an intake duct 44. The intake duct 44 is connected via a mixture formation apparatus 17 to an air filter 31. In the air filter 31 is disposed a filter material 32, which filters the combustion air sucked into the intake duct 44. The intake duct 44, in the two-stroke engine 1 shown in FIG. 1, is divided into a mixture duct 21 and a feed duct 8 by a dividing wall 19 downstream of the carburetor 17.

[0106] In the case of full-load operation, the feed duct 8 supplies combustion air with a fuel content lower than the fuel content in the mixture duct 21. Advantageously, the combustion air in the feed duct 8 has a low level of fuel or is largely fuel-free. The mixture duct 21 opens out with a mixture inlet 20 in the cylinder 2. The mixture inlet 20 is slot-controlled by the piston 5 and is open to the crankcase 4 in the region of top dead center of the piston 5. The feed duct 8 opens out at a duct inlet 9 in the cylinder 2, which is closed off from the combustion chamber 3 and from the crankcase 4 by the piston 5 in any position of the piston 5.

[0107] An outlet 10 for offgases leads out of the combustion chamber 3. A spark plug 11 projects into the combustion chamber 3, which ignites an air-fuel mixture in the combustion chamber 3.

[0108] Moreover, the two-stroke engine 14 has transfer ducts 12, 15 in a symmetric arrangement on the cylinder 2 with respect to the section plane in FIG. 1. The two transfer ducts 12 close to the inlet open into the combustion chamber 3 with transfer windows 13. The transfer ducts 15 close to the outlet open into the combustion chamber 3 with transfer windows 16. The piston 5 has at least one piston pocket 14 which, in the region of top dead center of the piston, connects the duct inlet 9 to the transfer windows 13 and 16, such that combustion air can flow out of the feed duct 8 into the transfer ducts 12 to 15.

[0109] In an intake duct section 18 formed in the mixture formation apparatus 17, there is a pivotably mounted throttle element, namely a throttle flap 24. The throttle flap 24 is disposed on a throttle shaft 25. The dividing wall 19 projects into the region of the throttle flap 24. The dividing wall 19 has a contact face 35 adjoined by the throttle flap 24 in the fully open position. In the region of the throttle flap 24, secondary fuel openings 27 open into the mixture duct 21.

[0110] In the intake duct 44, combustion air flows from the air filter 31 to the two-stroke engine 1 in flow direction 22. In the intake duct section 18, based on the flow direction 22, a choke flap 29 is disposed upstream of the throttle flap 24 and is pivotably mounted with a choke shaft 30. In a region between the choke shaft 30 and the throttle shaft 25, a Venturi 23 is formed in the intake duct section 18, where the flow cross section in the intake duct section is constricted. In the region of the Venturi 23, a main flow opening 28 opens into the mixture duct 21. In flow direction between the choke flap 29 and the throttle flap 24 is disposed a dividing wall section, in the form of a flow-directing element 40.

[0111] FIG. 2 shows the mixture formation apparatus 17 in the form of a membrane carburetor in enlarged form. The mixture formation apparatus 17 has a mixture formation apparatus housing 26. The mixture formation apparatus housing 26 preferably includes aluminium or an aluminium alloy, or preferably consists of aluminium or aluminium alloy. A surface, especially an outer surface and/or inner surface, of the mixture formation apparatus housing 26 is or has been provided at least partly, especially only partly, or completely with a layer structure 56 for protection from corrosion and/or deposits, where the layer structure 56 has at least one aluminium oxide layer having a layer thickness of at least 10 m. Along the at least one aluminium oxide layer, the layer structure 56 preferably has at least one pore-sealing layer, especially at least one nickel acetate layer and/or at least one aluminium hydroxide layer, especially with a layer thickness of 5 m. The at least one aluminium oxide layer may especially be formed here directly on the surface of the mixture formation apparatus housing 26, and the at least one pore-sealing layer especially directly on the at least one aluminium oxide layer, such that the at least one pore-sealing layer forms at least one layer that concludes the layer structure 56 on the outside.

[0112] The intake duct section 18 is formed in the mixture formation apparatus housing 26. In particular, an inner surface of the intake duct section 18 may be provided at least partly, especially only partly, or completely with the layer structure 56.

[0113] If the throttle flap 24, as shown in FIG. 2, is in its fully open position, the throttle flap 24 separates the intake duct section 18 into the feed duct 8 and the mixture duct 21 in the region of the throttle flap 24. Moreover, an inner surface of the feed duct 8 and/or of the mixture duct 21 may be provided at least partly, especially only partly, or completely with the layer structure 56.

[0114] In FIG. 2, the mixture duct 21 is disposed at the top, by contrast with the representation in FIG. 1. The fuel openings 27 and 28 open out in the mixture duct 21, these being fed by a fuel-filled control chamber 34. An inner surface of the control chamber 34 may especially be provided at least partly, especially only partly, or completely with the layer structure 56.

[0115] The fuel is sucked into the intake duct 44 from the control chamber 34 via the fuel openings 27, 28 depending on the reduced pressure that exists in the intake duct section 18. The control chamber 34 is separated from a compensation chamber 38 by means of a control membrane 37. The compensation chamber 38 may be connected to the environment or the clean side of the air filter 31. In particular, it is (also) possible to provide an inner surface of the compensation chamber 38 at least partly, especially only partly, or completely with the layer structure 56.

[0116] The control membrane 37 actuates an inlet valve 36 via a lever mechanism. Also disposed within the carburetor housing 26 is a fuel pump 33, which conveys fuel to the inlet valve 36 and to the control chamber 34. For adjustment of the amount of fuel supplied to the secondary fuel openings 27, an idling adjuster screw 39 is provided.

[0117] The throttle flap 24 is fixed to the throttle shaft 25 by a screw 43. The head 47 of the screw 43 constricts the flow cross section in the mixture duct 21 and constitutes a throttle site. The throttle shaft 25 also projects into the mixture duct 21 and forms a throttle. This can have the effect that the flow in the mixture duct 21, in the fully open position of the throttle flap 24, is more significantly throttled in the region of the throttle shaft 25 than in the region of the Venturi 23. This is undesirable since the greatest throttling and hence the greatest negative pressure is supposed to exist in the region of the Venturi 23 in order to assure sufficient supply of fuel. In flow direction 22 between the choke flap 29 and the throttle flap 24 is disposed a flow-directing element 40 which reduces the throttling generated by the throttle shaft 25 and the head 47 of the screw 43 in the mixture duct 21. For this purpose, the flow-directing element 40 has a flow profile 41 on the side facing the mixture duct 21. It may be the case that a flow profile is formed at the flow-directing element 40 on the side facing the feed duct 8 as well, in order to influence the flow conditions in the intake duct 44. The flow profile 41 is in ramp form and reduces the flow cross section in the mixture duct 21 to an increasing degree in flow direction 22. Viewed in flow direction 22, the flow-directing element 41 increasingly projects into the mixture duct 21. A longitudinal intake duct axis 46 runs parallel to the flow direction 22 in the geometric middle of the flow cross sections of the intake duct 44. The throttle flap 24 is also fixed to the throttle shaft 25 by a screw 42.

[0118] It is preferable that especially all non-aluminium-containing or non-aluminium alloy-containing components, especially non-aluminium-containing or non-aluminium alloy-containing insert parts, of the mixture formation apparatus 17 are not provided with the layer structure.

[0119] Especially preferably, only the mixture formation apparatus housing 26 is or has been provided with the layer structure.

[0120] FIG. 3 shows a schematic of an embodiment of a method according to the invention for manufacture of a mixture formation apparatus 17.

[0121] The method has a step a): [0122] a) degreasing and/or pickling a surface 48 of a mixture formation apparatus housing 26 (see a,b).

[0123] The degreasing and/or pickling can especially remove oil 49 present on the surface 48 of the mixture formation apparatus housing 26. For this purpose, the surface 48 may be treated with an organic, especially halogenated, solvent, especially selected from the group consisting of hydrochlorocarbons, hydrofluorocarbons and mixtures thereof, and/or with an aqueous solution-which is preferable for environmental reasons.

[0124] The pickling can advantageously remove particles 50 present on the surface 48 of the mixture formation apparatus housing 26. The surface 48 may especially be treated with the aid of an alkaline solution 51, for example sodium hydroxide solution.

[0125] The method also has a step b): [0126] b) at least partly, especially only partly, or completely, i.e. throughout or over the full area, providing the surface 48 of the mixture formation apparatus housing 26 with at least one aluminium oxide layer 52, where the at least one aluminium oxide layer 52 has a layer thickness of at least 10 m (see f).

[0127] An aluminium oxide layer having a layer thickness of at least 10 m has been found to be particularly advantageous with regard to the formation of a continuous aluminium oxide layer.

[0128] Step b) can be conducted immediately after or not immediately after step a).

[0129] Preferably, step b) is conducted by anodizing, especially eloxing.

[0130] Preferably, step b) is conducted by means of DC current. Alternatively, step b) can be conducted with AC current or with the aid of a combination of both types of current, i.e. DC current and AC current. In the DC current variant, the mixture formation apparatus housing is connected as the anode. The counter electrode used is a material which is not attacked by an electrolyte (which is used for performance of step b)).

[0131] Moreover, step b) can be conducted with a voltage of 5 V to 40 V.

[0132] Moreover, step b) can be conducted over a period of 20 min to 120 min, especially 30 min to 90 min.

[0133] Moreover, step b) can be conducted with an electrolyte, especially selected from the group consisting of sulfuric acid, oxalic acid, and mixtures of at least two of the aforementioned electrolytes.

[0134] In particular, step b) can be conducted with a solution, especially an aqueous solution, containing the electrolyte, especially where the electrolyte has a concentration of 150 g/l to 250 g/l, especially 190 g/l to 220 g/l, based on the total weight of the solution.

[0135] Moreover, the method may also have, between steps a) and b), a step ab): [0136] ab) removing a natural aluminium oxide layer 53 from the surface 48 of the mixture formation apparatus housing 26 (see d).

[0137] Step ab) may especially be conducted by neutralizing the surface 48 of the mixture formation apparatus housing 26 by treatment with an acid, especially inorganic acid, for example sulfuric acid.

[0138] Step ab) can be conducted immediately or not immediately after step a) and/or immediately or not immediately before step b).

[0139] Moreover, the method may also have, between steps a) and b), especially between steps ab) and b), a step ab): [0140] ab) polishing, especially chemically polishing or chemomechanically polishing, the surface of the mixture formation apparatus housing 26 (see e).

[0141] Step ab) may be conducted immediately or not immediately after step a), especially after step ab), and/or immediately or not immediately before step b).

[0142] Moreover, the method may also have, after, especially immediately or not immediately after, step b), a step c): [0143] c) treating the surface 48 of the mixture formation apparatus housing 26 with a pore-sealing material, especially nickel acetate and/or water, especially water vapour, to form at least one pore-sealing layer 54 (see g).

[0144] Step c) can advantageously seal pores 55 in the at least one aluminium oxide layer 52 and hence lower or even completely prevent any risk of corrosion.

[0145] In the case of treatment of the surface 48 of the mixture formation apparatus housing 26 with nickel acetate, step c) can be conducted at a temperature of 80 C. to 100 C., especially 85 C. to 95 C., and/or over a period of 5 min to 30 min, especially 10 min to 20 min.

[0146] In the case of treatment of the surface 48 of the mixture formation apparatus housing 26 with water, especially water vapour, step c) can be conducted at a temperature of 80 C. to 100 C., especially 85 C. to 95 C., and/or over a period of 5 min to 30 min, especially 10 min to 20 min.

[0147] Preferably, step b) is conducted only once, i.e. not repeatedly. This is particularly advantageous for reasons of cost and time.

[0148] With regard to further features and advantages of the method, reference is made completely to the features and advantages disclosed in the general description, which are applicable mutatis mutandis.

[0149] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.