MOBILE POWER TOOL AND METHOD

Abstract

A mobile power tool comprising a drive unit is disclosed. The drive unit has an aqueous lubricant and/or the drive unit is set up for operation with the aqueous lubricant, wherein, before the start of a running-in phase of the drive unit, a bond roughness sigma of two interacting contact surfaces of the drive unit is greater than 0.01 m, preferably at least 0.1 m.

Claims

1. A mobile power tool comprising a drive unit, wherein the drive unit has an aqueous lubricant and/or in that the drive unit is set up for operation with the aqueous lubricant, wherein, before the start of a running-in phase of the drive unit, a bond roughness sigma of two interacting contact surfaces of the drive unit is greater than 0.01 m.

2. The mobile power tool as claimed in claim 1, wherein the bond-roughness sigma before the start of the running-in phase of the drive unit is at most 3 m.

3. The mobile power tool as claimed in claim 1, wherein the aqueous lubricant is designed in such a way that the lubricating film thickness is between 10% and 80% of a non-aqueous or at least substantially non-aqueous polyglycol-based lubricant.

4. The mobile power tool as claimed in claim 1, wherein the aqueous lubricant comprises at least 5% water.

5. The mobile power tool as claimed in claim 1, wherein the aqueous lubricant comprises at most 90% water.

6. The mobile power tool as claimed in claim 1, wherein the aqueous lubricant has at least one additive.

7. The mobile power tool as claimed in claim 1, wherein the aqueous lubricant has a kinematic viscosity in the range of at most 320 mm.sup.2/s at 40 C.

8. The mobile power tool as claimed in claim 1, wherein the mobile power tool is set up so that internal temperature of the drive unit during operation of the mobile power tool at an ambient temperature of 20 C. is at most 80 C.

9. The mobile power tool as claimed in claim 1, wherein the mobile power tool is set up to limit input power of the drive unit in such a way that internal temperature of the drive unit during operation of the mobile power tool at an ambient temperature of 20 C. is at most 80 C.

10. The mobile power tool as claimed in claim 1, wherein the mobile power tool has a solids filter which is set up to remove particles from the aqueous lubricant.

11. The mobile power tool as claimed in claim 1, wherein the aqueous lubricant is free of solids or at least substantially free of solids and/or formed without solid residues, at least before the start of the running-in phase.

12. The mobile power tool as claimed in claim 1, wherein the aqueous lubricant contains nano-friction particles.

13. The mobile power tool as claimed in claim 1, wherein the mobile power tool can be operated cordlessly.

14. The mobile power tool as claimed in claim 1, wherein the mobile power tool is set up to drive a diamond-containing tool.

15. A method for the energy-efficient operation of the mobile power tool as claimed in claim 1, wherein the drive unit of the mobile power tool in which, before the start of a running-in phase, a bond roughness sigma of two interacting contact surfaces of the drive unit is greater than 0.01 m is lubricated with an aqueous lubricant.

16. The mobile power tool of claim 1, wherein the bond-roughness sigma of two interacting contact surfaces of the drive unit is at least 0.1 m.

17. The mobile power tool of claim 2, wherein the bond-roughness sigma before the start of the running-in phase of the drive unit is at most 1 m.

18. The mobile power tool of claim 3, wherein the lubricating film thickness is between 30% and 60% of the non-aqueous or at least substantially non-aqueous polyglycol-based lubricant.

19. The mobile power tool of claim 4, wherein the aqueous lubricant comprises at least 15% water.

20. The mobile power tool of claim 5 wherein the aqueous lubricant comprises at most 70% water.

Description

IN THE FIGURES

[0056] FIG. 1 shows a hand-held power tool;

[0057] FIG. 2 shows a diagram of lubricating film thicknesses of different lubricants and

[0058] FIGS. 3a to 3c show schematic representations of various frictional states;

[0059] FIGS. 4a to 4b show micrographs of transmission parts and

[0060] FIGS. 5a to 5b show micrographs of bearing balls.

[0061] In order to make it easier to understand the invention, the same reference signs are used in each case for identical or functionally corresponding elements in the following description of the figures.

[0062] Although the invention generally encompasses mobile power tools and therefore for example construction robots or hand-held power tools, the invention is explained using the example of a hand-held power tool, only to make it easier to understand.

[0063] FIG. 1 shows a mobile power tool in the form of a hand-held power tool 10. The hand-held power tool 10 is designed as a drill, in particular as a diamond drill. It is cordless. To this end, it has a rechargeable battery 14 in the region of a housing 12. The battery 14 comprises lithium. The hand-held power tool 10 is configured as a portable device. It has a weight of between 0.5 and 15 kg and generally of less than 25 kg.

[0064] The hand-held power tool 10 also has a tool fitting 16. A tool 18 is held in the tool fitting 16. The tool 18 is designed as a diamond drilling tool. It is therefore diamond-containing. It is alternatively or additionally conceivable that the mobile power tool is designed and/or can be used as a hammer drill and/or as a chiseling machine.

[0065] In a schematic representation, a drive unit 20 of the hand-held power tool 10 is also discernible in FIG. 1. The drive unit 20 is located inside the housing 12 and is shown in a manner superposed on the housing 12 only for reasons of illustration.

[0066] The drive unit 20 drives a shaft, to which in turn the tool fitting 16 is coupled.

[0067] The drive unit 20 has an electropneumatic impact mechanism and a rotary drive, which drive the shaft in a striking and rotating manner, respectively. The impact mechanism and the rotary drive are mechanically connected via a transmission of the drive unit 20 to an electric motor of the drive unit 20 and are able to be driven thereby.

[0068] The drive unit 20 has an aqueous lubricant by means of which transmission elements, for example gear wheels, of the drive unit 20 are lubricated. The drive unit 20 is designed to be water-vapor resistant. For this purpose, in particular all of the seals of the drive unit 20 that can come into contact with the aqueous lubricant are made from a water-vapor-resistant material. The water-vapor-resistant material may preferably be temperature-resistant, at least up to 120 C. In addition, the hand-held power tool 10 has a cooling system which is designed such that the internal temperature of the drive unit 20 during operation of the hand-held power tool 10 at an ambient temperature of 20 C. is at most 60 C.

[0069] Surfaces in the interior of the drive unit 20, in particular respectively interacting contact surfaces of paired gear wheels, are produced with a bond roughness sigma of at least 0.1 m, and consequently have such a bond roughness before the start of a running-in phase.

[0070] FIG. 2 shows a diagram of lubricating film thicknesses of different lubricants, the lubricating film thicknesses being shown standardized to 100% for a substantially non-aqueous, polyglycol-based lubricant, identified in FIG. 2 as lubricant S0. The lubricant S0 has a kinematic viscosity of 80 mm.sup.2/s at 40 C.

[0071] Water W is also additionally shown schematically in the diagram for comparison.

[0072] Lubricants S1, S2, S3, S4 and S5 are aqueous lubricants which, according to the invention, can be used in the hand-held power tool 10 (FIG. 1). They have lubricating film thicknesses of between 30% and approx. 60% of the lubricating film thickness of the substantially non-aqueous lubricant S0 serving as a reference. The lubricants have a kinematic viscosity of 100 mm.sup.2/s at 40 C.

[0073] The lubricants S1, S2, S3, S4 and S5 each have a water content of between 30% and 35%. They also each contain at least between 40% and 60% polyglycols. Like the lubricant S0, they are fully formulated.

[0074] All of the aforementioned aqueous lubricants S1 to S5 contain further additives, in particular biocidal, anti-corrosive, wear-resistant, high-pressure and foam-controlling additives.

[0075] The aqueous lubricants S1 to S5 are formed without solid residues.

[0076] From the overall view of FIG. 2 it can be seen that the lubricants S1, S2, S3, S4 and S5 have reduced lubricating film thicknesses compared to the lubricant S0 serving as a reference, which however remain greater than that of the water W.

[0077] FIGS. 3a to 3c show in schematic representations different frictional states of the drive unit 20 (FIG. 1).

[0078] Two interacting contact surfaces 22, 24 are shown greatly enlarged as schematic sectional views. The contact surfaces 22, 24 may be for example regions of intermeshing gear wheels of the drive unit 20.

[0079] The surface shapings of the contact surfaces 22, 24 are not shown true to scale for reasons of illustration, in particular in order to show the waviness of the surfaces in a recognizable manner.

[0080] Depending on the frictional state, there is aqueous lubricant 26 with different film thicknesses between the contact surfaces 22, 24. The aqueous lubricant 26 may correspond to one of the lubricants S1, S2, S3, S4 or S5 (all FIG. 2).

[0081] In the state according to FIG. 3a, there is boundary friction. The bond roughness sigma of the contact surfaces 22, 24 is 0.1 m, so that peaks 28, of which only individual ones are marked by way of example and provided with reference signs in FIGS. 3a to 3c, of the contact surfaces 22, 24 meet when the contact surfaces 22, 24 move relative to one another.

[0082] It can also be seen that the thickness of the lubricating film that forms is on average less than the bond roughness sigma. The relative lubricating film thickness is therefore less than 1, for example between 0.1 and 0.4, in particular between 0.1 and 0.2, at a test temperature of 40 C. and under a surface pressure of 1 GPa with 20% slip.

[0083] The state according to FIG. 3a corresponds to a state of the hand-held power tool 10 (FIG. 1) directly after its manufacture, i.e. before the start of a running-in phase.

[0084] According to the method according to the invention, it is envisaged to operate the hand-held power tool 10 during a running-in phase. The drive unit 20 is thereby lubricated by the lubricant 26 contained in the drive unit 20. For this purpose, the hand-held power tool may be operated for example over a period of 1 to 10 hours, for example 7 hours.

[0085] The boundary friction prevailing at least at the beginning of the running-in phase leads to the removal of particles from the contact surfaces 22, 24 and in this way to an automatic smoothing of the contact surfaces 22, 24. For this purpose, in FIGS. 3a to 3c individual particles 30 in the aqueous lubricant 26 are shown by way of example and provided with a reference sign.

[0086] FIG. 3b shows a frictional state in which there is mixed friction between the contact surfaces 22, 24.

[0087] Overall, the bond roughness sigma of the contact surfaces 22, 24 has already been reduced considerably, so that only a few individual peaks 28 of the contact surfaces 22, 24 can contact one another. The relative lubricating film thickness is in the range between 1 and 3.

[0088] This state corresponds to an advanced stage of the running-in phase.

[0089] FIG. 3c shows a frictional state in which there is pure fluid friction between the contact surfaces 22, 24. This state corresponds to a state of the drive unit 20 after the end of the running-in phase.

[0090] The bond roughness sigma of the contact surfaces 22, 24 has been further reduced considerably. The surface shaping of the contact surfaces 22, 24 is shown greatly exaggerated merely for reasons of illustration.

[0091] The relative lubricating film thickness has increased to greater than 3.

[0092] As a result of the automatically smoothed contact surfaces 22, 24, further operation of the hand-held power tool 10, and in particular of the drive unit 20, is therefore possible with considerably reduced friction.

[0093] FIGS. 4a and 4b show micrographs of regions of transmission parts after completion of an endurance test.

[0094] While FIG. 4a shows the result for a mobile power tool of which the drive unit is lubricated with the substantially non-aqueous lubricant S0 serving as a reference, the images according to FIG. 4b show the result for a mobile power tool of which the drive unit is correspondingly lubricated, according to the invention, with the aqueous lubricant S3.

[0095] In FIG. 4a there is considerable pitting, while FIG. 4b has remained almost free of pitting.

[0096] Also, FIG. 5a and FIG. 5b show micrographs of bearing balls after the endurance test has been carried out. By analogy with the two previous representations, the upper figure, FIG. 5a, shows the result for a drive unit where the substantially non-aqueous lubricant S0 has been used as the lubricant and the lower figure, FIG. 5b, shows the result for a drive unit in the case of which the aqueous lubricant S3 has been used.

[0097] It can be seen that the bearing ball of FIG. 5b has a significantly more pronounced clear metallic luster than the bearing ball of FIG. 5a, which is attributable to a significantly reduced surface roughness compared to the conventionally lubricated bearing ball.

[0098] It is particularly noteworthy here that the aqueous lubricant S3 is free of solids. In the tests associated with FIG. 5b, no nano-friction particles were added to the lubricant S3 either.

[0099] Furthermore, with the invention described above, it has been possible to achieve energy savings of up to 180 W of saved power loss, or approximately 8 percent of the mechanical transmission efficiency, in the case of a mobile power tool supplied with power from the grid.

[0100] Thanks to the significantly improved lubrication, it has also been possible to determine that the sump temperature of aqueous lubricants could be reduced by up to 8 C. or by up to approx. 13% while at the same time increasing the mechanical transmission output power by up to approx. 9% compared to the reference lubricant S0.

[0101] In contrast to the sump temperature of the reference lubricant S0, it has been possible to keep the sump temperatures of the aqueous lubricants below 60 C. even with an electrical input power of the power tool of 2.8 kW.

[0102] It has also proven to be particularly beneficial in terms of reducing the sump temperature if the aqueous lubricant has a viscosity of between 40 and 50 mm.sup.2/s, in particular of 46 mm.sup.2/s, at 40 C.