US20100054853A1

US20100054853A1 - Coupling element

Info

Publication number: US20100054853A1
Application number: US12/550,675
Authority: US
Inventors: Mark Jesse
Original assignee: Dolmar GmbH
Current assignee: Makita Engineering Germany GmbH
Priority date: 2008-09-02
Filing date: 2009-08-31
Publication date: 2010-03-04
Also published as: DE102009038371A1; DE202008011648U1; CN101663936A

Abstract

A coupling element is provided for a detachable plug connection of a guide tube, which is dividable into at least two sections, with a drive shaft mounted therein for torque transmission between an engine unit and a tool head of a hand-operated string trimmer. A first, upper guide tube section is arranged between the engine unit and the coupling element, and a second, lower guide tube section is arranged between the coupling element and a tool head. The coupling element has a coupling sleeve that provides both an exact alignment of the cutting tool as well as a simple and secure assembly of the guide tube sections. A latching connection with at least one latching element is arranged on the coupling sleeve so that it latches into place in only the correct rotational position on a latching seat of the guide tube section upon insertion of one of the guide tube sections into the coupling sleeve.

Description

TECHNICAL FIELD

The invention relates to a coupling element for a detachable plug connection of a guide tube, which is dividable into at least two sections, with a drive shaft mounted therein for torque transmission between an engine unit and a tool head of a hand-operated string trimmer according to type indicated in the preamble of claim 1.

PRIOR ART

String trimmers, which are also known as trimmers, serve to cut grass, brushwood or the like. For cutting purposes, they have a tool head with a cutting tool that is arranged on one end of a relatively long guide tube. A drive unit with an engine is attached at the opposite end of the guide tube. For the purposes of torque transmission between the engine unit and the cutting tool, a drive shaft is introduced within the guide tube.
To simplify transport of the string trimmer, it is known to divide the guide tube into two or a plurality of sections. The individual guide tube sections are each connectable by means of a coupling sleeve.
A division of the guide tube can also be advantageous in order to make length adjustment possible for individuals of different heights. In this manner, intermediate pieces can be inserted.
Document DE 202 04 015 U1 discloses an extension element for a guide tube with an interiorly positioned drive shaft of a string trimmer. In order to make possible an optimal alignment and therewith an untiring work experience for individuals operating said string trimmer who are of different heights, the elongation element has a tube section and a shaft section, which is arranged in the tube section and connected to the drive shaft in a torsional manner, as well as a clamping element for fixing the tube section to a free end of the guide tube. The clamping element is designed as a tooless gripper clamp with a thumb-screw screwed connection. A fastening sleeve of the clamping element furthermore has an interiorly positioned receiving groove, which extended in the longitudinal direction, with which a radially outward extending guide lug engages during assembly. The receiving groove works together with the guide lug as an anti-twist device and also operates as an alignment aid for a predetermined rotation angle position of individual components of the string trimmer. For a defined axial position of the tube section relative to the fastening sleeve, the latter has in its interior a radially inward protruding annular shoulder and a stop.
In order to make it possible to transport the string trimmer, documents DE 29 809 694 U1 and DE 29 907 780 U1 both suggest similar constructions of a coupling sleeve that permits a separation of the guide tube. Two tube sections of the guide tube are plug connected to one another by means of the coupling sleeve in order for the string trimmer to be operated. The tube sections are inserted into one another and are secured only by a clamping connection comprising a tommy screw.
With these solutions, however, the tube sections can detach from one another if the thumb screw or the tommy screw is not securely tightened enough.
Document U.S. Pat. No. 4,463,498 discloses a further coupling element designed as a coupling sleeve for tube section of a string trimmer. A coupling sleeve is divided into two parts, a total of four screwed connection being provided for clamping the tube section, wherein one thereof comprises a thumb screw. A lip is arranged on the coupling sleeve in the region of the lower guide tube, said lip engaging with an external, radial recess of the lower guide tube. The lip with its recess is designed in such a manner that a relative rotation of the lower tube section is intended to be possible. In the region of the upper tube section, an inwardly protruding lug is attached to the coupling sleeve, said lug engaging with a bore hole on the upper tube section in such a manner that anti-twist protection is provided between the upper tube section and coupling sleeve. This construction is disadvantageous in that different designs of the string trimmer are possible and thus also erroneous adjustments.

DETAILED DISCLOSURE OF THE INVENTION

Object, Solution, Advantages

The object addressed by the invention is that of improving a coupling element of the type previously mentioned in such a manner that not only an exact adjustment of the cutting tool is possible but also a simple and secure assembly of the guide tube sections is given, wherein the effort expended in assembly is intended to be minimal.
This object is solved by a coupling element having the features of claim 1.
The coupling element according to the invention simplifies both the handling because the cutting tool is already in the correct rotational position, that is to say parallel to the ground to be worked, owing to the latching element latching into place in its latching seat, handling furthermore being simplified because the string trimmer can be held with one hand on the upper part while an upward movement is possible with the other hand, namely with the upper tube section being able to detach and fall during the assembly of the sleeve. This very assembly-friendly configuration can be realised very simply and cost-effectively.
The guide to be connected is inserted into a formed fitting and locks into place by means of the latching element used in connection with its latching seat.
In terms of the alignment of the cutting tool, it is of particular relevance that the angle of rotation of the guide tube must be correct with the tool head.
Additional advantageous configurations of the invention are characterised in the dependent claims.
In an advantageous development of the invention, it is furthermore provided that the latching element and the latching seat are designed in such a manner that the latching connection engages with only a rotational position and an axial position of the guide tube section.
It is advantageous if the latching element is designed as a latching lug with a springily resilient latching arm and it is furthermore advantageous that the latching seat is designed as receiving opening present on the guide tube section, said receiving opening being for the latching lug. Allowance can be made for the latching lug and the spring arm by means of corresponding shaping of the manufacturing tool. The required elasticity can be selected by means of selecting the arm length and/or the material used. The receiving opening can be created in a simple manner as a circular through hole, by means of blanking or by a chip removing process, for example. While the latching lug and the receiving opening are preferably circular, other shapes, such as a rectangular form, for example, are also conceivable.
In order to further simplify the assembly and disassembly, it is therefor provided in a coupling element according to the invention in an additional advantageous embodiment, that the latching lug guided onto the coupling sleeve in an axially displaceable manner and works together with one of the platforms adjacent the receiving opening in such a manner that upon insertion of the guiding tube section, the latching lug moves axially on the receiving opening and is raised until the receiving opening is engaged by the latching lug and can dip thereinto. For this, the latching lug slips down the platform again. In this manner, the guide tube can be inserted thereinto and held therein with minimal hand movements. The latching lug can be designed in such a manner that, it is automatically raised upon insertion of the guide tube section in that it is pressed against the platform. When the receiving opening of the guide tube section reaches the lug, it automatically falls into the opening by means of the spring force of the then pre-tensioned arm, thereby leading to the creation of a locking mechanism or interlocking.
To disconnect the connection, the latching arm can be pushed back by hand in such a manner that the latching lug emerges from the receiving opening. It is therefore advantageous is the latching arm is integrally formed on its end that is opposite the latching lug with an actuating part that is externally axially displaceable on the coupling sleeve in order to detach the latching connection. The actuating part with its latching arm and its latching lug can be manufactured from a plastic.
Yet another advantageous development of the coupling element is characterised in that the latching lug has a substantially trapezoidal cross-section that tapers in the direction of the drive shaft. This has the advantage that the latching lug can very easily dip into receiving opening. The trapezoidal shape can also be selected in such a manner that upon insertion of the guide tube section, the tube end presses against the slant of the latching lug in such a manner that it can emerge independently, or at least with minimal additional force.
In theory, with this coupling sleeve, the connection of the guide tube can be separated on both sides. The latching lug can also be arranged on the side of the engine unit. It is preferably with the guide tube section, which works together with the latching element, of the lower section that is opposite the cutting head so that it can be separated from the coupling element, the upper tube section practically being fixedly connected to the coupling element by means of a clamping connection without tommy screws or thumb screws, for example, which are detachable only with a tool.
In order to create a fixed connection between the lower guide tube section and the upper guide tube section, it has proven of value that at additionally at least one screwed clamping connection for creating a clamping connection of the coupling sleeve is present on the guide tube section. It is very assembly friendly if the screwed clamping connection comprises a tooless gripper clamp with a tommy screw or thumb screw. The combination of latching and screwed connections creates a more and secure and rapid connection of the separated guide tube.
In order for a required shaft division to be possible, it is advantageous that a shaft coupling is arranged on the coupling sleeve for a power transmission of the drive shaft.
It is furthermore favourable that the latching connection is designed in such a manner that it engages only if the shaft coupling engages both of the to-be-coupled shaft ends of the drive shaft. In this manner, it is ensured that a shaft connection is present prior to the attachment of the tube that is to be fixed. In this manner, the shaft coupling can comprise a shaft sleeve fastened on one shaft end, said shaft sleeve being provided with radial, rotationally symmetrical slits on its edges in order to connect a star-shaped shaft end of a shaft end to be coupled in a form-fitting manner. A complete insertion of the tube end is possibly only if the star-shaped shaft end is inserted into the shaft sleeve.
In a preferred embodiment of the shaft sleeve, it is provided that it consists of two such separated shaft sections that are held on a shaft end by means of circumferential clamping rings. The sleeve halves that are identical, in particular, can easily be installed on the shaft and furthermore improve warehousing. The clamping rings, which are assembled subsequent to the assembly of the sleeve halves, hold the sleeve halves together on the shaft.
Yet a further advantageous embodiment is characterised in that the latching connection is designed in such a manner that the latching element is displaceable on the coupling sleeve. Proceeding from a locked state of the coupling element, this makes a detachment of a guide tube easier in that the latching element can be automatically raised. It is particularly favourable for this to occur if the latching connection is designed in an independently resilient manner. In order to make a screwless assembly possible, advantageous is the latching connection 25 being clippable onto the coupling sleeve 22 with independent latching means.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment is described in greater detail using the drawings, while additional advantageous developments of the invention and advantages thereof are described. In purely schematic drawing, it is shown in:

FIG. 1 an abstracted drawing of a string trimmer,

FIG. 2 a perspective drawing of the string trimmer,

FIG. 3 a section drawing of a coupling element according to the invention with a latching lug,

FIG. 4 a section drawing of the coupling element according to the invention with a different position of the latching lug,

FIG. 5 a section drawing of the coupling element according to the invention in which a lower guide tube section is partially inserted,

FIG. 6 a section drawing of the coupling element according to the invention in which the lower guide tube section is completely inserted, however not latched,

FIG. 7 a section drawing of the coupling element according to the invention in which the lower guide tube section is completely inserted and latched,

FIG. 8 a perspective drawing of the coupling element according to the invention.

THE BEST WAY TO EXECUTE THE INVENTION

FIGS. 1 and 2 show a string trimmer 10. Said string trimmer comprises a drive unit with an engine or an engine unit 11 and a tool head 12 for a cutting tool that is not more closely shown. The engine unit 11 and the cutting tool are connected to a guide tube 13 in such a manner that the engine unit 11 is situated on one end of the guide tube 13 and the tool head is positioned on the opposite end. During use, the tool head is located, as FIG. 2 shows, near the ground, while the drive unit is held at a certain height of a person. The string trimmer 10 can comprise a belt, which is not shown, or a belt system in order to promote a work experience that is not tiring. For operation, a handhold 14 is provided on the guide tube 13 as well as is an operating lever that is provided between said handhold and drive unit. The guide tube is shown in FIG. 2 in the use position while held at an angle so that a relatively long guide tube 13 is present.
In order to be able to transport the guide tube 13 more easily and/or to be able to adjust it for individuals of different heights with an extension adapter, for example, a coupling element 16 is provided for a detachable plug connection of the guide tube 13 that can be divided into at least two sections.
The guide tube 13 comprises, as is shown in principle in FIG. 1, a drive shaft 17 mounted therein for power transmission or torque transmission between the engine unit 11 and the tool head 12 or the cutting tool of the hand-operated string trimmer. A first, upper guide tube section 20 is arranged between the engine unit 11 and the coupling element 16. A second, lower guide tube section 21 is arranged between the coupling element 16 and the tool head 12.
The coupling element 16 has a coupling sleeve 22 that is shown in greater detail in FIG. 3. A first drive coupling 23 is positioned within the coupling element 16.
The tool head 12 can be detachably fixed on the free or lower end of the guide tube or of the lower guide tube section 21 by means of a connection that is not more closely shown, for example a clamping connection. The drive shaft 17 is provided with a second drive coupling 24 in this region, as can be seen in FIG. 1.
According to the invention, a latching connection 25 is provided with a at least one latching element 26 that is arranged on the coupling sleeve, said latching element being designed in such a manner that, upon insertion of the lower guide tube section 21 into the coupling sleeve 22 on a latching seat, which is referred to with a reference number in FIG. 5, of the lower guide tube section 21, it latches into place only in correct rotational position.
FIGS. 3 to 7 show a preferred embodiment of the latching connection 25. The latching element 26 is designed as a latching lug 30 with a springily elastic latching arm 31. The latching seat 27 is designed as a receiving opening 32, intended for the latching nose 30, present on the lower guide tube section 2 or as a through hole present on the tube sleeve.
As arrow “A” in FIG. 5 indicates, the latching nose 30 is guided on the coupling sleeve 22 in an axially displaceable manner. As FIGS. 3 to 7 show, the latching nose 30 has a substantially trapezoidal cross-section that tapers in the direction of the drive shaft 17. With an inserted guide tube section 20, a platform 33 is present in the region of the receiving opening 32 or at an opening 35 provided for the latching lug 30 of the coupling sleeve 22 (FIG. 6), said platform 33 being positioned on an edge 36 distant from the insertion side 34 (FIG. 4). The latching lug 30 works together with the platform 33 adjacent the opening 35 or the receiving opening 32 (FIG. 6). As FIG. 6 shows, the latching lug 30 is axially moved from the insertion side to the platform upon insertion of the guide tube section 21 and is raised in the direction of the arrow “B”. This occurs until the receiving opening 31 is engaged by the latching lug 30. Then the latching lug 30 is inserted into the receiving opening 32, as FIG. 7 shows. The movement of the latching nose 30 on the platform 33 can occur as a result from a pulling back of the latching arm 31 by hand or can also occur automatically by means of shaping the latching lug 30.
As FIGS. 3 to 7 show, the latching connection 25 is designed in such a manner that the latching element 26 can be displaced onto the coupling sleeve 22, as arrow “A” shows in particular. Additional displaceable solutions are, however, also possible. The latching connection 25 can be displaceable on the coupling element 16 or the coupling sleeve. In order to simplify assembly, it is advantageous that the latching connection 25 be able to be clipped onto the coupling element 16 or onto the coupling sleeve.
As FIG. 7 shows, the latching arm 31 is integrally formed on its end opposite the latching lug 30 with an actuating part 37 externally axially displaceable on the coupling sleeve 27 for disconnecting the latching connection 35, said latching arm not being rotatably arranged on the coupling sleeve 22. The actuating part 37 with its latching arm 31 and its latching lug 30 is preferably produced out of a plastic.
The insertion-withdrawal operation of the lower guide tube section 21 can be seen most clearly in FIGS. 5 to 7. FIG. 5 shows how subsequent thereto, the lower end of the guide tube section 21 abuts the latching lug 30. By pulling the actuating part 37 back, as FIG. 6 shows, the latching lug 30 is raised, thereby bringing about the guide tube section 21 being able to be completely slid up to an arrester 40 (FIG. 5) that is integral with the interior of the coupling sleeve. The stopper ensures the proper axial position of the guide tube section 21. Subsequent thereto, the actuating part 37 can be moved back into its original position, that is to say in the direction of “C”. If the latching lug drops out of the platform 33, it then penetrates into the receiving opening 32 in such a manner that the latching lug 30 engages the guide tube section in an anti-swiveling fashion. As FIGS. 5 to 7 show, the latching lug 20 engages the receiving opening 32 only in a rotational and axial position of the guide tube section 21.
So that the latching lug 30 travels independently into an original position, a spring, which is not more closely shown, can be provided so that the latching connection 25 independently springs back. The spring force is preferably directed in the direction of the tool head 12.
Furthermore, FIGS. 3 to 7 show that a screw clamping connection is present for creating a clamping connection of the coupling sleeve 22 to the guide tube section 20. The screwed clamping connection comprises a tooless gripper clamp having a tommy screw 42. This can also be a thumb screw. A screw nut 43 is arranged on one screw end, said screw nut effecting the clamping connection with the screw 42.
FIGS. 1 and 8 show a clamping connection 44 for the upper guide tube section 20. This clamping connection is not, however, tooless, that is to say is not provided with tommy screw or a thumb screw, but rather comprises a simple screw for a screwdriver, for example. This connection is also a gripper clamp.
FIG. 8 moreover shows the shaft coupling 23, in particular its front face into which a shaft end is inserted. The shaft coupling 23, which is for the transmission of power of the drive shaft 17, is namely arranged in the coupling sleeve 22. The shaft coupling 23 comprises a shaft sleeve 45 attached to a shaft end, as FIG. 3 shows, for example. The edges of the shaft sleeve 45 are provided with radial, rotationally symmetrical slits 46 in order to connect in a form-fitting manner a rectangular or star-shaped shaft end of the shaft end to be coupled.
Alternatively, a different configuration of the shaft coupling is possible. Preferably, the latching connection is designed in such a manner that it engages only if the shaft coupling 23 engages both of the to-be-coupled shaft ends of the drive shaft 17.
As FIG. 3 or one other of the FIGS. 4 to 7 shows, the shaft sleeve consists of two identical sleeve halves 47 a, 47 b. Said sleeve halves are held by circumferential clamping rings 50 on the shaft end of the shaft 17.
The invention is not limited to this example, which is to say that instead of the latching lug shown, a different latching means can effect the rotationally correct position. It is also possible for more than one since coupling element to be used. Thus, the guide tube can also have three parts. Instead of a receiving opening of the guide tube section 21, a different latching seat can also be used. It follows that a rectangular, depression that is not punched through can also be used.

REFERENCE NUMBER LIST

10 String trimmer
11 Engine unit
12 Tool head
13 Guide tube
14 Handhold
15—
16 Coupling element
17 Drive shaft
18—
19—
20 Upper guide tube section
21 Lower guide tube section
22 Coupling sleeve
23 First shaft coupling
24 Second shaft coupling
25 Latching connection
26 Latching element
27 Latching seat
28—
29—
30 Latching lug
31 Latching arm
32 Receiving opening
33 Platform
34 Insertion side
35 Opening
36—
37 Actuating part
38—
39—
40—
41—
42 Tommy screw
43 Screw nut
44 Clamping connection
45 Shaft sleeve
46 Slit
47 a-b Sleeve halves
48—
49—
50 Clamping rings

Claims

1. A coupling element for a detachable plug connection of a guide tube, which is dividable into at least two sections, with a drive shaft mounted therein for torque transmission between an engine unit and a tool head of a hand-operated string trimmer, comprising:

a first, upper guide tube section arranged between the engine unit and the coupling element;

a second, lower guide tube section arranged between the coupling element and the tool head, wherein the coupling element has a coupling sleeve; and

a latching connection having at least one latching element arranged on the coupling sleeve, said latching element being designed in such a manner that it latches in place in only the correct rotational position when one of the guide tube sections is inserted into the coupling sleeve on a latching seat of the guide tube section.

2. The coupling element as specified in claim 1, characterised in that the latching element and the latching seat are designed in such a manner that the latching connection engages only in a rotational and axial position of the guide tube section.

3. The coupling element as specified in claim 1, characterised in that the latching element is designed as a latching lug with an elastic latching arm, and furthermore in that the latching seat is configured as a receiving opening of the latching lug, said receiving opening being present on the guide tube section.

4. The coupling element as specified in claim 3, characterised in that the latching lug is guided on the coupling sleeve in an axially displaceable manner, and moreover works together with a receiving opening of an adjacent platform in such a manner that upon insertion of the guide tube section, the latching lug moves axially on the platform and is raised until the receiving opening is engaged by the latching lug and is inserted thereinto.

5. The coupling element as specified in claim 3, characterised in that an external actuating part, which is axially displaceable on coupling sleeve is integrally formed on the end of the latching arm that is opposite the latching lug for disconnecting the latching connection.

6. The coupling element as specified in claim 5, characterised in that the actuating part with its latching arm and its latching lug is manufactured out of a plastic.

7. The coupling element as specified in claim 3, characterised in that the latching lug has a substantially trapezoidal cross-section that tapers in the direction of the drive shaft.

8. The coupling element as specified in claim 1, characterised in that the guide tube section that works together with the latching element is the lower section.

9. The coupling element as specified in claim 1, characterised in that additionally at least one screwed clamping connection for the clamping connection of the coupling sleeve is present on the guide tube section.

10. The coupling element as specified in claim 9, characterised in that the screwed clamping connection comprises a tooless gripper clamp with a tommy screw or a thumb screw.

11. The coupling element as specified in claim 1, characterised in that a shaft coupling for transmitting the power of the drive shaft is arranged in the coupling sleeve.

12. The coupling element as specified in claim 11, characterised in that the latching connection is designed in such a manner that it engages only if the shaft coupling engages both of the to-be-coupled shaft ends of the drive shaft.

13. The coupling element as specified in claim 11, characterised in that the shaft coupling comprises a shaft sleeve fastened on one shaft end, the edges of said shaft sleeve being provided with radial, rotationally symmetrical slits in order to connect a star-shaped shaft end of a to-be-coupled shaft end in a form-fitting manner.

14. The coupling element as specified in claim 13, characterised in that the shaft sleeve consists of two or a plurality of sleeve sections divided in such a manner that they are held on a shaft end by circumferential clamp rings.

15. The coupling element as specified in claim 1, characterised in that the latching connection is designed in such a manner that the latching element is displaceable on the coupling sleeve.

16. The coupling element as specified in claim 15, characterised in that the latching connection can be clipped onto the coupling sleeve.

17. The coupling element as specified in claim 16, characterised in that the latching connection is designed in such a manner that it is independently springs back on the coupling sleeve.