GB2416726A

GB2416726A - Hand-held grinding tool with a brake

Info

Publication number: GB2416726A
Application number: GB0514726A
Authority: GB
Inventors: Joerg Dehde
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-07-22
Filing date: 2005-07-18
Publication date: 2006-02-08
Anticipated expiration: 2025-07-18
Also published as: GB2416726B; GB0514726D0; DE102004035520A1; CN1724214B; CN1724214A

Abstract

A motorised hand-held grinding tool comprises a housing unit 10a, grinding unit 12a and a brake 14a and 16a for slowing the grinding unit relative to the housing. The brake comprises a first means 14a attached to the housing unit 10a and second means 16a attached to the grinding unit 12a. One of these braking means 16a has a lower wear resistance than the other 14a and is replaceable.

Description

Motorised hand tool, in particular motorised hand grinder

The prior art

The invention is based on a motorised hand tool according to the preamble of claim 1.

A generic motorised hand tool is known from DE 199 52 108 Al. The motorised hand tool formed by a motorised hand grinder has a motorised hand tool unit (hereinafter tool unit) comprising an electric motor and a grinding means carrier unit (hereinafter grinding unit) formed by a grinding disc unit. The motorised hand tool also includes a brake unit for braking the grinding unit relative to the tool unit. For this purpose the brake unit has braking means associated with the tool unit and braking means corresponding to the first braking means and associated with the grinding unit.

Advantages of the invention The invention is based on a motorised hand tool, in particular a motorised hand grinder, comprising a tool unit and a grinding unit driveable via the tool unit, and a brake unit for braking the grinding unit relative to the tool unit, which brake unit includes at least one first braking means associated with the tool unit and at least one second braking means corresponding to the first braking means and associated with the grinding unit.

It is proposed that with regard to a braking operation one of the braking means has higher wear resistance than the other braking means, and that the braking means having the lower wear resistance is provided as an exchangeable part.

In this context the term "provided" should be understood to mean, in particular, specially "equipped" and/or specially "designed". An "exchangeable part" should be understood in this context to mean a component that is provided, in particular, for removal by a user with little complexity or cost, preferably directly, without dismantling further components and in particular without dismantling housing parts of the tool unit. The exchangeable part is preferably fixed by means of releasable fixing means that are easily accessible from outside, such as screws, quick-action clamping mechanisms, etc. Through the device according to the invention wear can advantageously be displaced in a specified manner on to a component which is provided to be exchanged. The wear on the braking means having the higher wear resistance can be reduced and the service life of the motorized hand tool and customer satisfaction can be enhanced.

The braking means having the lower wear resistance may be an exchangeable part on its own or, advantageously, may be formed jointly with a further functional component, such as, especially advantageously, a component undergoing increased wear, so that at least two functional components can be advantageously replaced with one exchange operation.

The braking means having the lower wear resistance may be formed at least partially in one piece with the further functional component or it may be formed by a component separate from this part. In this context a "functional component" should be understood to mean a component which performs a further function in relation to the braking means, for example, a support function, a housing function, etc. In a further embodiment of the invention it is proposed that the braking means having the lower wear resistance is associated with the grinding means carrier. The grinding means carrier is frequently subjected to high stresses and is therefore advantageously formed as an exchangeable part jointly with the braking means having the lower wear resistance.

It is further proposed that the braking part having the higher wear resistance with regard to a braking operation has higher wear resistance than at least one housing part of the tool unit arranged in the area of the first braking means. In principle, the braking means having the higher wear resistance might have the same wear resistance as the housing part or possibly might be formed by a housing part.

However, service life can be further increased by the proposal according to the invention.

By contrast, the braking means having the lower wear resistance advantageously has lower wear resistance with regard to a braking operation than at least one housing part of the tool unit arranged in particular in the area of the first braking means, whereby, in particular in case of undesired contact of the second braking means with the housing part, damage to the housing part is at least largely avoided and especially clear allocation of wear can be achieved.

The braking means may be formed by various materials that appear appropriate to the person skilled in the art.

Preferably, however, the braking means having the higher wear resistance is made of a high-strength plastics material, such as polytetrafluoroethylene, of a material known under the trade name "Teflon" or the trade name "Delrin", of metal and/or ceramic material, etc. The braking means having the lower wear resistance is preferably formed by a foamed material and/or by an elastomer.

In particular, the materials are preferably so selected that the braking material having the higher wear resistance has a lower coefficient of friction, in particular a lower coefficient of sliding friction, than the braking means having the lower wear resistance, whereby a desired allocation or distribution of wear can be achieved in a simple manner. The braking means having the higher wear resistance advantageously has on a reference component of grey cast-iron a coefficient of sliding friction of less than 0.28 and in particular less than 0.18.

It is further proposed that the second braking means is formed at least partially in one piece with a functional component, in particular a support component, of the grinding unit, whereby additional components, assembly complexity and cost can be saved.

If the braking means are provided to generate a forced motion, additional components for generating a forced motion can be at least largely avoided and an operating mode can be made available to the user which makes possible a increased removal of material as compared to an operating mode without forced drive.

If the braking means include at least two corresponding friction surfaces facing at least partially in a radial direction with respect to an axis of rotation of the grinding unit, an increase in frictional force, in particular through a jamming effect, can be achieved when working on an edge of a grinding unit or of a grinding disc, and a forced rotation and therefore an increased removal of material can be achieved in that one friction surface rolls on the other.

If the braking means have at least two corresponding friction surfaces facing at least partially in an axial direction with respect to an axis of rotation of the grinding unit, an advantageous distance between the friction surfaces can be set especially simply. In addition, changes to the friction surfaces can be carried out simply and said friction surfaces can be adapted especially simply to different applications.

In a further embodiment it is proposed that at least one braking means has an L-profile in its edge portion, whereby a radial and an axial friction surface can be obtained in a constructionally simple manner.

If the motorised hand tool has at least one flow channel in the region of at least one friction plane of at least one braking means, said flow channel can be utilised advantageously for dust extraction. Undesired sucking fast of the motorised hand tool on a substrate can be avoided and fine dust beside the motorised hand tool can be advantageously sucked away via the flow channel. The phrase "in the region of a friction plane" should be understood in particular to mean that the friction plane intersects the flow channel, a friction surface forms a wall of the flow channel and/or the friction plane is at a distance of less than 1 cm from a wall of the flow channel.

If at least one of the braking means has an at least partially bulbous configuration, precisely defined friction surfaces can be achieved in a simple manner and flow channels can be simply produced by varying the height of a bulbous portion and/or by recesses. In addition, an axial and a radial friction surface can be advantageously and simply achieved with a bulbous configuration.

Drawings Further advantages are apparent from the following description of the drawings showing embodiments of the invention. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will usefully also consider the features in isolation and link them together to form advantageous further combinations.

In the drawings: Fig. 1 shows a portion of a motorised hand tool according to the invention in a schematic, partially sectional view; Fig. 2 is a top view of a schematically represented grinding disc from Fig. 1; Fig. 3 is a top view of an alternative, schematically represented grinding disc; Fig. 4 shows a section along the line IV-IV in Fig. 3; Fig. 5 shows a portion of an alternative, schematically represented motorised hand tool according to the invention, and Fig. 6 shows an enlarged section of Fig. 5.

Description of the embodiments

Fig. 1 shows in a schematic representation a portion of a motorized hand tool according to the invention formed by a hand-held eccentric grinder. The motorised hand tool includes a tool unit lOa having an electric motor (not shown in detail) arranged in a motorised hand tool housing (hereinafter tool housing) 34a and a grinding unit 12a formed by a grinding disc and driveable via the tool unit lOa. The tool unit lOa and the grinding unit 12a are coupled by a drive shaft 40a. In addition, the motorised hand tool includes a brake unit for braking the grinding unit 12a relative to the tool unit lea, which brake unit includes a first braking means 14a associated with the tool unit lea and a second braking means 16a corresponding to the first braking means 14a and associated with the grinding unit 12a.

According to the invention the second braking means 16a associated with the grinding unit 12a has, with regard to a braking operation, lower wear resistance than the first braking means 14a associated with the tool unit lea.

The second braking means 16a is formed in one piece with a functional component 18a of the grinding unit 12a formed by a rubber-elastic carrier component and is provided as an exchangeable part jointly with the functional component 18a and, in particular, jointly with the whole grinding unit 12a. In case of wear the grinding unit 12a is exchanged jointly with the second braking means 16a and is available as a replacement part.

The functional component 18a is made of a rubber-elastic elastomer. The second braking means 16a is formed on a side 42a of the functional component 18a facing towards the tool unit lea as a bulbous projection oriented in the direction of an end face 36a of the tool unit lea and extends over 360 of the grinding unit 12a (Figs. 1 and 2). A grinding means holder (not shown in detail) formed by a hook-and- loop textile is arranged on a side 44a of the functional component 18a opposite the side 42a.

The first braking means 14a associated with the tool unit lea is formed by an annular disc made of a plastics material known under the trade name "Teflon" and is inset in the end face 36a of the tool unit lea facing towards the grinding unit 12a, flush with the end face 36a, in an annular recess 38a adapted to the braking means 16a.

In addition, the first braking means 14a has, with regard to a braking operation, higher wear resistance than the tool housing 34a and, in particular, than a housing part 20a of the tool unit lea directly adjacent to the first braking means 14a. In contrast, the second braking means 16a has, with regard to a braking operation, lower wear resistance than the tool housing 34a and, in particular, than the housing part 20a directly adjacent to the first braking means 14a.

In addition, because of the particular choice of material, the first braking means 14a having the higher wear resistance has a lower coefficient of friction than the second braking means 16a having the lower wear resistance.

Alternatively or additionally to a difference of coefficient of a friction resulting from the material used, a difference of coefficient of friction could be produced as a result of the form used.

The braking means 14a, 16a are constantly in contact and loaded with a low normal force with respect to one another via two corresponding friction surfaces 28a, 30a facing in an axial direction with respect to an axis of rotation 22a of the grinding unit 12a. If the grinding unit 12a is loaded more heavily on its outer edge in operation, the grinding unit 12a is elastically deformed and the normal force between the braking means 14a, 16a, and therefore a braking effect on the grinding unit 12a, is increased. In principle, it would also be possible that the braking means 14a, 16a only come into abutment in a particular operating mode of the grinding unit 12a, or that the position of one of the braking means 14a, 16a is adjustable, in particular in an axial direction with respect to the axis of rotation 22a of the grinding unit 12a, for example, via a mechanical, pneumatic and/or hydraulic adjustment mechanism 46a, whereby a braking mode could be activated and deactivated in a specified way via the adjustment mechanism 46a. The adjustment mechanism 46a is indicated schematically in Fig. 1.

Figs. 3 to 6 show alternative embodiments. In the description of the embodiments substantially identical components and features are designated in principle by the same reference symbols, the letters "a" and "b" being added to distinguish the embodiments. With regard to features and functions that remain the same, reference may also be made to the description of the embodiment in Figs. 1 and 2. The following description is restricted substantially to the differences from the embodiment shown in Figs. 1 and 2.

In Figs. 3 and 4 an alternative grinding unit 12b is shown.

Unlike the grinding unit 12a, the grinding unit 12b in Figs. 3 and 4 includes a second braking means 16b that has lower wear resistance and is formed by bulbous projections that are formed on a functional component 18b formed by a carrier part of the grinding unit 12a and are distributed as segments around the circumference, so that, if the grinding unit 12b is used with a tool unit lea according to Fig. 1, flow channels 32b are present between the segmentally arranged projections. In this case the friction surface 28a of the first braking means 14a, a friction surface 30b of the second braking means 16b and, in particular, surfaces of the functional component 18a form walls of the flow channels 32b in the circumferential direction between the friction surfaces 30b.

Figs. 5 and 6 show the grinding unit 12a of Figs. 1 and 2 with an alternative tool unit lob. The tool unit lob includes a first braking means 14b substantially in the form of an annular plate and having higher wear resistance, which has an L-profile in its edge portion. If a grinding unit 12a according to Figs. 1 and 2 or a grinding unit 12b according to Figs. 3 and 4 is used with a tool unit lob the braking means 14b, 16a, 16b have friction surfaces 24b, 26a, 26b facing in a radial direction with respect to an axis of rotation 22a, 22b of the grinding unit 12a, 12b, and the braking means 16a, 16b each have a friction surface 26a, 26b formed by their bulbous projections and facing radially outwards, and the braking means 14b has a radially inwardly facing friction surface 24b formed by a flange facing in an axial direction with respect to the grinding unit 12a, 12b.

In principle, i.e. when the grinding unit 12a or 12b is not under load, the radial friction surfaces 24b, 26a or 26b and the axial friction surfaces 28b, 30a or 30b of the tool unit lOa and of the grinding unit 12a or 12b are arranged at a distance from one another. If the grinding unit 12a or the grinding unit 12b is operated on its outer edge during use of the tool unit lob, the grinding unit 12a or 12b is deformed elastically and the braking means 14b and 16a or 16b come into abutment with an increased jamming force via their axial friction surfaces 28b, 30a or 30b and their radial friction surfaces 24b and 26a or 26b, whereby the grinding unit 12a or 12b rolls with an eccentric drive on the friction surface 24b of the braking means 14b via the friction surface 26a or 26b of the braking means 16a or 16b and a forced rotational movement is produced. The braking means 14b, 16a or 16b are provided to generate the forced rotational movement of the grinding unit 12a or 12b.

Increased removal of material can be achieved by means of the forced rotational movement.

Reference numerals Tool unit 12 Grinding unit 14 Braking means 16 Braking means 18 Functional component Housing part 22 Axis of rotation 24 Friction surface 26 Friction surface 28 Friction surface Friction surface 32 Flow channel 34 Tool housing 36 End face 38 Recess Drive shaft 42 Side 44 Side 46 Adjusting mechanism

Claims

Claims 1. Motorised hand tool, in particular motorised hand grinder,

comprising a tool unit (lea, lob) and a grinding unit (12a, 12b) driveable via the tool unit (lea, lob), and a brake unit for braking the grinding unit (12a, 12b) relative to the tool unit (lea, lob), which brake unit includes at least one first braking means (14a, 14b) associated with the tool unit (lea, lob) and at least one second braking means (16a, 16b) corresponding to the first braking means (14a, 14b) and associated with the grinding unit (12a, 12b), characterized in that one of the braking means (14a, 14b) has, with regard to a braking operation, higher wear resistance than the other braking means (16a, 16b), and the braking means (16a, 16b) having the lower wear resistance is provided as an exchangeable part.
2. Motorised hand tool according to claim 1, characterized in that the braking means (16a, 16b) having the lower wear resistance is formed jointly with a further functional component (18a, lab) as an exchangeable part.
3. Motorised hand tool according to claim 1, characterized in that the braking means (16a, 16b) having the lower wear resistance is associated with the grinding unit (12a, 12b).
4. Motorised hand tool according to any one of the preceding claims, characterized in that the braking means (14a, 14b) having the higher wear resistance has higher wear resistance with regard to a braking operation than at least one housing part (20a, 20b) of the tool unit (lea, lob).
5. Motorised hand tool according to any one of the preceding claims, characterized in that the braking means (16a, 16b) having the lower wear resistance has lower wear resistance with regard to a braking operation than at least one housing part (20a, 20b) of the tool unit (lea, lob).
6. Motorised hand tool according to any one of the preceding claims, characterized in that the braking means (14a, 14b) having the higher wear resistance has a lower coefficient of friction than the braking means (16a, 16b) having the lower wear resistance.
7. Motorised hand tool according to any one of the preceding claims, characterized in that the second braking means (16a, 16b) is formed at least partially in one piece with a functional component (18a, lab) of the grinding unit (12a, 12b).
8. Motorised hand tool according to any one of the preceding claims, characterized in that the braking means (14b, 16a, 16b) are provided in order to generate a forced motion.
9. Motorised hand tool according to any one of the preceding claims, characterized in that the braking means (14b, 16a, 16b) have at least two corresponding friction surfaces (24b, 26a, 26b) facing at least partially in a radial direction with respect to an axis of rotation (22a, 22b) of the grinding unit (12a, 12b).
10. Motorised hand tool according to any one of the preceding claims, characterized in that the braking means (14a, 14b, 16a, 16b) have at least two corresponding friction surfaces (28a, 28b, 30a, 30b) facing at least partially in an axial direction with respect to an axis of rotation (22a, 22b) of the grinding unit (12a, 12b).
11. Motorised hand tool according to any one of the preceding claims, characterized in that at least one braking means (14b) has an L-profile in its edge portion.
12. Motorised hand tool according to any one of the preceding claims, characterized by at least one flow channel (32b) in the region of at least one friction plane of at least one of the braking means (14a, 14b, 16b).
13. Motorised hand tool according to any one of the preceding claims, characterized in that at least one of the braking means (16a, 16b) has at least partially a bulbous configuration.
14. Grinding means carrier unit for a motorised hand tool according to any one of the preceding claims.
15. Motorised hand tool unit for a motorised hand tool according to any one of claims 1 to 13.
16. A grinding means carrier substantially as herein described with reference to the accompanying drawings.
17. A tool unit for a motorised hand tool substantially as herein described with reference to the accompanying drawings.
18. A motorized hand tool substantially as herein described with reference to the accompanying drawings.