WO2012019344A1

WO2012019344A1 - Portable power tool with quick brake assembly

Info

Publication number: WO2012019344A1
Application number: PCT/CN2010/075890
Authority: WO
Inventors: Jizhong Fu; Aigui Wang; Songtao Jin
Original assignee: Bosch Power Tools (China) Co., Ltd.
Priority date: 2010-08-11
Filing date: 2010-08-11
Publication date: 2012-02-16
Also published as: CN103079772B; DE112010005799T5; CN103079772A

Abstract

A portable power tool comprises a motor (2) having a rotary spindle (6) and a cam brake assembly. The cam brake assembly comprises a brake plate (10) attached to the spindle (6), a brake cam (30) carrying a friction material and formed with at least two cam portions, and a stationary support (50) formed with at least two cam portions at positions corresponding to the cam portions of the brake cam (30). The brake cam (30) is rotatable around the rotation axis of the spindle (6). When the brake cam (30) rotates, by the cam action between the cam portions of the brake cam (30) and the cam portions of the stationary support (50), the brake cam (30) is moved in either of dual directions along the rotation axis of the spindle (6) so that the friction material is moved into contact with the brake plate (10) or away from the brake plate (10).

Description

Portable Power Tool with Quick Brake Assembly

Technical Field

The invention relates to a portable power tool having an improved brake assembly which shuts down the power tool quickly after operation.

Background Art

Portable power tools having rotational output are widely used. Many portable power tools do not have brake function. Generally, after the operation of a portable power tool, an operator has to hold the power tool for a period of time until the spindle of the power tool is totally stopped. Then, the operator can put the tool down. This is time-consuming and not convenient for the operator. In addition, it has a high risk of injury. Specifically, if the operator puts down the tool when the spindle of the tool is still rotating, the tool may hurt other items or people.

For addressing this problem, some portable power tools are equipped with a brake for stopping the tool quickly and smoothly, which gives the operator higher safety and better feeling.

In the prior art, one solution for stopping the tool is using an electrically controlled brake for providing a braking force to the power tool. The tool comprises a braking module, located between a motor and a power supply, for applying a current limited braking force to the motor when the power supply is disconnected from the motor. The electrically controlled brake has high cost and low reliability.

Another solution is using a mechanical brake, like the brakes adopted in vehicles. Specifically, a brake wheel is fixed on a motor spindle of the power tool, and a lever covered with rubber is adapted to contact and stop the brake wheel under the force of a compression spring. The manipulation of the mechanical brake is independent of the operation of the motor. That is to say, after the operation of the tool, the operator needs to perform an additional action to stop the tool. This is cumbersome.

Thus, it is desirable to provide a portable power tool with a simple and reliable brake, which can stop the rotation of the spindle of the tool quickly and smoothly after operation.

Summary of the Invention

In view of the problems existed in the prior art, an object of the invention is to provide a portable power tool having an improved quick brake. For achieving this object, in one aspect, the present invention provides a portable power tool comprising:

a motor having a rotary spindle; and

a cam brake assembly which comprises:

a brake plate attached to the spindle,

a brake cam having a first surface carrying a friction material at a position opposing to the brake plate and a second surface formed with at least two cam portions, and

a stationary support having a surface opposing to the second surface of the brake cam and formed with at least two cam portions at positions corresponding to the cam portions of the brake cam,

wherein the brake cam being rotatable around the rotation axis of the spindle, and wherein when the brake cam rotates, by the cam action between the cam portions of the brake cam and the cam portions of the stationary support, the brake cam is moved in either of dual directions along the rotation axis of the spindle so that the friction material is moved into contact with the brake plate or away from the brake plate.

In accordance with a preferred embodiment of the invention, the portable power tool further comprises a fan fixed to the spindle, wherein the brake plate is mounted to the fan, and the brake cam is axially arranged between the stationary support and the fan.

In accordance with another preferred embodiment of the invention, the portable power tool further comprises a trigger which is adapted to be actuated and released for switching on and off the motor respectively; wherein the brake cam is kinematically connected with the trigger so as to be rotated by the trigger such that: when the trigger is actuated, the brake cam is moved towards the stationary support to bring the friction material out of contact with the brake plate; and when the trigger is released, the brake cam is moved away from the stationary support to bring the friction material into close contact with the brake plate.

In accordance with another preferred embodiment of the invention, the cam brake assembly further comprises a returning spring connected between the brake cam and the stationary support and being configured to apply a returning force to the brake cam; wherein the returning spring tends to force the brake cam to rotate in a direction reverse to that caused by the actuation of the trigger.

In accordance with another preferred embodiment of the invention, the cam brake assembly further comprises guiding means formed on/in the brake cam and the stationary support for guiding the brake cam rotate with respect to the stationary support while moving in the direction of the rotation axis under the cam action.

In accordance with another preferred embodiment of the invention, the stationary support has a cylindrical main body on which the cam portions of the stationary support are formed, and a cylindrical protruded portion protruded from cylindrical main body; and the brake cam has a substantially circular ring shape and is moveably mounted around the cylindrical protruded portion of the stationary support.

In accordance with another preferred embodiment of the invention, the stationary support carries a bearing which rotatably supports the spindle.

In accordance with another preferred embodiment of the invention, the cam portions of the brake cam are symmetrically arranged in the circumferential direction of the brake cam; and the cam portions of the stationary support are symmetrically arranged in the circumferential direction of the stationary support.

In accordance with another preferred embodiment of the invention, the guiding means comprises a guiding slot formed in a pillar portion of the brake cam and a guiding ridge formed on the outer periphery surface of the cylindrical main body of the stationary support, the guiding slot being configured to receive the guiding ridge therein and slidable along the guiding ridge. Alternatively, the guiding means comprises a guiding ridge formed on a pillar portion of the brake cam and a guiding slot formed in the outer periphery surface of the cylindrical main body of the stationary support, the guiding ridge being slidable in the guiding slot.

In accordance with another preferred embodiment of the invention, the brake cam and the stationary support each have lowered portions between the cam portions, the lower portions being planar or concaved.

The invention provides a portable power tool having a new cam brake mechanism which is kinematically coupled with and automatically operated by the trigger. Thereby, the cam brake assembly of the invention is simple and easy to operate.

In addition, the cam action area for brake of is large, which results in smooth, quick and reliable braking and locking.

This cam brake concept of the invention can be used on circular saws, angle grinders, marble cutters, and such power tools whose output is rotation.

Brief Description of the Drawings

The invention will be further understood by reading the following detailed description with reference to the drawings in which:

Fig. 1 is a schematic cross-sectional view showing a part of a portable power tool according to an embodiment of the invention;

Fig. 2 is a schematic front view of a brake cam of the cam brake assembly of the portable power tool of Fig. 1 , taken in the same direction as Fig. 1 ;

Fig. 3 is a schematic plan view of the brake cam taken in the direction indicated by arrow A in Fig. 1 ;

Fig. 4 is a schematic side view of the brake cam taken in the direction indicated by arrow B in Fig. 1 ;

Fig. 5 is a schematic front view of a stationary support of the cam brake assembly of the portable power tool of Fig. 1 , taken in the same direction as Fig. 1 ;

Fig. 6 is a schematic plan view of the stationary support taken in the direction indicated by arrow A in Fig. 1 ; and

Fig. 7 is a schematic side view of the stationary support taken in the direction indicated by arrow B in Fig. 1.

Detailed Description of Preferred Embodiments

Now, a portable power tool according to a preferred embodiment of the invention will be described with reference to Fig. 1.

The portable power tool comprises a housing (not shown), a motor 2 fixedly mounted in the housing and having a rotary spindle 6 which defines a rotation axis Z, a fan 4 fixed to the rotary spindle 6 so as to be rotated by the spindle for cooling the motor, and a stationary support 50 fixed to or integrally formed with the housing, for carrying a bearing 8 which rotatably supports the spindle 6.

The portable power tool further comprises a brake assembly for stopping the rotation of the spindle after the operation of the tool is ended.

The cam brake assembly mainly comprises a ring-shaped brake plate 10 mounted on the front surface of the fan 4 (the surface facing away from the motor 2), a brake cam 30 disposed between the stationary support 50 and the fan 4, and a friction material pad 12 mounted on the back surface of the brake cam 30 at a position facing backwardly towards the brake plate 10.

As shown in Figs. 2-4, the brake cam 30 is formed in a substantially circular ring shape having a central hole and opposite front and back surfaces 31 a and 31b. The front surface 31a faces forwardly towards the stationary support 50, while the back surface 31b faces backwardly towards the fan 4. The back surface 31b is substantially planar and is formed with an annular recess 37 for receiving the friction material pad 12 therein. The front surface 31 a has lower portions and at least two cam portions 40 (two in the illustrated embodiments, but more than two is also possible) raised forwardly from the lower portions and symmetrically disposed in the circumferential direction of the brake cam 30. Each cam portion 40 has a peak portion (highest potion from the lower portions) 40a and transition portions 40b and 40c smoothly formed between the peak portion and the lower portions. The lower portions may be planar portions or concaved portions.

As shown in Figs. 5-7, the stationary support 50 has a cylindrical main body and a cylindrical protruded portion 52. The main body has an annular-shaped back surface 51 which faces backwardly towards the front surface 31a of the brake cam 30, and the cylindrical protruded portion 52 protrudes backwardly from the inner circumference of the back surface 51.

The stationary support 50 is hollow in the direction of the rotation axis Z for receiving the bearing 8 and allowing the spindle 6 passing therethrough.

The protruded portion 52 has an outer cylindrical periphery surface which is corresponding to the inner surface of the central hole of the brake cam 30. In the assembled state of the tool as shown in Fig. 1 , the protruded portion 52 is inserted into the central hole of the brake cam 30 and allows the brake cam 30 to move in dual directions along the rotation axis Z and rotate about the rotation axis Z.

The back surface 51 of the stationary support 50 has lower portions (planar portions or concaved portions) and cam portions 60 raised backwardly from the lower portions and symmetrically disposed in the circumferential direction of the stationary support 50. The number of the cam portions 60 equals to that of the cam portions 40 of the brake cam 30. Although two cam portions 60 are shown in the illustrated embodiments, more than two is also possible. Each cam portion 60 has a peak portion (highest potion from the lower portions) 60a and transition portions 60b and 60c smoothly formed between the peak portion and the lower portions.

When the brake cam 30 and the stationary support 50 are assembled together, with the protruded portion 52 of the stationary support 50 inserted through the central hole of the brake cam 30, the back surface 51 of the stationary support 50 and the front surface 31 a of the brake cam 30 contact each other. When the brake cam 30 is rotated about the rotation axis Z, the cam portions 40 of the brake cam 30 contact and move along the cam portions 60 and the lower portions of the stationary support 50, so that the brake cam 30 moves towards and away from the stationary support 50. Specifically, when the peak portions 40a of the brake cam 30 moves from the facing peak portions 60a towards the lower portions of the stationary support 50, the brake cam 30 moves towards the stationary support 50 in the direction of the rotation axis Z as indicated by arrow Rl shown in Fig. 1 ; when the peak portions 40a moves from the facing lower portions of the stationary support 50 towards the peak portions 60a, the brake cam 30 moves away from the stationary support 50 in the direction of the rotation axis Z as indicated by arrow R2 shown in Fig. 1.

By cam action between the brake cam 30 and the stationary support 50 as described above, the brake cam 30 obtains axial movements. As a result, the friction material pad 12 carried by the brake cam 30 correspondingly moves towards and away from the brake plate 10 carried by the fan 4. When the friction material pad 12 contacts the brake plate 10, the rotation of the spindle 6 can be restricted, and thus braking is performed to the motor 2. When the friction material pad 12 is away from the brake plate 10, the spindle is allowed to rotate.

Fig. 1 shows a stand-by state of the tool, wherein the peak portions 40a directly face and contact the peak portions 60a and thus the friction material pad 12 is pushed by the brake cam 30 against the brake plate 10.

For achieving the rotation of the brake cam 30 with respect to the stationary support 50, the brake cam 30 is provided with an actuating bar 35 which is formed on and extending radially from the outer circumferential surface of circular ring body of the brake cam 30 at a middle position between the two cam portions 40 (or two of the cam portions 40 when the number of them is larger than two).

The actuating bar 35 is formed with a recess 36 near its tip end for kinematically connecting the actuating bar 35 with the trigger 100 of the tool. The trigger and the kinematically connection between it and the actuating bar is schematically shown in Fig. 3. Those skilled in the art can understand that the trigger nay have any suitable shape and structure and the kinematically connection between it and the actuating bar can be established by any suitable kinematic mechanism. For example, a movement transmitting mechanism can be used for connecting the actuating bar 35 with the trigger so as to transmitting the actuating movement of the trigger into a movement of the actuating bar 35 in a direction as indicated by arrow S in Fig. 3, so as to rotate the brake cam 30 about the rotation axis Z in a direction as indicated by arrow S I in Fig. 3, which results in the brake cam 30 moving towards the stationary support 50 in the direction indicated by arrow Rl in Fig. 1.

The actuating bar 35 is also formed with an integral pillar portion 32 which extends forwardly from a front surface of the actuating bar. The pillar portion 32 is formed with a guiding slot 33 facing towards the outer circumferential surface of the main body of the stationary support 50 and a connecting end 34 for connecting an end of a returning spring as described later.

On the outer circumferential surface of the main body of the stationary support 50, a guiding ridge 16 is formed at a position engaging with the guiding slot 33 along a trace which corresponds to the moving path of the guiding slot 33 when the brake cam 30 is rotated by means of the actuating bar 35 actuated by the trigger and under the cam action between the brake cam 30 and the stationary support 50.

The above described guiding ridge and guiding slot can be arranged in a reverse manner. That is, the pillar portion 32 can be formed with a guiding ridge which is slidable in a guiding slot formed in the stationary support 50.

A returning spring 18 is used for pulling the brake cam 30 to its original position shown in Fig. 1. The returning is an extension coil spring having two ends, with one end connected to the connecting end 34 formed on the pillar portion 32 of the brake cam 30 and the other end connected to a connecting part 55 formed on the outer circumferential surface of the main body of the stationary support 50. The returning spring 18 normally apply a returning force to the pillar portion 32 of the brake cam 30 which tends to pull the brake cam 30 in a direction indicated by arrow S2 in Figs. 3 and 6, which is reverse to the direction indicated by arrow S I .

When the trigger is released, by the pulling force of the returning spring 18, the brake cam 30 rotates about the rotation axis Z in the direction indicated by arrow S2, which results in the brake cam 30 moving away from the stationary support 50 in the direction indicated by arrow R2 in Fig. 1. The friction material pad 12 carried by the brake cam 30 moves towards and contacts the brake plate 10 carried by the fan 4, and thus braking is performed to the motor 2.

It can be understood that although two transition portions 40b and 40c are formed on opposite of each peak portion 40a (and two transition portions 60b and 60c are formed on opposite of each peak portion 60a), only one of them is effective in the cam action between the brake cam 30 and the stationary support 50. Specifically, only transition portions 40b and transition portions 60b as shown in Figs. 3 and 6 are engaged with each other for the cam action, while transition portions 40c and transition portions 60c are untouched during the cam action.

The rotation angle for the brake cam 30 is set to allow each of the peak portions 40a to move from the position directly facing a corresponding peak portion 60a and along a corresponding transition portion 60b to a position contacting a corresponding lower portion of the stationary support 50. Thus, for a transition portion 40b having an arc angle a as shown in Fig. 3 and a transition portion 60b having an arc angle β as shown in Fig. 6, the guiding ridge 16 may extends around the rotation axis Z through an arc angle which is equal to or slightly larger than the larger on of the arc angles a and β.

The guiding ridge 16 may have a stop 16a at the traveling end of the pillar portion 32 for preventing the pillar portion 32 from being pulled by the trigger beyond a travelling limit along the guiding ridge 16. A similar stop (not shown) may be provided for preventing the pillar portion 32 from being pulled back beyond another travelling limit by the returning spring along the guiding ridge 16.

According to the above described portable power tool, when the tool is in a stand-by state, the brake cam 30 is in a position with respect to the stationary support 50 shown in Fig. 1 , that is, the peak portions 40a face directly towards and contact the peak portions 60a. Thus, the friction material pad 12 contacts the brake plate 10 to restrict the rotation of the spindle 6.

When the operator operates the tool by actuating the switch trigger, the switch trigger pulls the actuating bar 35 in the direction as indicated by arrow S so that the brake cam 30 rotates in the direction as indicated by arrow S I . As a result, the brake cam 30 moves towards the stationary support 50 under the above described cam action, and the friction material pad 12 moves away from the brake plate 10; thus, the brake cam 30 releases the spindle 6, allowing the spindle to rotate. By the moment of the actuating bar 35, the returning spring 18 is extended by the pillar portion 32.

When the operation of the tool is ended or should be stopped, the operator releases the switch trigger. As a result, the power supply to the motor is disconnected. By the pulling force of the returning spring 18, the brake cam 30 rotates in the direction indicated by arrow S2, which results in the brake cam 30 moving away from the stationary support 50 under the above described cam action, and the friction material pad 12 moves towards and contacts the brake plate 10; thus, the brake cam 30 performs brake to the spindle 6 for restricting the rotation of the spindle.

It can be seen that the basic concept of the invention is providing a cam brake assembly for the portable power tool. The cam brake assembly is connected with the trigger and automatically operated by the trigger such that the cam brake assembly releases the spindle when the trigger is activated and performs brake to the spindle when the trigger is released. Any structures that can constitute a cam brake assembly having the above functions fall within the scope of the invention.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. The attached claims and their equivalents are intended to cover all the modifications, substitutions and changes as would fall within the scope and spirit of the invention.

Claims

1. A portable power tool comprising:

a motor having a rotary spindle; and

a cam brake assembly which comprises:

a brake plate attached to the spindle,

2. The portable power tool of claim 1 , further comprising a fan fixed to the spindle, wherein the brake plate is mounted to the fan, and the brake cam is axially arranged between the stationary support and the fan.

3. The portable power tool of claim 1 or 2, further comprising a trigger which is adapted to be actuated and released for switching on and off the motor respectively;

wherein the brake cam is kinematically connected with the trigger so as to be rotated by the trigger such that:

when the trigger is actuated, the brake cam is moved towards the stationary support to bring the friction material out of contact with the brake plate; and

when the trigger is released, the brake cam is moved away from the stationary support to bring the friction material into close contact with the brake plate.

4. The portable power tool of claim 3, wherein the cam brake assembly further comprises a returning spring connected between the brake cam and the stationary support and being configured to apply a returning force to the brake cam; and wherein the returning spring tends to force the brake cam to rotate in a direction reverse to that caused by the actuation of the trigger.

5. The portable power tool of claim 3 or 4, wherein the cam brake assembly further comprises guiding means formed on/in the brake cam and the stationary support for guiding the brake cam rotate with respect to the stationary support while moving in the direction of the rotation axis under the cam action.

6. The portable power tool of claim 5, wherein the stationary support has a cylindrical main body on which the cam portions of the stationary support are formed, and a cylindrical protruded portion protruded from cylindrical main body; and

wherein the brake cam has a substantially circular ring shape and is moveably mounted around the cylindrical protruded portion of the stationary support.

7. The portable power tool of claim 6, wherein the stationary support carries a bearing which rotatably supports the spindle.

8. The portable power tool of claim 6, wherein the cam portions of the brake cam are symmetrically arranged in the circumferential direction of the brake cam; and wherein the cam portions of the stationary support are symmetrically arranged in the circumferential direction of the stationary support.

9. The portable power tool of claim 6, wherein the guiding means comprises a guiding slot formed in a pillar portion of the brake cam and a guiding ridge formed on the outer periphery surface of the cylindrical main body of the stationary support, the guiding slot being configured to receive the guiding ridge therein and slidable along the guiding ridge.

10. The portable power tool of claim 6, wherein the guiding means comprises a guiding ridge formed on a pillar portion of the brake cam and a guiding slot formed in the outer periphery surface of the cylindrical main body of the stationary support, the guiding ridge being slidable in the guiding slot.

11. The portable power tool of any one of claims 1 to 10, wherein the brake cam and the stationary support each have lowered portions between the cam portions, the lower portions being planar or concaved.

12. The portable power tool of any one of claims 1 to 11 , wherein the portable power tool is a circular saw, an angle grinder, or a marble cutter.