WO2015050484A1

WO2015050484A1 - Selectively braked motor

Info

Publication number: WO2015050484A1
Application number: PCT/SE2013/051151
Authority: WO
Inventors: Markus Maag
Original assignee: Husqvarna Ab
Priority date: 2013-10-02
Filing date: 2013-10-02
Publication date: 2015-04-09

Abstract

A selectively braked electric motor (1) having a housing (2) and a rotating outer surface (4), such as an external rotor (3), which rotates relative to the housing (2), the braked motor (1) further comprising a brake element (5) comprising a flexible elongate member such as a flexible band surrounding the rotating outer surface (4), application of tension to the flexible elongate member (5) causing it to tighten around the rotating outer surface (4) so as to brake the motor (1).

Description

SELECTIVELY BRAKED MOTOR

TECHNICAL FIELD

This invention relates to a selectively braked electric motor such as, non-exclusively, may be used in an electric power tool.

BACKGROUND OF THE INVENTION

It is well known to provide a brake for an electric motor in, for example, a power tool, so that the motor can be quickly brought to rest. Typically, the brake can be provided on a shaft of the motor, and will typically comprise a drum fixed relative to the shaft and a shoe that can be brought into engagement with the shaft when it is desired to exert a braking force on the motor, for example when power is cut to a power tool and the tool should stop quickly. Often, a clutch is provided between the output shaft of the motor and the brake. The brake and any clutch represent numerous components that add weight, space and complexity to a motor.

An example of one such brake acting on the output shaft of a motor can be found in the International patent application published as WO2013/007962. SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a selectively braked electric motor having a housing and a rotating outer surface which rotates relative to the housing, the selectively braked motor further comprising a brake element comprising a flexible elongate member surrounding the rotating outer surface, application of tension to the flexible elongate member causing it to tighten around the rotating outer surface so as to brake the motor.

Thus, rather than relying upon a separate clutch and drum, the brake element can act directly on part of the motor, thus reducing the number of elements that are required. The brake element can be wound around the motor; typically it would be wrapped approximately once around the motor, but can be wrapped as many times as is necessary to achieve a desired braking force.

The motor may comprise an external rotor, with the rotating outer surface being provided on the external rotor. As such, the motor may be an outrunner motor, typically a brushless outrunner motor. Such motors are commonly used in situations where a large torque is required from a relatively small motor.

The flexible elongate member may be of the form of a band and may be flat (when unwound from the motor), and may have two ends along a length of the flexible elongate member. Alternatively, the flexible elongate member could be of the form of any other suitable member, such as wire, cable, rope, line, netting, webbing, tubing or the like. When wound around the motor, drawing the two ends of the flexible elongate member apart, preferably in opposing directions (i.e. with an angle of between 90 and 270 degrees between the two directions, typically around 180 degrees) may act to apply tension to the flexible elongate member and so brake the motor. The motor may further comprise a brake activation mechanism, arranged to selectively draw the ends of the flexible elongate member apart. The ends of the flexible elongate member may be joined by a central section of the flexible elongate member. The widths perpendicular to the length of each of the ends of the flexible elongate member may be different to the width of the central section. For example, the ends of the flexible elongate member may be wider than the central part of the flexible elongate member if the central part is relatively narrow, or the ends of the flexible elongate member may be narrower than the central parts of the flexible elongate member if the central part is relatively wide; typically, the sum of the widths of the two ends will be less than or equal to the width of the central section. Typically, the width of each end will be half of the width of the central section. This will allow the two ends to lie side by side when the central section is wrapped around the rotating outer surface. As such, the central section may typically have a length approximately the same as the circumference of the rotating outer surface.

According to a second aspect of the invention, we provide an apparatus comprising a housing and a motor in accordance with the first aspect of the invention supported in the housing. As an example, the apparatus could be an electric power tool, such as a chainsaw, a hedge trimmer, a lawn mower, a lawn trimmer, a drill, an electric screw driver, an angle grinder, a circular saw or other such apparatus. The housing may support the brake activation mechanism relative to the flexible elongate member.

BRIEF DESCRIPTION OF THE DRAWINGS

There now follows, by way of example only, embodiments of the invention, described with reference to the accompanying drawings, in which:

Figures la and lb each show a perspective view of a motor in accordance with an embodiment of the present invention, with the respective figures showing different embodiments of the brake element;

Figure 2 shows a perspective view of the motor of Figure 1 , provided with a brake activation mechanism; and Figures 3 to 5 each show an elevation of the motor and brake activation mechanism of Figure 2, in three positions of the brake activation mechanism, respectively.

DETAILED DESCRIPTION OF THE INVENTION

A selectively braked motor 1 in accordance with an embodiment of the invention is shown in the accompanying Figures, in which the motor is embodied in an electric power tool, such as an electric chainsaw. The motor 1 , which is a brushless outrunner motor, has a housing 2 and an external rotor 3, which is free to rotate relative to the housing 2. The external rotor 3 has an external surface 4.

In order to be able to brake the motor 1 , a brake band 5 is provided. The brake band 5 is of the form of a flat flexible elongate member, having two ends 6a, 6b joined by a central portion 7. The central portion 7 is wrapped once around the external surface 4, and so has a length approximately equal to the circumference of the external surface, although it equally well could be wrapped any number of times around the external surface. Two embodiments are shown in the accompanying drawings, in Figures l a and lb respectively.

The central portion 7 has a width iv_c that may be equal to, larger than or smaller than the width w_e of the two ends 6a, 6b. In the "equal width" embodiment of Figure l a, the strip is wrapped around the motor to form an approximate helix. In the embodiment shown in Figure lb, the width w_c of the central portion is twice the width w_e of the two ends 6a, 6b. This allows the ends to lie next to one another when the central portion 7 is wrapped around the external surface 4.

Figure 2 of the accompanying drawings demonstrates that the ends 6a, 6b of the brake band 5 can be wider than the central portion. Furthermore, whilst the ends 6a, 6b are shown as coplanar but extending in opposing directions, as long as they extend in opposing directions, it is possible for there to be any convenient angle between them.

The motor 1 is provided with a brake activation mechanism 10 as shown in Figures 2 to 5 of the accompanying drawings. This comprises first and second links 1 1 , 12 working in corresponding slots 13, 14 in the ends 6. The housing 2 of the motor 1 is fixed relative to a housing of a power tool in which the motor is embodied, as is brake activation mechanism 10.

When it is desired to brake the motor 1 , at least one of the links 1 1 , 12 acts to draw the ends 6 apart, thus tightening the brake band 5 and bringing the central portion 7 from the position shown in Figure 3 of the accompanying drawings, where it is not in contact with the external surface 4 into the position shown in Figure 4 or 5 of the accompanying drawings where it is in contact and will exert a frictional force against any rotation of the external rotor 3 relative to the housing 2.

The braking of the motor can be achieved in one of two ways. In the first way, the first link 1 1 is allowed to rotate clockwise from the position shown in Figure 3 to the position shown in Figure 4. In that case, a spring 15 will act to tighten the brake band 5 by pulling one end 6a; effectively, the first link 1 1 presses against the edge of slot 13 to take the brake band 5 off the motor 1 , and when the link is allowed to rotate clockwise the spring brings the brake band 5 back into contact. As this first link 1 1 will typically be coupled to the trigger of the chainsaw, this is a failsafe action, as force is required to deactivate the brake.

The second way uses the second link 12. This would typically be coupled to the kickback brake and front guard of the chainsaw. Once activated, a pivoting part 12a of the second link 12 will pivot (upwards in the figures) from the position in Figure 3 to the position in Figure 5, allowing the second link to be pressed outwards by spring 16, which is much stronger than spring 15. The second link 12 then forces the brake band 5 to tighten around the motor by pulling the other end 6b, regardless of whether the first link 1 1 is in the position to loosen the brake band 5.

This can be seen in the accompanying Figures 3 to 5. In Figure 3 the trigger is activated while the kickback brake is not. Only in this case the brake band 5 is allowed to loosen and so allow the outer surface 4 and so the rotor 3 to turn. In the case of Figure 4, the trigger is not activated, and so the spring 15 holds the brake band 5 on the outer surface 4. In the case of Figure 5, the trigger is activated and counteracts the spring 15, but the kickback brake has been activated, thus allowing the significantly stronger spring 16 to hold the brake band 5 against the outer surface.

Thus, given that the brake band 5 is acting on the external surface 4 of the rotor 3 rather than a separate braking member through a clutch, the number of elements required in this braked motor are reduced, although the claimed invention is not restricted to the precise mechanism employed in this embodiment. In particular, it is possible for the brake activation mechanism to act on only one end 6a, 6b of the brake band 5, the other end being suitably secured.

The skilled reader will appreciate that the band brake could be provided in alternative ways whilst still falling within the appended claims. For instance, by providing the band brake as a flexible elongate member instead of a band brake as such, the flexible elongate member could be of the form of any other suitable member, such as wire, cable, rope, line, netting, webbing, tubing or the like.

Claims

1. A selectively braked electric motor (1) having a housing (2) and a rotating outer surface (4) which rotates relative to the housing

(2), the motor (1) further comprising a brake element (5) comprising a flexible elongate member surrounding the rotating outer surface (4), application of tension to the flexible elongate member (5) causing it to tighten around the rotating outer surface (4) so as to brake the motor (1)· 2. The motor of claim 1 , comprising an external rotor (3), with the rotating outer surface (4) being provided on the external rotor (3).

3. The motor of claim 2, in which the motor (1) is an outrunner motor, such as a brushless outrunner motor.

4. The motor of any preceding claim, in which the flexible elongate member has two ends (6) along a length of the flexible elongate member, and in which drawing the two ends (6) of the flexible elongate member (5) apart acts to apply tension to the flexible elongate member and so brake the motor (1).

5. The motor of claim 4, comprising a brake activation mechanism ( 10), arranged to selectively draw the ends (6) of the flexible elongate member (5) apart.

6. The motor of any of claims 4 to 5, in which the ends (6) of the flexible elongate member (5) are joined by a central section (7) of the flexible elongate member (5), with the widths (iv_e) perpendicular to the length of each of the ends (6) of the flexible elongate member being less than the width (iv_c) of the central section.

7. The motor of claim 6, in which the sum of the widths (iv_e) of the two ends (6) is less than or equal to the width (iv_c) of the central section (7).

8. The motor of claim 6 in which the width (iv_e) of each end (6) is half of the width (iv_c) of the central section (7).

9. The motor of any of claims 4 to 5 , in which the ends (6) of the flexible elongate member (5) are joined by a central section (7) of the flexible elongate member (5) , with the widths (w_e) perpendicular to the length of each of the ends (6) of the flexible elongate member being greater than the width (iv_c) of the central section.

10. The motor of any of claims 6 to 9, in which the central section (7) has a length approximately the same as the circumference of the rotating outer surface (3) .

1 1. The motor of any preceding claim, in which the flexible elongate member is flat and has the form of a band.

12. An apparatus comprising a housing and a motor ( 1 ) in accordance with any preceding claim supported in the housing.

13. The apparatus of claim 12, in which the motor is in accordance with claim 5 or any claim dependent thereon, in which the housing of the apparatus supports the brake activation mechanism ( 10) relative to the flexible elongate member (5).