Patent Description:
Hand-held work tools for cutting and/or abrading hard materials such as concrete and stone comprise powerful motors in order to provide the required power for processing the hard materials. These motors generate a substantial amount of heat and therefore need to be cooled in order to prevent overheating. Electrical work tools generate heat by the electrical motor, and also by the battery and control electronics. There is a need for efficient methods of cooling such work tools.

The work tools also normally generate vibration which may be harmful or at least cause discomfort to an operator of the tool. It is desired to protect the operator from prolonged exposure to strong vibration.

To summarize, there are challenges associated with hand-held work tools. <CIT> describes a hand-held work having a support arm according to the preamble of claim <NUM> tool with a circular cutting tool that is driven by an electric motor via a drive belt. The drive belt is enclosed in a belt chamber, such that it is sealed off from the ambient environment.

<CIT> shows an abrasive cutting machine comprising a closed belt chamber which is arranged in connection to a cutting tool support arm. <CIT> relates to a portable grinding tool where an angle between a tool holder and a handle is adjustable.

<CIT> shows a multi-purpose tool for restoration of glass, wooden or marble surfaces by various rotating brushes.

<CIT> relates to an electric power tool with improved cooling of the electric motor.

It is an object of the present disclosure to provide improved hand-held work tools which address the above-mentioned issues.

This object is obtained by means of a support arm for a hand-held work tool, the work tool comprising an electric motor arranged to drive a circular cutting tool. The support arm is arranged to support the circular cutting tool on a first end of the support arm, and to support the electric motor at a second end of the support arm, opposite to the first end. The support arm is arranged to at least partially enclose the electric motor.

According to some aspects, the support arm is a thermally conductive support arm arranged to support the electric motor by a support surface at the second end of the support arm, wherein the support arm comprises one or more cooling flanges arranged to conduct heat away from the electric motor via the support surface.

This way, heat dissipation from the motor is improved since the cooling air flow is more efficiently utilized to transport the heat away from the motor.

According to some aspects, the support arm and the electric motor are at least partially integrally formed.

This way, manufacturing is simplified and heat dissipation from the motor is further improved,
According to some aspects, at least <NUM>% and preferably at least <NUM>% of a volume of the electric motor is enclosed by the support arm and/or wherein at least <NUM>% and preferably at least <NUM>% of an axial length of the electric motor is enclosed by the support arm.

This way both structural integrity of the motor and support arm assembly, as well as heat transport away from the electric motor, are improved.

This object is also obtained by means of a hand-held work tool comprising an interface for holding a cutting tool, an electric motor arranged to drive the cutting tool, a battery compartment for holding a battery arranged to power the electric motor, and a support arm according to the above.

According to some aspects, the hand-held work tool comprises a fan, configured to generate a flow of cooling air, and a belt guard, where the belt guard and at least a part of the support arm are configured to enclose an interior space. A portion of the flow of cooling air is arranged to be guided via at least one opening into the interior space, thereby increasing an air pressure in the belt guard interior space above an ambient air pressure level.

The increase in air pressure in the interior space means that a flow of air will exit through all openings into the interior space, i.e., any cracks and the like. This in turn means that water, dust, debris, and slurry will have to overcome this flow of air in order to enter into the interior. Thus, accumulation of unwanted material inside the work tool is reduced.

According to some aspects, the electric motor arranged to drive the fan. In this way, only one motor is needed.

According to some aspects, a cooling air conduit is arranged to guide a portion of the flow of cooling air towards the battery compartment for cooling the battery.

In this way, cooling can be provided to the battery as well, where a single fan can be used to cool both the electrical motor and the battery.

According to some aspects, the belt guard and/or the support arm comprises an air outlet through which the flow of cooling air exits the interior space. The air outlet is configured with an area such that the air pressure in the belt guard interior space increases above the ambient air pressure level by a desired amount during operation.

This enables control of the air flow, and dust and slurry that has entered the interior space can be dispatched into ambient air.

According to some aspects, the opening has an area between <NUM><NUM> and <NUM><NUM>, and more preferably between <NUM><NUM> and <NUM><NUM> where the air outlet has a an area between <NUM><NUM> and <NUM><NUM> and more preferably between <NUM><NUM> and <NUM><NUM>.

According to some aspects, the area of the air outlet is greater than the area of the opening.

In this way, a sufficient amount of cooling air is led into the interior space to prevent dust and slurry to enter, while the battery receives cooling air.

According to some aspects, the air outlet is located in the area of a lower portion of either the belt guard or the support arm, i.e. the portion of the belt guard or support arm that is closest to a surface in a normal rest position of the handheld work tool on said surface.

In this way, water and slurry can be efficiently drained during work and during cleaning.

According to some aspects, the air outlet is arranged as a through-hole in the belt guard. This enables cost-effective manufacturing.

According to some aspects, the belt guard is made of plastic and the support arm is made of magnesium.

According to some aspects the wherein the opening is a plurality of openings located along a circle surrounding a rotational axis of the electric motor.

According to some aspects, the air outlet comprises a plurality of outlets which span over an angle relative to the rotational axis of the motor axle. The angle is greater than <NUM> degrees, and preferably more than <NUM> degrees, and the air outlets are preferably located at least partly to the rear of said axis, i.e. closer to the user in a normal operative position of the handheld work tool.

In this manner, the openings and outlets are efficiently distributed.

According to some aspects, the hand-held work tool comprises a first part and a second part, the first part comprising the interface for holding a cutting tool, the electric motor arranged to drive the cutting tool, and the support arm, and the second part comprising the battery compartment. The first part and the second part are arranged vibrationally isolated from each other.

This minimizes vibration that can be uncomfortable for an operator using the work tool and that can reduce the lifetime of tool components such as cable connections and electronics.

The present disclosure will now be described in more detail with reference to the appended drawings, where.

<FIG> shows a hand-held work tool <NUM>. The work tool <NUM> in <FIG> comprises a rotatable circular cutting tool <NUM>, but the techniques disclosed herein can also be applied to other cutting tools such as chain-saws, core drills, and the like. An electric motor <NUM> is arranged to drive the cutting tool. This motor is powered from an electrical energy storage device which is arranged to be held in a battery compartment <NUM>.

The electrical motor generates a substantial amount of heat during operation. To prevent the motor from overheating, a fan <NUM> is arranged to be driven by the motor <NUM>. This fan may, e.g., be attached directly to the motor axle, or by some means of transmission arrangement. The fan generates an airflow which transports heat away from the electric motor, thereby cooling the motor.

The work tool <NUM> is arranged to be held by a front handle <NUM> and a rear handle <NUM> and operated by a trigger <NUM> in a known manner. It is desirable to minimize vibration in the handles and trigger, since excessive vibration may be uncomfortable for an operator using the work tool <NUM>. Excessive vibration may also reduce the lifetime of tool components such as cable connections and electronics. To reduce these vibrations, the work tool <NUM> comprises a first part <NUM> and a second part <NUM> arranged vibrationally isolated from each other. The first part <NUM> comprises an interface for holding the cutting tool <NUM> and also comprises the electric motor <NUM> arranged to drive the cutting tool. Thus, the first part comprises the main vibration generating elements of the work tool.

Notably, the second part <NUM> comprises the handles <NUM>, <NUM> and the trigger <NUM> and therefore is the part which interfaces with the operator of the work tool <NUM>. The second part <NUM> also comprises the battery compartment <NUM> for holding the electrical storage device, and the control electronics for controlling various operations of the work tool <NUM>.

Since vibration generated in the first part <NUM> is not transferred, or at least not transferred in a significant amount, to the second part <NUM>, an operator of the device <NUM> will not be subjected to the vibration, which is an advantage since he or she may be able to work for a longer period of time under more comfortable work conditions.

Vibration is normally measured in units of m/s<NUM>, and it is desired to limit tool vibration in front and rear handles below <NUM>/s<NUM>. Tool vibration, guidelines for limiting tool vibration, and measurement of the tool vibration are discussed in "VIBRATIONER - Arbetsmiljöverkets föreskrifter om vibrationer samt allmänna råd om tillämpningen av föreskrifterna", Arbetsmiljöverket, AFS <NUM>:<NUM>.

According to some aspects, the work tool <NUM> comprises a first part <NUM> and a second part <NUM> arranged vibrationally isolated from each other by a vibration isolation system arranged to limit front and rear handle vibration to values below <NUM>/s<NUM>.

A cooling air conduit is arranged to guide a portion of the flow of cooling air <NUM> from the first part <NUM> and into the second part <NUM> for cooling the electrical storage device. This means that the fan <NUM> is used to cool both the electrical motor <NUM>, and the electrical energy source, which is an advantage since only a single fan is needed.

Herein, a conduit is a passage arranged to guide a flow, such as a flow of air. A cooling air conduit may be formed as part of an interior space enclosed by work tool body parts, or as a hose of other type of conduit, or as a combination of different types of conduits.

Any control electronics comprised in the second part <NUM> may also be arranged to be cooled by the portion of the flow of cooling air <NUM> which is guided from the first part <NUM> and into the second part <NUM>. <FIG> schematically shows a cooling flange <NUM> associated with such control electronics, which cooling flange <NUM> is optional, i.e., the portion of the flow of cooling air can be used to cool the control unit directly in which case the control unit constitutes the cooling flange. Thus, optionally, the portion of the flow of cooling air <NUM> from the first part <NUM> and into the second part <NUM> is arranged to pass a cooling flange <NUM> associated with a control unit of the hand-held work tool <NUM>.

It may be a challenge to efficiently guide the portion of air <NUM> from the first part and into the second part, at least partly since the first part and the second part are arranged vibrationally isolated from each other. Some aspects of the disclosed work tool solve this challenge by providing bellows or some other type of flexible air flow conduit between the first part and the second part to guide the portion of air from the fan <NUM> towards the battery compartment <NUM>. These bellows <NUM> will be discussed in more detail below in connection to <FIG>. Bellows are sometimes also referred to as flexible covers, convolutions, accordions, or machine way covers. A hose formed in a flexible material may be used instead of the bellows.

To summarize, <FIG> schematically illustrates a hand-held work tool <NUM> comprising a first part <NUM> and a second part <NUM> arranged vibrationally isolated from each other. According to some aspects, the first part <NUM> is vibrationally isolated from the second part <NUM> by one or more resilient elements.

The hand-held work tool may be a cut-off tool as shown in <FIG>, but it can also be a chain saw or other work tool for cutting hard materials. The first part comprises an interface for holding a cutting tool <NUM> and an electric motor <NUM> arranged to drive the cutting tool. The drive arrangement may, e.g., comprise a belt drive or a combination of belt drive and geared transmission. The electric motor <NUM> is arranged to drive a fan <NUM> configured to generate a flow of cooling air for cooling the electric motor <NUM>. The fan may, e.g., be directly connected to the electric motor shaft, or it can be indirectly connected to the motor shaft via some sort of transmission or drive arrangement, like a belt drive or a geared transmission.

The second part <NUM> comprises a battery compartment <NUM> for holding an electrical storage device arranged to power the electric motor <NUM>, and a cooling air conduit is arranged to guide a portion of the flow of cooling air <NUM> from the first part <NUM> and into the second part <NUM> for cooling the electrical storage device. The electrical energy source may be a battery, or some type of fuel-cell or the like.

<FIG> show different views of an example hand-held work tool <NUM> arranged to hold a cutting tool by a cutting tool interface <NUM>. The resilient elements separating the first part <NUM> from the second part <NUM> are here compression springs <NUM>. However, as mentioned above, some type of resilient material members, such as rubber bushings, may also be used as an alternative to the springs or in combination with the springs. Leaf springs may also be an option for vibrationally isolating the first part <NUM> from the second part <NUM>.

<FIG> shows a holder <NUM> for an extra blade bushing. Cutting discs may have varying dimensions when it comes to the central hole in the blade. Some blade holes are <NUM> across, while some other holes are <NUM>,<NUM> across. There are even some markets where blade central holes of <NUM>,<NUM> are common. To allow use with different types of blades, having different dimensions on the central blade hole, the hand-held work tool <NUM> comprises a holder <NUM> arranged on the work tool body for holding a blade bushing. This extra blade bushing preferably has a different dimension compared to the blade bushing mounted in connection to the cutting tool interface <NUM>.

<FIG> shows an example electrical storage device <NUM>, here a battery, fitted in the battery compartment <NUM>. This battery may be held in position by means of a battery lock mechanism which will be discussed in more detail below in connection to <FIG>, <FIG>. Other types of electrical energy sources which can be used together with the herein disclosed devices and techniques include, e.g., fuel cells, super-capacitors, and the like.

According to some aspects, the flow of cooling air for cooling the electric motor <NUM> extends transversally <NUM>, <NUM>, <NUM> through the hand-held work tool, with respect to an extension plane of the circular cutting tool <NUM>. Here, with reference to <FIG>, transversally is to be interpreted relative to an extension direction <NUM> of the work tool extending from the rear handle <NUM> towards the cutting tool and in relation to an extension plane of the cutting tool <NUM> which is more or less vertical in <FIG>). Air from the environment is sucked into the work tool interior via an air intake <NUM> on one side of the tool and at least partly pushed out from the work tool interior via a first air outlet <NUM> on the other side of the tool formed in a direction transversal from the air intake <NUM>.

A portion of the air flow sucked into the work tool via the air inlet <NUM> is guided via an air conduit into the second part <NUM> where it is used to cool the electrical storage device and optionally also cool portions of electrical control circuitry. With reference to, e.g., <FIG>, this portion of the air flow is guided downwards from the fan and then backwards in the tool towards the battery compartment <NUM> before it exits the work tool via a second air outlet <NUM> formed in the second part <NUM> of the tool.

It is appreciated that the air flow can be directed also in the reverse direction if the fan is run in reverse. , the air outlets <NUM>, <NUM> can also be used to suck cool air from the environment into the work tool <NUM>, <NUM>, and the air intake <NUM> can be re-purposed to instead allow hot air to exit the work tool.

With reference to <FIG>, the portion of the air flow <NUM> guided downwards from the fan and then backwards in the tool also exits the work tool via a third air outlet <NUM> formed inside the battery compartment <NUM>. This third outlet is mainly arranged to cool a battery received in the battery compartment <NUM>.

<FIG> illustrates some aspects of the disclosed work tool, wherein the first part <NUM> comprises a thermally conductive support arm <NUM> arranged to support the circular cutting tool <NUM> on a first end of the support arm <NUM>, and to support the electric motor <NUM> by a support surface <NUM> at a second end of the support arm <NUM> opposite to the first end <NUM>. The motor <NUM> is then arranged to drive the cutting tool via some type of drive arrangement, such as a belt drive or a combination of belt drive and geared transmission. The belt is not shown in <FIG>, only the belt pulley. The support surface <NUM> represents a relatively large interfacing area between the motor <NUM> and the support arm <NUM>, which allows for a significant amount of heat transfer from the motor and into the support arm material, at least if the electric motor comprises a corresponding surface for interfacing with the support surface. This heat is then dissipated from one or more cooling flanges <NUM> formed on the support arm <NUM>. Thus, the support arm <NUM> comprises one or more cooling flanges <NUM> arranged to dissipate heat away from the electric motor <NUM> via the support surface <NUM>.

The support arm <NUM> is an arm of the cut-off tool, it may equivalently be referred to as a cut-off arm <NUM>.

This heat transfer arrangement improves the heat dissipation from the motor since the cooling air flow is more efficiently utilized to transport the heat away from the motor.

The more thermally conductive the support arm is, the more efficient is the heat dissipation. According to some aspects, at least some parts of the support arm is formed in a material having a thermal conductivity property above <NUM> Watts per meter and Kelvin (W/mK). For instance, at least some parts of the support arm may be formed in aluminum, which has a thermal conductivity of about <NUM> W/mK. Iron or steel is another option which would provide the desired thermal conductivity. The support arm may also be formed in different materials, i.e., one highly thermally conductive material such as copper, magnesium or aluminum can be used for the cooling flanges and another material, such as cast iron or steel, to provide general structural support.

<FIG> and <FIG> show details of an example support arm <NUM> arranged to support the circular cutting tool <NUM> on a first end of the support arm <NUM>, and to support the electric motor <NUM> by a support surface <NUM> at a second end of the support arm <NUM> opposite to the first end <NUM>. <FIG> shows a view of the support arm <NUM> and the interior space <NUM> discussed above. <FIG> shows a first cross-sectional view along line A-A and <FIG> shows a second cross-sectional view along line B-B. The motor <NUM> comprises a motor axle extending through the motor housing <NUM> in a known manner.

A first end <NUM> of the axle is arranged to hold a pulley for driving the circular cutting tool <NUM>. <FIG> shows a view of the support arm <NUM> with the drive pulleys and the drive belt in place to drive the circular cutting tool <NUM>.

A second end <NUM> of the motor axle is arranged to drive the fan <NUM>. The example fan <NUM> shown in <FIG> is a regular axial fan. Another more advanced example of the fan <NUM> will be discussed below in connection to <FIG>. Here, a rotational axis <NUM> of the electric motor <NUM> is indicated.

The support arm <NUM> is arranged to enclose the electric motor at least partially <NUM>, thereby protecting the motor and improving the cooling efficiency of the air flow <NUM> past the motor. Towards this end, the support arm <NUM> comprises a cup-shaped recess, seen in detail in <FIG>, where the support surface <NUM> makes up the bottom portion of the recess and a cylinder shaped wall <NUM> extends out from a perimeter of the support surface <NUM> to enclose the motor housing <NUM> of the electric motor <NUM> when the motor is supported on the support surface <NUM>. The motor <NUM> is arranged to be firmly bolted onto the support surface <NUM> through bolt holes <NUM>, thereby ensuring good thermal conduction between the motor <NUM> and the support arm <NUM> as well as mechanical integrity. A slot is formed between the cylinder shaped wall <NUM> and the motor <NUM>, i.e., the recess wall <NUM> is distanced radially from the motor housing. This slot is arranged to guide a flow of cooling air <NUM> from the fan <NUM> past the motor <NUM>. The flow <NUM> extends transversally from the fan <NUM> through the support arm <NUM> to cool the electric motor <NUM>. The flow of cooling air <NUM> then passes through the openings <NUM> and into the interior space <NUM> and then out via the first air outlet <NUM> shown in <FIG>.

According to some aspects, at least <NUM>% and preferably at least <NUM>% of a volume of the electric motor <NUM>, i.e., the volume of the electric motor including its housing <NUM>, is enclosed by the support arm <NUM>. This means that the cylinder shaped wall <NUM> extends a distance <NUM> from the support surface <NUM> to enclose at least <NUM>% and preferably at least <NUM>% of the volume of the motor housing <NUM>. Thus, the motor is optionally significantly embedded into the support arm, or even entirely embedded as shown in <FIG>, thereby improving both structural integrity of the motor and support arm assembly, as well as improving heat transport away from the electric motor. The cooling of the electric motor <NUM> is also improved by the slot formed between the cylinder shaped wall and the electric motor housing, which cooperates with the thermally conductive support arm and the cooling flanges to cool the motor efficiently.

The support arm <NUM> and the electric motor <NUM> may also be at least partially integrally formed. This means that some parts of the electric motor <NUM> may be shared with the support arm <NUM>. For instance, a part of the support arm <NUM> may constitute part of the electric motor housing, such as a motor gable facing the support arm. The common part shared between the support arm <NUM> and the electric motor <NUM> may, e.g., be machined or molded. Also, optionally, the electric motor axle may bear against a surface of the support arm, to improve mechanical integrity.

It is noted that the feature of an at least partially integrally formed support arm and electric motor can be advantageously combined with the other features disclosed herein but is not dependent on any of the other features disclosed herein. Thus, there is disclosed herein a support arm <NUM> and electric motor <NUM> assembly for a work tool <NUM>, where the support arm and the electric motor are at least partially integrally formed.

With reference to <FIG>, the first part <NUM> optionally comprises a belt guard <NUM> configured to enclose the interior space <NUM>. As discussed above, a portion of the flow of cooling air is arranged to be guided into the interior space <NUM>, thereby increasing an air pressure in the belt guard <NUM> interior space <NUM> above an ambient air pressure level. The interior space <NUM> is delimited on one side by the support arm (discussed below in connection to <FIG>), and on the other side by the belt guard <NUM>, which assumes the function of a lid arranged to engage the support arm to protect the drive belt among other things. The belt guard <NUM> comprises an air outlet <NUM> through which the flow of cooling air exits the interior space. This air outlet <NUM> is configured with an area such that the air pressure in the belt guard <NUM> interior space <NUM> increases above the ambient air pressure level by a desired amount.

The increase in air pressure in the interior space <NUM> means that a flow of air will exit through all openings into the interior space <NUM>, i.e., any cracks and the like, and not just the air outlet <NUM>. This in turn means that water, dust, debris, and slurry will have to overcome this flow of air in order to enter into the interior. Thus, accumulation of unwanted material inside the work tool is reduced.

Water inside the interior space <NUM> may cause the belt drive to slip and is therefore undesirable. The increase in air pressure in the belt guard <NUM> interior space <NUM> means that less water is able to enter the interior space, which is an advantage. As a consequence, requirements on the belt can be reduced, such that, e.g., belts with a smaller number of ribs can be used.

As noted above, the portion of the flow of cooling air <NUM> guided from the first part <NUM> and into the second part <NUM> may pass via a bellows or other flexible air flow conduit <NUM> arranged in-between the first <NUM> and the second <NUM> parts. <FIG> shows an example of such bellows <NUM> in detail.

According to some aspects, the bellows <NUM> is associated with a Shore durometer value, or Shore hardness, between <NUM>-<NUM>, and preferably between <NUM>-<NUM>, measured with durometer type A according to DIN ISO <NUM>-<NUM>.

The bellows <NUM> optionally comprises a poka-yoke feature <NUM>, <NUM>. This poka-yoke feature comprises at least one protrusion <NUM>, <NUM> configured to enter a corresponding recess formed in the first part <NUM> and/or in the second part <NUM>, thereby preventing erroneous assembly of the bellows with the first <NUM> and second <NUM> parts.

The bellows <NUM> also optionally comprises at least one edge portion <NUM>, <NUM> of increased thickness. Each such edge portion is arranged to enter a corresponding groove formed in the first part <NUM> or in the second part <NUM>, thereby fixing the bellows <NUM> in relation to the first or second part similar to a sail leech fitting into a mast. <FIG> schematically illustrate a bellows fitted onto the first and second parts, respectively, by the edge portions.

The bellows illustrated in <FIG> is arranged with a shape that is symmetric about a symmetry plane <NUM> parallel to an extension direction of the edge portions <NUM>, <NUM>. Thus, advantageously, the bellows can be assembled with the first and second parts independently of which side of the bellows that is facing upwards. , the bellows can be rotated <NUM> degrees about the symmetry axis <NUM> and assembled with the first and second parts.

<FIG> schematically illustrate aspects of the battery compartment <NUM>, where the battery compartment comprises a battery lock mechanism <NUM>. The battery lock mechanism comprises a locking member <NUM> rotatably supported on a shaft <NUM>. The locking member comprises a leading edge portion <NUM> arranged to enter a recess <NUM> formed in the electrical energy source <NUM> to lock the electrical energy source in position, wherein the leading edge portion <NUM> has an arcuate form with a curvature corresponding to that of a circle segment with radius <NUM> corresponding to the distance from the leading edge portion <NUM> to the center of the shaft <NUM>, and wherein the recess <NUM> formed in the energy source <NUM> comprises a surface <NUM> arranged to engage the leading edge portion <NUM>, wherein the surface <NUM> has an arcuate form to match that of the leading edge portion <NUM>.

This way, as the electrical energy source <NUM> is received in the battery compartment <NUM>, the locking member is inactive, simply yielding to the electrical energy source as it enters the compartment. This phase of inserting the electrical energy source <NUM> into the compartment <NUM> by moving it in an insertion direction <NUM> is schematically illustrated in <FIG>. The locking member <NUM> then swings into the recess <NUM> where it prevents the battery to be retracted from the battery compartment. The locking position is illustrated in <FIG>. Notably, the arcuate form of the leading edge portion <NUM> allows the locking mechanism to be rotated out of the locking position with less resistance even if there is some friction between the leading edge portion <NUM> and the surface <NUM> arranged to engage the leading edge portion <NUM>.

The locking member may be arranged spring biased towards the locking position, and operable by means of a lever or push-button mechanism, discussed below in connection to <FIG>.

It is appreciated that there may be any number of locking members arranged in the battery compartment in the way described above, i.e., anywhere from a single locking member up to a plurality of locking members.

According to some aspects, the battery compartment <NUM> comprises at least one resilient member <NUM> arranged to urge the electrical energy source into the locking position, i.e., urge the electrical energy source in a direction opposite that of the insertion direction <NUM>. The resilient member <NUM>, when compressed by the electrical energy source, pushes onto the electrical energy source to repel it from the battery compartment <NUM>. This pushing force increases the contact pressure between the leading edge portion <NUM> and the surface <NUM> arranged to engage the leading edge portion <NUM>, thereby improving the holding effect on the electrical energy source.

According to an example, a user inserts a battery into the battery compartment in an insertion direction. When the battery is inserted all the way, it contacts the resilient member <NUM> and the locking member <NUM> enters the recess <NUM> formed in the electrical energy source <NUM> to lock the electrical energy source in position. The resilient member, when compressed by the battery, pushes back in a direction opposite to the insertion direction. This pushing force from the resilient member increases a contact force between the leading edge portion <NUM> of the locking member and the surface <NUM> arranged to engage the leading edge portion <NUM>, to hold the battery more securely in position.

The resilient member <NUM> optionally comprises any of a resilient material member, a compression spring, and/or a leaf spring.

The resilient member <NUM> will also eject the electrical energy source <NUM> a short distance from the battery compartment <NUM> when the electrical energy source is released by the locking mechanism <NUM>. Thus, when a push-button mechanism <NUM> is operated to release a battery, the battery is ejected from the battery compartment <NUM>, making it easier to grasp the battery and pull it out from the battery compartment.

<FIG> schematically shows an example of such resilient members <NUM>. The resilient members urge the electrical energy source in direction <NUM>, but the electrical energy source is prevented from moving in this direction by the locking member <NUM> engaging the recess <NUM>. The arrangement of resilient member <NUM> and locking member <NUM> on opposite sides S1, S2, of the electrical energy source <NUM> generates a twisting motion <NUM> or rotation moment which further increases the holding effect by increasing friction between battery and battery compartment wall, in a manner similar to a stuck cupboard or desk drawer. This further increase in holding effect reduces vibration by the battery since it is now held even more snugly in the battery compartment.

<FIG> shows an example work tool <NUM> which comprises the battery lock mechanism <NUM>. The locking member <NUM> is rotatably supported on a shaft <NUM>, where it is allowed to rotate about an axis <NUM> of rotation. A push-button mechanism <NUM> can be used by the operator to rotate the locking member <NUM> such that it exits the recess, thereby allowing removal of the battery in direction <NUM>.

According to some aspects the locking member <NUM> is spring biased towards the locking position. Thus, as an electrical energy source <NUM> is inserted into the recess <NUM>, the locking member <NUM> snaps into the locking position. The spring bias force can be overcome by the push-button mechanism <NUM> when the electrical energy source is to be removed from the battery compartment.

<FIG> illustrates details of a battery lock mechanism <NUM> for a battery compartment <NUM>. This battery lock mechanism can be used with many different types of tools, i.e., abrasive tools, grinders, chainsaws, drills, cut-of tools, and the like. Thus, the battery lock mechanisms disclosed herein are not limited to use with the cut-off tools discussed above in connection to <FIG>.

The battery lock mechanism <NUM> shown in <FIG> comprises a locking member <NUM> rotatably supported on a shaft <NUM> and optionally spring biased into a locking position as discussed above. The locking member comprises a leading edge portion <NUM> arranged to enter a recess <NUM> formed in the electrical energy source <NUM> to lock the electrical energy source in position, as discussed above in connection to <FIG>. The leading edge portion <NUM> may have an arcuate form with a curvature corresponding to that of a circle segment with radius <NUM> corresponding to the distance from the leading edge portion <NUM> to the center of the shaft <NUM>. The recess <NUM> formed in the energy source <NUM> comprises a surface <NUM> arranged to engage the leading edge portion <NUM>. This surface <NUM> has an arcuate form to match that of the leading edge portion <NUM>. Notably, the battery lock mechanism <NUM> illustrated in <FIG> comprises two locking members <NUM> separated by a distance. This double arrangement of locking members improves robustness of the lock mechanism <NUM>.

Thus, as explained in connection to <FIG>, an electrical energy source such as a battery can be inserted into the battery compartment in an insertion direction <NUM>, i.e., into the compartment <NUM> shown in <FIG>. At some point the locking member is able to enter into the locking position, i.e., it enters the recess <NUM>. In this position the battery is prevented from moving in a direction <NUM> opposite to the insertion direction <NUM>. However, it may rattle some and may not be firmly secured. To improve the battery lock mechanism and to better hold the electrical energy source in position, one or more resilient members <NUM>, such as compression springs or rubber bushings, are arranged in the battery compartment <NUM> and/or on the electrical energy source to push on the electrical energy source as it is inserted all the way into the compartment. The pushing force increases a contact force between the leading edge portion <NUM> and the surface <NUM> configured to engage the leading edge portion. This increased contact force increases friction to better hold the electrical energy source in position.

According to some aspects, the at least one resilient member <NUM> and the battery lock mechanism <NUM> are arranged at opposite sides S1, S2 of the battery compartment <NUM>, i.e., there is a plane <NUM> that divides the battery compartment in two parts, where the resilient member <NUM> is comprised in one part and the battery lock mechanism is comprised in the other part. This means that the resilient member or members push onto the electrical battery source from a direction to cause a twisting motion <NUM> or torque. This twisting motion can be compared to a drawer which gets stuck in a cupboard or desk. The electrical energy source is then prevented from rattling and is more firmly secured in the battery compartment <NUM>.

<FIG> show an example work tool <NUM> comprising a special type of fan <NUM>. This fan comprises a member, preferably but not necessarily discoid shaped, arranged on the axle of the electric motor <NUM> which also constitutes an axis of rotation of the fan. The member extends in a plane perpendicular to the axis of rotation and comprises two different types of fan portions. A first portion acts as an axial fan and pushes cooling air transversally <NUM> across the work tool <NUM> to cool the electric motor <NUM>. A second section of the fan acts as a radial fan, also known as a centrifugal fan, to push cooling air downwards and into the second part of the work tool in cooperation with a fan scroll matched to the radial fan portion. The fan <NUM> is schematically illustrated in <FIG> and an example of the fan is shown in <FIG> where the direction of rotation <NUM> and the axis of rotation <NUM> have been indicated. <FIG> also indicates the direction <NUM> referred to as 'radially outwards' from the axis of rotation <NUM>.

<FIG> shows an example tool where According to some aspects, the portion of the flow of cooling air <NUM> from the first part <NUM> and into the second part <NUM> is arranged to enter the electrical energy source <NUM> via a third outlet <NUM> arranged inside the battery compartment <NUM>. This connection to the electrical energy source improves cooling efficiency by better cooling, e.g., the cells in a battery.

The fan <NUM> comprises an axial fan portion <NUM> arranged peripherally on the fan <NUM>, i.e., circumferentially along the fan disc border as shown in <FIG> and in <FIG>, and a radial fan portion <NUM> arranged centrally on the fan <NUM>, i.e., radially inwards from the axial fan portion as shown in <FIG>. Thus, the axial fan portion is arranged radially outwards <NUM> in the extension plane from the axis of rotation <NUM>. The axial fan portion <NUM> is arranged to generate the flow of cooling air <NUM> for cooling the electric motor <NUM>, and the radial fan portion <NUM> is arranged to generate the portion of the flow of cooling air <NUM> from the first part <NUM> and into the second part <NUM> for cooling the electrical storage device.

Axial flow fans, or axial fans, have blades that force air to move parallel to the shaft about which the blades rotate, i.e., the axis of rotation. This type of fan is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in wind tunnels. The axial fan is particularly suitable for generating large air flows in straight tube-line conduits, which is the case here when cooling the electric motor <NUM>.

Radial fans, or centrifugal fans, uses the centrifugal power supplied from the rotation of impellers to increase the kinetic energy of air/gases. When the impellers rotate, the gas particles near the impellers are thrown off from the impellers, then move into the fan housing wall. The gas is then guided to the exit by a fan scroll. A radial fan, compared to the axial fan, is better at pushing cooling air at a pressure passed air conduits with bends and narrow passages, which is the case for the air conduit passing into the second part and towards the battery compartment <NUM>.

According to some aspects, the axial fan and the radial fan are formed as separate parts mounted on the same motor axle.

The radius of the radial fan may correspond to the radius of the electrical motor gable.

The relationship between the radius of the radial fan and the radius of the fan may be on the order of <NUM>-<NUM> percent.

Thus, advantageously, the fan illustrated in <FIG> provide both efficient motor cooling as well as efficient cooling of tool members in the second part, e.g., the control unit and the electrical energy source. This is achieved by providing two different types of fans on a single fan member.

<FIG> shows a more detailed view of the part of the support arm which comprises the one or more cooling flanges <NUM> arranged to dissipate heat away from the electric motor <NUM> via the support surface <NUM>. The openings <NUM> for letting air enter the interior space <NUM> discussed above can also be seen. The axial fan portion <NUM> pushes air past the motor and through these holes, thereby cooling the electric motor <NUM>.

The fan <NUM> may optionally be assembled in a fan housing <NUM> exemplified in <FIG>. The fan housing comprises at least one opening <NUM> arranged peripherally and radially outwards from the axis of rotation <NUM> to receive the flow of cooling air <NUM> from the axial fan portion <NUM> for cooling the electric motor <NUM>. The fan housing also comprises a fan scroll <NUM> arranged centrally in the housing to interface with the radial fan portion <NUM> for guiding the portion of the flow of cooling air <NUM> from the first part <NUM> and into the second part <NUM> for cooling the electrical storage device.

<FIG> also shows the grooves <NUM> and the recesses <NUM> for receiving the bellows <NUM> with the edge portions <NUM> and the poka-yoke feature <NUM> illustrated in <FIG>.

The fan discussed in connection to <FIG>, B, <NUM>, <NUM>, and <NUM> is not only applicable to the types of work tools disclosed herein. On the contrary, this fan can be used with advantage in any type of work tool where a first flow of cooling air and a second flow is desired. Thus, there is disclosed herein a fan <NUM> for a hand-held work tool <NUM>, <NUM>, <NUM>, <NUM>. The fan <NUM> extends in a plane perpendicular to an axis of rotation of the fan <NUM>. The fan comprises an axial fan portion <NUM> arranged radially outwards <NUM> from a radial fan portion <NUM> arranged centrally on the fan <NUM> with respect to the axis of rotation <NUM>, wherein the axial fan portion <NUM> is arranged to generate a first flow of cooling air for cooling a first hand-held work tool member, and wherein the radial fan portion <NUM> is arranged to generate a second flow of cooling air <NUM> for cooling a second hand-held work tool member.

Optionally, the axial fan portion <NUM> has an annular shape centered on the axis of rotation <NUM>, and wherein the radial fan portion <NUM> has a discoid shape centered on the axis of rotation <NUM>.

There is also disclosed herein a hand-held work tool <NUM> comprising the fan discussed in connection to <FIG>, and a fan housing <NUM>. The fan <NUM> is assembled in the fan housing <NUM>, which fan housing comprises at least one opening <NUM> arranged peripherally in the fan housing and radially outwards from the axis of rotation <NUM> of the fan <NUM> to receive the first flow of cooling air from the axial fan portion <NUM> for cooling the first hand-held work tool member, the fan housing also comprises a fan scroll <NUM> arranged centrally in the fan housing to interface with the radial fan portion for guiding the second flow of cooling air <NUM> for cooling a second hand-held work tool member.

<FIG> illustrates details of an optional connector arrangement <NUM> for a water hose which is preferably mounted in vicinity of the rear handle <NUM> where it is easily accessible by an operator to attach and to detach a water hose. The connector arrangement <NUM> comprises a water hose connector part <NUM>, here shown as a nipple, i.e. a connector male part, for a water hose quick connector system facing rearwards away from the circular cutting tool <NUM>. The connector nipple <NUM> is mounted fixedly onto the machine housing by a bracket <NUM> such that the water hose connector part <NUM> is fixedly held in relation to the work tool. Alternatively, a female water hose connector part can be fixedly mounted onto the work tool by a similar bracket to obtain the same technical effect and advantages. A water hose <NUM> extends away from the connector part <NUM> towards the cutting tool <NUM>. The water hose <NUM> is arranged at least partly embedded into the tool housing, in order to protect the water hose from damage during use of the tool <NUM>.

Known water hose connector arrangements often comprise a segment of hose in-between a bracket on the work tool and the connector part (male or female connector part), which means that it is difficult to connect and to disconnect the water hose with a single hand. The connector arrangement <NUM>, however, allows for attachment and detachment of a water hose for supplying water to the cutting tool <NUM> during operation by one hand, since the connector nipple <NUM> is mounted fixedly onto the machine housing by the bracket <NUM>. Thus, the connector part is firmly supported by the machine housing where it is easily accessible and does not move around. An operator may, for instance, hold the tool by the front handle <NUM> with one hand and connect the water hose with the other hand. The connector part <NUM> may be adapted for interfacing with any quick connector system on the market, such as the Gardena ® water hose system.

The water hose connector arrangement <NUM> comprising the connector part <NUM> and the bracket <NUM> can be implemented on any power tool requiring a supply of water, it is not limited to the particular tools discussed herein.

<FIG> show views of the connector arrangement <NUM> in more detail. <FIG> is a view corresponding to that in <FIG>, while <FIG> shows the connector arrangement <NUM> from an opposite point of view. The connector part <NUM> and the bracket <NUM> are preferably integrally formed, i.e., machined or molded from one piece of material, such as a piece of plastic or metal. An internal nipple <NUM> for attaching the water hose <NUM> may be arranged opposite to the connector part <NUM> for convenient assembly of the connector arrangement on the hand-held work tool.

<FIG> illustrate details of an example battery compartment <NUM>. An electrical energy source such as a battery can be inserted into the battery compartment in an insertion direction <NUM>, i.e., into the compartment <NUM> as also shown in <FIG>. <FIG> is a view opposite to the insertion direction <NUM>, while <FIG> is a view looking into the compartment <NUM> in the insertion direction <NUM>. The locking members <NUM>, discussed above in connection to, e.g., <FIG> can be seen in <FIG>. The battery, which will be discussed in more detail below in connection to <FIG> optionally comprises a rearward face formed as a handle to simplify both insertion and removal of the battery in the battery compartment <NUM>.

Batteries for powering heavy duty cut-off tools such as the work tools discussed herein are normally quite heavy. Thus, the batteries must be held in the battery compartment <NUM> in a robust and reliable manner. Towards this end, the battery compartment <NUM> comprises a battery holding mechanism specifically adapted to support a heavy battery, i.e., weighting on the order of <NUM>, such as between <NUM>-<NUM>.

The battery compartment <NUM> extends transversally through the housing of the tool <NUM>, <NUM> as discussed above, where it defines a volume for receiving a battery. The volume is delimited by a rear wall Rw and a front wall Fw, where the rear wall Rw is located towards the rear handle <NUM> on the tool <NUM> and the front wall Fw is located towards the front of the tool <NUM>, i.e., towards the cutting tool <NUM>. A bottom surface Bs and a top surface Fs also delimits the volume. The example volume in <FIG> is of a rectangular shape with rounded corners.

The battery holding mechanism comprises a supporting heel <NUM> arranged on a middle section of a side wall of the battery compartment, more specifically on the rear wall Rw closest to the rear handle <NUM>. The heel is <NUM> elongated with an elongation direction extending transversally through the battery compartment aligned with an insertion direction of the battery in the battery compartment <NUM>. When the machine is resting on the ground support member <NUM>, the supporting heel <NUM> is parallel to ground. Also, when the tool <NUM> is held in a normal operating position, the supporting heel is parallel to ground, and therefore supports the battery against gravity. It is appreciated that the supporting heel <NUM> can also be arranged on the front wall, i.e., on any of the front wall and/or the rear wall of the battery compartment. The battery, which is exemplified in <FIG> and will be discussed below, comprises a corresponding groove matched to the supporting heel.

According to some aspects the supporting heel <NUM> is metal shod for increased mechanical integrity, i.e., the supporting heel <NUM> is optionally constructed with an outer layer metal layer for increased mechanical robustness.

According to some other aspects, the battery compartment also comprises an upper dove-tail groove <NUM> and a lower dove-tail groove <NUM> for supporting the battery in the battery compartment <NUM>. The dove-tail grooves are arranged to mate with corresponding ridge structures on the battery, such that the battery can be inserted into the battery compartment <NUM> in mating position with the dove-tail grooves in the insertion direction <NUM>. Thus, the supporting heel <NUM> and the dove-tail grooves <NUM>, <NUM> collaborate to support the battery in the battery compartment in a safe and roust manner. The dove-tail grooves <NUM>, <NUM> have the function to guide the battery as it is inserted into the battery compartment <NUM> and prevents snagging as the battery is removed from the battery compartment <NUM>.

According to some aspects, the dove-tail grooves <NUM>, <NUM> are metal shod for increased mechanical strength, i.e., the grooves are reinforced with a lining layer of metal for increased mechanical robustness.

<FIG> also shows two resilient members <NUM> as discussed above in connection to <FIG>, arranged to urge the battery into the locking position, i.e., urge the electrical energy source in a direction opposite that of the insertion direction <NUM>.

Contact strips <NUM> extending in the insertion direction <NUM> are arranged in the battery compartment <NUM> to mate with corresponding electrical connectors configured in slots on the battery.

There is also disclosed herein a battery <NUM> as shown in <FIG> for insertion into the battery compartment <NUM>. The battery <NUM> has a weight between <NUM>-<NUM> and comprises a groove <NUM> arranged on one side of the battery to mate with a corresponding supporting heel <NUM> arranged on a wall of a battery compartment <NUM>. The groove optionally has an initial bevel to simplify mating with the supporting heel <NUM>. The battery <NUM> further comprises an upper ridge structure <NUM> and a lower ridge structure <NUM> on an opposite side of the battery compared to the groove <NUM>, as shown in <FIG>, for mating with corresponding dove-tail grooves <NUM>, <NUM> of the battery compartment <NUM>. Thus, the battery <NUM> is configured for insertion into the battery compartment <NUM> discussed in connection to <FIG>.

The battery <NUM> comprises at least one recess <NUM> configured to receive a respective locking member <NUM> of a battery lock mechanism <NUM> as discussed above. The locking member comprises a leading edge portion <NUM> with an arcuate form and the recess <NUM> comprises a surface <NUM> arranged to engage the leading edge portion <NUM>. The surface <NUM> has an arcuate form to match that of the leading edge portion <NUM>. Two recesses are advantageously arranged on either side of the elongated supporting heel <NUM> as shown in <FIG>.

The battery <NUM> exemplified in <FIG> also comprises one or more electrical connectors <NUM> arranged protected in slots extending in the insertion direction to mate with corresponding contact strips <NUM> arranged in the battery compartment <NUM>.

Optionally, the battery <NUM> comprises a forward face F1 facing in the insertion direction <NUM> when the battery <NUM> is inserted in the battery compartment <NUM>, and a rearward face F2 opposite to the forward face, wherein the rearward face is formed as a handle <NUM> to allow gripping by one hand.

The battery also comprises electrical connectors <NUM> configured in slots extending in the insertion direction to mate with corresponding contact strips <NUM> arranged in the battery compartment <NUM>. The electrical connectors are thereby protected from mechanical impact.

To promote cooling of the battery, there is an air inlet arranged on a bottom side of the battery which is in fluid communication with an air outlet <NUM> arranged on the upper side of the battery, as seen in <FIG>. Thus, the air stream <NUM> from the fan <NUM> can be guided through the battery <NUM> to better cool the battery cells.

The battery and the battery compartments discussed in connection to <FIG> and <FIG> can also be used with other handheld tools. Thus, the features disclosed in connection to the battery compartment and battery are not dependent on any other particular features of the tools discussed herein.

<FIG> illustrates an example hand-held electrically powered cut-off tool <NUM> comprising a first part <NUM> and a second part <NUM> arranged vibrationally isolated from each other by one or more damping members <NUM>, <NUM> optionally in combination with one or more resilient members such as the metal springs <NUM> shown in, e.g., <FIG> and <FIG>.

A problem which may potentially occur in the type of hand-held cut-off tools discussed herein is that the cutting disc <NUM> turns slightly oval during use. This is an undesired situation since an excessively oval shaped cutting disc hampers cutting performance and may cause discomfort to the operator. An oval shaped cutting disc may also be associated with an increased risk of kickback, which is undesired. An example of an oval shaped cutting disc <NUM> is illustrated in the insert <NUM> of <FIG>. An oval shaped cutting disc is associated with a variation in disc "diameter" D1, D2 measured over the disc, i.e., D1 and D2 in <FIG> are not equal but differ by some non-negligible amount. The measurements D1 and D2 may be seen as half of the semi-minor and semi-major axes of an ellipse, although it is appreciated that an oval shaped cutting disc will often not be perfectly elliptical but exhibit an unevenness in radius along its perimeter.

This problem with oval-shaped cutting discs tends to be more pronounced for lower cutting disc angular speeds ω, such as when the cut-off tool is operated below <NUM> rpm, or below <NUM> rpm or so, measured at the axis of rotation of the cutting disc <NUM>. Hand-held electrically powered cut-off tools which comprise vibrationally isolated first and second parts, such as the tools <NUM>, <NUM>, <NUM>, <NUM>, <NUM> discussed herein, may be particularly prone to the problem of oval shaped cutting discs.

According to some aspects, the hand-held electrically powered cut-off tools discussed herein, and in particular in connection to <FIG> are arranged to operate at a cutting disc rotational speed ω below <NUM> rpm and preferably at about <NUM> rpm.

A solution to the problem with oval discs can be to simply increase the cutting disc rotational speed ω to, say, speeds above <NUM> rpm. However, such high cutting disc speeds are undesired for many reasons.

When dry cutting, i.e., when cutting concrete or stone by the hand-held electrically powered cut-off tool without adding fluid such as water to the cutting zone, it becomes very difficult to efficiently collect the generated dust if the cutting disc speed is too high, it is therefore desired to reduce cutting disc speed in dry cutting applications. Suitable cutting disc speeds for dry cutting application are normally on the order of about <NUM>-<NUM> rpm and preferably about <NUM> rpm.

High cutting disc speeds also mean that the cutting disc stores more energy during operation. This, in turn, means that it becomes harder to quickly reduce cutting disc speed by braking, such as during a kickback event. Thus, for safety reasons, it may be desirable to limit cutting disc speeds to speeds around <NUM>-<NUM> rpm, e.g., to about <NUM> rpm.

Furthermore, electrically powered cut-off tools may face challenges in generating sufficient torque for efficient cutting operation if the cutting disc speed is too high. For this reason cutting disc speeds ω on the order of about <NUM>-<NUM> rpm may be preferred.

It is appreciated that the cutting disc speeds mentioned above are just examples which are dependent on many aspects such as type of tool, cutting disc size, electric motor specification, and the like.

It has been realized that the problem with oval shaped cutting discs can be mitigated if damping members are arranged in-between the first part <NUM> and the second part <NUM>, optionally in combination with metal springs for efficient vibration isolation. These damping members are different from the customary spring-based anti-vibration elements normally used on this type of tool, since they are formed in a resilient material associated with a damping coefficient. The damping members suppress oscillating behavior between the two masses of a hand-held electrically powered cut-off tool comprising a first part and a second part arranged vibrationally isolated from each other. By this suppression, the tendency to form oval shaped cutting blades at low cutting disc speeds is mitigated. This is at least in part because, without the damping members, the two masses of a de-vibrated cut-off tool operated at a given cutting disc speed, may come into such oscillating behavior as to exert different cutting pressure on different sections of the cutting blade. That is, the oscillation motion may become synchronous with the rotation of the cutting disc. When the system comprising the first part <NUM> and the second part <NUM> enters into this type of oscillating state, an oval shaped cutting disc may result.

Combustion engine powered cut-off tools, as a rule, comprise resilient elements in the form of metal springs to suppress vibration between the motor and cutting disc part, and the part with the handles. However, these springs are not damping members in the sense of suppressing oscillating behavior of one mass in relation to another mass. Simple harmonic motion is often modeled by a mass on a spring, where the restoring forces obey Hooke's Law and is directly proportional to the displacement of an object from its equilibrium position. Any system that obeys simple harmonic motion is known as a simple harmonic oscillator. This type of oscillating behavior can be mitigated by adding a damping effect to the system, which can be done by adding a damping member associated with a damping coefficient (often denoted c) or an arrangement which limits a stroke length of one part in relation to the other part. The damping ratio is a measure describing how rapidly the oscillations decay from one "bounce" to the next. The damping ratio can vary from undamped (ζ = <NUM>), underdamped (ζ < <NUM>) through critically damped (ζ = <NUM>) to overdamped (ζ > <NUM>).

<FIG>, with reference also to <FIG>, shows a hand-held electrically powered cut-off tool <NUM> comprising a first part <NUM> and a second part <NUM> arranged vibrationally isolated from each other. The first part <NUM> comprises an arm <NUM> arranged to support a cutting disc <NUM> (illustrated in the insert <NUM> in <FIG>) and an electric motor <NUM> arranged to drive the cutting disc. The second part <NUM> comprises front <NUM> and rear <NUM> handles for operating the cut-off tool, and a battery compartment <NUM> for holding an electrical storage device <NUM>, <NUM> such as a battery arranged to power the electric motor <NUM>.

An example of this battery was discussed above in connection to <FIG>.

Notably, one or more damping members <NUM>, <NUM> are arranged in-between the first part <NUM> and the second part <NUM>, where at least one damping member <NUM>, <NUM> is formed in a resilient material associated with a damping coefficient.

The damping member or members are arranged to suppress or interfere with an oscillation of the second part <NUM> relative to the first part <NUM>. Thus, the risk of ending up with an oval shaped cutting disc is mitigated.

According to aspects, the at least one damping member <NUM>, <NUM> is made of rubber, a resilient plastic material, closed-cell foam, or a resilient synthetic resin. Common to these damping members is that they introduce a damping coefficient into the resonance equations of the mechanical system comprising the first part <NUM> and the second part <NUM>. This damping coefficient effectively suppresses oscillating behavior of the first part in relation to the second part. For example, a collar of closed cell-foam may be arranged around the flexible air flow conduit <NUM> shown in <FIG>, or the collar of closed cell foam may even constitute the flexible air flow conduit <NUM>.

Preferably, since metal springs are more effective when it comes to vibrationally isolating parts from each other, the first part <NUM> is vibrationally isolated from the second part <NUM> by one or more resilient elements <NUM> in addition to the at least one damping member <NUM>, <NUM>, wherein the one or more resilient elements <NUM> comprises at least one metal spring. Thus, a combination of metal springs and resilient material damping members together provide both efficient vibrational isolation as well as a reduced risk of getting an oval shaped cutting disc during operation of the cut-off tool.

<FIG> illustrates two example types of damping members which can be used independently of each other or in combination. It is also appreciated that the present teaching encompasses other types of damping members, applied in other places in-between the first and second parts. For instance, in-between may also be construed as encompassing a damping member which is attached to both the first and the second part but extends outside of the slot <NUM> formed between the first and the second part.

<FIG> illustrates two example damping members <NUM>, <NUM>. A first damping member <NUM> is integrated with a bellows <NUM> (shown in more detail in <FIG>) or other flexible air flow conduit arranged in-between the first <NUM> and the second <NUM> parts. This bellows or flexible air flow conduit provides a damping coefficient and also acts to limit a stroke length associated with a relative motion of the first part <NUM> relative to the second part <NUM>. As the first part <NUM> moves towards the second part <NUM> in direction C, shown in <FIG>, the reinforcement elements <NUM> arranged on at least one side of the bellows, such as on two or more sides of the bellows <NUM>, limit compression of the bellows and thereby limits the stroke length of the oscillating motion, thus interfering with an oscillating behavior.

The compressibility, associated with the Shore hardness, of the bellows can be adjusted by selecting a type of material to use in the reinforcement elements <NUM> or by dimensioning thickness of the material used in the elements and in the bellows. The compressibility can also be adjusted by arranging one or more cavities <NUM> in the reinforcement elements <NUM> as shown in <FIG>. According to aspects, a bellows <NUM> is arranged in-between the first <NUM> and the second <NUM> parts, where the bellows <NUM> is associated with a Shore durometer value, or Shore hardness, between <NUM>-<NUM>, and preferably between <NUM>-<NUM>, measured with durometer type A according to DIN ISO <NUM>-<NUM>. Thus, it is appreciated that the Shore hardness and also material thickness of a bellows such as that illustrated in <FIG> and/or in <FIG> can be adjusted to mitigate the occurrence of oval shaped cutting discs in a hand-held electrically powered cut-off tool, either by the introduction of a damping coefficient in the mass-spring system to suppress oscillation, or by introducing a limitation of the stroke length to interfere with oscillation, or both.

According to another example, as also shown in <FIG>, at least one damping member <NUM> is fixedly attached to one of the first part <NUM> or to the second part <NUM>, and arranged distanced from the other of the first part <NUM> or the second part <NUM>. Thus, the at least one damping member <NUM> is arranged to limit a stroke length associated with a relative motion of the first part <NUM> relative to the second part <NUM>. This damping member has a function similar to that of the reinforcement elements <NUM> discussed above in connection to <FIG>. It is located to limit a stroke length of an oscillating motion between the first and the second parts. A more detailed view of the damping member <NUM> is shown in <FIG>. According to this example, it is integrally formed in a single piece of resilient material and mounted onto the body of the first part <NUM> or the second part <NUM>.

Due to the reduced cutting disc speeds which can now be maintained without risk of getting oval shaped cutting discs, electric kickback protection mechanisms can be implemented with advantage. This is because kickback protection mechanisms based on braking by the electric motor <NUM> may not be effective at very high cutting disc speeds. Thus, according to some aspects, the electric motor <NUM> is arranged to be controlled by a control unit of the cut-off tool via a motor control interface. The control unit is arranged to obtain data indicative of an angular velocity of the cutting disc <NUM>, and to detect a kickback condition based on a decrease in angular velocity. The control unit is also arranged to control an electromagnetic braking of the electric motor <NUM> in response to detecting a kickback condition.

To provide a kickback mitigation function which is suitable also for high powered cut-off tools associated with significant tool inertia, that responds fast enough and with sufficient braking force, there is disclosed herein a hand-held electrically powered cut-off tool for cutting concrete and stone by a rotatable cutting disc <NUM>. The cut-off tool comprises an electric motor <NUM> arranged to be controlled by a control unit via a motor control interface. The control unit is arranged to obtain data indicative of an angular velocity of the cutting disc <NUM>, and to detect a kickback condition based on a decrease in angular velocity. The control unit is also arranged to control electromagnetic braking of the electric motor <NUM> in response to detecting a kickback condition, and optionally also to actively regulate an energy outtake from the electric motor over the control interface during the electromagnetic braking.

The detection mechanism is based on monitoring the angular velocity of the cutting disc <NUM>. If an abrupt decrease in velocity is seen, such as a high level of retardation in electric rotor angle or cutting disc angle, a kickback condition is detected. Immediately after a kickback event has been detected by the control unit, the electric motor is forcefully braked in order to mitigate the effects of the kickback event. This braking involves an active control of the energy outtake from the electric motor in order to provide a strong braking force without damaging the electrical components of the cut-off tool. This braking is facilitated by the fact that the cutting disc is operated at speeds below <NUM> rpm, say at <NUM> rpm, which is made possible by the presence of the damping members.

The kickback detection and braking of the cutting disc is often so rapid as to stop the blade before it even leaves the object which is processed. Even if some kickback motion occurs, the energy transferred from the cutting disc <NUM> to the machine body will be reduced to a level as to mitigate the harmful effects of the kickback event. Notably, the electric motor is not just disconnected from the power source as in many of the prior art documents. Rather, the energy outtake from the electric motor is actively regulated to provide a strong enough braking action to halt the kickback event.

With reference also to <FIG>, <FIG> illustrates details of a hand-held electrically powered cut-off tool <NUM> comprising a fan <NUM> arranged to be driven by an electric motor <NUM> to generate a flow of cooling air <NUM> and a battery compartment <NUM> comprising an electrical storage device <NUM>, <NUM>, such as a battery, arranged to power the electric motor <NUM>. A cooling air conduit is arranged to guide the flow of cooling air <NUM> towards an outlet aperture <NUM> (seen, e.g., in <FIG>) formed in a wall of the battery compartment <NUM>. The outlet aperture <NUM> faces a corresponding inlet aperture <NUM> formed in an enclosure of the electrical storage device <NUM>, <NUM> for receiving cooling air and thereby generating an air pressure above atmospheric pressure in the electrical storage device <NUM>, <NUM>. With reference to <FIG> which illustrates the cooling flow more schematically, a first slot section S1 is formed by a distance between the outlet aperture <NUM> and the inlet aperture <NUM> on the electrical storage device <NUM>, such that a first portion <NUM> of the flow of cooling air <NUM> air leaks out to an exterior of the cut-off tool via the first slot section S1.

This first portion <NUM> of the flow of cooling air <NUM> generates an air pressure inside the first slot section which must be overcome by dirt and slurry entering the slot between the electrical storage device <NUM> and the compartment wall. Thus, dirt and slurry is prevented from entering into the slot, and the battery compartment is kept clean, which is an advantage. A clean battery compartment without accumulated dust and slurry simplifies insertion and removal of the electrical storage device <NUM> from the tool.

According to an example, the first slot section S1 is delimited on one side by a guiding means that guides the electrical storage device <NUM> into the compartment.

According to aspects, the distance between the electrical storage device <NUM>, <NUM> and the wall of the battery compartment <NUM> is between <NUM> and <NUM>, and preferably about <NUM>. This distance may vary around the electrical storage device <NUM>.

The electrical storage device <NUM>, <NUM> may further comprise one or more electrical connectors <NUM> arranged to mate with corresponding contact strips <NUM> arranged in the battery compartment <NUM>. An example of these electrical connectors is seen more clearly in <FIG>. An opening in the enclosure of the electrical storage device <NUM>, <NUM> is formed in connection to the electrical connectors <NUM> such that a second portion <NUM> of the flow of cooling air leaks out to an exterior of the cut-off tool through the opening and via a second slot section S2 formed between the electrical storage device <NUM>, <NUM> and the wall of the battery compartment <NUM>. Thus, since the battery housing is not hermetically sealed around the electrical connectors <NUM>, the over pressure of cooling air inside the electrical storage device <NUM> generates a flow of air which exits via the electrical connectors and passes via the second slot section. Again, this flow of air exiting the machine via the slot must be overcome by dirt and slurry if it is to enter into the slot. This is unlikely since the leakage is of considerable flow relative to the more diffuse motion of the dust and slurry generated by the cutting operation. The electrical connectors are therefore kept clean and free of slurry during operation, which is an advantage, in particular since it becomes more easy to insert and to remove the electrical storage device <NUM> if the connectors and guiding means are clean. The second slot section S2 may, e.g., be delimited by the upper ridge structure <NUM> and the lower ridge structure <NUM> shown in <FIG>.

Finally, an air outlet <NUM> may also be formed in the electrical storage device enclosure opposite to the inlet aperture <NUM> to form a passage for cooling air to flow through the electrical storage device. A third slot section S3 can be formed by a distance between the air outlet <NUM> and the wall of the battery compartment <NUM>, such that a third portion <NUM> of the flow of cooling air <NUM> air leaks out to an exterior of the cut-off tool via the third slot section S3. This third slot section also provides a passage for cooling air to leak out via the slot, thereby keeping the space between the electrical energy device <NUM> top part and the battery compartment wall clean and free from dust and slurry.

<FIG> schematically illustrates a mass distribution of a work tool such as the cut-off tools discussed above in connection to <FIG>. It has been found that the weight distribution between parts of hand-held electrically powered cut-off tools comprising first and second parts arranged vibrationally isolated from each other can be optimized in order to obtain a more efficient cutting operation and at the same time a reduced operator discomfort due to vibrations propagating from the machine and to the operator via the handles.

De-vibrated petrol fueled cut-off tools are known, i.e., combustion engine powered tools. However, these known tools have sub-optimal weight distributions between the handle part and the part comprising the combustion engine and the cutting disc. Some known petrol powered cut-off machines have handle portions weighting about <NUM> with empty fuel tank and <NUM> with full tank compared to the motor and arm portion which weighs about <NUM>, i.e., an empty tank ratio of <NUM>/<NUM> (which amounts to about <NUM>,<NUM>), and <NUM>/<NUM> with a full tank (which is about <NUM>,<NUM>).

It is an advantage if the part with the handles, i.e., the masses M2 and M3 in <FIG>, is of a sufficient weight to withstand vibration propagating via the damping elements and the resilient elements discussed above. However, the part with the cutting blade, i.e., masses M1 and M4, cannot be too light in relation to the handle part, since this would result in an unbalanced tool.

It has been found trough experimentation and computer analysis that a ratio of the second mass M2 to the sum of the first and second masses M1+M2 should preferably be at least <NUM>,<NUM> and preferably more than <NUM>,<NUM>, i.e., the second mass should make up a considerable part of the total mass of the cut-off tool without cutting disc and electrical storage device mounted. The ratio M2/(M1+M2) can, for example, be about <NUM>,<NUM> for a <NUM> inch blade device and about <NUM>,<NUM> for a <NUM> inch blade device. The second mass M2 should, however, not be too large in relation to the first mass. Hence, the ratio of the second mass M2 to the sum of the first and second masses M1+M2 should preferably be below about <NUM>,<NUM> and preferably below about <NUM>,<NUM>.

It has also been found that a ratio of a sum of the second and the third mass (i.e., M2+M3) to the sum of the first and fourth masses (M1+M4) should be at least <NUM>,<NUM>, and preferably above <NUM>,<NUM> and even more preferably more than <NUM>,<NUM>. These ratios provide a well-balanced tool with excellent antivibration capability. It has also been found that a ratio of a sum of the second and the third mass (M2+M3) to the sum of the weight of the entire device including electrical energy storage and cutting disc (i.e., M1+M2+M3+M4) should be at least <NUM>,<NUM>, and preferably more than <NUM>,<NUM>. This ratio provides a stable tool with good antivibration characteristics.

To summarize, there has been disclosed herein a hand-held electrically powered cut-off tool <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> comprising a first part <NUM> and a second part <NUM> arranged vibrationally isolated from each other,.

There has also been disclosed herein a hand-held electrically powered cut-off tool <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> comprising a first part <NUM> and a second part <NUM> arranged vibrationally isolated from each other, a cutting tool <NUM> and an electrical storage device <NUM>,.

There has furthermore been disclosed herein a hand-held electrically powered cut-off tool <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> comprising a first part <NUM> and a second part <NUM> arranged vibrationally isolated from each other, a cutting tool <NUM> and an electrical storage device <NUM>,.

The table below provides an example weight distribution which may be used with advantage together with the hand-held electrically powered cut-off tools discussed herein. Examples for two different sizes of battery have been included in the table, a large battery weighting about <NUM> (denoted M32) and a smaller battery weighting about <NUM> (denoted M31).

The support arm <NUM> does not have to be thermally conductive, but should be arranged to at least partially enclose the electric motor <NUM>.

In the case of a thermally conductive support arm <NUM>, it may optionally comprises one or more cooling flanges <NUM> arranged to conduct heat away from the electric motor <NUM> via the support surface <NUM>.

The present disclosure also relates to a hand-held work tool <NUM>, <NUM>, <NUM>, <NUM> comprising an interface for holding a cutting tool <NUM>, an electric motor <NUM> arranged to drive the cutting tool, a battery compartment <NUM> for holding a battery <NUM> arranged to power the electric motor <NUM>, and the support arm <NUM> according to the above.

According to some aspects, hand-held work tool <NUM>, <NUM>, <NUM>, <NUM> comprises a fan <NUM>, configured to generate a flow of cooling air, and a belt guard <NUM>. The belt guard <NUM> and at least a part of the support arm <NUM> are configured to enclose an interior space <NUM>, wherein a portion of the flow of cooling air is arranged to be guided via at least one opening <NUM> into the interior space <NUM>, thereby increasing an air pressure in the belt guard <NUM> interior space <NUM> above an ambient air pressure level.

According to some aspects, the electric motor <NUM> is arranged to drive the fan <NUM>. According to some aspects, the rotational axis <NUM> of the electric motor <NUM> then coincides with the rotational axis <NUM> of the fan <NUM>. According to some aspects, the fan is propelled by a separate fan motor.

According to some aspects, a cooling air conduit is arranged to guide a portion of the flow of cooling air <NUM> towards the battery compartment <NUM> for cooling the battery <NUM>.

According to some aspects, the belt guard <NUM> and/or the support arm <NUM> comprises an air outlet <NUM> through which the flow of cooling air exits the interior space <NUM>, where the air outlet <NUM> is configured with an area such that the air pressure in the belt guard <NUM> interior space <NUM> increases above the ambient air pressure level by a desired amount during operation.

According to some aspects, the opening <NUM> has an area between <NUM><NUM> and <NUM><NUM>, and more preferably between <NUM><NUM> and <NUM><NUM> where the air outlet <NUM> has a an area between <NUM><NUM> and <NUM><NUM> and more preferably between <NUM><NUM> and <NUM><NUM>. In this context, an area of an opening or outlet is defined as a minimum area of an aperture that defines the opening or outlet. Each opening and outlet may be constituted by a respective plurality of smaller openings and/or outlets.

According to some aspects, the area of the air outlet <NUM> is greater than the area of the opening <NUM>. This is advantageous since this ensures that a sufficient amount of coolant air is led towards the electric motor.

According to some aspects, the air outlet <NUM> comprises a plurality of air outlets <NUM>, preferably more than four air outlets <NUM>, and more preferably more than ten air outlets <NUM>.

According to some aspects, the air outlet <NUM> is located at a rear end portion of either the belt guard <NUM> or the support arm <NUM>, said rear end portion being the portion of the belt guard <NUM> and support arm <NUM> that is closest to the user in a normal operative position of the hand held work tool.

According to some aspects, the air outlet <NUM> is located in the area of a lower portion of either the belt guard or the support arm, i.e. the portion of the belt guard <NUM> or support arm <NUM> that is closest to a surface in a normal rest position of the handheld work tool on said surface. In this way, water and slurry can be efficiently drained during work and during cleaning.

According to some aspects, the air outlet <NUM> is arranged as a through-hole in the belt guard <NUM>. This enables cost-effective manufacturing.

According to some aspects, the belt guard <NUM> is made of plastic and the support arm <NUM> is made of magnesium.

According to some aspects, the air outlet <NUM> is mainly positioned at a lower half of the belt guard <NUM> and/or the support arm <NUM> when the hand-held work tool <NUM>, <NUM>, <NUM>, <NUM> is in an upright rest position.

According to some aspects, wherein the opening <NUM> is a plurality of openings <NUM> located along a circle surrounding a rotational axis <NUM> of the electric motor <NUM>.

According to some aspects, the air outlet <NUM> comprises a plurality of outlets <NUM>. According to some aspects, these outlets <NUM> span over an angle relative to the rotational axis <NUM> of the motor axle, wherein said angle is greater than <NUM> degrees, and preferably more than <NUM> degrees, and wherein the air outlets <NUM> are preferably located at least partly to the rear of said axis, i.e. closer to the user in a normal operative position of the handheld work tool.

According to some aspects, a shortest distance D1 between the rotational axis <NUM> of the motor and the outlet <NUM> is greater than a shortest distance D2 between said rotational axis <NUM> and the opening <NUM>, as schematically indicated in <FIG> and <FIG>. It should be appreciated that according to some aspects, the rotational axis <NUM> of the electric motor <NUM> may coincide with the rotational axis <NUM> of the fan <NUM>.

According to some aspects, the support arm <NUM> comprises cooling flanges and wherein the opening <NUM> is located between a pair of cooling flanges.

Claim 1:
A support arm (<NUM>) for a hand-held work tool (<NUM>, <NUM>, <NUM>, <NUM>), the work tool comprising an electric motor (<NUM>) arranged to drive a circular cutting tool (<NUM>), wherein the support arm (<NUM>) is arranged to support the circular cutting tool (<NUM>) on a first end (<NUM>) of the support arm, and to support the electric motor (<NUM>) at a second end of the support arm (<NUM>) opposite to the first end (<NUM>), characterized in that the support arm (<NUM>) is arranged to at least partially enclose the electric motor (<NUM>).