TECHNICAL FIELD

The present invention relates to a handheld power tool having an exhaust gas cooling system.

BACKGROUND

Typically, a handheld power tool, for example (but not limited to) a hedge trimmer, includes a housing having an internal combustion engine. The engine is generally positioned with the top of a cylinder pointing in a forward direction. A muffler is connected to an exhaust port located on one side of the internal combustion engine. Generally, the exhaust gases are discharged towards the vegetation. The muffler usually includes a catalytic converter to substantially reduce the toxicity of the exhaust gases. However, the catalytic converter increases the temperature of the exhaust gases. Therefore, even though the exhaust gases are mixed with cooling air before being discharged, the temperature of the exhaust gases still remains substantially high. Thus, there is a risk of the vegetation getting burnt.

To prevent the vegetation getting burnt, certain prior art hedge trimmers are provided with a pipe for conveying the exhaust gases from the muffler to a region above a cutting unit of the hedge trimmer. However, the temperature of the exhaust gases still is higher than statutory limits.

To lower the temperature of the exhaust gases, some prior art hedge trimmers have an engine which is positioned such that the axial direction of the cylinder is substantially perpendicular to a longitudinal direction of the cutting unit. The muffler is thereby located at the front of the housing such that exhaust gases from the muffler undergo cooling by mixing with the cooling air. However, such an orientation of the engine may increase vibrations of the hedge trimmer.

Additionally, U.S. Published patent application No. 20100122674 (hereinafter referred to as '674 application), published on May 20, 2010 and assigned to Andreas Stihl, titled "Cooling Air Passage for a Motor Chain Saw", discloses a cooling arrangement for the exhaust gases of a motor chain saw. In the '674 application, the cooling air exits at a side of a housing of the motor chain saw. A fraction of the cooling air is then diverted to cool the exhaust gases which exit a muffler at the front of the housing. However, the fraction of the cooling air may not cool the exhaust gases sufficiently. Further, positioning the muffler at the front of the housing may not be optimum.

Further, U.S. Patent No. 4,890,690 (hereinafter referred to as '690 patent) issued on January 2, 1990, and assigned to Andreas Stihl, titled "Exhaust gas muffler for a two-stroke engine" discloses an exhaust guide tube conducting exhaust gases to a side of a housing from a muffler located at the front of the housing. The exhaust gas exiting the exhaust guide tube is entrained by cooling air flowing outwardly from the cylinder. However, discharging the exhaust gases at the side of the housing may not be favourable. Further, positioning the muffler at the front of the housing may not be optimum. This arrangement also fails to effectively cool down the temperature of the gases.

There is a need for an improved system for cooling exhaust gases discharged from handheld power tools, which will overcome the abovementioned disadvantages.

SUMMARY

In view of the above, it is an objective to provide an improved system for cooling the exhaust gases of a handheld power tool. In particular, an objective is to provide a handheld power tool exhaust cooling system that effectively cools the exhaust gases while overcoming the abovementioned disadvantages.

This objective is achieved by the invention as defined by claim 1 . In accordance with the present invention there is provided a handheld power tool comprising a housing enclosing an internal combustion engine with a muffler, the muffler being arranged on the left or right side of the handheld power tool drive unit and having an exhaust gas outlet for discharging exhaust gases of the internal combustion engine. The handheld power tool further includes a cutting unit extending from a front portion of the housing. Further, an outlet pipe is provided for conveying the exhaust gases from the exhaust gas outlet of the muffler and expelling them in an area located in front of the housing and above and/or aside said cutting unit. An air flow passage is formed from within the housing and through an outlet port arranged at the front of the housing for conveying cooling air to said area. Such an arrangement lowers the temperature of the exhaust gases below a threshold temperature.

According to claim 2, the outlet pipe includes a first end portion and a second end portion. The first end portion is positioned in close vicinity of the exhaust gas outlet of the muffler and the second end portion is positioned proximate to the outlet port of the air flow passage. As the second end portion of the outlet pipe is located proximate to the outlet port of the air flow passage, the exhaust gases and the cooling air mix efficiently and the exhaust gases are sufficiently cooled down.

According to claim 3, the second end of the outlet pipe and the outlet port of the air flow passage are positioned over the cutting arrangement. Since the exhaust gases are expelled over the cutting unit, and mixing of the exhaust gases and the cooling air occurs substantially over the cutting unit, the risk of vegetation getting burnt is reduced.

According to claim 4, the muffler is equipped with a catalytic converter. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be described in more detail with reference to the enclosed drawings, wherein:

FIG. 1 illustrates a perspective view of a handheld power tool, according to an embodiment of the present invention;

FIG. 2 illustrates a perspective view of the handheld power tool without a front handle, according to an embodiment of the present invention;

FIG. 3 illustrates another perspective view of the handheld power tool with a top cover removed, according to an embodiment of the present invention; and

FIG. 4 illustrates a perspective view of the handheld power tool with a left cover and muffler removed, according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of the invention incorporating one or more aspects of the present invention are illustrated. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For example, one or more aspects of the present invention can be utilized in other embodiments and even other types of devices. In the drawings, like numbers refer to like elements.

FIG. 1 illustrates a perspective view of a handheld power tool 100, according to an embodiment of the present invention. In the exemplary embodiment illustrated in FIG. 1 , the handheld power tool 100 is a hedge trimmer. However, the present invention may be used in any type of powered equipment, such as, but not limited to, chainsaws, rotary cutters, any other cutting or pruning tools, without departing from the essence of the present invention. In addition, any suitable size, shape or type of elements or materials could be used. Further, as used herein, the terms "left" and "right", used to describe the position of any component or portion, may in general refer to left and right sides of the handheld power tool 100 as viewed by an operator of the handheld power tool 100 during usage. Similarly, the terms "top" and "bottom", used to describe the position of any component or portion, may in general refer to the top and bottom of the handheld power tool 100.

The handheld power tool 100 includes a housing 102 having a front handle 104 arranged at a front portion 106 of the housing 102. Additionally, the housing 102 carries a starting handle 108 arranged on a rear portion 110 of the housing 102 and a rear handle (not illustrated) carrying a throttle trigger. The housing 102 encloses an internal combustion engine (illustrated in FIG. 3) provided with a muffler (not illustrated). The engine also includes a cylinder and a crankcase. The muffler is connected to an exhaust port of the internal combustion engine (hereinafter referred to as "the engine"). The muffler reduces noise emanating from the exhaust gases. The muffler may also include a catalytic converter to substantially reduce toxicity of the exhaust gases.

As illustrated in FIG. 1 , the housing 102 is of a modular construction. Specifically, the housing 102 includes a front cover 111, a top cover 112, a left cover 114 and a right cover 116. The muffler is mounted on the left side of the engine and the left cover 114 at least partially covers the muffler. Alternatively, the muffler may be mounted on the right side of the engine and the right cover 116 at least partially covers the muffler. A combustion air supply assembly (not shown) for the engine is arranged on the right side of the housing 102 and at least partially enclosed by the right cover 116. In case the muffler is arranged on the right side of the housing 102, the combustion air supply assembly is arranged on the left side of the housing 102. Further, the handheld power tool 100 includes a cooling air supply assembly (illustrated in FIG. 3) for supplying cooling air and/or combustion air to the engine and other components of the handheld power tool 100. The cooling air supply assembly is mounted in a top portion of the housing 102 and is at least partially covered by the top cover 112. It is apparent to a person ordinarily skilled in the art that the various details of the housing 102 as described above are purely exemplary in nature, and the housing 102 may be of any other shape or configuration without departing from the scope of the present invention.

As illustrated in FIG, 1, the handheld power tool 100 further includes a cutting unit 118. The cutting unit 118 extends from the front portion 106 of the housing 102. The cutting unit 118 includes a first blade 120 and a second blade 122. Each of the cutting blades 120 and 122 includes cutting members 124 on both sides. Alternatively, cutting members 124 may be present on only one side of the cutting blades 120 and 122. An end portion of each of the pair of cutting blades 120 and 122 is connected to a transmission assembly such the cutting blades 120 and 122 are driven in an oscillating manner. It is apparent to a person ordinarily skilled in the art that the handheld power tool 100 may include any other type of cutting unit 118, such as, but not limited to, a saw chain, a rotary blade, or the like.

As illustrated in FIG. 1 , a guide portion 126 is located at the front of the housing 102. The guide portion 126 is in fluid communication with an outlet port for cooling air and an outlet pipe for exhaust gases (described in FIG. 2). The guide portion 126 guides the mixture substantially in the longitudinal direction of the cutting unit 118 as indicated by an arrow 128.

FIG. 2 illustrates a perspective view of the handheld power tool 100 without the front handle 104 and the guide portion 126, according to an embodiment of the present invention. As illustrated in FIG. 2, the handheld power tool 100 includes an outlet pipe 202 for conveying the exhaust gases from an exhaust gas outlet of the muffler. The outlet pipe 202 is configured to expel exhaust gases, as indicated by an arrow 204, in an area 206 located in front of the housing. The outlet pipe 202 may expel the exhaust gases above and/or aside the cutting unit. The outlet pipe 202 includes a first end portion (illustrated in FIG. 4) and a second end portion 207. The first end portion is positioned in close vicinity to the exhaust gas outlet of the muffler, such that the exhaust gases are ejected into the outlet pipe 202. In order not to transfer vibrations from one part to another, the outlet pipe is not directly connected to the muffler. The exhaust gases are expelled through the second end portion 207.

Further, the handheld power tool 100 includes an outlet port 208 arranged at the front portion 106 of the housing 102. The outlet port 208 conveys cooling air from one or more air flow passages (illustrated in FIG. 3) formed from within the housing 102. The outlet port 208 may expel cooling air over and/or aside of the cutting unit 118. The guide portion 126 is in fluid communication of the outlet port 208 to guide cooling air to an area in front of the housing 102. The second end portion 207 of the outlet pipe 202 is located proximate to the outlet port 208 such that exhaust gases from the second end portion 207 and cooling air from the outlet port 208 mix with each other in the area 206 located in front of the housing 102. This may result in an efficient cooling of the exhaust gases, thereby substantially lowering a temperature of exhaust gases below a threshold temperature. Efficient cooling may be especially necessary in case the muffler includes a catalytic converter which increases the temperature of the exhaust gases. Thus, burning of vegetation exposed to exhaust gases is substantially prevented. Moreover, exhaust gases are discharged in the area in front of the housing 102 opposite to where an operator of the handheld power tool 100 is located.

It may be apparent to a person ordinarily skilled in the art that the shape and size of the outlet pipe 202 and the outlet port 208 are for illustrative purposes only, and the outlet pipe 202 and the outlet port 208 may be of any other shape or size within the scope of the present invention. For example, the outlet pipe 202 may have a non-circular cross-section, such as, rectangular, elliptical, or the like. Further, the outlet port 208 may have a circular or an elliptic shape.

FIG. 3 illustrates another perspective view of the handheld power tool 100 with the top cover 112 removed, according to an embodiment of the present invention. As illustrated in FIG. 3, a longitudinal direction of the cylinder 302 is substantially parallel to the longitudinal direction of the cutting blades, which means that a reciprocating movement of a piston inside the cylinder 302 is substantially parallel to an oscillating movement of the cutting blades 120 and 122. This arrangement may substantially decrease vibrations of the handheld power tool 100 as compared to if the cylinder 302 is positioned substantially perpendicular to the cutting blades 120 and 122. However, it may be apparent to a person ordinarily skilled in the art that the cylinder 302 may be aligned at any other orientation (For example, oblique) within the scope of the present invention.

As illustrated in FIG. 3, the air flow passage 304 is formed within the housing

102. The air flow passage 304 receives cooling air from the cooling air supply assembly 305. The cooling air supply assembly 305 includes a fan wheel 306 which draws in ambient air through one or more openings (not illustrated) in the housing 102. The fan wheel 306 may be radial, axial, or the like. The fan wheel 306 may be driven by a crankshaft of the engine 303. The cooling air supply assembly 305 may further include one or more guides (not illustrated) to control a flow of ambient air. In this embodiment, a part of the ambient air, which is drawn in by the fan wheel 306, may be diverted to the combustion air supply assembly and another part may be supplied as cooling air for one or more components of the handheld power tool 100. In an alternate embodiment of the present invention, the fan wheel 306 may only supply cooling air.

As illustrated in FIG. 3, cooling air flows through the air flow passage 304 as indicated by arrows 308. The air flow passage 304 is configured in such a way that it causes cooling air to impinge against the cylinder 302. The cylinder 302 may include one or more fins to enhance cooling. Subsequently, the air flow passage 304 conveys cooling air to flow through the outlet port 208. Cooling air then substantially flows through the guide portion 126. FIG. 4 illustrates a partial perspective view of the handheld power tool 100 with the left cover 114 and the muffler removed, according to an embodiment of the present invention. As illustrated in FIG. 4, the outlet port 208 is at least partially formed in the front cover 111 of the housing 102. The second end portion 207 of the outlet pipe 202 is inclined at an angle with respect to a substantially horizontal portion 404 of the outlet pipe 202. This inclination directs the exhaust gases such that they are efficiently mixed with the cooling air. The first end portion 402 has an expanded region giving the first end portion 402 a funnel like shape. This design creates an ejector effect, which causes ambient air to be drawn into the outlet pipe 202 and to mix with the exhaust gases. Thereby the cooling of the exhaust gases begins already in the outlet pipe 202. The outlet pipe 202 is retained in a fixed position by a holder 406.

Though the above mentioned invention explains the working with respect to a hedge trimmer, a person skilled in the art may know that such a system may be easily implemented on other tools like, but not limited to, chainsaws.

In the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims.