Cooling device for a motor saw

Abstract

A hand-held chainsaw with an internal combustion engine, wherein the internal combustion engine comprises a crankcase, a cylinder, a muffler, and a fan wheel arranged on one side of the crankcase, wherein a guide rail receptacle is arranged on the crankcase on a side opposite the fan wheel, and wherein the muffler is attached to screw bosses on the crankcase. The fan wheel directs cooling air along the outer walls of the cylinder and the crankcase, with a portion of the cooling air flowing in a gap between the muffler wall and the crankcase.A silencer wall is curved in one area towards the inside of the silencer in such a way that an air guidance area is created between the crankcase and the silencer wall that is larger than the gap, which has an inlet on one side of the silencer facing the fan wheel and an outlet on one side facing the guide rail mount, the outlet opening in the area of ​​a screw dome.

Description

[0001] The invention relates to a hand-held portable chainsaw with an internal combustion engine according to the preamble of claim 1.

[0002] German patent DE 10 2008 057 405 A1 describes a chainsaw with an internal combustion engine in which the engine drives a saw chain running on a guide bar. The engine also drives a fan that supplies cooling air to a cylinder of the engine, which flows within a housing surrounding the engine. The patent further describes the diversion of partial airflows for cooling other components, such as an exhaust silencer. It refers to technical solutions designed to prevent this diversion of partial airflows from impairing the cooling of the cylinder.

[0003] From EP 3 489 481 A1, a hand-held work device with an internal combustion engine and a fan wheel for supplying cooling air to the internal combustion engine is known. In addition to an outlet opening for the cooling air provided in a fan wheel housing, the work device has an additional through-opening in a front area of ​​the fan wheel housing, through which cooling air flows from the fan wheel housing to the outside of the crankcase.

[0004] US patent 2004 / 0206312A1 discloses an air-cooled, four-stroke internal combustion engine that incorporates a fan to generate a cooling airflow. The engine also features an oil pan with a cavity beneath it to allow cooling air to flow through.

[0005] From DE 41 20 877 A1, a power tool, in particular a chainsaw, is known, comprising a housing and an air-cooled internal combustion engine. A cylinder of the internal combustion engine is cooled by an airflow flowing transversely to the housing. The power tool also has a silencer, which is essentially L-shaped, with the silencer housing forming a guide wall for the cooling airflow.

[0006] From DE 37 13 074 A1, a chainsaw is known which has a housing with an engine chamber and an adjacent silencer chamber. In some sections, the silencer chamber has, in addition to an outer wall, an inner wall running parallel to it, thereby forming an air-filled thermal insulation space in part of the silencer chamber. This prevents the outer wall of the silencer chamber from overheating and thus prevents injury to the user.

[0007] From DE 44 20 530 A1 a hand-held work device with an air-cooled combustion engine and a cooling air blower is known, in which a channel is arranged on the pressure side of the blower to divert a portion of the main airflow without particles and supply it to the carburetor as combustion air.

[0008] The technological advancements in internal combustion engine-powered chainsaws have led to the use of increasingly powerful engines while maintaining roughly the same weight and housing size. This makes adequate cooling of the cylinder and other critical components very challenging. For example, it has been shown that the screw bosses, to which the muffler is attached to the magnesium crankcase, reach temperatures where the magnesium can melt in the threaded area. This can cause these screw connections to loosen and subsequently detach due to engine vibrations. Another challenge is that certain temperature differences around the outside of the cylinder must not be exceeded, as otherwise deviations in the cylinder or piston cross-section from a round shape would occur.In the worst-case scenario, this could lead to the piston seizing in the cylinder. Combined with the limited installation space described above, this means that even small changes to the cooling airflow pattern can cause temperature tolerances to be exceeded at other points in the cylinder.

[0009] The invention is based on the objective of ensuring sufficient cooling of the screw domes of the silencer and at the same time ensuring that the differences in temperatures occurring in the circumferential direction on the cylinder do not exceed the permissible limits.

[0010] The problem is solved according to the invention by the characterizing features of claim 1. By curving a portion of the silencer wall towards the inside of the silencer, an airflow area is created that is larger than the remaining gap areas between the silencer wall and the crankcase wall. By designing such an airflow area between the crankcase and a suitable area of ​​the silencer wall, a small partial airflow is directed with low flow resistance from the cooler side of the chainsaw, facing the fan wheel, to a screw boss located on the opposite, warmer side. In this way, the screw boss, where the highest temperatures occur, can be sufficiently cooled without diverting too much of the cooling air supplied to the cylinder.The lower part of the rear wall of the silencer has proven to be a suitable area. This area serves, among other things, as a flow guide element, deflecting a portion of the cooling airflow, which flows around the lower front part of the cylinder, upwards towards the upper part of the cylinder. By designing the inlet area in this section of the silencer wall, which is directly exposed to the fan wheel, a portion of the airflow, flowing at a comparatively high velocity, can be efficiently diverted towards the screw dome, which experiences the highest temperatures.

[0011] The air guide section comprises a first section extending essentially transversely from the inlet towards the side of the silencer facing the guide rail mount, and a second section fluidly connected to the first section, extending along the side of the silencer facing the guide rail mount and essentially longitudinally towards the outlet. This design allows cooling air to be conveyed along the shortest possible path from the cooler side to the warmer side and to the screw boss located further forward. Consequently, the resulting flow losses and pressure losses can be reduced to a minimum.

[0012] The second section runs essentially coaxially with the screw boss of one of the bolts that attach the silencer to the crankcase. This causes the cooling air to flow along the longitudinal axis of this bolt, thus increasing the time for heat transfer from the screw boss to the cooling air.

[0013] The outlet is shaped so that air flows out of the air guide area in two partial flows in the circumferential direction of the screw boss. In this way, the screw boss can be cooled as effectively as possible.

[0014] Both sections of the air duct have a cross-sectional shape that is essentially circular arcs. This design allows for very low-resistance flow of the partial airflow.

[0015] The cross-section of the air duct area remains essentially constant along its entire length. Maintaining this cross-section allows the flow velocity to be kept nearly constant despite the necessary geometric changes along the length of the air duct area, thus minimizing flow and pressure losses.

[0016] The radius of the circular arc cross-section of the first section is smaller than the radius of the circular arc cross-section of the second section. This results in a narrower, taller passage in the first section of the air ducting area and a wider, shallower passage in the second section. This allows a comparatively small portion of the cooling airflow to be diverted and subsequently directed along a larger surface area of ​​the screw boss.

[0017] A first maximum distance between the crankcase wall and the silencer wall, located in the first section of the air duct area, is at least twice as large as a second maximum distance between the crankcase wall and the silencer wall, located in a first gap area adjacent to a first side of the air duct area, or as large as a third maximum distance between the crankcase wall and the silencer wall, located in a second gap area adjacent to a second side of the air duct area. Due to the significantly larger cross-section of the air duct area compared to the adjacent gap areas, the cooling air can flow to the screw dome to be cooled with a significantly reduced pressure loss.

[0018] In the silencer wall, a bore is provided in the area of ​​the air guide outlet for a screw to the screw boss. In the area of ​​this bore, a portion of the silencer wall, within the arc-shaped cross-section of the air guide, also features a further, smaller bulge towards the interior of the silencer. This increases the distance between the portion of the silencer wall forming the air guide and the portion of the silencer wall containing the bore. This helps to counteract the formation of cracks due to vibrations in this highly stressed part of the silencer wall.

[0019] Further features of the invention will become apparent from the description and the drawings, in which an embodiment of the invention is illustrated. The drawings show: Fig. 1 a supervisor of a hand-held chainsaw with an internal combustion engine, Fig. 2a side view of a hand-held chainsaw with an internal combustion engine, Fig. 3 an isometric view of a hand-held chainsaw with an internal combustion engine and a mounted muffler, Fig. 4 an isometric view of a hand-held chainsaw with an internal combustion engine without a mounted muffler and Fig. 5 An isometric view of an unmounted rear shell of a muffler for a handheld chainsaw with an internal combustion engine.

[0020] The in Fig. 1 The chainsaw shown has a housing 1 on, in which an internal combustion engine is arranged, which has a crankcase 2 and a cylinder attached to it 3 exhibits. On one side of the crankcase. 2 is a fan wheel 4 arranged, driven by a shaft of the internal combustion engine. On one of the fan wheels 4 opposite side of the crankcase 2is a guide rail mount 5 arranged. The guide rail mount 5 It is designed to accommodate a guide rail to which a saw chain driven by the combustion engine can be mounted. In the cylinder 3 A piston is arranged which drives the crankshaft, and thus the drive shaft of the internal combustion engine, via a connecting rod. Parallel to the guide rail mount 5 The chainsaw has a longitudinal direction. A transverse direction runs perpendicular to the longitudinal direction of the chainsaw. In the following description, the side of the chainsaw where the cylinder is located will be referred to as the side where the cylinder is located. 3 is located as the upper side and the side of the chainsaw where the crankcase is located. 2 The area is considered the lower side. Furthermore, the end where the guide bar mount is located is considered longitudinally along the chainsaw. 5The front end of the chainsaw is considered the front end, and the opposite end is considered the rear end of the chainsaw.

[0021] As in Fig. 2 As can be seen, the crankcase 2 and the cylinder 3 a silencer 6 attached to the silencer 6 It is a hollow body consisting of a front shell. 7 and a rear shell 8 is composed of... Regarding the front shell... 7 and the rear shell 8 These are all deep-drawn sheet metal parts.

[0022] As in the Figs. 3 and 4 As can be seen, the silencer 6 with screws on screw bosses 9 attached, which are in the crankcase 2 are provided. Regarding the crankcase 2 It is a component made of magnesium. The silencer 6 It is also attached to the cylinder with screws. 3attached that a rear wall 10 on part of the cylinder 3 is located. The threaded holes provided for this purpose in the cylinder. 3 are located near an exhaust outlet 11 in the cylinder 3 arranged by the exhaust gas from the combustion chamber of the cylinder 3 in the silencer 6 can flow. Between parts of the silencer wall 12 and parts of the crankcase wall 13 remains in the mounted state of the silencer 6 a comparatively narrow gap 14. The fan wheel 4 is designed to allow cooling air to circulate between the inside of the housing 1 and the outer surfaces of the cylinder 3, of the crankcase 2 and the silencer 6 to promote. On the side of the chainsaw where the fan wheel is located. 4When located, outside air is drawn in and directed towards the side of the chainsaw where the guide bar mount is located. 5 is located on the side of the chainsaw where the fan wheel is located. For this reason, the side of the chainsaw where the fan wheel is located is 4 is located slightly cooler than the side of the chainsaw where the guide rail mount is located. 5 This is further exacerbated by the fact that on the side of the chainsaw where the guide bar mount is located... 5 Hot exhaust gas flows out of the silencer. This uneven temperature distribution must not exceed a certain level. Should it occur in the circumferential direction of the cylinder... 3 If one side is significantly hotter than the opposite side, this could, in extreme cases, lead to the cylinder bore warping. 3or the piston's cross-sections might deviate too much from a round shape. This could then lead to damage to the internal combustion engine. To counteract this, a comparatively high level of effort is invested in developing the airflow pattern for cooling air around the cylinder. 3 operated around. It is known that even small structural changes at one point inside the housing 1 This could lead to exceeding the permissible maximum temperatures during operation of the chainsaw at another point.

[0023] It is also known that with chainsaws of the described design, a screw boss located on the generally warmer side of the chainsaw can cause problems. 9 in the crankcase 2 Furthermore, the temperature during operation of the chainsaw can rise to around 130°C. At these temperatures, magnesium, from which the crankcase is made, can degrade. 2Once manufactured, fluids begin to flow. To reliably prevent failure of this bolted connection, improved cooling is provided in this area.

[0024] As in Fig. 5 As can be seen, there is the aforementioned narrow gap. 14 between parts of the silencer wall 12 and parts of the crankcase wall 13 in certain areas, the silencer wall is enlarged by partially arcing in a circular arc towards the inside of the silencer. 6 It is curved. This creates a tunnel-shaped air duct area. 15 between parts of the silencer wall 12 and parts of the crankcase wall 13. The air duct area 15 or air duct is bounded on both sides by areas where the distance between the silencer wall 12 and the crankcase wall 13significantly less than in air duct area 15. In the following, only those laterally adjacent to the air duct area will be discussed. 15 adjacent areas between the silencer wall 12 and the crankcase wall 13 considered as a gap or gap area and not all areas where the silencer wall 12 and the crankcase wall 13 They are opposite each other. The distance between the silencer wall 12 the crankcase wall 13 May vary, but all are located in the air duct area. 15 Adjacent areas should have a maximum distance between the silencer wall 12 and the crankcase wall 13 be smaller than half of the maximum distance between the silencer wall 12 and the crankcase wall 13 inside the air duct area 15.

[0025] A first section 16 of the tunnel-shaped air duct area15 is in the lower part of the rear wall 10 the rear shell 8 shaped. The first section 16 runs from one side of the silencer 6, the one on the fan wheel 4 the cooler side of the chainsaw facing the silencer is located on one side. 6, the guide rail mount 5 The warmer side of the chainsaw is located near the fan wheel. 4 facing side of the first section 16 There is an entrance 17. The first section begins here 16 directly with one of the fan wheel 4 generated cooling airflow. At the guide rail mount 5 facing side of the rear shell 8 is a second section 18 of the tunnel-shaped air duct area 15, the fluidic with the first section 16It is connected. It runs lengthwise along the chainsaw from the lower part of the rear wall. 10 the rear shell 8 towards a flange area 19 the rear shell 8. In this flange area 19 When assembled, the front shell lies 7 and the rear shell 8 to each other. For connecting the front shell 7 and the rear shell 8 together and for attaching the entire silencer 6 on the crankcase 2 are drill holes 20 in this flange area 19 planned. The drilling 20 on the lower side of the silencer 6 are designed for the insertion of screws into screw bosses 9 in the crankcase 2 are screwed in. The longitudinal axes of the screw bosses 9These run along the length of the chainsaw. The longitudinal axis of the second section 18 It also runs in the longitudinal direction of the chainsaw, with the second section 18 is arranged so that it rests on the guide rail mount 5 screw dome facing the warmer side of the chainsaw 9 essentially surrounds it coaxially. This design of the airflow area... 15 can a partial flow of the airflow from the fan wheel 4 generated cooling airflow from the cooler side of the chainsaw to the screw dome located on the warmer side 9 to be channeled across, where it flows along this over a large area until it reaches an outlet. 21 empties in. The outlet 21 It is designed in such a way that air flows in two partial streams in the circumferential direction of the screw dome. 9 from the air duct area 15 flows out. In the area of ​​the outlet. 21is part of the silencer wall 12 In addition to the arc-shaped bulge towards the inside of the silencer, there is another arc-shaped bulge towards the inside of the silencer. This additional, smaller bulge... 22 The distance between the silencer wall increases 12 for drilling 20, which increases the strength of the silencer at this point. It has been shown that the screw boss 9 The cooling device described above reduces the temperature by up to 10°C compared to operating without such a device. Nevertheless, this form of diverting a partial flow from the fan wheel leads to... 4 The generated cooling airflow does not cause parts of the cylinder to overheat or excessively large temperature differences to occur around the cylinder. Reference symbol list

[0026] 1 Housing 2 crankcase 3 cylinder 4 fan wheel 5Guide rail mount 6 silencer 7 Front shell 8 Rear shell 9 Screw bosses 10 back wall 11 exhaust outlet 12 Silencer wall 13 Crankcase wall 14 gap 15 air duct area 16 First section 17 inlet 18 Second section 19 Flange area 20 Drilling 21 Outlet

Claims

1. Hand-held chainsaw with an internal combustion engine, wherein the internal combustion engine comprises a crankcase (2), a cylinder (3), a silencer (6), and a fan wheel (4) arranged on one side of the crankcase (2), wherein a guide rail receptacle (5) is arranged on the crankcase (2) on a side of the crankcase (2) opposite the fan wheel (4), wherein the silencer (6) is attached to screw bosses (9) of the crankcase (2) by means of screws, and wherein the fan wheel (4) is designed to convey cooling air along outer walls of the cylinder (3) and the crankcase (2), wherein a portion of the cooling air flows in a gap (14) between the silencer (6) and the crankcase (2), wherein the gap (14) is at least partially bounded by a silencer wall (12) and a crankcase wall (13).wherein the chainsaw has a longitudinal direction running parallel to the guide rail mount (5) and a transverse direction running orthogonally to it, characterized by the fact that the silencer wall (12) and / or the crankcase wall (13) are shaped at least in one area such that an air guide area (15) larger than the gap (14) is created between the crankcase wall (13) and the silencer wall (12), which has an inlet (17) on a side of the silencer (6) facing the fan wheel (4) and an outlet (21) on a side facing the guide rail receptacle (5), wherein the outlet (21) opens in the area of ​​one of the screw bosses (9).

2. Hand-held chainsaw according to claim 1, wherein an inlet area is designed to be acted upon by a partial airflow generated by the fan wheel (4).

3. Hand-held chainsaw according to one of the preceding claims, wherein the air guide area (15) has a first section (16) extending substantially from the inlet (17) in a transverse direction to the side of the silencer (6) facing the guide rail receptacle (5) and a second section (18) fluidically connected to the first section (16) and extending along the side of the silencer facing the guide rail receptacle (5) and substantially in a longitudinal direction to the outlet (21).

4. Hand-held chainsaw according to one of the preceding claims, wherein the second section (18) extends substantially coaxially to the screw boss (9) of one of the screws fastening the silencer (6) to the crankcase (2).

5. Hand-held chainsaw according to one of the preceding claims, wherein the outlet (21) is shaped such that air flows out of the air guide area (15) in two partial flows in the circumferential direction of the screw dome (9).

6. Hand-held chainsaw according to one of the preceding claims, wherein both sections of the air guidance area (15) are substantially arc-shaped in cross-section.

7. Hand-held chainsaw according to one of the preceding claims, wherein the cross-section of the air guide area (15) remains substantially constant over its entire length.

8. Hand-held chainsaw according to one of the preceding claims, wherein a radius of the arc-shaped cross-section of the first section (16) is smaller than a radius of the arc-shaped cross-section of the second section (18).

9. Hand-held chainsaw according to one of the preceding claims, wherein a first maximum distance between the crankcase wall (13) and the silencer wall (12) located in the area of ​​the first section (16) of the air guidance area (15) is at least twice as large as a second maximum distance between the crankcase wall (13) and the silencer wall (12) located in a first gap area adjacent to a first side of the air guidance area (15) or as a third maximum distance between the crankcase wall (13) and the silencer wall (12) located in a second gap area adjacent to a second side of the air guidance area (15).

10. Hand-held chainsaw according to one of the preceding claims, wherein a bore (20) for the passage of a screw to the screw boss (9) is provided in the silencer wall (12) in the area of ​​the outlet (21) of the air guide area (15) and wherein a part of the silencer wall (12) in the area of ​​this bore (20) in the area of ​​the arc-shaped cross-section of the air guide area (15) additionally has a further, smaller bulge (22) towards the interior of the silencer.

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