hand-held tool

Abstract

A hand-held power tool (1) has an internal combustion engine (5) with one cylinder (9). The cylinder (9) has cooling fins (22, 22a, 22b, 26). The internal combustion engine (5) has a crankshaft (16). A fan (24) is arranged in a fan housing (25) on one side (29) of the internal combustion engine (5) and conveys a cooling airflow (37) to the cylinder (9). The fan (24) is driven by the crankshaft (16) about a pivot axis (17). The cylinder (9) has first cooling fins (22, 22a, 22b) extending along the fan side (29) of the internal combustion engine (5). A cooling air channel (31) is formed between two adjacent first cooling fins (22, 22a, 22b). The cylinder (9) has a transverse rib (23) which extends in the cooling air duct (31) transversely to the two first cooling ribs (22a and 22b).

Description

The invention relates to a hand-held work device of the type specified in the preamble of claim 1. From DE 10 2015 013 784 A1, a hand-held work device with an internal combustion engine is known. The cylinder of the internal combustion engine has cooling fins over which cooling air flows. DE 21 56 754 B discloses a cylinder for a two-stroke engine in which adjacent cooling fins are connected to each other in pairs via webs. The AT 414 263 B shows an air-cooled internal combustion engine in which the cooling fins of the cylinder are arranged in such a way as to divide the cooling airflow between an exhaust-side side wall and the top surface of the cylinder. AT 003 672 U1 shows an internal combustion engine in which the cooling fins of the cylinder have a curved stiffening area in which the cooling fin wall is arranged outside a cooling fin plane. A hand-held power tool comprises an internal combustion engine, the internal combustion engine having a cylinder with cooling fins. The internal combustion engine has a crankshaft. A fan wheel is arranged in a fan housing on one side of the internal combustion engine, conveying a cooling airflow to the cylinder. The cylinder has first cooling fins extending along the fan wheel side of the internal combustion engine. A cooling air channel is formed between two adjacent first cooling fins. According to the invention, the cylinder has a transverse fin extending in the cooling air channel transversely to the two first cooling fins. It has been shown that the cylinder is often very well cooled on the fan wheel side, as a large portion of the cooling air flows along this side of the cylinder. It has also been shown that it is advantageous for the cylinder to be cooled as uniformly as possible during operation in order to maintain the roundness of the cylinder bore relatively well, even when the cylinder heats up. In hand-held power tools, there is often insufficient installation space to implement the desired size of cooling fins on each side of the cylinder. The transverse fin, which extends perpendicular to the first two cooling fins in the cooling air duct, at least partially obstructs the free flow cross-section of the cooling air duct. This allows for a simple reduction in the amount of cooling air flowing along the fan wheel side during operation and an increase in the amount flowing along the adjacent side of the cylinder.The transverse rib is an integral part of the cylinder, specifically molded as a single unit and therefore easily manufactured. No additional components are required. The transverse rib and the cylinder are typically produced together in a single casting process. In particular, the transverse rib is designed to be shorter than at least one of the first cooling fins that defines the cooling air channel. The height of the transverse rib is measured midway between the two first cooling fins, and the height of the first cooling fins is measured at the transverse rib. Because the transverse rib is shorter than at least one of the first cooling fins that defines the cooling air channel, it only partially obstructs the cooling air channel formed between the two cooling fins. By appropriately designing the height of the transverse rib, the amount of cooling air flowing along the fan wheel side can be easily adjusted within certain limits. Specifically, the height of the transverse rib is at least half the height of at least one of the two first cooling fins. The transverse rib extends, in particular, from one cooling rib to the other that defines the cooling air duct. However, it can also be provided that the transverse rib does not completely close off the cooling air duct with respect to a width of the cooling air duct measured between the cooling ribs. For this purpose, it is specifically provided that the transverse rib does not extend from one cooling rib to the other that defines the cooling air duct. In particular, the transverse rib extends over at least 60% of the flow cross-section of the cooling air duct directly upstream of the transverse rib. The internal combustion engine has, in particular, a central plane that contains a longitudinal axis of the cylinder and runs parallel to the axis of rotation of the fan wheel. Specifically, the cooling airflow travels from the fan housing to the cylinder on a first side of this central plane. The transverse rib is also located on this first side of the central plane of the internal combustion engine. Because the transverse rib and the transfer of the cooling airflow from the fan housing to the cylinder occur on the same side of the central plane, the cooling airflow can be directed to an adjacent side of the cylinder before excessive heating of the cooling airflow occurs on the fan wheel side of the cylinder. In particular, at least one first cooling fin bounding the cooling air channel has a recess upstream of the transverse fin, relative to the direction of the cooling airflow. Specifically, the first cooling fin furthest from the fan wheel has this recess. The recess allows a portion of the cooling airflow to easily pass to the side of the cylinder adjacent to the fan wheel. In particular, several first cooling fins have a recess upstream of the transverse fin. This allows the cooling airflow to flow through the recess in the cooling fins in the direction of the cylinder's longitudinal axis and thus distribute itself effectively across the cooling fins in the direction of the cylinder's longitudinal axis. In particular, the first cooling fin at the recess has a lower height than at the transverse fin. The recess is specifically formed by the reduced height of the first cooling fin. Alternatively, the recess can also be formed by an opening in at least one of the first cooling fins. In particular, a second cooling fin is arranged between the two first cooling fins that define the cooling air channel, at least upstream of the transverse fin. The second cooling fin extends, in particular, to the transverse fin. The second cooling fin improves heat dissipation upstream of the transverse fin. The second cooling fin has a lower height, measured at the transverse fin, than the transverse fin. In particular, the first cooling fins in a side view of the internal combustion engine are arranged at an angle towards the axis of rotation relative to the cylinder's longitudinal axis. This allows for an aerodynamically optimized arrangement of the cooling fins and prevents excessive deflection of the cooling airflow from the fan housing to the cylinder. In particular, the work device includes a tool, and the combustion engine is intended to power the tool. The hand-held work device can, for example, be a chainsaw, and the tool a saw chain. An embodiment of the invention is explained below with reference to the drawing. The drawings show: Fig. 1 a schematic side view of a work device, Fig. 2 a schematic sectional view of the internal combustion engine of the work device from Fig. 1, Fig. 3 a schematic side view of the fan wheel and the cylinder of the work device from Fig. 1, Fig. 4 a partial perspective view of the cylinder and the fan wheel of the work device, Fig. 5 a schematic top view of the hand-held work device in the direction of arrow V in Fig. 1. Fig. 1 shows a chainsaw as an exemplary embodiment of a hand-held power tool 1. The hand-held power tool 1 can also be another type of power tool, for example, an angle grinder, a brush cutter, a pole pruner, a blower, or the like. The power tool 1 has a housing 2 to which a handle 3 and a grip tube 4 are attached. The power tool 1 has an internal combustion engine 5. Control elements for operating the internal combustion engine 5 can be arranged on the handle 3, which is designed, in particular, as a rear handle. The power tool 1 has a tool 7. The internal combustion engine 5 serves to drive the tool 7. In the exemplary embodiment, the tool 7 is a saw chain that is guided circumferentially on a guide rail 6. During operation, the tool 7 is driven circumferentially by the internal combustion engine 5 on the guide rail 6. Instead of the saw chain, another tool can also be used. The internal combustion engine 5 comprises a crankcase 8 and a cylinder 9. The cylinder 9 has a longitudinal axis 10. The design of the internal combustion engine 5 is shown in detail in Fig. 2. In the exemplary embodiment, the internal combustion engine 5 is a two-stroke engine. However, the internal combustion engine 5 can also be a four-stroke engine, in particular a four-stroke engine with premix lubrication. In particular, the internal combustion engine 5 is a single-cylinder engine. As Fig. 5 shows, a combustion chamber 12 is formed in the cylinder 9. The combustion chamber 12 is bounded by a piston 14 which is mounted to reciprocate within the cylinder 9. A spark plug 13 projects into the combustion chamber 12. During operation, the piston 14 drives a crankshaft 16, which is rotatably mounted in the crankcase 8 about an axis of rotation 17, via a connecting rod 15. A crankcase interior 28 of the crankcase 8 is connected to the combustion chamber 12 in the region of the bottom dead center of the piston 14 via at least one transfer port 18, and in the exemplary embodiment via several transfer ports 18.The transfer ports 18 open into a cylinder bore 11 of the cylinder 9 via transfer ports 19. An inlet port 20 is formed in the cylinder bore 11, which in this embodiment is controlled by the piston 14. An intake port 42 opens into the inlet port 20. An exhaust port 21 leads from the combustion chamber 12. The exhaust port 21 is primarily controlled by the piston 14. An exhaust port 43 connects to the exhaust port 21. The movement of the piston 5 from the crankcase 8 to the combustion chamber 12 is hereinafter referred to as the upward stroke of the piston 14. The movement of the piston 14 from the combustion chamber 12 to the crankcase 8 is hereinafter referred to as the downward stroke of the piston 14. Fuel is supplied to the internal combustion engine 5 via a fuel supply device (not shown), for example, a fuel valve or a carburetor. The fuel can be supplied to the intake port 42, the crankcase interior 28, one or more transfer ports 18, and / or the combustion chamber 12. During the operation of the internal combustion engine 5, on the upward stroke of the piston 14, after the opening of the intake port 20, air or a fuel / air mixture is drawn from the intake manifold 42 into the crankcase interior 28. On the downward stroke of the piston 14, the air or fuel / air mixture in the crankcase interior 28 is compressed and flows into the combustion chamber 12 as soon as the transfer ports 19 to the combustion chamber 12 are open. On the subsequent upward stroke of the piston 14, the air or fuel / air mixture is compressed in the combustion chamber 12. At the top dead center of the piston 14, the fuel / air mixture in the combustion chamber 12 is ignited. The subsequent combustion in the combustion chamber 12 accelerates the piston 14 towards its bottom dead center. When the exhaust port 21 has been opened by the downward-moving piston 14, exhaust gases flow out of the combustion chamber 12. As shown in Fig. 3, the cylinder 9 has first cooling fins 22, 22a, 22b. Cooling air channels 31 are formed between adjacent cooling fins 22, 22a, 22b. A fan wheel 24 is fixed to the crankshaft 16 and, during operation, is driven by the crankshaft 16 to rotate about the axis of rotation 17 in a direction 27. The fan wheel 24 is arranged in a blower housing 25. The blower housing 25 is designed to expand in an approximately spiral shape. During operation, the fan wheel 24 directs a cooling airflow 37 towards the cylinder 9. This cooling airflow 37 splits into a first partial cooling airflow 38 and a second partial cooling airflow 39, as schematically indicated in Figures 3 and 4. Specifically, the division of the cooling airflow 37 into the partial cooling airflows 38 and 39 occurs outside the fan housing 25. The fan wheel 24 is located on a fan wheel side 29 of the internal combustion engine 5. The first partial cooling airflow 38 flows along the fan wheel side 29 at the cylinder 9. The internal combustion engine 5 has a central plane 32. The central plane 32 contains the cylinder longitudinal axis 10 and runs parallel to the axis of rotation 17. In particular, the axis of rotation 17 lies in the central plane 32. The central plane 32 has a first side 33 and a second side 34. On the first side 33 of the central plane 32, the cooling airflow 37 in the exemplary embodiment flows from the blower housing 25 to the cylinder 9. The cylinder 9 has a transverse side 35. The transverse side 35 runs along the side of the cylinder 9 facing the handle 3 (Fig. 1). The transverse side 35 runs on the first side 33 of the central plane 32. The second partial cooling airflow 39 flows along the transverse side 35 on the cylinder 9. In addition to the first partial cooling airflow 38 and the second partial cooling airflow 39, further partial cooling airflows may be provided. In Fig. 3, two of the first cooling fins 22 are designated as cooling fins 22a and 22b for easier identification. All other first cooling fins 22 are designated with the reference numeral 22. As shown schematically in Fig. 3, a transverse rib 23 is arranged between two first cooling fins 22a and 22b. The transverse rib 23 extends in the cooling air duct 31 transversely to the two first cooling fins 22a and 22b. The transverse rib 23 partially obstructs the free flow cross-section of the cooling air duct 31. This increases the second partial cooling airflow 39. Consequently, the air mass flow of cooling air along the transverse side 35 is increased, and the air mass flow along the fan wheel side 29 is decreased. This allows the cooling effect on the transverse side 35 to be increased. As a result, more uniform heating of the cylinder 9 on the fan wheel side 29 and on the transverse side 35 can be achieved. The transverse rib 23 is arranged in a cooling air duct 31, which has a width d measured perpendicular to at least one first cooling rib 22a, 22b. The transverse rib 23 extends over the entire width d of the cooling air duct 31. As shown in Fig. 3, the first cooling fins 22, 22a, 22b are inclined to the longitudinal axis of the cylinder 10 at an angle α of less than 90° in the exemplary embodiment. An angle α of 90° is also possible. The angle α is particularly 30° to 90°, more particularly 30° to 75°, and more particularly 50° to 70°. The transverse rib 23 runs, in particular, perpendicular to the first cooling fins 22a and 22b. The first cooling fins 22a and 22b form an angle α with the longitudinal axis of the cylinder 10 in a side view of the internal combustion engine 5, looking towards the axis of rotation 17. As shown schematically in Fig. 3, the cylinder 9 has a second cooling fin 26 that extends between the first cooling fins 22a and 22b to the transverse fin 23. The second cooling fin 26 is arranged in the cooling air channel 31 between the first cooling fins 22a and 22b, between which the transverse fin 23 runs. As shown in Fig. 3, the transverse rib 23 and the second cooling rib 26 are arranged on the first side 33 of the internal combustion engine 5. As shown in Fig. 3, the cooling air flows on the first side 33 along the outer circumference of the fan wheel 24 towards the cylinder 9 and exits the blower housing 25 onto the cylinder 9 on the first side 33. On the second side 34, the cooling air flows away, particularly from the cylinder 9. As shown in Fig. 1, the rear handle 3 is arranged on the first side 33 of the central plane 32 of the internal combustion engine 5. The guide rail 6 and the tool 7 are arranged on the second side 34. Fig. 4 shows the detailed design of the cooling fins 22, 22a, 22b and 26. In particular, the first cooling fins 22 and 22a, 22b extend largely, and especially completely, around the circumference of the cylinder 9. In particular, at least some of the first cooling fins 22 extend completely around the cylinder 9. As shown in Fig. 4, the fan wheel 24 has a plurality of fan blades 36 that convey the cooling air. The cooling airflow 37 divides into the first partial cooling airflow 38 and the second partial cooling airflow 39. The first partial cooling airflow 38 flows through cooling air channels 31 formed between adjacent first cooling fins 22, 22a, 22b. The transverse fin 23 is arranged between cooling fin 22a and cooling fin 22b. As shown in Fig. 4, cooling fin 22a has a height a at the transverse fin 23. In the exemplary embodiment, cooling fin 22b has a corresponding height a on the opposite side of the cooling air channel 31, which is not shown in Fig. 4. The transverse fin 23 has a height b measured at the first cooling fin 22a or 22b. As shown in Fig. 4, the height b is less than the height a. In particular, the height b of the transverse rib 23 is at least half the height a of at least one of the first two cooling fins 22a and 22b between which the transverse rib 23 runs. In particular, the first two cooling fins 22a and 22b on the transverse rib 23 are of the same height. However, different heights of the cooling fins 22a and 22b on the transverse fin 23 can also be advantageous. As shown in Fig. 4, the transverse rib 23 extends from the first cooling rib 22a to the first cooling rib 22b. The transverse rib 23 covers at least 60% of the flow cross-section of the cooling air duct 31. The flow cross-section is measured directly upstream of the transverse rib 23. As also shown in Fig. 4, the second cooling rib 26 has a height c, measured at the transverse rib 23, which is less than the height of the transverse rib 23. In particular, the height c of the second cooling rib 26 is at most 80% of the height b of the transverse rib 23. As shown in Fig. 4, the cooling fin 22a, which runs along the side of the cooling air duct 31 furthest from the fan wheel 24, has a recess 30 upstream of the transverse fin 23. In the exemplary embodiment, the first cooling fin 22a has a reduced height a' at the recess 30. The height a' is, in particular, at most 50%, and in particular at most 20%, of the height a. Alternatively, the recess 30 can also be formed by an opening in the cooling fin 22a. As Fig. 4 also shows, all further first cooling fins 22, which run on the side of the first cooling fin 22a furthest from the fan wheel 24, also have recesses 30. The recesses 30 of the cooling fins 22, 22a form a flow channel for the second partial cooling airflow 39. This enables good transfer of the second partial cooling airflow 39 to the transverse side 35. Fig. 5 shows a schematic top view of the hand-held tool 1. The fan 24 is located on the fan wheel side 29. The internal combustion engine 5 has an opposite end face 40. The fan wheel side 29 and the end face 40 are connected by the transverse side 35 and a second transverse side 41. The transverse side 35 is the transverse side of the internal combustion engine 5 closest to the handle 3. The transverse side 41 is the transverse side furthest from the handle 3 and closest to the tool 7. Fig. 5 also schematically shows the position of the transverse rib 23 on the fan wheel side 29. The transverse rib 23 and the transverse side 35 are located on the first side 33 of the central plane 32. Fig. 5 also schematically shows the partial cooling airflows 38 and 39.

Claims

Hand-held work device with an internal combustion engine (5), wherein the internal combustion engine (5) has a cylinder (9) carrying cooling fins (22, 22a, 22b, 26), wherein the internal combustion engine (5) has a crankshaft (16), with a fan wheel (24) arranged on a fan wheel side (29) of the internal combustion engine (5) in a blower housing (25), which conveys a cooling air flow (37) to the cylinder (9), wherein the fan wheel (24) is driven by the crankshaft (16) about a pivot axis (17), wherein the cylinder (9) has first cooling fins (22, 22a, 22b) extending on the fan wheel side (29) of the internal combustion engine (5), wherein a cooling air channel (31) is formed between two adjacent first cooling fins (22, 22a, 22b), characterized in that the cylinder (9) has a transverse rib (23) which extends in the cooling air duct (31) transversely to the two first cooling fins (22a, 22b). Working device according to claim 1, characterized in that the transverse rib (23) has a lower height (b) than at least one first cooling rib (22a, 22b) limiting the cooling air channel (31), wherein the height (b) of the transverse rib (23) is measured midway between the two first cooling ribs (22a, 22b) and wherein the height (a) of the first cooling ribs (22a, 22b) is measured at the transverse rib (23). Working device according to claim 2, characterized in that the height (b) of the transverse rib (23) is at least half the height (a) of at least one of the two first cooling ribs (22a, 22b). Working device according to claim 2 or 3, characterized in that the transverse rib (23) extends from one to the other of the first cooling rib (22a, 22b) which defines the cooling air channel (31). Working device according to one of claims 1 to 4, characterized in that the transverse rib (23) extends over at least 60% of a flow cross-section of the cooling air duct (31) directly upstream of the transverse rib (23). Working device according to one of claims 1 to 5, characterized in that the internal combustion engine (5) has a central plane (32) which contains a longitudinal axis (10) of the cylinder (9) and which runs parallel to the axis of rotation (17) of the fan wheel (24), that the cooling air flow (37) flows from the blower housing (25) to the cylinder (9) on a first side (33) of the central plane (32) and that the transverse rib (23) is arranged on the first side (33) of the central plane (32) of the internal combustion engine (5). Working device according to one of claims 1 to 6, characterized in that at least one first cooling fin (22a) limiting the cooling air channel (31) has a recess (30) on the transverse fin (23) with respect to a flow direction of the cooling air flow (37). Working device according to claim 7, characterized in that the first cooling fin (22a) at the recess (30) has a lower height (a') than at the transverse fin (23). Working device according to one of claims 1 to 8, characterized in that a second cooling rib (26) is arranged at least upstream of the transverse rib (23) between the two first cooling ribs (22a, 22b) limiting the cooling air channel (31). Working device according to claim 9, characterized in that the second cooling fin (26) has a lower height (c) measured at the transverse fin (23) than the transverse fin (23). Working device according to one of claims 1 to 10, characterized in that the first cooling fins (22a, 22b) are arranged inclined in a side view of the internal combustion engine (5) in the direction of the axis of rotation (17) to the longitudinal axis of the cylinder (10).

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