Work machine with internal combustion engine and carburetor cooling

Description

[0001] The invention relates to a working device with an internal combustion engine according to claim 1.

[0002] Internal combustion engines, especially two-stroke and four-stroke engines, are available in a wide variety of configurations. In one particular application, two-stroke engines have proven successful in powering work equipment, such as rammers for soil compaction or motor-driven drilling and / or impact hammers.

[0003] Typically, such an internal combustion engine has one or more cylinders, each of which houses a piston that moves axially back and forth to drive an engine shaft (crankshaft) in rotation. The crankshaft, in turn, is mounted in a crankcase, and additional lubrication devices may be provided.

[0004] Two-stroke engines have a carburetor, such as a diaphragm carburetor, which generates the air-fuel mixture required for combustion in a conventional manner. Diaphragm carburetors are usually mounted on the outside near the cylinder and are cooled by natural convection. A fan is usually provided to cool the cylinder, generating an airflow that is directed over the cylinder and the crankcase.

[0005] Typical diaphragm carburetors are designed with a diaphragm side and a valve side, between which an air passage is routed, through which the combustion air for the cylinder is supplied. The carburetor mixes fuel into the air passage, creating an air-fuel mixture that can then be fed to the combustion chamber in the cylinder.

[0006] US 9,016,246 B2 and DE 10 2009 008 055 A1 each disclose a hand-held tool with an internal combustion engine in which, for winter operation, a portion of the cooling air is preheated by the cooling fins of the engine cylinder and subsequently fed into the carburetor to heat it. A similar solution is described in DE 36 04 166 A1.

[0007] DE 1 281 138 B discloses a chainsaw in which a carburettor box can be arranged in the engine housing.

[0008] At high outside temperatures, for example, when operating the combustion engine on a sunny construction site, the carburetor heats up considerably. Natural convection may then no longer be sufficient to prevent the formation of vapor bubbles in the fuel system due to fuel evaporation. However, if vapor bubbles form in the fuel system, particularly in the fuel supply, the suction effect of the diaphragm pump in the carburetor is reduced or even completely eliminated, so that no more fuel can be pumped. The two-stroke engine then stops due to an acute lack of fuel.

[0009] The invention is therefore based on the object of providing a working device with an internal combustion engine in which the risk of the formation of vapor bubbles in the fuel system can be reduced.

[0010] The object is achieved according to the invention by a working device with an internal combustion engine having the features of claim 1. Advantageous embodiments are specified in the dependent claims.

[0011] An internal combustion engine is specified, comprising a cylinder in which a piston is axially reciprocating to drive an engine shaft in rotation, a carburettor device for generating an air-fuel mixture for a combustion process in the cylinder, a fan device for generating a cooling air flow, a cooling air guide for guiding the cooling air flow generated by the fan device, a flow divider for dividing the cooling air flow into a cylinder cooling air flow and a carburettor cooling air flow, a cylinder cooling air flow guide for guiding the cylinder cooling air flow to an outer wall of the cylinder, and a carburetor cooling air flow guide for guiding the carburetor cooling air flow to an outer wall of the carburettor device.

[0012] The internal combustion engine can, in particular, be a two-stroke engine and have a known design with a cylinder, piston, and engine shaft. Such a two-stroke engine with a single cylinder has proven itself, for example, for powering a work tool.

[0013] The carburetor system generates the air-fuel mixture in a conventional manner. A diaphragm carburetor with a well-known design has proven to be a suitable solution for this purpose. A diaphragm carburetor has the advantage of being driven by the pressure pulses in the engine's intake area and thus functioning in any position, which is not guaranteed with a float carburetor, for example.

[0014] The fan assembly is a conventional blower or a fan serving as a fan impeller (e.g., a radial fan). The fan assembly can be driven directly via the motor shaft (crankshaft), so the fan impeller can be mounted directly on the motor shaft.

[0015] According to the invention, the total cooling air flow generated by the fan device is divided at the flow divider, so that two cooling air flows, the cylinder cooling air flow and the carburetor cooling air flow, are subsequently directed. The two cooling air flows are directed separately to the respective desired location (the target of the flows to be cooled) in order to effectively cool both the cylinder and the carburetor.

[0016] More than 80% of the (total) cooling air flow generated by the fan system is directed as cylinder cooling air flow, while the remainder of the (total) cooling air flow can be directed as carburetor cooling air flow. Since heat generation is significantly greater in the cylinder, due to its own heat generated by combustion, the cylinder cooling air flow can be even larger, for example, comprising approximately 90% of the total cooling air flow. However, a smaller carburetor cooling air flow is sufficient for cooling the carburetor.

[0017] The airflow through the cylinder cooling airflow duct and the carburetor cooling airflow duct can each be diverted by 90°. However, the 90° diversion can also occur just before the flow divider, when the two flows are not yet split. By diverting the airflow by 90°, the cylinder cooling airflow can be directed precisely between the cooling fins on the outer cylinder wall, ensuring optimal cylinder cooling. The carburetor cooling airflow can also be directed directly to the carburetor.

[0018] The cooling air duct can comprise a fan cover, wherein the fan cover at least partially encloses the fan device, and wherein the cylinder cooling air flow duct and the carburetor cooling air flow duct are formed in the fan cover. The fan cover can be constructed of metal, plastic, or both materials. If the two cooling air flow ducts are formed in the fan cover, no further structural measures are required on the internal combustion engine to, on the one hand, effect the division of the overall cooling air flow and, on the other hand, to precisely guide the two separate cooling air flows to the location where cooling is to be achieved.

[0019] A partition wall can be provided between the cylinder and the carburetor to maintain the separation of the carburetor cooling air flow from the cylinder cooling air flow. The partition wall can, for example, be arranged as a cover between the cylinder and the carburetor. It makes it possible to keep the two cooling air flows separate from each other and direct them to their intended destination even when the cylinder cooling air flow guide formed in the fan cover and the carburetor cooling air flow guide are no longer effective because the respective cooling air flow has already exited the fan cover.

[0020] The carburetor device can have a fuel-carrying area covered by a carburetor outer wall, with the carburetor cooling air flow directed such that it impinges on the carburetor outer wall. It can be particularly advantageous if the air flow impinges perpendicularly on the carburetor outer wall. However, a parallel or oblique flow to the carburetor outer wall can also be advantageous if this allows for effective heat dissipation under appropriate structural conditions of the carburetor.

[0021] The carburetor, particularly in a diaphragm carburetor design, has a chamber or line connected to the fuel supply line (the fuel-carrying area). During operation of the carburetor, a slight vacuum is created here to exert a suction effect on the fuel and thus achieve a pumping effect. If vapor bubbles form in this area—as explained above—no vacuum can be generated, and thus no pumping effect can be achieved. By specifically cooling the outer wall of the carburetor with the aid of the carburetor cooling air flow, the risk of vapor bubbles forming can be significantly reduced.

[0022] The fan device can have a fan wheel, wherein the fan wheel can lie in a first plane and wherein the carburetor device, the cylinder and a crankcase forming the cylinder can be arranged in a second plane parallel to the first plane. The carburetor device, the cylinder and the crankcase can accordingly lie in a common plane that differs from the (first) plane of the fan wheel. This arrangement allows the fan wheel to generate a transverse flow - with respect to the longitudinal axis of the cylinder - which then strikes the carburetor device and the cylinder laterally. In particular, the carburetor cooling air flow and the cylinder cooling air flow flow perpendicular to the second plane.

[0023] A working device can be driven by the motor shaft, wherein a clutch can be provided operatively between the motor shaft and the working device for interrupting or closing a torque flow from the motor shaft to the working device, and wherein the clutch can be arranged in a third plane parallel to the first and second planes. The working device can be, for example, a percussion mechanism or a stamping mechanism. The clutch can be, for example, a centrifugal clutch which closes the torque flow from the motor shaft to the working device when a certain speed (switching speed) is exceeded. The operator thus has the option of starting the working device from idle by increasing the speed.

[0024] The combustion engine is used in a work device.

[0025] The working device is a tamping device for soil compaction with a corresponding tamping mechanism or a motor-driven drilling and / or percussion hammer with an impact mechanism.

[0026] The implement can be handheld or hand-guided, whereby the carburetor cooling airflow and the cylinder cooling airflow are directed away from the operator holding the implement during intended use. This means that the two cooling airflows do not hit the operator holding the implement. This is not only comfortable because the cooling airflows would be unpleasant due to their blowing effect. It also protects the operator from being undesirably heated by the resulting warm cooling airflows.

[0027] These and other advantages and features of the invention are explained in more detail below using examples with the aid of the accompanying figures. They show: Fig. 1 a side view of an internal combustion engine according to the invention; Fig. 2 a front view of the combustion engine of Fig. 1 ; Fig. 3 a sectional view along section AA of the combustion engine of Fig. 1 ; Fig. 4 a detailed enlargement of the combustion engine of Fig. 1 ; and Fig. 5 a variant of the combustion engine.

[0028] The Fig. 1 bis 4 show an internal combustion engine according to the invention in various representations. The internal combustion engine is designed as a two-stroke engine and can be advantageously used in various work equipment, such as, in particular, rammers for soil compaction or motor-driven hammers (demolition hammers, drilling hammers, and / or impact hammers) for driving a corresponding work device (according to the invention, a rammer or impact mechanism).

[0029] The internal combustion engine comprises a cylinder 1 with a cylinder housing, in which a piston (not shown) is axially movable back and forth to drive an engine shaft 2 coupled to the crankshaft via a connecting rod and a crankshaft. Adjacent to the cylinder 1 is a crankcase 1a in which the crankshaft / engine shaft 2 is mounted. The crankshaft and the engine shaft 2 can be connected to one another in one piece. The design of such an internal combustion engine has long been known, so a more detailed description of its design and operation is unnecessary here.

[0030] An air-fuel mixture is combusted in cylinder 1 to drive the piston. This air-fuel mixture is generated by a carburetor 3, which serves as a carburetor device, and is pumped into the interior of cylinder 1.

[0031] The carburetor 3 is typically designed as a so-called diaphragm carburetor.

[0032] Diaphragm carburetors have proven themselves for their intended purpose, as they can be used reliably in any position and at any inclination. Unlike float carburetors, for example, a diaphragm carburetor does not require constant horizontal operation.

[0033] The structure of a diaphragm carburetor is also well known, so a detailed description is unnecessary. In principle, the function of a diaphragm carburetor is based on the pressure fluctuations caused by the piston in the engine's intake tract acting on the air side of a diaphragm, which moves in accordance with the pressure fluctuations. The fuel side is located on the opposite side of the diaphragm. The movement of the diaphragm creates a pumping effect, so that with the help of suitable check valves (e.g., flutter valves), fuel is sucked in from a fuel supply and transported further. The fuel is finally injected into an air duct provided in the carburetor 3, forming the air-fuel mixture.Due to the movement of the piston and the associated suction effect, the air-fuel mixture is sucked into the combustion chamber inside cylinder 1, where the mixture is then compressed and burned.

[0034] During operation of the internal combustion engine, considerable combustion heat is generated inside the cylinder 1, which must be dissipated via the outer wall of the cylinder 1. For this purpose, a plurality of cooling fins 4 are provided on the outer wall of the cylinder, which dissipate the heat from the outer wall of the cylinder 1 and overall increase the cooling surface.

[0035] The cooling fins 4 are subjected to an air flow to increase the cooling effect.

[0036] For this purpose, a fan device 5 with a fan 6 serving as a fan wheel and a cooling air guide 7 is provided in the combustion engine. The fan 6 can in particular be designed as a radial fan, as Fig. 3 shows.

[0037] As from Fig. 1 As can be seen, the fan 6 is located inside the fan cover 8 in a first plane, while the carburetor 3, the cylinder 1 with the piston (not shown) and the crankcase 1a are located in a common second plane, which is parallel to the first plane. The drive of a working device (not shown) is via an optional centrifugal clutch (also not shown), which is mounted at the end of the motor shaft 2 (right-hand end in Fig. 1 ) and is located in a third level.

[0038] The fan 6 is mounted directly on the motor shaft 2 and thus automatically rotates with the engine speed during operation of the combustion engine. The rotation of the fan 6 generates a cooling air flow. For this purpose, the fan 6 is at least partially enclosed by a fan cover 8, which thus forms part of the cooling air duct 7. The fan cover 8 has several air inlets 9 in the form of circular segment-shaped air slots, through which the fan 6 draws in ambient air 10.

[0039] The fan cover 8 is thus part of the cooling air duct 7. Inside the fan cover 8, the conveying effect of the fan 6 creates a cooling air flow 11, which is guided through the cooling air duct 7.

[0040] The blower cover 8 can also serve as a starter cover and, for example, enclose a spool on which a rope for a pull starter is wound.

[0041] Inside the fan cover 8 and thus the cooling air guide 7, a flow divider 12 is formed, at which the cooling air flow 11 is divided into a cylinder cooling air flow 13 and a carburettor cooling air flow 14 ( Fig. 3 ).

[0042] More than 80%, for example, approximately 90%, of the total cooling air flow 11 is guided as cylinder cooling air flow 13 to the outer wall of cylinder 1 or the cooling fins 4 in order to achieve effective cooling of the outer wall of cylinder 1. A much smaller portion of the total cooling air flow 11, namely, for example, approximately 10% of the mass flow, is branched off as carburetor cooling air flow 14 and guided to carburetor 3 separately from the cylinder cooling air flow 13. The carburetor cooling air flow 14 and the carburetor cooling air flow guide 16 thus form a carburetor bypass for the total air mass flow.

[0043] To guide the cylinder cooling air flow 13, a cylinder cooling air flow guide 15 is formed in the fan cover 8, which in particular deflects the air flow by 90°. For this purpose, the cylinder cooling air flow guide 15 has an inclined wall in the fan cover 8, which changes the flow direction ( Fig. 1 ).

[0044] The cylinder cooling air flow 13 flows after its deflection by the cylinder cooling air flow guide 15 essentially horizontally through the spaces between the cooling fins 4, as can be seen from Fig. 1 This effectively directs airflow onto the surface of cylinder 1, which is enlarged by the cooling fins 4, thus achieving a good cooling effect. The air flow is particularly perpendicular to the longitudinal direction (main direction of cylinder 1).

[0045] To guide the carburetor cooling air flow, a carburetor cooling air flow guide 16 is provided in the interior and in the lateral area of ​​the blower cover 8, on the upper edge of which the flow divider 12 is formed and thus branches off the carburetor cooling air flow 14 as a partial flow ( Fig. 1 and 4 ).

[0046] With the help of the carburetor cooling air flow guide 16, the carburetor cooling air flow 14 is directed to the carburetor 3, in particular to the outer wall of the carburetor 3 behind which the fuel side is located. This allows for targeted cooling of the fuel side of the carburetor 3, thus preventing the formation of vapor bubbles in the fuel supply even during operation at higher ambient temperatures.

[0047] The carburetor cooling air flow guide 16 is inserted inside or on the side of the fan cover 8 and can, for example, be manufactured directly with it. In particular, the fan cover 8 can be made of plastic or metal, or a combination of both, so that the additional carburetor cooling air flow guide 16 can be manufactured on the inside of the fan cover 8 without significant additional effort.

[0048] For this purpose, the carburetor cooling air flow guide 16 has - analogously to the cylinder cooling air flow guide 15 - an inclined wall which deflects the carburetor cooling air flow 14 by 90° so that the outer wall of the carburetor 3 can be fully hit ( Fig. 4 ).

[0049] Fig. 5 shows a variant of the combustion engine of the Fig. 1 bis 4 .

[0050] The embodiment of Fig. 5 differs from the design of the Fig. 1 bis 4 in that a partition 17 is arranged between the carburetor 3 and the cylinder 1 or its cooling fins 4. The partition 17 serves as a cover between the cylinder 1 and the carburetor 3 and ensures that the two cooling air streams, namely the cylinder cooling air stream 13 and the carburetor cooling air stream 14, are separated from each other. This prevents mixing of the two cooling air streams, which could lead to turbulent flow and, in particular, could prevent the carburetor cooling air stream 14 from actually reaching the carburetor 3.

[0051] The partition wall 17 thus complements the two cooling air flow guides 15, 16. It can be formed in particular as a cover made of plastic or metal and also protects the carburetor 3 from the heat radiation of the cylinder 1.

[0052] A flange (not shown) may be formed on the partition 17 for attaching the carburetor 3 to the flange and thus to the partition 17. The carburetor 3 can thus be easily held to the partition 17. Furthermore, an opening through the partition 17 may be provided in the flange, through which the air-fuel mixture can be directed from the carburetor 3 to the cylinder 1.

[0053] In addition, Fig. 5 For the sake of completeness, fuel lines 18 are also shown, via which fuel can be supplied to the carburettor 3 or - e.g. for venting the diaphragm chamber - discharged.

Claims

1. Work device comprising a combustion motor, wherein - the work device is a tamping apparatus for ground compaction having a tamping unit or a motor-operated drill hammer and / or impact hammer having a tamping unit; and wherein the combustion motor is provided, having - a cylinder (1) in which a piston is movable axially in a reciprocating manner in order to rotationally drive a motor shaft (2); - a carburettor device (3) for producing an air-fuel mixture for a combustion procedure in the cylinder (1); - a fan device (5) for producing a cooling air flow (11); - a cooling air guide (7) for guiding the cooling air flow (11) produced by the fan device (5); - a flow splitter (12) for splitting the cooling air flow (11) into a cylinder cooling air flow (13) and into a carburettor cooling air flow (14); - a cylinder cooling air flow guide (15) for guiding the cylinder cooling air flow (13) to an outer wall of the cylinder (1); and having - a carburettor cooling air flow guide (16) for guiding the carburettor cooling air flow (14) to an outer wall of the carburettor device (3); wherein - the two cooling air flows (13, 14) are guided separately from one another to the cylinder (1) and the carburettor device (3) such that the cylinder cooling air flow (13) is guided to the cylinder (1), whereas the carburettor cooling air flow (14) is guided to the carburettor device (3); - the cooling air guide (7) has a blower cover (8); - the blower cover (8) encloses the fan device (5) at least partially; - the cylinder cooling air flow guide (15) and the carburettor cooling air flow guide (16) are formed in the blower cover (8); - the blower cover (8) has a plurality of air inlets (9) in the form of circular segment-shaped air slits, via which ambient air (10) is drawn in by the fan device (5); and wherein - a partition wall (17) is provided between the cylinder (1) and the carburettor device (3) in order to maintain the separation of the carburettor cooling air flow (14) from the cylinder cooling air flow (13).

2. Work device as claimed in claim 1, wherein more than 80 percent of the cooling air flow (11) produced by the fan device (5) is guided further as cylinder cooling air flow (13), whereas the rest of the cooling air flow (11) is guided further as carburettor cooling air flow (14).

3. Work device as claimed in claim 1 or 2, wherein the air flows are deflected by the cylinder cooling air flow guide (15) and the carburettor cooling air flow guide (16) in each case by 90 degrees.

4. Work device as claimed in any one of the preceding claims, wherein - the carburettor device (3) has a fuel-guiding region which is covered by a carburettor outer wall; and wherein - the carburettor cooling air flow (14) is guided such that it impinges upon the carburettor outer wall.

5. Work device as claimed in any one of the preceding claims, wherein - the fan device (5) has a fan wheel (6); - the fan wheel (6) lies in a first plane; and wherein - the carburettor device (3), the cylinder (1) and a crank housing (1a) which adjoins the cylinder are arranged in a second plane in parallel with the first plane.

6. Work device as claimed in any one of the preceding claims, wherein - a drive apparatus can be driven by the motor shaft (2); - a coupling is operatively provided between the motor shaft (2) and the work apparatus in order to interrupt or close a torque flow from the motor shaft (2) to the work apparatus; and wherein - the coupling is arranged in a third plane in parallel with the first and the second plane.

7. Work device as claimed in any one of the preceding claims, wherein - when the work device is used as specified, the carburettor cooling air flow (14) and the cylinder cooling air flow (13) are guided away by an operator holding the work device.