A drive system for a tool, particularly a chain saw, includes a fresh air inlet and an intake manifold arranged after the fresh air inlet in the flow direction of the fresh air that opens into a carburettor. A combustion engine is provided that is arranged after the carburettor in the flow direction of an air-fuel mixture produced in the carburettor, in which the carburettor is exposed to a lower level of thermal stress. At least one heat conducting cooling vane is connected to the carburettor and protrudes outwards into direct contact with the ambient fresh air.

TECHNICAL AREA

The invention relates to a drive system for a tool, particularly a chain saw, having a fresh air inlet and an aspiration chamber disposed after the fresh air inlet in the flow direction of the fresh air that opens into a carburettor, and a combustion engine that is disposed after the carburettor in the flow direction of an air-fuel mixture produced in the carburettor.

RELATED ART

According to the related art, drives for motorised chain saws may include a combustion engine and a carburettor arranged upstream thereof. While the combustion engine is running, a thermal equilibrium is created in the cylinder of the combustion engine. The heat that is generated by the combustion of the fuel-air mixture in the combustion chamber is dissipated in the hot exhaust gases, and the cylinder that surrounds the combustion chamber is also cooled by the fresh inflow of cooler fuel-air mixture. This equilibrium keeps the temperature of the cylinder constant. The equilibrium is upset as soon as the combustion engine is switched off. Not only is heat no longer removed in the escaping exhaust gases, but the cooling effect due to the inflow of the fuel-air mixture into the combustion chamber is also stopped. The brief, significant increase in the temperature of the cylinder is also transferred to the carburettor via the fuel-air mixture duct. As a consequence, the carburettor heats up. The heat that is generated in the carburettor places harmful stress on that component.

A multiple cylinder combustion engine having heat exchange surfaces on the outer wall of the air and fuel supply ducts is described in U.S. Pat. No. 4,256,093 A. Heat is absorbed from the hot exhaust duct through these and is used to preheat the flow as it enters the combustion chamber.

BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a drive system for a tool in which the carburettor is exposed to less thermal stress.

The object is solved by a drive system having the features of the main claim.

The drive system is designed for use with tools, particularly hand-guided tools, such as chain saws, angle grinders, hedge trimmers for example. The drive system has a fresh air inlet and an inlet manifold disposed after the fresh air inlet in the direction of the flow of fresh air. The manifold opens into an air intake of a carburettor. The drive system also includes a combustion engine, preferably a 4-stroke combustion engine provided after the carburettor in the flow direction. It is also conceivable to provide 2-stroke combustion engines. According to the invention, the drive system has at least one cooling vane that is connected in heat conducting manner to the carburettor, and protrudes outwards so as to come into contact with ambient fresh air. Particularly shortly after the combustion engine is switched off, additional heat is transferred from the cylinder surrounding the combustion chamber to the carburettor through an air-fuel mixture duct. This conventionally causes the carburettor to heat up considerably for a short time. The at least one cooling vane discharges heat particularly shortly after the drive system has been switched off, thus protecting the carburettor.

The at least one cooling vane preferably protrudes from an outer manifold wall of the manifold that is located between the carburettor and the at least one cooling vane. The manifold is preferably made entirely from a material that conducts heat exceptionally well.

The manifold may be delimited on the side facing the carburettor by an inner manifold wall that is in contact with the outer carburettor wall, and on the side facing away from the carburettor by an outer manifold wall furnished with at least one cooling vane. In this context, heat is removed from the carburettor via the contact surface with the inner manifold wall and via preferably two short lateral manifold walls and a manifold base to the outer manifold wall. From there, the heat is radiated via the at least one cooling vane. The at least one cooling vane may be added inexpensively with just a minor modification to the manifolds already in use.

In a further aspect of the invention, the intake manifold is furnished with an inlet for lubricant into the stream of fresh air. The drive system according to the invention includes an element for diverting a small fraction of the fuel after the carburettor in the flow direction of a fuel-air mixture. This small fraction of the fuel is fed into the lubrication circuit and used as a lubricant with the addition of oil. The drive system and other components as necessary are lubricated with the fuel-oil mixture. Accordingly, no further lubricants need to be added. After it has circulated through the entire lubrication circuit, the lubricant is returned for combustion. An inlet for the lubricant is provided in the intake manifold for this purpose. The fresh air flowing into the manifold takes up the lubricant that emerges there and transports it to the carburettor as air—with a small fraction of fuel. In the carburettor, a controllable quantity of additional fuel is added to the air and a fuel-air mixture is formed, which is then passed to the combustion engine for combustion.

The lubricant is heated as it passes through the lubrication circuit. In order to be able to discharge as much heat as possible from the lubricant into the fresh air via the at least one cooling vane of the invention, a thermally conductive lubricant duct that is in thermally conducting communication with the at least one cooling vane is provided before the inlet in the flow direction of the lubricant.

The lubricant duct preferably passes along the outer wall of the intake manifold. Particularly if the at least one cooling vane protrudes from the outer manifold wall, the thermally conductive connection between the lubricant duct and the cooling vane is exceptionally efficient.

The intake manifold may advantageously be assembled from several parts. The intake manifold may have an outer wall element arranged between a manifold component and an air filter component with the fresh air inlet, and an outer wall of the intake manifold component together with the outer wall element and an outer wall of the air filter component may form the outer wall of the intake manifold. The intake manifold component is furnished with an air duct preferably having an essentially elongated rectangular cross section extending across the direction of flow in cross section, and which is preferably delimited by the inner and the outer walls, and two lateral walls sloping from the inner to the outer walls of the intake manifold. The preferred multi-component construction of the intake manifold facilitates maintenance and access to the carburettor.

Multiple cooling vanes may be arranged parallel to each other particularly advantageously, in which case the cooling vanes lie flush with each other and are connected to each other at one end one by a transverse strip, and the other ends thereof are connected to each other by a U-shaped arch. The cooling vanes thus form a preferably single-part component that is correspondingly inexpensive to install.

The intake manifold is preferably made from light metal, particularly from aluminium. Aluminium is a particularly thermally conductive.

The drive system is preferably installed in a tool. In this case, the at least one cooling vane is arranged such that they are exposed to fresh air, or for example that openings in the tool housing allow direct contact between fresh air and the at least one cooling vane.

BEST METHOD OF IMPLEMENTING THE INVENTION

A carburettor1is shown partially concealed inFIG. 1. An intake manifold2,3,4includes a manifold component2and an outer wall element2inserted therein and an air filter component4engaged therein. An inner manifold component wall6of manifold component2is disposed so as to be in contact over a large area with the side of an outer carburettor wall. The contact surface between carburettor1and inner manifold component wall6is highly thermally conductive.

The wall of carburettor1facing manifold component2is furnished with an air inlet7for air that is supplied through intake manifold2,3,4. The air that is supplied to carburettor1is already a mixture of fresh air originating from the ambient air with the addition of a small faction of a fuel-oil mixture. An aperture8is provided in inner wall6of manifold component2and is aligned with air inlet7. Inner wall6and an outer wall9of manifold component2together with lateral manifold walls11standing perpendicularly thereto form a duct section, and they are constructed as a double wall at the upper, open edge.FIG. 1shows the intended orientation of the components relative to each other and the ground during operation.

An edge of wall element3facing manifold component2is inserted in the double-walled edge of manifold component2. An end of outer wall element3located opposite manifold component3is equipped with a latching mechanism12. Latching mechanism12enables a free edge of air filter component4at the bottom to be engaged by a hook. Air filter component4is furnished with a fresh air inlet13. An air filter (not illustrated) is provided in air filter component4downstream of fresh air inlet13.

The fresh air is drawn in from the outside and flows through air inlet13of air filter component4through the air filter, along the inside of outer wall element3and into manifold component2. Manifold component2is constructed with an essentially elongated rectangular cross section perpendicular to flow direction S of the fresh air. In manifold component2, the fresh air is mixed with lubricant that is fed into manifold component2through an inlet—obscured inFIG. 1by support3. The fresh air with the addition of a small quantity of lubricant is then passed as air to carburettor1.

The air flows into carburettor1through a throttle valve (not illustrated) along a venturi injector and collects a controllable quantity of fuel. The fuel-air mixture thus created flows out of carburettor1through of a fuel-air mixture outlet—obscured by carburettor1—and into a fuel-air mixture inlet of the combustion engine (not illustrated). In this case, the combustion engine is designed as a 4-stroke engine.

Outer manifold component wall9of manifold component2is equipped with cooling vanes14disposed parallel to each other. Cooling vanes14are arranged vertically and are aligned essentially parallel to flow direction S. The upper ends of cooling vanes14facing air filter component4are flush with each other and are connected to each other by a heat conducting strip, while a heat conducting strip connecting the lower ends of cooling vanes14forms a U-shaped arch16.

Three adjusting screws17are provided on carburettor1. A connector18for the fuel pump is provided on the outside at the top of the carburettor wall. The end of manifold component2facing away from air filter component4is furnished with a connecting port19for a lubricant hose.

An element (not illustrated) for diverting a small quantity of fuel is provided between carburettor1and the combustion engine. About 3% of the fuel passing through the element is diverted. The diverted fuel is able to be introduced into the lubrication circuit and is used exclusively as lubricant. Thus, the drive system according to the invention does not require a separate supply of lubricant. The lubricant that is diverted via the diverting element in the form of fuel-oil is pumped into the lubrication circuit and at the end of the circuit is fed into manifold component2via connecting port19, from where it is transported by the fresh air flowing past and introduced into carburettor1as air with a small fraction of fuel.

FIG. 2shows a rear view of manifold component2. The rear view is the view from carburettor1. Manifold component2is furnished with aperture8that passes through inner wall6of the manifold component. Fixing holes21are also provided for screwing manifold component2to carburettor1. Inner manifold wall6has a lubricant pipe23that opens into the air duct through an inlet22. Connecting port19for the lubricant hose is provided at the end of lubricant tube23opposite inlet22.

FIG. 3shows the front view of intake manifold2ofFIG. 2. About half of aperture8in inner manifold wall6is obscured by outer manifold wall9. Inner and outer manifold walls6,9together form two interface surfaces of the air duct of manifold component2. The two lateral boundary walls are also formed by a double-edged lateral manifold wall11. A plurality of interconnected, heat conducting cooling vanes14are provided on the outside of outer manifold wall9. Cooling vanes14are also connected in thermally conductive manner to outer manifold wall9.

Cooling vanes14not only radiate heat that is collected from carburettor1. Cooling vanes14also radiate the heat that is transferred from the lubricant via lubrication pipe23.

Particularly the cylinder of the combustion engine heats up considerably during operation. However, a thermal equilibrium is established in the cylinder during operation. The heat that is generated by combustion of the fuel-air mixture is balanced by the heat that is dissipated by discharge of the hot exhaust gas and the additional cooling effect of the cold fuel-air mixture flowing into the cylinder. This equilibrium is upset as soon as the combustion engine is switched off. The cylinder continues to heat up for a short while. This brief additional heating of the cylinder is caused by the fact that the dissipation of heat by the escaping exhaust gases suddenly ceases, and the introduction of the cool fuel-air mixture into the cylinder has also stopped suddenly. The heat radiated by the cylinder is transferred to the adjacent carburettor1particularly via a metal fuel-air mixture duct between the combustion engine and carburettor1, and causes the carburettor to heat up considerably. The heat absorbed by carburettor1is dissipated directly into the ambient fresh air via the cooling vanes14according to the invention.

The drive device described in the above is part of the drive system of a tool, particularly a hand-guided tool such as a chain saw. Cooling vanes14are in direct contact with the fresh air surrounding the tool.

The lubrication circuit—not shown—starts at the diverter element (not shown) downstream of carburettor1. The fuel passes through a non-return valve and along a lubrication line into the crank case. From there, it is agitated and pumped via a separate line by the underpressure or overpressure of the piston stroke into the cylinder head, where it lubricates valve flaps and other such components. At the same time, a second non-return valve ensures that the lubricant only flows in one direction. From the cylinder head, the lubricant passes into the control chamber of the crankshaft, and from here it is returned to intake manifold2via lubricant duct23. In the course of its path through the lubrication circuit, the lubricant absorbs heat. At least some of this absorbed heat is discharged to the fresh air outside of the drive system in the area of lubricant duct23through the thermally conductive connection between lubricant duct23and cooling vanes14.

LEGEND