Engine-driven working machine

Abstract

An engine-driven working machine according to the present invention has a controller and a muffler. The controller is operated from starting of the engine in a rotational speed limitation mode in which the engine is prevented from rotating at a rotational speed that is higher than the predetermined limitation rotational speed. The controller forces to stop the engine, after a predetermined period has passed, during which the engine operates in the rotational speed limitation mode.

Claims

1. An engine-driven working machine comprising: an engine; an actuating part driven by the engine; a centrifugal clutch disposed between the engine and the actuating part; and a controller detecting a rotational speed of the engine to control the rotational speed, wherein the engine has a carburetor including a throttle valve, wherein when the rotational speed of the engine is higher than a predetermined clutch-in rotational speed, the centrifugal clutch connects the engine with the actuating part so as to transmit rotations of the engine to the actuating part, and wherein in a fast idling state in which the engine is operated while a throttle valve of a carburetor of the engine is maintained in a half-opened position, the controller is operated from starting of the engine in a rotational speed limitation mode in which the engine is prevented from rotating at a rotational speed that is higher than a predetermined limitation rotational speed by appropriately performing misfiring cycles, further comprising a muffler containing a catalyst for purifying exhaust gas of the engine, wherein the controller is configured to completely stop the engine to prevent a temperature of the catalyst from increasing after a predetermined period has passed, during which the engine operates in the rotational speed limitation mode.

2. The engine-driven working machine according to claim 1, wherein the predetermined limitation rotational speed is the clutch-in rotational speed.

3. The engine-driven working machine according to claim 1, wherein the predetermined period is a predetermined time period.

4. The engine-driven working machine according to claim 1, wherein the predetermined period is a period until the number of the rotations of the engine reaches a predetermined accumulating number of times.

5. The engine-driven working machine according to claim 1, wherein the predetermined period is a period until a temperature of the muffler reaches a predetermined temperature.

6. The engine-driven working machine according to claim 1, wherein the predetermined period is a period until a number of times of the misfiring of the engine reaches a predetermined number of times.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of a chain saw.

(2) FIG. 2 is a cross-sectional view of a driving part of the chain saw.

(3) FIG. 3 is a schematic view of a throttle valve and a choke valve.

(4) FIG. 4 is a perspective view of a chain saw.

DETAILED DESCRIPTION OF EMBODIMENTS

(5) Referring to the drawings, a chain saw which is an engine-driven working machine according to the present invention will be explained. As shown in FIG. 1, a chain saw 1 has an engine 2, a chain 4 with cutting edges which is an actuating part 4 driven by the engine 2, and a centrifugal clutch 6 (shown in FIG. 2) disposed between the engine 2 and the actuating part 4. The centrifugal clutch 6 connects the engine 2 with the chain 4 with cutting edges to transmit rotations of the engine 2 to the chain 4 with cutting edges when a rotational speed of the engine 2 is higher than a predetermined clutch-in rotational speed. The chain saw 1 also has a brake lever 7 which actuates a brake (not shown) to stop an output side of the centrifugal clutch 6. Since the engine 2, the chain 4 with cutting edges, the centrifugal clutch 6, and other structures in the chain saw 1 are those which are conventionally known, detail explanations thereof are omitted.

(6) As shown in FIG. 2, the engine 2 is preferably a two-stroke gasoline engine, and as shown in FIG. 3, a carburetor 8 provided in the engine 2 has a throttle valve 10 and a choke valve 12. The throttle valve 10 and the choke valve 12 are those which are conventionally known. The throttle valve 10 and the choke valve 12 may be configured to be moved independently or moved together so as to perform a specific operation. In the present embodiment, when a choke lever 14 (shown in FIG. 1) is actuated, the choke valve 12 is configured to be moved from a fully-opened position to a fully-closed position, while the throttle valve 10 is configured to be moved from a fully-closed position to a half-opened position, as shown in FIG. 3(a). Further, when the choke lever 14 is returned, the choke valve 12 is configured to be moved from the fully-closed position to the fully-opened position, while the throttle valve 10 is configured to be maintained in the half-opened position, as shown in FIG. 3(b). Further, the throttle valve 10 is configured to return from the half-opened position to the fully-closed position by actuating and then returning a throttle lever 16 (shown in FIG. 1), as shown in FIG. 3(c).

(7) The engine 2 also has a controller 18 which detects a rotational speed of the engine 2 and controls the rotational speed. In the present embodiment, the rotational speed of the engine 2 is detected by detecting a magnet 2b attached to a crankshaft 2a of the engine 2 (or integrated with a flywheel), as shown in FIG. 2 and treating the detected magnet 2b with a program. For example, a time period required for one rotation of the crankshaft 2a of the engine 2 (or a crankshaft cycle period) is detected and the rotational speed is calculated based on the time period.

(8) The working machine 1 has also a muffler 20. The muffler 20 has a shape of a housing and contains a catalyst 20a for purifying exhaust gas of the engine 2. Concretely, the muffler 20 has a partition (not shown) dividing an inside of the housing into two rooms (not shown), and the catalyst 20a is disposed at the partition. Thus, the muffler 20 is configured so that the exhaust gas is introduced into one of the rooms, passed through the catalyst 20a, and exhausted out of the other room.

(9) Next, a method of starting the engine 2 will be explained.

(10) By actuating the choke lever 14, the choke valve 12 is moved from the fully-opened position to the fully-closed position, while the throttle valve 10 is moved to the half-opened position, as shown in FIG. 3(a). This is called as a fast idling start and is especially effective to a cold-state start when the engine 2 is cold. Then, the engine 2 is started by pulling a recoil rope 20 (shown in FIG. 1). Since the choke valve 12 is in the fully-closed position, when a pressure inside of a crankcase 2c (shown in FIG. 2) becomes negative, a relatively large amount of fuel is supplied so that the engine 2 becomes in an easily-combusting state. A matter that the engine 2 becomes in a combustible state can be found when a first explosion is heard after the recoil rope 20 is pulled several times.

(11) Then, the choke lever 14 is returned so that the choke valve 12 is moved to the fully-opened position, while the throttle valve 10 is maintained in the half-opened position, as shown in FIG. 3(b). Then, by pulling the recoil rope 20, the engine 20 is started. Since the throttle valve 10 is in the half-opened position, the engine 2 is operated in a fast idling state.

(12) In the fast idling state in which the engine 2 is rotated while the throttle valve 10 of the engine 2 is maintained in the half-opened position, the controller 18 is operated from the starting of the engine 2 in a rotational speed limitation mode in which the engine 2 is prevented from rotating at a rotational speed which is higher than the clutch-in rotational speed. For example, in the rotational speed limitation mode, the controller 18 properly causes misfiring cycles in the engine 2 so as to prevent the engine 2 from rotating at a rotational speed which is higher than the clutch-in rotational speed. Concretely, when the rotational speed of the engine 2 exceeds a predetermined rotational speed (for example, 3200 rpm) which is lower than the clutch-in rotational speed, a misfiring cycle is caused to disable ignition plugs 2d (shown in FIG. 2) so that an increase of the rotational speed of the engine 2 is prevented. The rotational speed of the engine 2 in the fast-idling state is about 3000-4500 rpm.

(13) When the misfiring cycle is performed in the rotational speed limitation mode, uncombusted gas is generated, and then exhausted and supplied into the muffler. Further, when the ignition timing is retarded, since the exhaust port is opened before the entire mixture is combusted, uncombusted gas is generated, and then exhausted and supplied into the muffler. When the uncombusted gas enters the muffler 20, the catalyst 20a in the muffler 20 reacts with the uncombusted gas to purify the exhaust gas. Further, due to heat caused by the reaction, the temperature of the catalyst 20a is increased. As a result, the temperature of the muffler 20 itself is increased and durability of the catalyst may be degraded.

(14) In the present invention, the controller 18 forces to stop the engine 2 after a predetermined period has passed, during which the engine 2 operates in the rotational speed limitation mode. Thus, even if the operator does not notice that the working machine is not in use after it is started, it can be prevented from increasing the temperature of the muffler or degrading durability of the catalyst.

(15) In order to force to stop the engine 2, the controller 18 may stop supplying fuel or stop ignitions.

(16) The predetermined period is a predetermined time period, for example, 10-30 seconds. Alternatively, the predetermined period may be a period until the number of the rotations of the engine reaches a predetermined accumulating number of times, for example, 500-1500 rotations. Further, the predetermined period may be a period until a temperature of the muffler reaches a predetermined temperature, for example, 150-400 C. In this case, a temperature sensor may be provided at an inlet or outlet of the muffler 20. Further, the predetermined period may be a period until a number of times of the misfiring of the engine reaches a predetermined number of times, for example, 400-1200 times.

(17) Although the above-stated embodiments of the present invention have been explained, the present invention is not limited to the above-stated embodiments, namely, a various modifications are possible within the scope of the present invention recited in the claims. It goes without saying that such modifications are also within the scope of the present invention.