Hand-held work tool with a generator

Details Hand-held work tool with a generator Hand-held work tool with a generator

1999-11-12

2001-05-15

Ponomarenko, Nicholas (Department: 2834)

Prime-mover dynamo plants

Miscellaneous

Drive gearing

C322S046000, C123S003000

Reexamination Certificate

active

06232672

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a hand-guided work tool, especially a motor chainsaw, a cut-off saw, etc., comprising an internal combustion engine with an ignition system which comprises a pole wheel mounted on the crankshaft of the internal combustion engine and having permanent magnets positioned about the periphery in a sequential arrangement. The ignition system further comprises a plurality of charge armatures connected to the housing which close a magnetic circuit between the poles of the permanent magnets. The legs of the charge armatures support excitation coils and the permanent magnets of the pole wheel induce in the excitation coils of the charge armatures an electrical current which is supplied to the carburetor heater and a grip heater of the work tool.
The electrical energy for the ignition system of the internal combustion engine of motor chainsaws is, in general, generated by a pole wheel revolving with the crankshaft and having permanent magnets arranged in the circumferential direction in a row after one another that generate an electrical current in the excitation coils of charge armatures connected to the housing. The excitation coils are connected in series and together supply, among other consumers, a grip heater and a carburetor heater of the motor chainsaw in order to allow use of the chainsaw at low temperatures. The available power output of the generator is thus divided to the grip and to the carburetor depending on the resistance ratios of the respective heat coils. When only one of the two heaters is in use, it is supplied with a very high power output which for carburetor heaters can result in excessive temperatures and thus in fuel vapor bubble formation within the carburetor. When the windings of the excitation coil are adjusted to achieve a certain heating output for the carburetor, an insufficient total output is provided when the carburetor heater and the grip heater are operated simultaneously so that especially the grip heater will not operate satisfactorily, i.e. the temperature achieved is then too low. When adjusting the output by using different load resistors, negative effects in the heating circuits will occur during operation because of the electrical coupling in the coil resistors of the generator and the magnetic coupling in the magnetic circuit.
The invention has the object to improve a hand-held portable work tool with an internal combustion engine such that the carburetor heater and the grip heater can be supplied with respectively adjusted electrical energy.
SUMMARY OF THE INVENTION
The hand-held work tool of the present invention has a housing having a carburetor heater and a grip heater. An internal combustion engine is mounted in the housing and has a crankshaft and an ignition system. The ignition system has a pole wheel comprising permanent magnets fastened sequentially at the periphery of the pole wheel in the circumferential direction. Charge armatures are mounted in the housing for closing a magnetic circuit between neighboring ones of the permanent magnets. The charge armatures have legs and excitation coils mounted on the legs. Upon rotation of the pole wheel, the permanent magnets generate an electric current in the excitation coils. A first set of excitation coils is combined to a first partial generator and connected to an electric circuit of the carburetor heater and a second set of excitation coils is combined to a second partial generator and connected to the electric circuit of the grip heater such that the generated electric current is supplied to the carburetor heater and the grip heater, respectively. The excitation coils of the first set are arranged in a row adjacent to one another in the circumferential direction and the excitation coils of the second set are arranged in a row adjacent to one another in the circumferential direction.
By separating the generator windings into individual, electrically separated groups of excitation coils, an adaptation to the respective heating device with an optimal operating point is possible. The electrical separation into individual excitation coils and their selective combination into sets of excitation coils, which in the circumferential direction of the pole wheel are arranged in a row adjacent to one another, has furthermore the effect that a voltage drop caused by field weakness as a result of a load current has only a minimal effect on the other set of excitation coils. The coupling by a common coil resistor of the generator coil is thus eliminated.


REFERENCES:
patent: 4286675 (1981-09-01), Tuggle
patent: 5705917 (1998-01-01), Scott et al.
patent: 6034511 (2000-03-01), Scott et al.
patent: 6118186 (2000-09-01), Scott et al.

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