Internal-combustion engines – Cooling – Air-cooled
Reexamination Certificate
1999-06-25
2001-03-06
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Cooling
Air-cooled
C123S041700
Reexamination Certificate
active
06196170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention refers to a driving device for a lawn trimmer with a two-stroke motor having an injection valve, a coupling, air intake and air blow-off devices and a fuel pump as well as eventual further additional aggregates.
2. Prior art
For a driving device known from EP-A-0428 186, the lawn trimmer driving gear is aligned in such a way that the crankshaft axis is placed in a straight line with the main shaft or the main pipe, thus with the drift. A fan driven by the crankshaft (fan wheel) feeds cooling air, mostly sucked below the crankcase, to the cylinder block, whereby the cooling air discharges above a separating plane lying at the level of the cylinder base over the motor unit which has lamellar type walls which should effect an appropriate air guiding with optimal cooling. This known lawn trimmer is provided with a carburetor.
Since lawn trimmers are hand-operated portable implements, a compact, light construction with a weight as low as possible, which makes an optimal cooling or air guiding difficult, is aimed at. The operativeness of the motor decisively depends on a thermally controlled air guiding.
For a chain saw known from DE-U-296 06 668, an injection installation is provided for.
SUMMARY OF THE INVENTION
The aim of the present invention is to indicate, for the driving device mentioned at the beginning, a new compact construction which guarantees the operativeness by using an injection system, and which represents a functional arrangement for a special kind of motor scythes, namely the trimmers.
This aim is reached by the driving device described in claim
1
. Hereby, it is provided for that the injection valve is placed on the coupling side with a nozzle jet orientation directed in direction of the ignition plug or of the cylinder head. Moreover, the coupling and a fan (fan wheel) are placed axially side by side on the crankshaft on the side on which the driven shaft is placed. The injection valve is then placed above the fan wheel of the fan casing. Thus, we obtain that the cooling air conveyed by the fan wheel can cool the injection valve and the fuel supply line connected herewith before the cylinder block is flown around. For the further optimization, the invention provides for that the injection valve penetrates an air guiding wall of the two-stroke motor unit. This arrangement brings the following advantages: on the one hand, there is a relatively big free construction space on the coupling side so that the arrangement of the injection valve allows for a compact outer casing form. Further advantages consist in the cooling of the valve as well as of the fuel supply system and in the arrangement of the valve or of the fuel supply system to the directed air guiding/air transmission to other hot places on the cylinder with a great cooling air requirement.
As it has already been proposed in a previous application of the applicant, the injection valve should be connected to an electronic control unit which is placed, according to a configuration of the invention, on the side opposite to the coupling side, preferably near a tank placed under the crankcase. This measure also is useful for a compact construction as well as for the providing of short connecting lines to sensors in the intake casing and finally for a cooling by the continously flowing fresh intake air. A further advantage of this arrangement of the control unit consists in the simple accessibility for maintenance operations.
Further developments of the driving device are described in the subclaims.
According to another embodiment of the invention, the nozzle opening of the injection valve is preferably placed above or in the upper area of a transfer passage.
Preferably, the fuel pump is directly driven by the crankshaft, whereby an optimal place for the fuel pump exists between the crankcase placed under the two-stroke motor cylinder block and the fan casing. Thus, the fuel pump is effectively cooled by the cooling air sucked by the fan wheel. Furthermore, this arrangement creates relatively short distances between the fuel supply pipes and the injection valve.
The starter casing is placed on the drive side between the coupling casing and the fan casing.
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Haussner Torsten
Schoenhaar Jochen
Singer Andreas
Dolmar GmbH
Kamen Noah P.
McCormick Paulding & Huber LLP
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