| 摘要 |
PURPOSE: Provided is a walk-behind working machine including a clutch for transmitting driving power from an engine to running wheels of the machine, and a pivotable grip clutch lever for engaging and disengaging the clutch. CONSTITUTION: A walk-behind working machine providing a first state and a second state, the working machine in the first state running at a high load, the working machine in the second state running at a low load, includes: (A) a drive source; (B) running wheels; and (C) a traveling clutch(30) interposed between the drive source and the running wheels; the traveling clutch including: (a) a case(24) containing a lubricating oil(Ju); (b) a driving member(22b) having a friction surface(38); and (c) a driven member(32) having a friction surface(39); the driving and driven members being disposed within the case in such a manner as to be submerged in the lubricating oil; the friction surfaces of the driving and driven members being arranged to contact each other to produce a surface pressure(P) therebetween; the surface pressure determining whether the traveling clutch is brought from an off-state in which the friction surfaces of the driving and driven members do not contact each other to a slipped state in which the driven member slips on the driving member; the traveling clutch providing a characteristic curve shown in a coordinate system including a vertical axis representing a coefficient of friction(mu) between the friction surfaces of the driving and driven members and a horizontal axis representing a parameter obtained by dividing by the surface pressure a product of a viscosity(eta) of the lubricating oil and the number of times (N) the driven member rotates relative to the driving member per second, the characteristic curve including a first straight line(C1) and a second straight line(C2) connected to the first straight line via a bent point(Cp), the surface pressure being determined such that the bent point corresponds to a switch point when the working machine is switched from the first state to the second state or vice versa.
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