| 摘要 |
PURPOSE:To prevent the engine load from suddenly increasing due to the sudden increase of vehicular load by a structure wherein a variable area orifice is provided in order to return the swash plate of HST to its neutral position when load is suddenly increased. CONSTITUTION:When the rotational frequency of an engine 1 is increased, the rotational frequency of a charging pump 2 is also increased and the delivery of pressure oil is increased. Accordingly, the flow rate passing through the orifice 10 is also increased, resulting in producing the difference between the pressure in a left chamber 17 and that in a right chamber 18 and consequently operating an actuator 11 in order to shift the swash plate 7 from its neutral position so that a HST pump 3 delivers pressure oil. A HST motor 4 is driven into rotation by said delivered pressure oil. When the load applied to a loading cylinder 5 is increased, the pressure in the delivery circuit 9 of the charging pump 2 is increased, resulting in thrusting a piston 26a leftward. Consequently, a spool 19 is moved leftward so that the opening area of the orifice 10 is inreased, resulting in decreasing the difference between the pressures in the chambers 17 and 18 and accordingly returning the swash plate 7 to its neutral position. |
