TRAVELLING HYDRAULIC SYSTEM OF CONSTRUCTION MACHINERY

摘要

PURPOSE:To make it possible to travel over a downward slope at a high speed by connecting a brake oil line interconnecting a negative brake cylinder and a counterbalance valve to a pilot room for use in low speed position of a speed changeover valve. CONSTITUTION:In order to cause a hydraulic shovel to travel over a downward slope at a high speed, a speed selection switch 14 is turned on and a speed changeover valve 17 is set at a high speed position. And when the shovel is caused to travel at a high speed, a brake pressure is generated in a return oil line 9 of a travelling motor 3; however, said pressure is not applied to a pilot room 19 for low speed position of the changeover valve 17. The lowered pressure of a main pump is applied from the main pump 1R through a pipeline 42, position E of a travelling changeover valve 2R, pipeline 43, oil line 49, left position of a counterbalance valve 7 and through a brake oil line 38 and oil line 51 to the pilot room 19 of the valve 17. Further, the valve 17 is held at a high speed position D and the shovel travels over a downward slope at a high speed.