초록 ▼

A travel control device enables a crawler type hydraulic excavator to start slowly regardless of the preset speed ratio whenever the manipulation amount of a manual travel control device is small. The travel control device includes left and right travel motors respectively provided with speed changi

A travel control device enables a crawler type hydraulic excavator to start slowly regardless of the preset speed ratio whenever the manipulation amount of a manual travel control device is small. The travel control device includes left and right travel motors respectively provided with speed changing mechanisms, a high speed shifting valve provided on a high speed signal line for cutting off or transmitting a high speed signal pressure to the speed changing mechanisms, a travel signal detection means for detecting a travel control signal pressure outputted from manual travel control devices. A shutoff valve is provided on the high speed signal line for closing or opening the high speed signal line to keep the speed changing mechanisms in a low speed condition or a high speed condition depending on the magnitude of the travel control signal pressure supplied from the travel signal detection means.

대표청구항 ▼

What is claimed is: 1. A travel control device for excavators, comprising: at least one main fluid pump (1, 2) and an auxiliary pump (4) each for discharging a hydraulic flow; left and right travel motors (12, 14) driven by the hydraulic flow of the main fluid pump (1, 2) and respectively provided

What is claimed is: 1. A travel control device for excavators, comprising: at least one main fluid pump (1, 2) and an auxiliary pump (4) each for discharging a hydraulic flow; left and right travel motors (12, 14) driven by the hydraulic flow of the main fluid pump (1, 2) and respectively provided with speed changing mechanisms (13, 15); travel control spools (16, 18) for controlling the hydraulic flow to the left and right travel motors (12, 14); manual travel control devices (20, 22) for receiving the hydraulic flow from the auxiliary pump (4) and supplying a travel control signal pressure to the travel control spools (16, 18); a high speed shifting valve (26) provided on a high speed signal line (24) interconnecting the auxiliary pump (4) and the speed changing mechanisms (13, 15) for cutting off or transmitting a high speed signal pressure to the speed changing mechanisms (13, 15); a travel signal detection means (32) for detecting the travel control signal pressure outputted from the manual travel control devices (20, 22); and a shutoff valve (28) provided on the high speed signal line (24) in a serial relationship with the high speed shifting valve (26) for closing the high speed signal line (24) to keep the speed changing mechanisms (13, 15) in a low speed condition if the travel control signal pressure supplied from the travel signal detection means (32) is no greater than a predetermined pressure value and for opening the high speed signal line (24) to keep the speed changing mechanisms (13, 15) in a high speed condition if the travel control signal pressure supplied from the travel signal detection means (32) exceeds the predetermined pressure value. 2. The device as recited in claim 1, wherein the travel signal detection means (32) comprises a shuttle valve for sensing the travel control signal pressure outputted from the manual travel control devices (20, 22). 3. The device as recited in claim 1, wherein the shutoff valve (28) is provided with a shutoff spool (28a) shiftable between a closing position and an opening position and a spring (28b) disposed at one side of the shutoff spool (28a) for resiliently biasing the shutoff spool (28a) into the closing position, and wherein the travel control spools (16, 18) is provided with springs (16a, 16b, 18a, 18b) for biasing each of the travel control spools (16, 18) into a neutral position, the spring (28b) of the shutoff valve (28) having a greater spring constant than the respective springs (16a, 16b, 18a, 18b) of the travel control spools (16, 18). 4. The device as recited in claim 1, further comprising a selection valve (29) provided on the high speed signal line (24) in between the high speed shifting valve (26) and the shutoff valve (28) and a selection switch (27) for, when activated, shifting the selection valve (29) into a bypass position where a pump-side extension part of the high speed signal line (24) upstream the shutoff valve (28) is connected through a bypass signal line (24a) to a motor-side extension part of the high speed signal line (24) downstream the shutoff valve (28). 5. A travel control device for excavators, comprising: at least one main fluid pump (1, 2) and an auxiliary pump (4) each for discharging a hydraulic flow; left and right travel motors (12, 14) driven by the hydraulic flow of the main fluid pump (1, 2) and respectively provided with speed changing mechanisms (13, 15); travel control spools (16, 18) for controlling the hydraulic flow to the left and right travel motors (12, 14); electric travel control devices (20, 22) for generating an electric current in proportion to the amount of displacement thereof; a high speed shifting valve (26) provided on a high speed signal line (24) interconnecting the auxiliary pump (4) and the speed changing mechanisms (13, 15) for cutting off or transmitting a high speed signal pressure to the speed changing mechanisms (13, 15); a travel signal detection means (32) for detecting the magnitude of the electric current outputted from the electric travel control devices (20, 22); and a solenoid-operated shutoff valve (28) provided on the high speed signal line (24) in a serial relationship with the high speed shifting valve (26) for closing the high speed signal line (24) to keep the speed changing mechanisms (13, 15) in a low speed condition if the electric current detected by the travel signal detection means (32) is no greater than a predetermined current value and for opening the high speed signal line (24) to keep the speed changing mechanisms (13, 15) in a high speed condition if the electric current detected by the travel signal detection means (32) exceeds the predetermined current value.