Four-legged construction machine having slope stability system with locking valves

A machine for road work comprising:

• a frame;
• a plurality of ground engaging units including a first rear ground engaging unit and a second rear ground engaging unit;
• a plurality of vertically moveable legs, each leg connecting one of the plurality of ground engaging units to the frame, the plurality of vertically moveable legs including a first rear leg connected to the first rear ground engaging unit and a second rear leg connected to the second rear ground engaging unit;
• and
• a hydraulic system to control a height of each of the plurality of vertically moveable legs, the hydraulic system comprising:
• a fluid circuit to control fluid between the first rear leg and the second rear leg;
• a load holding valve to let fluid into and out of the fluid circuit;
• a control valve system to let fluid into and out of the load holding valve, the control valve connected to a source of pressurized hydraulic fluid and a fluid reservoir;
• a first lock valve to control flow of fluid from the first rear leg to the second rear leg in a first direction;
• a second lock valve to control flow of fluid from the second rear leg to the first rear leg in a second direction;
• a first float valve configured to connect the first rear leg to the control valve system;
• and
• a second float valve configured to connect the second rear leg to the control valve system,
• wherein each of the first and second legs comprises:
• a cylinder;
• a piston disposed in the cylinder;
• and
• a rod extending from the piston out of the cylinder;
• wherein the first and second lock valves connect to piston-ends of the cylinders;
• and
• wherein the first and second float valves connect the first and second lock valves to the load holding valve.

A method for controlling side-to-side slope of a four-legged construction machine having multiple independent propulsors each mounted to a hydraulic lifting device, the method comprising:

• adjusting a height of first and second rear hydraulic lifting devices of the multiple independent propulsors by connecting to a high pressure source;
• traversing a ground surface having a changing topography with the multiple independent propulsors;
• floating individual heights of the first and second rear hydraulic lifting devices in a fluid circuit;
• activating a lock valve positioned between the first and second rear hydraulic lifting devices to inhibit flow out of a piston-end of the first rear hydraulic lifting device;
• activating a float valve positioned between the lock valve and the second rear hydraulic lifting device to connect a piston-end of the second rear hydraulic lifting device to a low pressure source;
• and
• lifting the first rear hydraulic lifting device by:
• activating a second lock valve positioned between the first lock valve and the first rear hydraulic lifting device to connect the piston-end of the first rear hydraulic lifting device to the high pressure source.

A method for controlling side-to-side slope of a four-legged construction machine having multiple independent propulsors each mounted to a hydraulic lifting device, the method comprising:

• adjusting a height of first and second rear hydraulic lifting devices of the multiple independent propulsors by connecting to a high pressure source;
• traversing a ground surface having a changing topography with the multiple independent propulsors;
• floating individual heights of the first and second rear hydraulic lifting devices in a fluid circuit;
• activating a lock valve positioned between the first and second rear hydraulic lifting devices to inhibit flow out of a piston-end of the first rear hydraulic lifting device;
• activating a float valve positioned between the lock valve and the second rear hydraulic lifting device to connect a piston-end of the second rear hydraulic lifting device to a low pressure source;
• and
• lowering the first rear hydraulic lifting device by:
• closing the first lock valve;
• and
• moving a control valve to connect a piston-end of the first rear hydraulic lifting device to a tank.