Electronically controlled hydraulic system for lowering a boom in an emergency

In a machine having a pump, a boom, and a load carrier coupled to the boom, wherein the boom is moved by a first hydraulic actuator that has first and second chambers and the load carrier is moved with respect to the boom by a second hydraulic actuator that has third and fourth chambers, a method for lowering the boom during an abnormal operating condition comprising:

• coupling the first hydraulic actuator to a supply line and a tank return line by a first valve assembly, wherein the supply line receives pressurized fluid from the pump under normal operating conditions;
• coupling the second hydraulic actuator to the supply line and the tank return line by a second valve assembly;
• when pressurized fluid is unavailable from the pump, activating the first valve assembly to drain hydraulic fluid under pressure from the first chamber of the first hydraulic actuator into the supply line, which results in the boom lowering;
• and
• when pressurized fluid is unavailable from the pump, selectively activating the second valve assembly to cause hydraulic fluid to flow from the supply line into the third chamber of the second hydraulic actuator, wherein as the boom lowers, an angular relationship of the load carrier with respect to a surface on which the machine is supported is maintained substantially constant.

In a machine having a boom, that is moved by a first hydraulic actuator, and a load carrier, that is coupled to the boom and moved with respect thereto by a second hydraulic actuator;

• a method for moving the boom comprising:
• when pressurized fluid from a source is not available draining hydraulic fluid under pressure from the first hydraulic actuator;
• when pressurized fluid from the source is not available, conveying the hydraulic fluid from the first hydraulic actuator to the second hydraulic actuator;
• sensing inclination of the load carrier with respect to a given axis;
• and
• controlling flow of the hydraulic fluid into the second hydraulic actuator to produce movement of the load carrier which maintains the inclination of the load carrier with respect to the given axis substantially constant.