Abstract: A swing control apparatus and a swing control method for a construction machine are provided. The swing control apparatus includes a start position estimation unit, a stop target position calculation unit, and a swing motor position control unit. Even if an operator releases a lever or commands a stop at different times, an upper swing structure of the construction machine (for example, excavator) can be stopped within a predetermined range, and thus the inconvenience caused by an additional driving operation, which is required as the stop position differs according to the time point where the stop command starts, can be solved.

Abstract: Hydraulic center and lock structure for the caster wheel of, for example, a tractor-drawn plow, operative on a centering element rigid with the standard of the caster wheel for forcibly centering the standard and ultimately locking the standard against turning about its axis when the caster wheel is in its straight-ahead position. The hydraulic device is bi-directionally operative for disengagement from the centering element to enable free castering of the wheel, as when the plow is raised for transport. The invention also provides two forms hydraulic control for coordinating the raising and lowering of the plow with unlocking and locking the caster wheel. In one form, the system provides for trapping fluid in the caster wheel cylinder in its straight-ahead position, with a separate valve operated manually to release the fluid when the plow is lowered to operating condition. In another form the valve that releases the trapped fluid is made responsive to a predetermined pressure.