Control apparatus and control method for a forklift and forklift

A method of controlling a forklift having a lift lever;

• a hydraulic motor;
• a hydraulic pump;
• an oil tank;
• a lift cylinder;
• and a flow rate control valve coupled to the oil tank, wherein, at a time of a lift-up operation based on an operation of the lift lever, the hydraulic motor drives the hydraulic pump to supply oil from the oil tank to a lift cylinder by the hydraulic pump thereby to extend the lift cylinder, whilst at a time of a lift-down operation based on an operation of the lift lever, the oil is collected to the oil tank from the lift cylinder due to a shrinking operation of the lift cylinder,
• the method comprising:
• detecting an operation amount of the lift lever;
• obtaining a target acceleration of the hydraulic motor based on the operation amount thus detected;
• obtaining a torque command value of the hydraulic motor based on the target acceleration;
• determining as a non-regeneration state or as a regeneration state, based on the torque command value;
• coupling the flow rate control valve with the lift cylinder when determined as the non-regeneration state;
• and
• coupling the hydraulic pump with the lift cylinder and controlling an output of the hydraulic motor by controlling an inverter in accordance with the torque command value when determined as the regeneration state.

A forklift comprising:

• a lift lever;
• a hydraulic motor;
• a hydraulic pump;
• an oil tank;
• a lift cylinder;
• and
• a control apparatus including:
• an inverter controller for controlling an output of the hydraulic motor;
• a flow rate control valve, coupled to the oil tank, for limiting a flow rate of the oil collected to the oil tank;
• a change-over member for selectively coupling the lift cylinder to the flow rate control valve or the hydraulic pump;
• and an operation amount detector for detecting an operation amount of the lift lever,
• wherein at a time of a lift-up operation based on an operation of the lift lever, the hydraulic motor drives the hydraulic pump to supply oil from the oil tank to a lift cylinder by the hydraulic pump thereby to extend the lift cylinder, whilst at a time of a lift-down operation based on an operation of the lift lever, the oil is collected to the oil tank from the lift cylinder due to a shrinking operation of the lift cylinder,
• wherein the control apparatus obtains a target acceleration of the hydraulic motor based on the operation amount detected by the operation amount detector;
• the control apparatus obtains a torque command value of the hydraulic motor based on the target acceleration;
• the control apparatus determines as a non-regeneration state or as a regeneration state, based on the torque command value;
• and the control apparatus switches the change-over member so as to couple the lift cylinder to the flow rate control valve when determined as the non-regeneration state, and switches the change-over member so as to couple the lift cylinder to the hydraulic pump and making the inverter controller control the hydraulic motor in accordance with the torque command value when determined as the regeneration state.