Quick coupler circuit and quick coupler attachment/detachment method

1. A quick coupler circuit for attaching an attachment to a quick coupler and detaching the attachment from the quick coupler, the quick coupler circuit comprising:

a coupler cylinder configured to be driven due to a supply of hydraulic fluid, the coupler cylinder being driven in a locking direction to lock the attachment to the quick coupler and in an unlocking direction to unlock the attachment from the quick coupler;

an actuator configured to be driven due to the supply of hydraulic fluid, the actuator being a work implement cylinder configured to drive a work implement;

a hydraulic pump configured to be connected in parallel with the coupler cylinder and the actuator, and the hydraulic pump being configured to supply the hydraulic fluid to the coupler cylinder and the actuator, the hydraulic pump being a variable displacement pump;

a boosting valve configured to switch between

a boosting position to raise a pressure of the hydraulic fluid supplied from the hydraulic pump to the coupler cylinder, and

a non-boosting position to not change the pressure of the hydraulic fluid supplied from the hydraulic pump to the coupler cylinder;

a coupler changeover valve configured to switch between

a lock-side position to supply hydraulic fluid from the hydraulic pump to the coupler cylinder so as to drive the coupler cylinder in the locking direction, and

an unlock-side position to supply the hydraulic fluid from the hydraulic pump to the coupler cylinder so as to drive the coupler cylinder in the unlocking direction; and

a changeover switch configured to switch between an unlock position, a lock position, and a hold position,

wherein

when the changeover switch switches to the lock position, the boosting valve switches to the boosting position and the coupler changeover valve switches to the lock-side position,

when the changeover switch switches to the hold position, the boosting valve switches to the non-boosting position, the coupler changeover valve switches to the lock-side position, and the hydraulic fluid is supplied from the hydraulic pump to the coupler cylinder in response to driving of the hydraulic pump, and

when the changeover switch switches to the unlock position, the boosting valve switches to the boosting position and the coupler changeover valve switches to the unlock-side position, and

when the changeover switch switches to the unlock position or the lock position, a portion of the hydraulic fluid supplied from the hydraulic pump to the coupler cylinder is returned to the hydraulic pump via the boosting valve, thereby causing the pressure of the hydraulic fluid supplied from the hydraulic pump to the coupler cylinder to rise.

2. A quick coupler circuit for attaching an attachment to a quick coupler and detaching the attachment from the quick coupler, the quick coupler circuit comprising:

a coupler cylinder configured to be driven due to a supply of hydraulic fluid, the coupler cylinder being driven in a locking direction to lock the attachment to the quick coupler and in an unlocking direction to unlock the attachment from the quick coupler;

an actuator configured to be driven due to the supply of hydraulic fluid;

a first hydraulic pump configured to be connected in parallel with the coupler cylinder and the actuator, and the first hydraulic pump being configured to supply the hydraulic fluid to the coupler cylinder and the actuator, the first hydraulic pump being a fixed displacement pump;

a boosting valve configured to switch between

a boosting position to raise a pressure of the hydraulic fluid supplied from the first hydraulic pump to the coupler cylinder, and

a non-boosting position to not change the pressure of the hydraulic fluid supplied from the first hydraulic pump to the coupler cylinder;

a coupler changeover valve configured to switch between

a lock-side position to supply hydraulic fluid from the first hydraulic pump to the coupler cylinder so as to drive the coupler cylinder in the locking direction, and

an unlock-side position to supply the hydraulic fluid from the first hydraulic pump to the coupler cylinder so as to drive the coupler cylinder in the unlocking direction; and

a changeover switch configured to switch between an unlock position, a lock position, and a hold position, the unlock position, the lock position, and the hold position being three discrete physical positions,

wherein

when the changeover switch switches to the lock position, the boosting valve switches to the boosting position and the coupler changeover valve switches to the lock-side position,

when the changeover switch switches to the hold position, the boosting valve switches to the non-boosting position, the coupler changeover valve switches to the lock-side position, and a portion of the hydraulic fluid supplied from the first hydraulic pump to the actuator is supplied to the coupler cylinder,

when the changeover switch switches to the unlock position, the boosting valve switching to the boosting position and the coupler changeover valve switching to the unlock-side position, and

when the changeover switch switches to the unlock position or the lock position, the hydraulic fluid supplied from the first hydraulic pump to the actuator is interrupted by the boosting valve, thereby causing the pressure of the hydraulic fluid supplied from the first hydraulic pump to the coupler cylinder to rise.

3. The quick coupler circuit according to claim 2 , further comprising:

a second hydraulic pump configured to supply hydraulic fluid to a work implement; and

a shuttle valve disposed between the coupler changeover valve and the boosting valve, and the shuttle valve being connected to the second hydraulic pump,

the shuttle valve being configured to allow hydraulic fluid having a highest pressure among the hydraulic fluid supplied from the first hydraulic pump and the hydraulic fluid supplied from the second hydraulic pump, to pass through to a coupler changeover valve side.

4. A quick coupler attachment/detachment method for attaching an attachment to a quick coupler and detaching the attachment from the quick coupler, the method comprising:

locking the attachment to the quick coupler;

holding the attachment to the quick coupler;

unlocking the attachment from the quick coupler; and

operating a changeover switch between a lock position, a hold position, and an unlock position when executing the locking of the attachment, the holding of the attachment, and the unlocking of the attachment, respectively,

wherein

when locking, hydraulic fluid is supplied from a hydraulic pump to a coupler cylinder so that the coupler cylinder is driven in a locking direction to lock the quick coupler to the attachment, a portion of the hydraulic fluid being returned to the hydraulic pump via a boosting valve in response to the changeover switch being in the lock position, thereby causing the pressure of the hydraulic fluid supplied from the hydraulic pump to the coupler cylinder to rise;

when holding, the hydraulic fluid is supplied from the hydraulic pump to the coupler cylinder in response to the driving of the hydraulic pump so that the coupler cylinder is driven in the locking direction, a portion of the hydraulic fluid not being returned to the hydraulic pump via the boosting valve in response to the changeover switch being in the hold position; and

when unlocking, the hydraulic fluid is supplied from the hydraulic pump to the coupler cylinder so that the coupler cylinder is driven in an unlocking direction to unlock the attachment from the quick coupler, a portion of the hydraulic fluid being returned to the hydraulic pump via the boosting valve in response to the changeover switch being in the unlock position, thereby causing the pressure of the hydraulic fluid supplied from the hydraulic pump to the coupler cylinder to rise.