Abstract: A first-side check valve prevents a hydraulic fluid from being discharged out of a retard chamber, and a second-side check valve prevents the hydraulic fluid from being discharged out of an advance chamber. A first-side control valve opens or closes a first-side discharge passage by a pilot pressure received through a retard pilot passage. A second-side control valve opens or closes a second-side discharge passage by the pilot pressure received through an advance pilot passage. Another check valve is disposed in a supply passage between a phase switch valve and a branch point, at which a supply passage is branched.

Abstract: A phase control valve, which supplies a drive hydraulic pressure to an advance chamber or a retard chamber, is integrated with a drain switch valve, which controls opening and closing of an advance drain control valve and opening and closing of a retard drain control valve, to form a solenoid spool valve. The advance drain control valve is provided in an advance check valve bypass passage, which bypasses an advance check valve, and is driven by a pilot hydraulic pressure to open and close the advance check valve bypass passage. The retard drain control valve is provided in a retard check valve bypass passage, which bypasses a retard check valve, and is driven by a pilot hydraulic pressure to open and close the retard check valve bypass passage.

Abstract: One of retard passages, which supplies working fluid to one of retard chambers, is a dedicated passage. The other remaining retard passages, which supply the working fluid to the other remaining retard chambers, are branch passages, which are branched from a retard passage that serves as a supply passage. With this construction, a flow quantity of working fluid per unit time supplied from the one of retard passages to the one of retard chambers becomes larger than a flow quantity of working fluid per unit time supplied from the other remaining retard passages to the other remaining retard chambers. Thus, the one of retard chambers can be filled with the working fluid earlier than the other remaining retard chambers.

Abstract: A first-side check valve prevents a hydraulic fluid from being discharged out of a retard chamber, and a second-side check valve prevents the hydraulic fluid from being discharged out of an advance chamber. A first-side control valve opens or closes a first-side discharge passage by a pilot pressure received through a retard pilot passage. A second-side control valve opens or closes a second-side discharge passage by the pilot pressure received through an advance pilot passage. Another check valve is disposed in a supply passage between a phase switch valve and a branch point, at which a supply passage is branched.

Abstract: A phase control valve, which supplies a drive hydraulic pressure to an advance chamber or a retard chamber, is integrated with a drain switch valve, which controls opening and closing of an advance drain control valve and opening and closing of a retard drain control valve, to form a solenoid spool valve. The advance drain control valve is provided in an advance check valve bypass passage, which bypasses an advance check valve, and is driven by a pilot hydraulic pressure to open and close the advance check valve bypass passage. The retard drain control valve is provided in a retard check valve bypass passage, which bypasses a retard check valve, and is driven by a pilot hydraulic pressure to open and close the retard check valve bypass passage.

Abstract: One of retard passages, which supplies working fluid to one of retard chambers, is a dedicated passage. The other remaining retard passages, which supply the working fluid to the other remaining retard chambers, are branch passages, which are branched from a retard passage that serves as a supply passage. With this construction, a flow quantity of working fluid per unit time supplied from the one of retard passages to the one of retard chambers becomes larger than a flow quantity of working fluid per unit time supplied from the other remaining retard passages to the other remaining retard chambers. Thus, the one of retard chambers can be filled with the working fluid earlier than the other remaining retard chambers.