Shovel and method of controlling shovel

1. A shovel comprising:

an excavation operation detection part configured to detect a complex excavation operation of the shovel, the complex excavation operation including a boom raising operation, and an arm closing operation or a bucket closing operation;

a position detection part configured to detect a position of the shovel;

a maximum allowable pressure calculation part configured to calculate, during the detected complex excavation operation, a maximum allowable pressure of a contraction-side oil chamber of a boom cylinder based on the position of the shovel detected during the detected complex excavation operation, the maximum allowable pressure being a pressure of the contraction-side oil chamber of the boom cylinder corresponding to an excavation reaction force at a time when the shovel is lifted by the excavation reaction force; and

a boom cylinder pressure control part configured to control the pressure of the contraction-side oil chamber of the boom cylinder not to exceed the maximum allowable pressure during the detected complex excavation operation.

2. The shovel as claimed in claim 1 , wherein the boom cylinder pressure control part is configured to increase a flow rate of hydraulic oil flowing out from the contraction-side oil chamber of the boom cylinder, in response to the pressure of the contraction-side oil chamber of the boom cylinder reaching a predetermined pressure that is less than or equal to the maximum allowable pressure.

3. The shovel as claimed in claim 1 , further comprising:

an arm cylinder pressure control part configured to control a pressure of an expansion-side oil chamber of an arm cylinder so as to prevent the pressure of the contraction-side oil chamber of the boom cylinder from exceeding the maximum allowable pressure when the complex excavation operation of the arm closing operation and the boom raising operation is performed.

4. The shovel as claimed in claim 3 , wherein the arm cylinder pressure control part is configured to reduce a flow rate of hydraulic oil flowing into the expansion-side oil chamber of the arm cylinder, in response to the pressure of the contraction-side oil chamber of the boom cylinder reaching the maximum allowable pressure.

5. The shovel as claimed in claim 1 , wherein the position detection part is configured to detect an angle of a boom relative to an upper-part turning body, an angle of an arm relative to the boom, and an angle of a bucket relative to the arm.

6. The shovel as claimed in claim 1 , wherein when the shovel is lifted, the shovel rotates around a position that is determined based on a turning angle between an upper-part turning body and a lower-part traveling body.

7. The shovel as claimed in claim 1 , wherein the maximum allowable pressure of the contraction-side oil chamber of the boom cylinder differs depending on the position of the shovel detected during the detected complex excavation operation.

8. A method of controlling a shovel that includes a processor configured to execute a program that causes the processor to implement processes of the method, the method comprising:

detecting a complex excavation operation of the shovel, the complex excavation operation including a boom raising operation, and an arm closing operation or a bucket closing operation;

detecting a position of the shovel;

calculating, during the detected complex excavation operation, a maximum allowable pressure of a contraction-side oil chamber of a boom cylinder based on the position of the shovel detected during the detected complex excavation operation, the maximum allowable pressure being a pressure of the contraction-side oil chamber of the boom cylinder corresponding to an excavation reaction force at a time when the shovel is lifted by the excavation reaction force; and

controlling the pressure of the contraction-side oil chamber of the boom cylinder not to exceed the maximum allowable pressure during the detected complex excavation operation.