A shovel includes a lower traveling body, an upper rotating body, an attachment including a boom and an arm, a controller, an engine, and a hydraulic pump that is driven by the engine and discharges hydraulic oil to drive the attachment. The controller is configured to obtain a hydraulic load applied to the attachment and calculate an engine speed command at predetermined time intervals based on the obtained hydraulic load.
1. A shovel, comprising:
a lower traveling body;
an upper rotating body;
an attachment including a boom and an arm;
a controller;
an engine; and
a hydraulic pump that is driven by the engine and discharges hydraulic oil to drive the attachment,
wherein the controller is configured to obtain a hydraulic load applied to the attachment, and increase an engine speed command as the hydraulic load increases and decrease the engine speed command after the hydraulic load increases, by predicting an engine speed that provides an engine output corresponding to the obtained hydraulic load based on the obtained hydraulic load and outputting the engine speed command corresponding to the predicted engine speed at predetermined time intervals.
2. The shovel as claimed in claim 1 , wherein the engine speed command reaches a maximal value at substantially a same time as the hydraulic load reaches a maximum value.
3. The shovel as claimed in claim 1 , wherein the engine speed command reaches a maximal value at a time earlier than a time at which an actual engine speed reaches a minimal value.
4. The shovel as claimed in claim 1 , wherein the engine speed command is based on a decrease in the engine speed predicted based on the hydraulic load.
5. The shovel as claimed in claim 1 , wherein the controller estimates the hydraulic load by using a model of the hydraulic pump.
6. The shovel as claimed in claim 1 , wherein the controller estimates the hydraulic load based on a value detected by a swash-plate angle sensor.
7. The shovel as claimed in claim 1 , wherein the controller estimates the hydraulic load based on a value detected by a hydraulic actuator pressure sensor.
8. The shovel as claimed in claim 1 , wherein the controller determines a maximum allowable value of target pump absorption torque based on one of a boost pressure and a fuel injection limiting value.
9. The shovel as claimed in claim 1 , wherein
the hydraulic pump is a variable-displacement, swash-plate hydraulic pump, and is configured to change a swash-plate angle according to a swash-plate angle command from the controller; and
the controller is configured to
generate the swash-plate angle command according to a horsepower control based on a discharge pressure of the hydraulic pump and target pump absorption torque, and
adjust the swash-plate angle command so that a deviation between a current swash plate angle received as feedback and the swash-plate angle command decreases.
10. The shovel as claimed in claim 1 , wherein the controller obtains pump absorption torque based on a discharge pressure and a discharge rate of the hydraulic pump.
11. The shovel as claimed in claim 1 , wherein the controller obtains a value detected by a toque sensor as pump absorption torque.
12. The shovel as claimed in claim 1 , wherein the controller calculates the engine speed command in real time based on an optimal control theory by using a model for prediction of a behavior of the engine.
13. The shovel as claimed in claim 1 , wherein the controller predicts the engine speed by adjusting a target engine speed set by an engine speed setter based on pump absorption torque, and outputs the adjusted target engine speed as the engine speed command.
14. The shovel as claimed in claim 13 , wherein the controller outputs the engine speed command that is lower than the target engine speed in response to a sharp decrease in the hydraulic load that causes an actual engine speed to become higher than the target engine speed.