Oil pressure unit and speed control method of motor in oil pressure unit

The present invention relates to an oil pressure unit for driving an oil pressure pump with a motor.

Conventionally, in an oil pressure unit having an oil pressure pump directly connected to a motor as a drive source, a speed control (PI control) calculation is executed to calculate a current command value through comparison of a speed command value of the motor and a current rotation speed, and a current control based on the current command value is realized by an inverter. The motor controlled by the inverter is then driven so that pressure oil is discharged from the oil pressure pump (e.g., patent document 1).

Patent document 1: Japanese Laid-Open Patent Publication No. 2004-162860

In such oil pressure unit, the pressure of oil (oil pressure) becomes larger as a total amount of the oil discharged from the oil pressure pump by a drive of the oil pressure pump increases. An increase in the oil pressure leads to an increase in a load of the oil pressure pump in discharge, and causes a load torque of the motor to become larger.

Thus, in such oil pressure unit, in a case where a stepwise speed command value is provided, if a rotation speed of the motor drastically rises in response to the speed command value, the load of the oil pressure pump drastically increases and the load torque of the motor drastically becomes large. If the load torque of the motor drastically becomes large, the speed control constituted by the PI control cannot follow, and the rotation speed of the motor might lower.

A method of preventing lowering of the rotation speed of the motor includes a method of improving a response of the control by shortening a control period of the PI control by improving a processing speed of a microcomputer that performs the PI control. However, a cost of the microcomputer increases if such method is adopted. Furthermore, since the improvement of the processing speed of the microcomputer has physical limitations, lowering in the rotation speed of the motor cannot be effectively prevented with such method.

Another method includes a method using the load torque for the speed control in which the load torque is estimated from acceleration information obtained by differentiating the rotation speed of the motor. However, since the rotation speed is discrete information, a noise component increases by differentiation. Thus, there is a possibility a behavior will become unstable if the speed control is executed using the load torque.

Moreover, if a gain of the speed control is increased to improve a response to the load variation, an oscillation might occur when the stepwise speed command value is provided.

In view of the above problems, it is an object of the present invention to provide a technique capable of improving a followability of the rotation speed of the motor with respect to the variation of the load of the oil pressure pump.

A first aspect of an oil pressure unit according to the present invention relates to the oil pressure unit for supplying oil to an actuator by driving an oil pressure pump (16A) with a motor (15), characterized in that it comprises an inverter (14) for supplying power to the motor (15), a load sensor (17) for detecting a load of the oil pressure pump (16A), a rotation sensor (21) for detecting a rotation speed of the motor (16), a current command value calculation means (12) for calculating a current command value so that a deviation between a speed command value representing a target rotation speed of the motor (15) and a rotation speed of the motor (15) converges to zero, a correction means (18A; . . . ; 18D) for correcting the current command value based on the load of the oil pressure pump (16A), and a control signal generation means (13) for outputting a control signal to the inverter (14) based on a corrected current command value.

According to a second aspect of the oil pressure unit, in the first aspect, it is characterized in that said correction means (18A; . . . ; 18D) corrects the current command value to raise the rotation speed of said motor (15) with an increase in the load of said oil pressure pump (16A).

According to a third aspect of the oil pressure unit, in the first or the second aspect, it is characterized in that said correction means (18A; . . . ; 18D) increases the current command value with an increase in the load of said oil pressure pump (16A).

According to a fourth aspect of the oil pressure unit, in any one of the first to the third aspects, it is characterized in that said correction means (18A) acquires a correction value (If) using a correction coefficient (Kf) set in advance, and adds said correction value (If) to said current command value.

According to a fifth aspect of the oil pressure unit, in any one of the first to the third aspects, it is characterized in that said correction means (18B; 18C; 18D) acquires a correction value (If) using a data table DT acquired in advance, and adds said correction value (If) to said current command value.

According to a sixth aspect of the oil pressure unit, in any one of the first to the fifth aspects, it is characterized in that said load sensor (17) is a pressure sensor (17) for detecting a pressure of oil in a discharge line (19) of said oil pressure pump (16A).

A seventh aspect of the oil pressure unit relates to a speed control method of a motor (15) in the oil pressure unit for supplying oil to an actuator by driving an oil pressure pump (16A) with the motor (15) controlled by an inverter (14) and, characterized in that it comprises the steps of: a) detecting a load of said oil pressure pump (16A); b) detecting a rotation speed of said motor (15); c) calculating a current command value so that a deviation between a speed command value representing a target rotation speed of said motor (15) and a rotation speed of said motor (15) converges to zero; d) correcting the current command value based on the load of said oil pressure pump (16A); and e) outputting a control signal to said inverter (14) based on the corrected current command value.

According to the first aspect to the seventh aspect of the oil pressure unit of the present invention, the followability of the rotation speed of the motor with respect to the variation of the load (load oil pressure) of the oil pressure pump can be improved since the current command value is corrected based on the load of the oil pressure pump.