Methods of measuring pressure of hydraulic fluid, methods of evaluating soundness and hydraulic drive devices for carrying out the methods

A method of evaluating soundness of a hydraulic drive device, wherein the hydraulic drive device comprises a pressure generator for generating a flow of a pressurized hydraulic fluid, a pressure-variable accumulator for accumulating the pressure of the pressurized hydraulic fluid supplied from the pressure generator, and a pressure control unit that is arranged and constructed to receive the pressurized hydraulic fluid from the accumulator and to control the pressure of the pressurized hydraulic fluid in response to an input from an external device, so that the pressurized hydraulic fluid having the controlled pressure is used for driving an operation device, comprising:

• detecting a first pressure of the hydraulic fluid within a flow path of the hydraulic fluid by a first pressure sensor, wherein the flow path extends between the pressure control unit and the operation device, and the first pressure sensor is coupled to the flow path,
• detecting a second pressure of the hydraulic fluid discharged from the accumulator by a second pressure sensor, wherein the second pressure sensor is coupled to the accumulator,
• determining a stabilization time by an operation control unit, wherein the stabilization time is a time when an absolute value of a pressure gradient per unit time of the pressurized hydraulic fluid supplied from the accumulator becomes smaller than a predetermined value during the supply of the hydraulic fluid from the pressure control unit to the operation device, and the operation control unit receives detection signals from the first and second pressure sensors,
• determining a pressure drop of the second pressure during a period between a time prior to starting the operation of the pressure control unit and the stabilization time,
• determining the first pressure at the stabilization time or at a time immediately after the stabilization time, and
• comparing the determined pressure drop with a pressure drop under a normal condition and/or comparing the detected first pressure at the stabilization time with a value under normal condition of the first pressure at stabilization time or at a time immediately after the stabilization time.

A method of measuring a pressure of a hydraulic fluid supplied from a hydraulic drive device to an operation device, wherein the hydraulic drive device comprises a pressure generator arranged and constructed to pressurize the hydraulic fluid, an accumulator arranged and constructed to receive the supply of the pressurized hydraulic fluid from the pressure generator in order to accumulate the pressure of the pressurized hydraulic fluid, and a pressure control unit arranged and constructed to receive the pressurized hydraulic fluid from the accumulator and to control the pressure of the hydraulic fluid to be supplied to the operation device in response to operation of an external device, comprising:

• measuring a first pressure (Pm) of the hydraulic fluid within a first flow path connecting the pressure control unit and the operation device,
• measuring a second pressure (Pa) of the hydraulic fluid within a second flow path connecting the accumulator and the pressure control unit,
• determining a stabilization time (T) that is the time when an absolute value of a pressure gradient per unit time of the second pressure becomes smaller than a predetermined value, and
• determining a third pressure (Pw) of the hydraulic fluid supplied to the operation device based on the first pressure that is measured at the stabilization time (T) or at a time immediately after the stabilization time (T).

A method of evaluating a condition of a hydraulic fluid supplied from a hydraulic drive device to an operation device, wherein the hydraulic drive device comprises a pressure generator arranged and constructed to pressurize the hydraulic fluid, an accumulator arranged and constructed to receive the supply of the pressurized hydraulic fluid from the pressure generator in order to accumulate the pressure of the pressurized hydraulic fluid, and a pressure control unit arranged and constructed to receive the pressurized hydraulic fluid from the accumulator and to control the pressure of the hydraulic fluid to be supplied to the operation device in response to operation of an external device, comprising:

• measuring a pressure (Pa) of the hydraulic fluid within a flow path connecting the accumulator and the pressure control unit,
• determining a stabilization time (T) that is the time when an absolute value of a pressure gradient per unit time of the pressure (Pa) becomes smaller than a predetermined value,
• determining a pressure drop (ΔPa) of the pressure (Pa) during a period between a time (T0) when the second pressure begins to decrease or at a time before the time (T0) and the stabilization time (T), and
• comparing the determined pressure drop (ΔPa) of the pressure (Pa) with a predetermined pressure drop to be obtained under a normal condition.