Hydraulic machine

Abstract

A hydraulic machine comprising: an actuator; a high-pressure accumulator; a high-pressure line that supplies pressurized oil to the actuator and to which the high-pressure accumulator is connected; a pump that supplies pressurized oil to the high-pressure line; a drive unit that drives the pump; and a control unit that controls the pump and the drive unit, wherein the control unit performs control such that, when the pressure in the high-pressure line is greater than or equal to a predetermined threshold pressure, the rotational speed of the drive unit is maintained at a predetermined first rotational speed, and when the pressure in the high-pressure line is less than the threshold pressure, the rotational speed of the drive unit is made a second rotational speed greater than the first rotational speed.

Description

Field of the InventionThe present disclosure relates to a hydraulic machine, and more particularly, to a hydraulic machine including a common pressure rail (CPR) that supplies pressurized fluid to actuators.General State of the ArtA hydraulic machine performs work by acquiring energy from the pressure of a fluid. Such a hydraulic machine includes, for example, heavy equipment such as an excavator. Recently, common pressure rail (CPR) hydraulic machines equipped with high pressure lines connected to an accumulator and supplying pressurized fluid to actuators have been known.Summary of the InventionTechnical SolutionAccording to a first aspect of the present disclosure, there is provided a hydraulic machine including: an actuator; a high-pressure accumulator; a high-pressure line for supplying pressurized fluid to the actuator and to which the high-pressure accumulator is connected; a pump for supplying pressurized fluid to the high-pressure line; a drive unit for driving the pump; and a control unit for controlling the pump and the drive unit, wherein the control unit controls the rotational speed of the drive unit to be maintained at a first rotational speed when the pressure in the high-pressure line is higher than a predetermined threshold pressure, and controls the rotational speed of the drive unit to be a second rotational speed higher than the first rotational speed when the pressure in the high-pressure line is lower than the threshold pressure.According to the first aspect of the present disclosure, there is an advantage that a hydraulic machine with CPR excellent in fuel consumption efficiency can be provided.In some examples, the first speed may be a speed within a range representing an optimal brake fuel consumption ratio.In some examples, the second speed may be determined based on a pressure within the high pressure line.In some examples, when the pressure in the high pressure line is higher than the threshold pressure, the controller may control the speed of the drive unit to be maintained at the first speed and control the torque of the drive unit to be maintained at a predetermined first torque; and when the pressure in the high pressure line is lower than the threshold pressure, control the speed of the drive unit to a second speed greater than the first speed and control the torque of the drive unit to the second torque.In some examples, the first speed and the first torque may be speed and torque within a range representing an optimal brake fuel consumption ratio of the hydraulic machine.In some examples, the second speed may be determined according to the pressure in the high pressure line, and the second torque may be a torque representing an optimal brake fuel consumption ratio at the second speed.In some examples, the control unit may control the volume of the pump according to an integral value obtained by integrating values obtained by multiplying the difference between the second torque and the current torque (T req- T cur) by the gain value and dividing the values by the difference value of the inlet and outlet pressures of the pump.In some examples, the controller may increase the volume of the pump as the integral value increases and may decrease the volume of the pump as the integral value decreases.In some examples, the controller may prevent the integral value from further increasing when the integral value reaches a predetermined maximum value.In some examples, the controller may calculate the torque of the pump from the pressure and volume of the pump and rotate the drive unit at a speed greater than the second speed when the instantaneous rate of change of the torque of the pump is positive and rotate the drive unit at a speed less than the second speed when the instantaneous rate of change of the torque of the pump is negative.In some examples, the controller may calculate the torque of the pump from the pressure and volume of the pump, and when the instantaneous rate of change of the torque of the pump is positive, rotate the drive unit at "the second speed + D*dT / dt" that is greater than the second speed, and when the instantaneous rate of change of the torque of the pump is negative, rotate the drive unit at "the second speed + D*dT / dt" that is less than the second speed, wherein D may be a gain value and dT / dt may be an instantaneous rate of change of the torque of the pump.The above aspects, the appended claims and the examples disclosed herein either before or hereinafter may be combined together as appropriate, as will be apparent to one skilled in the art.Further features and advantages will be apparent from the following description, claims, and drawings, and in part will be apparent to those skilled in the art or may be learned by practice of the disclosure described herein. Furthermore, control units, computer-readable media and computer program products are disclosed herein in connection with the aforementioned technical advantages.Brief Description of the DrawingsHereinafter, exemplary aspects of the present disclosure will be described in detail with reference to the accompanying drawings. FIG. 1 is a drawing schematically showing a configuration of a hydraulic machine according to an example of the present disclosure. FIG. 2 is a brake-specific fuel consumption (BSFC) card of a hydraulic machine according to an example of the present disclosure. FIG. 3 is a block diagram schematically showing the configuration of a drive unit torque regulator of a hydraulic machine control unit according to an example of the present disclosure. FIG. 4 is a graph showing that a drive unit torque regulator adjusts the volume of the pump to control the torque of the drive unit. FIG. 5 is a block diagram schematically showing the configuration of a drive unit speed compensator of a hydraulic machine control unit according to an example of the present disclosure. FIG. 6 is a graph showing that the drive unit speed compensator performs compensation. FIG. 7 is a block diagram schematically showing the general configuration of a control unit of a hydraulic machine according to an example of the present disclosure.Mode for Carrying Out the InventionHereinafter, exemplary aspects of the present disclosure will be described in detail with reference to the accompanying drawings. The aspects described below provide information necessary to enable those skilled in the art to practice the present disclosure.FIG. 1 is a drawing schematically showing a configuration of a hydraulic machine according to an example of the present disclosure.The hydraulic machine of the present disclosure typically relates to heavy equipment such as excavators, but may include, without limitation, any machine that performs work by acquiring energy from the pressure of a fluid.The hydraulic machine may include at least an actuator, a high pressure accumulator (310), a high pressure line (315), a pump (120), a drive unit (110), and a control unit (600). Additionally, in some examples, the hydraulic machine may include a low pressure accumulator (320) and a low pressure line (325). Additionally, in some examples, the hydraulic machine may include a tank. Additionally, in some examples, the hydraulic machine may include a valve (210) that opens or blocks the flow of fluid from the pump (120) to the high pressure line (315). Additionally, in some examples, the hydraulic machine may include a valve (210) that opens or blocks the flow of fluid from the pump to the low pressure line (325). Additionally, in some examples, the hydraulic machine may include a valve (not shown) that permits or blocks the flow of fluid from the high pressure line (315) to the actuator and a valve (not shown) that permits or blocks the flow of fluid from the actuator to the low pressure line (325).The actuator is connected to a high pressure line (315) and receives high pressure fluid from the high pressure line (315) and uses the energy from the pressure of the pressurized fluid to allow the hydraulic machine to perform work. Additionally, the actuator may be connected to the low pressure line (325) to discharge operating fluid into the low pressure line (325). The actuator may include, for example, a boom actuator ( 410), an arm actuator ( 420), a bucket actuator ( 430), a swing actuator ( 440), a travel actuator ( 451, 453), and the like. The boom actuator ( 410), the arm actuator ( 420), and the bucket actuator ( 430) may be hydraulic cylinders. The swing actuator ( 440) and the travel actuator ( 451, 453) may be hydraulic motors. The actuator may include an inlet port through which the actuator is connected to the high pressure line (315) and an outlet port through which the actuator is connected to the low pressure line (325).The high-pressure accumulator ( 310) is connected to the high-pressure line ( 315). Additionally, as described above, the high pressure line (315) may be connected to the actuator to supply pressurized fluid to the actuator.The low pressure accumulator (320) is connected to the low pressure line (325). Additionally, as described above, the low pressure line (325) may be connected to the actuator and the operating fluid may be discharged from the actuator through the low pressure line (325).The pump ( 120) pressurizes the operating fluid to generate pressurized fluid, and sends the pressurized fluid to the high-pressure accumulator ( 310) and the actuator through the high-pressure line ( 315). The pump (120) may be an axial piston pump in which the volume (volume of pressurized fluid discharged per revolution) is variable. The volume of the pump (120) may be controlled by the control unit (600). In some examples, the pump (120) includes a swashplate and the controller (600) may control the volume of the pump (120) by sending a signal that changes the angle of inclination of the swashplate of the pump (120) to the pump (120). The hydraulic machine may include at least one pump (120).The drive unit (110) is a component that drives the pump (120) and may typically include a motor. However, the present disclosure is not limited thereto, and may be other types of drive units capable of driving the pump ( 120), such as an electric motor.The control unit (600) may control each component of the hydraulic machine, in particular the volume of the pump (120) and the speed of the drive unit (110). The controller (600) may include an electronic controller that receives command input via an operator interface and / or reads values from various sensors, interprets the command and / or data, and then generates and outputs a control signal.The tank provides operating fluid to the hydraulic pump (120) and may store operating fluid returned from the actuator through the low pressure line (325).FIG. 2 is a brake-specific fuel consumption (BSFC) card of a hydraulic machine according to an example of the present disclosure.In a conventional hydraulic machine without an accumulator, the rotational speed of the drive unit (110) and the volume of the pump (120) for maintaining the output are variable. On the other hand, in a hydraulic machine with CPR according to an example of the present disclosure, in a normal state in which the actuator consumes a flow rate lower than the maximum flow rate that the pump ( 120) can supply, the rotational speed of the drive unit ( 110) may be controlled to be maintained at a predetermined first rotational speed. In addition, at this time, the torque of the drive unit ( 110) may be controlled to be maintained at a predetermined first torque.The first speed and the first torque may be the speed and the torque within a range representing the optimal brake fuel consumption ratio of the hydraulic machine, the so-called sweet spot. A low brake fuel consumption ratio means that the same energy can be achieved with relatively low fuel consumption.In some examples, the first speed and the first torque may be provided as predetermined values. Referring to FIG. 2, the first speed may be, for example, 1,400 U / min and the first torque may be, for example, set to 700 Nm, and at these settings, the pump ( 120) may supply the maximum flow rate that the pump ( 120) may supply to the high pressure line ( 315), for example, 220 Lpm.The rotational speed of the drive unit ( 110) can be controlled directly by a control signal. However, the torque of the drive unit (110) is controlled according to the volume of the pump (120) and the pressure difference between the inlet and the outlet of the pump (120) (i.e., the outlet pressure of the pump (120)-the inlet pressure of the pump (120)) (assuming that the majority of the torque is consumed by the pump (120)). When the drive unit (110) is operated at a speed of 1,400 U / min, the pump (120) may be controlled to have a maximum volume, for example, to correspond to a torque of 700 Nm. However, these settings may have the following restrictions:When the actuator consumes a flow rate exceeding the maximum flow rate that the pump ( 120) can supply, the pressure in the high-pressure line ( 315) rapidly drops, and the performance of the actuator deteriorates. Therefore, the flow rate of the pump (120) supplied to the high pressure line (315) must be increased to recharge the high pressure accumulator (310) and also send the required flow rate to the actuator. However, fixed speed and torque cannot meet these situations.Therefore, in a hydraulic machine according to an example of the present disclosure, in a normal state in which the actuator consumes a flow rate lower than the maximum flow rate that the pump ( 120) can supply, as described above, the control unit ( 600) may control the rotational speed of the drive unit ( 110) to be maintained at the first rotational speed and the torque of the drive unit ( 110) to be maintained at the first torque. However, if the actuator consumes a flow rate that exceeds the maximum flow rate that the pump (120) can supply, the controller (600) may control the speed of the drive unit (110) to a second speed that is greater than the first speed, so that the pump (120) can supply more flow rate to the high pressure line (315).Since the pressure in the high pressure line (315) drops when the actuator consumes a flow rate that exceeds the maximum flow rate that the pump (120) can supply, it can be determined by measuring the pressure in the high pressure line (315) whether the actuator consumes a flow rate that exceeds the maximum flow rate that the pump (120) can supply. Accordingly, the control unit (600) may control the rotational speed of the drive unit (110) to be maintained at a predetermined first rotational speed when the pressure in the high pressure line (315) is higher than a predetermined threshold pressure and the rotational speed of the drive unit (110) to be a second rotational speed higher than the first rotational speed when the pressure in the high pressure line (315) is lower than the threshold pressure. Here, the second rotation speed may be determined according to the pressure in the high-pressure line ( 315). In some examples, a lookup table mapping the values of pressure in the high pressure line ( 315) and the values of the second speed may be pre-stored in the memory and the second speed may be determined with reference to this lookup table.When the rotation speed of the drive unit ( 110) is controlled to a second rotation speed that is larger than the first rotation speed, the rotation speed of the drive unit ( 110) deviates from the sweet spot described above. Accordingly, the torque of the drive unit ( 110) needs to be readjusted, and the hydraulic machine may control the torque of the drive unit ( 110) to the second torque when the actuator consumes a flow rate that exceeds the maximum flow rate that the pump ( 120) can supply, i.e., when the pressure in the high pressure line ( 315) becomes less than the threshold pressure, according to an example of the present disclosure. The second torque is the torque representing the optimal fuel consumption efficiency at the second rotation speed, and the points of the second rotation speed and the second torque form a new dot line on the BSFC map as shown in FIG. 2. In some examples, a lookup table mapping the value of the second speed and the value of the second torque (or, as the second speed is determined depending on the pressure in the high pressure line (315), a lookup table mapping the value of the pressure in the high pressure line (315) and the value of the second torque) may be pre-stored in the memory and the second torque may be determined with reference to this lookup table.For example, referring to FIG. 2(1) When the safety lever is lowered, the drive unit (110) maintains a state of rest at 800 U / min. (2) When the driver lifts the safety lever but does not operate the actuator operating lever (not shown), the rotational speed of the drive unit (110) is maintained at 1,400 U / min and the torque is maintained at the minimum torque. (3) When the driver operates the actuator operation lever with the safety lever raised and the flow rate consumed by the actuator is less than the flow rate that the pump (120) can supply at the maximum volume at 1,400 U / min, the rotation speed is maintained at 1,400 U / min, and the torque of the drive unit (110) repeatedly increases and falls into the sweet spot. In this state, the hydraulic machine operates with maximum efficiency. (4) When the driver operates the actuator operating lever with the safety lever raised and the actuator consumes more than the maximum flow rate of the pump (120), the pressure in the high pressure line (315) drops because additional flow rate of the accumulator is used. In this case, the rotational speed of the drive unit (110) is controlled to increase to the second rotational speed according to the amount of pressure drop in the high-pressure pipe (315), thereby increasing the discharge flow rate of the pump (120). Further, the second torque corresponding to the second rotational speed on the sweet line is controlled as the torque of the drive unit (110). Referring to FIG. 2, the sweet line starts at 1,400 U / min, 700 Nm, for example, and along the sweet line, the second rotational speed increases and the second torque decreases slightly.FIG. 3 is a block diagram schematically showing the configuration of a drive unit torque regulator of a hydraulic machine control unit according to an example of the present disclosure, and FIG. 4 is a graph showing that the drive unit torque regulator adjusts the volume of a pump ( 120) to control the torque of the drive unit ( 110).Referring to FIG. 2, it has already been seen that in some examples, the control unit ( 600) may control the torque of the drive unit ( 110) to be the second torque (T req) on the sweet line. However, motor torque is the sum of the main pump torque, other small pumps torque, and other torques. Although the main pump accounts for a large portion of the torque of the drive unit (110), the torque of the drive unit (110) may deviate from the second torque (T req) due to other torques. In addition, it is difficult to predict how much the torque of the drive unit ( 110) will deviate.Therefore, in some examples, the control unit ( 600) may perform feedback control so that the current torque (T cur) of the drive unit ( 110) becomes equal to the second torque (T req).Referring to FIG. 3, in some examples, the control unit ( 600) may set the volume (V com) of the pump ( 120) according to the integral value obtained by integrating the values obtained by multiplying the difference (T req- T cur) between the second torque (T req) and the current torque (T cur) and dividing the values by the difference value of the inlet and outlet pressures (P Pumpe). The control unit ( 600) may increase the volume of the pump ( 120) as the integral value increases, and decrease the volume of the pump ( 120) as the integral value decreases. For example, it is possible to preset. Here, π represents the ratio of the circumference.The volume (V com) of the pump ( 120) has a maximum value which cannot be increased further from a hardware standpoint. Therefore, an anti-windup function can be added to the integrator. The anti-wind-up function prevents the integral value from increasing further as soon as the integral value reaches a predefined maximum value. As long as the integral value is within the maximum value, the anti-wind-up function does not function. Otherwise, the volume (V com) of the pump (120) reaches a maximum value while the integral value further increases, and even if and attempted to reduce the volume (V com) of the pump (120) at this time, the volume (V com) of the pump (120) cannot be reduced until the amount exceeding the maximum value of the integral value is resolved.In some examples, the hydraulic machine may include an engine sensor (520) to determine engine torque.FIG. 5 is a block diagram schematically showing the configuration of a drive unit speed compensator of a hydraulic machine control unit according to an example of the present disclosure, and FIG. 6 is a graph showing that the drive unit speed compensator performs compensation.When a high torque is applied to the drive unit (110), the rotation speed of the drive unit (110) decreases. Therefore, there is a need to deal with this phenomenon. As a solution, it could first be considered to compensate for the speed drop using the actual speed value. However, this may cause speed variations, which in turn may reduce fuel consumption. Therefore, other solutions are required.The main reason for the reduction in the rotational speed of the drive unit ( 110) is the rate of change in the torque of the drive unit ( 110). A majority of the torque of the drive unit (110) is related to the torque of the main pump, which is calculated by the following equation. where V is a volumetric delivery rate.Therefore, in a hydraulic machine according to an example of the present disclosure, the control unit ( 600) may compensate the rotational speed of the drive unit ( 110) using the instantaneous rate of change of the torque of the pump ( 120). For example, in some examples, the controller (600) calculates the torque of the pump (120) from the difference of the inlet and outlet pressures (Ppump) and the volume (Vcom) of the pump (120), and when the instantaneous rate of change of the torque of the pump (120) is positive, the drive unit (110) rotates at a rotational speed (ω com), which is greater than the second rotational speed (ω req) and when the instantaneous rate of change of the torque of the pump (120) is negative, the drive unit (110) rotates at a rotational speed (ω com), which is less than the second rotational speed (ω req). Since a speed drop is to be expected with a positive instantaneous rate of change of the torque of the pump (120), the drive unit (110) is rotated with a speed (ω com), which is greater than the second speed (ω req) in order to compensate for the speed drop, as a result of which the speed of the pump (120) which is to be maintained at the second speed (ω req) is ultimately controlled.In some examples, the control unit (600) may rotate the drive unit (110) at a "second speed (ω req) + D*dT / dt" that is greater than the second speed (ω req) when the instantaneous rate of change of the torque of the pump (120) is positive, and may rotate the drive unit (110) at a "second speed (ω req) + D*dT / dt" that is less than the second speed (ω req) when the instantaneous rate of change of the torque of the pump (120) is negative. Here, D is the gain value and dT / dt is the instantaneous rate of change of the torque of the pump (120).Referring to FIG. 5, in some examples, the control unit (600) multiplies the torque value of the pump (120) obtained by calculation by a gain value, and when the instantaneous change rate of the value is positive, the drive unit (110) may be rotated at "the second rotation speed (ω req) + D*dT / dt" that is larger than the second rotation speed (ω req) and when the instantaneous change rate of the value is negative, the drive unit (110) may be rotated at "the second rotation speed (ω req) + D*dT / dt" that is smaller than the second rotation speed (ω req).FIG. 7 is a block diagram schematically showing the general configuration of a control unit of a hydraulic machine according to an example of the present disclosure.According to one example, the control of the speed (ω com) of the drive unit (110) and the volume (V com) of the pump (120) are shown sequentially below.Method 1) Using a pressure sensor ( 510), the pressure in the high-pressure line ( 315) is measured and the rotational speed determination unit ( 630) determines the rotational speed of the drive unit ( 110). As described above with reference to FIG. 2, when the pressure in the high pressure line ( 315) is higher than the threshold pressure, the rotational speed is maintained at the predetermined first rotational speed, and when the pressure in the high pressure line ( 315) is lower than the threshold pressure, the rotational speed is increased to the second rotational speed (ω req).Method 2) The second rotation speed value (ω req) is received from Method 1, and a torque determination unit (640) finds a second torque value (T req), which corresponds to the second rotation speed (ω req) on the sweet line (i.e., a second torque value (T req), which represents an optimum fuel consumption efficiency at the second rotation speed).Method 3) receiving the second torque value (T req) of method 2 and reading the current torque value (T cur) of the drive unit (110) using the engine sensor (520). As illustrated in FIG. 3, the drive unit torque controller ( 610) transmits a pump volume command (V com), which controls the volume of the pump ( 120) to the pump ( 120).Method 4) The drive unit speed compensator (620) receives a pump volume command value (V com), which controls the volume of the pump (120) of Method 3, and also receives a second speed value (ω req) of Method 1. And using the pump volume command value (V com) and the second speed value (ω req) a speed command (ω com), how much the second speed (ω req) is to be increased or decreased to prevent the speed drop phenomenon is transmitted to the drive unit (110).The terms used herein are used to describe certain aspects only and are not intended to limit the present disclosure. Unless otherwise expressly indicated by context, a singular form may include a plural form. In addition, the term "and / or" includes any and all combinations of one or more of the associated listed items. The term "comprising" defines the presence of stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.Comparative terms such as "bottom," "top," "top," "bottom," "horizontal," or "vertical" may be used herein to describe the relationship of any element depicted in the drawings to another element. These terms and the above statements may include other orientations of the device in addition to the orientation depicted in the drawings. If an element is to be connected or coupled to another element, this may mean not only a direct connection, but also other intermediate elements. On the other hand, if an element is to be directly connected or coupled to another element, this implies that no intermediate elements are present.Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains. Terms used herein are to be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the related art, and are not interpreted in an idealized or overly formal sense unless expressly so defined herein.The present disclosure is not limited to the aspects described above and illustrated in the drawings, but it will be apparent to those skilled in the art that various changes and modifications may be made therein within the scope of the present disclosure and the appended claims. While many aspects have been disclosed in the drawings and the description for purposes of illustration and not limitation, the scope of the present inventive concept is set forth in the following claims.

Claims

A hydraulic machine comprising an actuator, a high-pressure accumulator, a high-pressure line supplying pressurized fluid to the actuator and to which the high-pressure accumulator is connected, a pump supplying pressurized fluid to the high-pressure line, a drive unit driving the pump, and a control unit controlling the pump and the drive unit; wherein the control unit controls the rotational speed of the drive unit to be maintained at the predetermined first rotational speed when the pressure in the high-pressure line is higher than the predetermined threshold pressure, and controls the rotational speed of the drive unit to be a second rotational speed larger than the first rotational speed when the pressure in the high-pressure line becomes lower than the threshold pressure.The hydraulic machine according to claim 1, wherein the first rotational speed is a rotational speed within the range representing the optimum brake fuel consumption ratio.The hydraulic machine of claim 1, wherein the second speed is determined according to the pressure within the high pressure line.The hydraulic machine of claim 1, wherein the control unit controls the rotational speed of the drive unit to be maintained at the first rotational speed and controls the torque of the drive unit to be maintained at the predetermined first torque when the pressure in the high pressure line is higher than the threshold pressure and controls the rotational speed of the drive unit to a second rotational speed that is higher than the first rotational speed and controls the torque of the drive unit to a second torque when the pressure in the high pressure line becomes lower than the threshold pressure.The hydraulic machine according to claim 4, wherein the first rotational speed and the first torque are rotational speed and torque within a range representing the optimal brake fuel consumption ratio of the hydraulic machine.The hydraulic machine according to claim 4, wherein the second rotational speed is determined according to the pressure inside the high-pressure line, and the second torque is the torque representing the optimum brake fuel consumption ratio at the second rotational speed.The hydraulic machine according to claim 4, wherein the control unit controls the volume of the pump according to an integral value obtained by integrating values obtained by multiplying the difference between the second torque and the current torque (T req- T cur) by the gain value and dividing the values by the difference value of the inlet and outlet pressures of the pump.The hydraulic machine according to claim 7, wherein the control unit increases the volume of the pump as the integral value increases, and decreases the volume of the pump as the integral value decreases.The hydraulic machine according to claim 8, wherein the control unit prevents the integral value from further increasing when the integral value reaches a predetermined maximum value.The hydraulic machine according to claim 1, wherein the control unit calculates the torque of the pump from the pressure and the volume of the pump, and rotates the drive unit at a rotational speed that is greater than the second rotational speed when the instantaneous change rate of the torque of the pump is positive, and rotates the drive unit at a rotational speed that is less than the second rotational speed when the instantaneous change rate of the torque of the pump is negative.The hydraulic machine according to claim 10, wherein the control unit calculates the torque of the pump from the pressure and the volume of the pump, and rotates the drive unit at "the second rotational speed + D*dT / dt" that is larger than the second rotational speed when the instantaneous change rate of the torque of the pump is positive, and rotates the drive unit at "the second rotational speed + D*dT / dt" that is smaller than the second rotational speed when the instantaneous change rate of the torque of the pump is negative; wherein D is the gain value and dT / dt is the instantaneous change rate of the torque of the pump.

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