Hydraulic rotary machine and hydraulic pump

Abstract

One embodiment of the hydraulic rotary machinery (1) includes a rotating shaft (11) and a housing (2) housing a cylinder (4) and a swashplate (5). The hydraulic rotary machinery (1) also includes a servo piston (7) for changing the angle of the swashplate (5) and an electric actuator (8) for driving the servo piston (7). The electric actuator (8) includes a threaded shaft (84), a nut (83), and an electric motor (86). The rotation angle of the electric motor (86) is detected by a rotation angle sensor (16), and the electric motor (86) is controlled by a control device (15). The control device (15) adjusts the current sent to the electric motor (86) to maintain the rotation angle of the electric motor (86) detected by the rotation angle sensor (16) at a predetermined value, and calculates the rotational speed of the rotating shaft (11) based on the waveform of the adjusted current.

Description

Technical Field

[0001] This disclosure relates to hydraulic rotating machinery and hydraulic pumps. Background Technology

[0002] Previously, hydraulic rotary machinery (hydraulic pumps or hydraulic motors) were known as swashplate-type axial piston pumps. In such hydraulic rotary machinery, a cylinder and a swashplate are housed within a housing (see, for example, Patent Document 1). The cylinder is fixed to a rotating shaft extending from the inside to the outside of the housing.

[0003] Multiple pistons are slidably held within the cylinder, and slippers mounted on the heads of these pistons slide against a swashplate. The angle of the swashplate is changed by a servo piston. Patent Document 2 discloses a hydraulic rotary machine that drives a servo piston via an electric actuator. Patent Document 2 describes a ball screw drive mechanism as a specific example of an electric actuator.

[0004] Existing technical documents: Patent documents: Patent Document 1: Japanese Patent Application Publication No. 8-100759; Patent Document 2: Japanese Patent Publication No. 2011-522194. Summary of the Invention

[0005] The problem the invention aims to solve: Another method of driving a servo piston is to change the hydraulic pressure acting on it. However, in this case, the driving of the servo piston is likely to be affected by changes in the temperature of the working fluid. To address this, as illustrated in the specific example of Patent Document 2, using a ball screw drive mechanism (i.e., an electric actuator comprising a threaded shaft, a nut, and an electric motor) to drive the servo piston avoids this problem.

[0006] However, in hydraulic rotating machinery, it is desirable to be able to detect the rotational speed of the shaft without a tachometer. Also, when the hydraulic rotating machinery uses a hydraulic pump, it is desirable to be able to detect the pump's output pressure without a pressure gauge.

[0007] Therefore, the object of this disclosure is to provide a hydraulic rotating machine that can detect the rotational speed of a rotating shaft without using a tachometer. Furthermore, the object of this disclosure is also to provide a hydraulic pump that can detect the discharge pressure without using a pressure gauge.

[0008] Solution methods: This disclosure provides a hydraulic rotary machine based on one aspect, comprising: a rotary shaft; a cylinder fixed to the rotary shaft and slidably holding a plurality of pistons; a swashplate sliding with a slipper mounted on the head of the plurality of pistons; a servo piston changing the angle of the swashplate; a housing housing the cylinder and the swashplate and slidably holding the servo piston; an electric actuator mounted on the housing and driving the servo piston, and including a threaded shaft extending axially along the servo piston, a nut threaded to the threaded shaft, and an electric motor for rotating the threaded shaft; a rotation angle sensor for detecting the rotation angle of the electric motor; and a control device for controlling the electric motor; the control device adjusting the current sent to the electric motor to maintain the rotation angle of the electric motor detected by the rotation angle sensor at a predetermined value, and calculating the rotational speed of the rotary shaft based on the waveform of the adjusted current.

[0009] Furthermore, this disclosure provides a hydraulic pump based on other aspects, comprising: a rotary shaft; a cylinder fixed to the rotary shaft and slidably holding a plurality of pistons; a swashplate sliding with a slipper mounted on the head of the plurality of pistons; a servo piston changing the angle of the swashplate; a housing housing the cylinder and the swashplate and slidably holding the servo piston; an electric actuator mounted in the housing and driving the servo piston, and including a threaded shaft extending axially along the servo piston, a nut threaded with the threaded shaft, and an electric motor for rotating the threaded shaft; a rotation angle sensor for detecting the rotation angle of the electric motor; and a control unit. The control device adjusts the current sent to the electric motor to maintain the rotation angle of the electric motor detected by the rotation angle sensor at a predetermined value. The control device pre-stores a map that determines the relationship between the hydraulic pump's discharge pressure, the tilt angle (as the angle of the swashplate), the rotational speed of the rotating shaft, and the electric motor's current value. The control device uses this map to determine the hydraulic pump's discharge pressure corresponding to: the tilt angle calculated from the electric motor's rotation angle detected by the rotation angle sensor, the rotational speed of the rotating shaft, and the average value of the adjusted current.

[0010] Invention effects: According to this disclosure, a hydraulic rotating machine is provided that can detect the rotational speed of a rotating shaft without the use of a tachometer, and a hydraulic pump is provided that can detect the discharge pressure without the use of a pressure gauge. Attached Figure Description

[0011] Figure 1 This is a cross-sectional view of one embodiment of a hydraulic rotating machine; Figure 2 It is a graph showing the waveform of the current; Figure 3 It is a diagram used to illustrate the mapping stored within the control device; Figure 4 This is a cross-sectional view of a modified hydraulic rotating machine. Detailed Implementation

[0012] Figure 1 A hydraulic rotary machine 1 according to one embodiment is shown. The hydraulic rotary machine 1 includes a housing 2 and a rotating shaft 11 extending from the inside of the housing 2 to the outside. In addition, the hydraulic rotary machine 1 includes a valve plate 3, a cylinder 4 and a swashplate 5 housed within the housing 2.

[0013] For ease of explanation, the axial direction of the rotating shaft 11 will be referred to as the front-rear direction (the side located outside the housing 2 is the front, and the other side is the rear), and the two directions orthogonal to the axial direction of the rotating shaft 11 will be referred to as the up-down direction. Figure 1 (The top side is above, the bottom side is below) and the left and right directions.

[0014] The housing 2 includes a rearwardly opening container-shaped housing body 22 and a valve cover 21 that closes the opening of the housing body 22. The housing body 22 includes a front wall 23 penetrated by a rotation shaft 11, and a bottom wall 24, a top wall 25, and a pair of side walls that surround the internal space. Bearings 12 and 13 that rotatably support the rotation shaft 11 are respectively held on the front wall 23 of the housing body 22 and the valve cover 21.

[0015] The valve plate 3 is mounted on the front surface of the valve cover 21. The valve plate 3 is provided with a first port 31 and a second port 32 that are arc-shaped and facing opposite directions. Figure 1 In the diagram, the first port 31 is drawn at the top dead center on the lower side (the position where the piston 61 retracts last, as described later), and the second port 32 is drawn at the bottom dead center on the upper side (the position where the piston 61 advances the most). However, the actual positions of the first port 31 and the second port 32 are on both sides of the rotation axis 11 in the left-right direction (a direction orthogonal to the separation direction of the top dead center and the bottom dead center).

[0016] In this embodiment, the hydraulic rotary machine 1 is a hydraulic pump that rotates in one direction. Therefore, the first port 31 is the suction port, and the second port 32 is the discharge port. That is, in the rotation direction of the rotating shaft 11, the first port 31, which is the suction port, is located on the downstream side of the top dead center and on the upstream side of the bottom dead center, and the second port 32, which is the discharge port, is located on the downstream side of the bottom dead center and on the upstream side of the top dead center.

[0017] The valve cover 21 is provided with a first flow path 2a communicating with the first port 31 and a second flow path 2b communicating with the second port 32. The first flow path 2a and the second flow path 2b have openings on the outer peripheral surface or rear surface of the valve cover 21, forming external connection ports. As described above, the hydraulic rotary machinery 1 is a hydraulic pump that rotates in one direction, so the first flow path 2a is the suction path and the second flow path 2b is the discharge path. That is, the pressure in the second flow path 2b is higher than the pressure in the first flow path 2a.

[0018] The cylinder body 4 is fixed to the rotating shaft 11 and slides against the valve plate 3 by rotating together with the rotating shaft 11. Inside the cylinder body 4, there are multiple forward-opening cylinder holes 41 around the rotating shaft 11. Multiple pistons 61 are inserted into these cylinder holes 41 respectively. Thus, the pistons 61 are slidably held in the cylinder body 4.

[0019] Furthermore, the cylinder body 4 is provided with cylinder ports 42 extending from each cylinder bore 41 to the valve plate 3. Some of these cylinder ports 42 are connected to the first port 31, and others are connected to the second port 32. For example, when there are nine cylinder bores 41 and cylinder ports 42, four or five cylinder ports 42 are connected to the first port 31 or the second port 32 depending on the rotational position of the cylinder body 4.

[0020] Multiple shoes 62 are mounted on the head of the piston 61. In this embodiment, the shoes 62 slide on the swashplate 5 via an annular support plate 63 mounted on the swashplate 5. However, the support plate 63 can be omitted, and the shoes 62 slide directly on the swashplate 5. The shoes 62 are pushed by the push plate 64 to maintain contact with the support plate 63.

[0021] The swashplate 5 is supported by a support platform 14 provided on the front wall 23 of the housing body 22, and is swaying about a swing axis extending in the left-right direction. The angle of the swashplate 5 is changed by a servo piston 7, which is slidably held against the top wall 25 of the housing body 22.

[0022] More specifically, the swashplate 5 includes a main body 50 through which the rotation shaft 11 passes and an operating part 51 protruding upward from the main body 50. In this embodiment, the tip 71 of the servo piston 7 is connected to the operating part 51 via a pin 52.

[0023] However, the servo piston 7 does not necessarily need to be connected to the operating part 51 of the swashplate 5. For example, the servo piston 7 can also abut against the operating part 51 of the swashplate 5 from the rear, with the operating part 51 being subjected to rearward force by a spring disposed between the operating part 51 and the front wall 23 of the housing body 22.

[0024] The top wall 25 of the housing body 22 is provided with a retaining hole 26 for inserting the servo piston 7. In this embodiment, the retaining hole 26 includes: a first guide portion 27 forming an opening relative to the internal space of the housing 2; and a second guide portion 28 located on the opposite side of the swashplate 5 relative to the first guide portion 27. The diameter of the second guide portion 28 is smaller than the diameter of the first guide portion 27.

[0025] On the other hand, the servo piston 7 includes: a first sliding portion 72 adjacent to the aforementioned tip 71 and slidably held in the first guide portion 27; and a second sliding portion 73 slidably held in the second guide portion 28. That is, the diameter of the first sliding portion 72 is approximately equal to the diameter of the first guide portion 27, and the diameter of the second sliding portion 73 is approximately equal to the diameter of the second guide portion 28.

[0026] Furthermore, an auxiliary pressure chamber 91 is formed between the annular end face of the first sliding portion 72 on the side of the second sliding portion 73 and the stepped portion between the first guide portion 27 and the second guide portion 28 in the retaining hole 26. This auxiliary pressure chamber 91 is used to push the servo piston 7 against the swashplate 5.

[0027] The housing body 22 and valve cover 21 are provided with an inlet path 2c that branches from the second flow path 2b to the auxiliary pressure chamber 91. In this embodiment, if the second flow path 2b is a discharge path, the inlet path 2c introduces working fluid from the discharge path to the auxiliary pressure chamber 91.

[0028] An electromagnetic proportional valve 92 is provided on the feed path 2c to set the pressure of the auxiliary pressure chamber 91. In this embodiment, the electromagnetic proportional valve 92 functions as a pressure reducing valve to reduce the output pressure of the hydraulic pump to the set pressure. In the illustration, the electromagnetic proportional valve 92 is an inverse proportional type where the command current is negatively correlated with the secondary pressure, but the electromagnetic proportional valve 92 can also be a direct proportional type where the command current is positively correlated with the secondary pressure.

[0029] An electric actuator 8 for driving the servo piston 7 is mounted on the top wall 25 of the housing body 22. The electric actuator 8 includes a threaded shaft 84 extending axially along the servo piston 7, a nut 83 engaging with the threaded shaft 84, and an electric motor 86 that rotates the threaded shaft 84.

[0030] Furthermore, the electric actuator 8 includes: a hollow rod 82 connected to the servo piston 7 and fixed with a nut 83; and a cylindrical housing 85 that slidably holds the rod 82 in the axial direction of the servo piston 7. The housing 85 is fixed to the top wall 25 of the outer casing 22, and an electric motor 86 is mounted on the housing 85.

[0031] In this embodiment, rod 82 is connected to servo piston 7 via a universal joint. Specifically, the front end of rod 82 is provided with a groove, in which ball 81 is held. On the other hand, the second sliding part 73 of servo piston 7 is provided with a plate-shaped protrusion 74 that inserts into the groove, and the protrusion 74 is provided with a hole that fits into ball 81.

[0032] However, contrary to this embodiment, a groove for retaining ball 81 can be provided on the second sliding part 73 of the servo piston 7, and a protrusion 74 inserted into the groove can be provided at the front end of the rod 82. Alternatively, the rod 82 can also be connected to the servo piston 7 through a connector other than a universal joint (e.g., a ball joint or spherical joint).

[0033] The electric motor 86 is controlled by the control device 15. The control device 15 is electrically connected to a rotation angle sensor 16 that detects the rotation angle of the electric motor 86. For example, the rotation angle sensor 16 is a rotary transformer or a rotary encoder. The control device 15 receives information to determine the angle of the swashplate 5, i.e., the tilt angle. The control device 15 adjusts the current sent to the electric motor 86 to maintain the rotation angle of the electric motor 86 detected by the rotation angle sensor 16 at a predetermined value corresponding to the input information.

[0034] For example, a hydraulic rotating machine 1, which is a hydraulic pump, supplies working fluid to a hydraulic actuator via a control valve. When an operating device is provided to operate the control valve, the operating amount of the operating device is input to the control device 15. The control device 15 makes the tilt angle of the hydraulic pump larger if the operating amount of the operating device is larger.

[0035] Regarding control device 15, the functions of the elements disclosed in this specification can be executed using a general-purpose processor, special-purpose processor, integrated circuit, ASIC (Application Specific Integrated Circuits), existing circuitry, and / or combinations thereof that are configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it contains transistors or other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs or is programmed to perform the listed functions. The hardware can be the hardware disclosed in this specification or other known hardware programmed or configured to perform the listed functions. When the hardware is considered a processor, a type of circuit, the circuit, means, or unit is a combination of hardware and software used in the configuration of the hardware and / or processor.

[0036] Furthermore, in this embodiment, the control device 15 calculates the rotational speed of the rotating shaft 11 based on the waveform of the adjusted current, and utilizes... Figure 3 The mapping shown determines the discharge pressure of the hydraulic pump.

[0037] Regarding the calculation of the rotational speed N [rpm] of the rotating shaft 11, as follows: Figure 2 As shown, the control device 15 determines the number of current oscillations K within a specified time T [s] from the waveform of the adjusted current, and uses this number of oscillations K and the number of pistons Z of the pistons 61 to calculate the rotational speed N of the rotating shaft 11 using the following formula. For example, the specified time T is 0.1 to 0.5 s; N = K / 2 × 1 / Z × 1 / T × 60.

[0038] In this embodiment, the hydraulic rotary mechanism 1 is a hydraulic pump, so a torque is applied to the swashplate 5 by the high pressure inside the cylinder 4, pushing the servo piston 7. Furthermore, this torque varies slightly depending on the relative position of the cylinder 4 and the valve plate 3 (in this embodiment, the connection between the cylinder port 42 of the cylinder 4 and the second port 32, which serves as the discharge port of the valve plate 3, is switched). Therefore, the current, adjusted to maintain the rotation angle of the electric motor 86 at a predetermined value, vibrates, and its vibration frequency is related to the rotational speed of the shaft 11. Therefore, the rotational speed of the shaft 11 can be calculated based on the waveform of the adjusted current, thus allowing the rotational speed of the shaft 11 to be detected without using a tachometer.

[0039] Furthermore, in this embodiment, a high-pressure working fluid is introduced into the auxiliary pressure chamber 91, and this pressure pushes the servo piston 7 toward the swashplate 5. Therefore, the electric actuator 8 can advance the servo piston 7 with a relatively small thrust.

[0040] The determination of the hydraulic pump's discharge pressure is pre-stored in the control device 15. Figure 3 The mapping shown defines the relationship between the hydraulic pump's discharge pressure, the tilt angle (as shown by the swashplate 5), the rotational speed of the rotating shaft 11, and the current value of the electric motor 86. Regarding the relationship between the hydraulic pump's discharge pressure and these parameters, a higher discharge pressure results in a higher current value for the electric motor 86; a larger tilt angle results in a lower current value for the electric motor 86 relative to the discharge pressure; and a higher rotational speed of the rotating shaft 11 results in a higher current value for the electric motor 86 relative to the discharge pressure.

[0041] Figure 3 The mapping shown can be obtained by conducting prior performance verification tests on the hydraulic rotating machinery 1, which functions as a hydraulic pump. Furthermore, Figure 3 In the figure, the relationship between the current value of the electric motor 86 and the discharge pressure of the hydraulic pump is represented by a straight line, but this relationship can also be represented by a curve.

[0042] Control device 15 utilizes Figure 3 The mapping shown determines the discharge pressure of the hydraulic pump corresponding to the following: the tilt angle obtained by converting the rotation angle of the electric motor 86 detected by the rotation angle sensor 16, the calculated speed, and the average value of the adjusted current.

[0043] The discharge pressure of the hydraulic pump is related to the tilt angle of the swashplate 5, the rotational speed of the rotating shaft 11, and the current value of the electric motor 86. Therefore, by using a mapping that determines these relationships, the discharge pressure of the hydraulic pump can be detected without the use of a pressure gauge.

[0044] (Modified Example) This disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of this disclosure.

[0045] For example, the hydraulic rotating machinery 1 could also be a hydraulic pump that rotates in both directions. In this case, such as... Figure 4 As shown in the modified hydraulic rotary machine 1A, the inlet path 2c is connected to both the first flow path 2a and the second flow path 2b via a high-pressure selector valve 93. In this structure, the inlet path 2c also introduces working fluid from the higher pressure side of the first flow path 2a and the second flow path 2b, i.e., the discharge path, into the auxiliary pressure chamber 91.

[0046] Alternatively, the hydraulic rotary machinery 1 can also be a hydraulic motor that rotates in two directions. In this case, depending on the direction of rotation, either the first flow path 2a or the second flow path 2b is the inflow path, and the other is the outflow path; either the first port 31 or the second port 32 is the inflow port, and the other is the outflow port.

[0047] When the hydraulic rotary machinery 1 is a hydraulic motor, a torque is applied to the swashplate 5 by the high pressure inside the cylinder 4, similar to pulling out the servo piston 7. As in the previous embodiment, this torque varies slightly depending on the relative position of the cylinder 4 and the valve plate 3 (the switching of connection between the cylinder port 42 of the cylinder 4 and the inlet port of the valve plate 3). Therefore, a current is oscillated to maintain the rotation angle of the electric motor 86 at a predetermined value, and this oscillation frequency is related to the rotational speed of the rotating shaft 11. Therefore, the rotational speed of the rotating shaft 11 can be calculated based on the waveform of the regulated current, thus eliminating the need for a tachometer to detect the rotational speed of the rotating shaft 11.

[0048] Furthermore, regarding the determination of the hydraulic pump's discharge pressure, the rotational speed of the prime mover driving the hydraulic pump can be used as the rotational speed of the rotating shaft 11 and input to the control device 15. The control device 15 then uses the input rotational speed instead of the calculated rotational speed to determine the hydraulic pump's discharge pressure.

[0049] (Summarize) This disclosure provides a hydraulic rotary machine based on one aspect, comprising: a rotary shaft; a cylinder fixed to the rotary shaft and slidably holding a plurality of pistons; a swashplate sliding with a slipper mounted on the head of the plurality of pistons; a servo piston changing the angle of the swashplate; a housing housing the cylinder and the swashplate and slidably holding the servo piston; an electric actuator mounted on the housing and driving the servo piston, and including a threaded shaft extending axially along the servo piston, a nut threaded to the threaded shaft, and an electric motor for rotating the threaded shaft; a rotation angle sensor for detecting the rotation angle of the electric motor; and a control device for controlling the electric motor; the control device adjusting the current sent to the electric motor in a manner that keeps the rotation angle of the electric motor detected by the rotation angle sensor at a predetermined value, and calculating the rotational speed of the rotary shaft based on the waveform of the adjusted current.

[0050] When the hydraulic rotating machinery is a hydraulic pump, the high pressure inside the cylinder creates a torque on the swashplate that pushes the servo piston. When the hydraulic rotating machinery is a hydraulic motor, the high pressure inside the cylinder creates a torque on the swashplate that pulls out the servo piston. Furthermore, this torque varies slightly depending on the relative position of the cylinder and the valve plate (when the hydraulic rotating machinery is a hydraulic pump, this varies depending on the connection between the cylinder port of the cylinder and the discharge port of the valve plate). Therefore, the current, adjusted to maintain the rotation angle of the electric motor at a predetermined value, vibrates, and the frequency of this vibration is related to the rotational speed of the rotating shaft. Therefore, the rotational speed of the rotating shaft can be calculated based on the waveform of the adjusted current, thus eliminating the need for a tachometer to detect the rotational speed of the rotating shaft.

[0051] For example, the control device may determine the number of current oscillations within a specified time period from the waveform of the regulated current, and use the number of oscillations to calculate the rotational speed of the rotating shaft.

[0052] Alternatively, the hydraulic rotary machinery can be a hydraulic pump, further comprising a valve plate housed in the housing, which slides against the cylinder body, including a first port and a second port in opposite directions. The housing includes: an auxiliary pressure chamber for pushing the servo piston toward the swashplate; a first flow path communicating with the first port; a second flow path communicating with the second port; and an inlet path for introducing working fluid from the higher pressure flow path (i.e., the discharge path) into the auxiliary pressure chamber. According to this structure, a higher-pressure working fluid is introduced into the auxiliary pressure chamber, and the servo piston is pushed toward the swashplate by this pressure. Therefore, the electric actuator can advance the servo piston with a relatively small thrust.

[0053] Alternatively, the hydraulic rotary machinery can be a hydraulic pump, and the control device pre-stores a mapping that determines the relationship between the hydraulic pump's discharge pressure, the tilt angle (as the swashplate angle), the rotational speed of the rotating shaft, and the current value of the electric motor. The control device uses this mapping to determine the hydraulic pump's discharge pressure corresponding to: the tilt angle calculated from the rotational angle of the electric motor detected by the rotation angle sensor, the calculated rotational speed, and the average value of the adjusted current. The hydraulic pump's discharge pressure is related to the tilt angle (as the swashplate angle), the rotational speed of the rotating shaft, and the electric motor's current value. Therefore, by using the mapping that determines these relationships, the hydraulic pump's discharge pressure can be detected without using a pressure gauge.

[0054] Furthermore, this disclosure provides a hydraulic pump based on other aspects, comprising: a rotary shaft; a cylinder fixed to the rotary shaft and slidably holding a plurality of pistons; a swashplate sliding with a slipper mounted on the head of the plurality of pistons; a servo piston changing the angle of the swashplate; a housing housing the cylinder and the swashplate and slidably holding the servo piston; an electric actuator mounted in the housing and driving the servo piston, and including a threaded shaft extending axially along the servo piston, a nut threaded with the threaded shaft, and an electric motor for rotating the threaded shaft; a rotation angle sensor for detecting the rotation angle of the electric motor; and a control unit. The control device adjusts the current sent to the electric motor in a manner that keeps the rotation angle of the electric motor detected by the rotation angle sensor at a predetermined value. The control device has a pre-stored map that determines the relationship between the discharge pressure of the hydraulic pump, the tilt angle as the angle of the swashplate, the rotational speed of the rotating shaft, and the current value of the electric motor. The control device uses the map to determine the discharge pressure of the hydraulic pump corresponding to the following: the tilt angle converted from the rotation angle of the electric motor detected by the rotation angle sensor, the rotational speed of the rotating shaft, and the average value of the adjusted current.

[0055] The discharge pressure of a hydraulic pump is related to the tilt angle (which is the angle of the swashplate), the rotational speed of the shaft, and the current value of the electric motor. Therefore, by utilizing the mapping of these relationships, the discharge pressure of the hydraulic pump can be measured without the use of a pressure gauge.

Claims

1. A hydraulic rotary machine characterized by, have: Rotation axis; A cylinder body, fixed to the rotating shaft, slidably holds a plurality of pistons; A swashplate that slides with a slipper mounted on the head of the plurality of pistons; A servo piston that changes the angle of the swashplate; A housing that accommodates the cylinder and the swashplate and slidably holds the servo piston; An electric actuator, mounted on the housing and driving the servo piston, includes a threaded shaft extending axially along the servo piston, a nut threaded to the threaded shaft, and an electric motor for rotating the threaded shaft. A rotation angle sensor that detects the rotation angle of the electric motor; as well as Control device, controlling the electric motor; The control device adjusts the current sent to the electric motor in a manner that keeps the rotation angle of the electric motor detected by the rotation angle sensor at a predetermined value, and calculates the rotational speed of the rotating shaft based on the waveform of the adjusted current.

2. The hydraulic rotary machinery according to claim 1, characterized in that, The control device determines the number of current vibrations within a specified time from the waveform of the regulated current, and uses this number of vibrations to calculate the rotational speed of the rotating shaft.

3. The hydraulic rotary machinery according to claim 1 or 2, characterized in that, The hydraulic rotating machinery is a hydraulic pump; It also includes a valve plate housed in the housing, which slides with the cylinder body and includes a first port and a second port in opposite directions. The housing includes: an auxiliary pressure chamber for pushing the servo piston toward the swashplate; a first flow path communicating with the first port; a second flow path communicating with the second port; and an inlet path for introducing working fluid into the auxiliary pressure chamber from the higher pressure of the first flow path and the second flow path, i.e., the discharge path.

4. The hydraulic rotary machinery according to claim 1 or 2, characterized in that, The hydraulic rotating machinery is a hydraulic pump. The control device has a pre-stored mapping that determines the relationship between the hydraulic pump's discharge pressure, the tilt angle as the angle of the swashplate, the rotational speed of the rotating shaft, and the current value of the electric motor. The control device uses the mapping to determine the discharge pressure of the hydraulic pump corresponding to: the tilt angle obtained by converting the rotation angle of the electric motor detected by the rotation angle sensor, the calculated speed, and the average value of the adjusted current.

5. A hydraulic pump characterized by, have: Rotation axis; A cylinder body, fixed to the rotating shaft, slidably holds a plurality of pistons; A swashplate that slides with a slipper mounted on the head of the plurality of pistons; A servo piston that changes the angle of the swashplate; A housing that accommodates the cylinder and the swashplate and slidably holds the servo piston; An electric actuator, mounted on the housing and driving the servo piston, includes a threaded shaft extending axially along the servo piston, a nut threaded to the threaded shaft, and an electric motor for rotating the threaded shaft. A rotation angle sensor that detects the rotation angle of the electric motor; as well as Control device, controlling the electric motor; The control device adjusts the current sent to the electric motor in a manner that keeps the rotation angle of the electric motor detected by the rotation angle sensor at a predetermined value; The control device has a pre-stored mapping that determines the relationship between the hydraulic pump's discharge pressure, the tilt angle as the angle of the swashplate, the rotational speed of the rotating shaft, and the current value of the electric motor. The control device uses the mapping to determine the discharge pressure of the hydraulic pump corresponding to: the tilt angle obtained by converting the rotation angle of the electric motor detected by the rotation angle sensor, the rotation speed of the rotating shaft, and the average value of the adjusted current.

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