Hydraulic pump

A rotational shaft 22 receives input of torque that is output from an electric motor 19. A housing 23 rotatably supports the rotational shaft 22. A cylinder block 24 inside the housing 23 rotates with the rotational shaft 22. The pistons 25 are supported relative to the respective cylinder chambers 24a in the cylinder block 24 so as to be slidably displaceable. A swash plate 26 is provided so as to come into contact with ends of the pistons 25 and be rotatable around the rotational shaft 22 with the pistons 25, and be rotatable about a rotation centerline that is obliquely inclined relative to the rotational shaft 22. A case 27 inside the housing 23 is pivotably supported relative to the housing 23. A bearing portion 28 holds the swash plate 26 relative to the case 27 so as to be rotatable around the rotation centerline.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2012-42266. The entire disclosure of Japanese Patent Application No. 2012-42266 is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a swash plate type hydraulic pump including a swash plate that can be installed obliquely inclined relative to a rotational shaft and a plurality of pistons whose axial displacement is defined by the swash plate and that rotate around the rotational shaft.

Description of Related Art

Conventionally, a swash plate type hydraulic pump is known that includes a swash plate that can be installed obliquely inclined relative to a rotational shaft, and a plurality of pistons whose axial displacement is defined by the swash plate and that rotate around the rotational shaft. A hydraulic pump such as the one mentioned above is disclosed in the article entitled “VARIABLE DISPLACEMENT PISTON PUMP-P**V SERIES”, which is published on the website of TOKYO KEIKI INC. In the case of the hydraulic pump disclosed in the aforementioned article of TOKYO KEIKI INC., a cylinder block that rotates with a rotational shaft receiving input of torque is provided with a plurality of cylinder chambers extending parallel to the rotational shaft. Also, a plurality of pistons are supported relative to the respective cylinder chambers such that the pistons can be slidably displaced along a direction parallel to the rotational shaft. Note that the above-described article of TOKYO KEIKI INC. is published on the Internet at the URL “http://www.tokyo-keiki.co.jp/hyd/j/products/pdf/a_002-005.pdf”.

In the case of the above-described hydraulic pump, oil is sucked into the cylinder chambers while the cylinder block makes a half rotation, the pressure of the oil is raised in the cylinder chambers while the cylinder block makes a further half rotation, and the oil is discharged. Then, the pressure oil discharged from the hydraulic pump will be supplied to various devices. Further, a shoe structure that slides against the swash plate is provided at the end portions of the pistons of the above-described hydraulic pump. With the provision of this shoe structure, the above-described hydraulic pump is configured such that the pistons can slide against the swash plate installed in the housing in a state in which it is obliquely inclined relative to the rotational shaft.

Note that JP 2008-249099A discloses, as a mechanism of a type completely different from a hydraulic pump that supplies pressure oil to various devices, a motorcycle hydrostatic continuously variable transmission configured by connecting a swash plate type plunger hydraulic pump with a swash plate type plunger hydraulic motor via a hydraulic closed circuit. This hydrostatic continuously variable transmission is configured to perform lockup by closing the hydraulic closed circuit when the amount of the oil flowing from the hydraulic pump to the hydraulic motor is decreased in accordance with the variable control of the inclination angle of the swash plate of the hydraulic motor such that the input rotation of the hydraulic pump and the output rotation of the hydraulic motor are substantially synchronous.

Further, in the hydraulic pump of the above-described hydrostatic continuously variable transmission, the torque that is output from the engine is input to a pump casing (20) via a gear. Also, a swash plate (pump swash plate member21), a pump cylinder (22), and a plurality of pistons (pump plungers23) are disposed inside the pump casing. The swash plate is installed so as to be rotatable relative to the pump casing in a state in which the swash plate is inclined at a predetermined angle relative to the rotation center axis of the pump casing. The pistons are respectively disposed in a plurality of cylinder chambers (pump plunger holes22a) that are provided in the pump cylinder installed facing the swash plate.

Also, in the hydraulic pump of the above-described hydrostatic continuously variable transmission, the swash plate pivots as a result of the pump casing being rotatably driven by the torque from the engine, and the pistons reciprocate in the cylinder chamber in response to the pivot movement of the swash plate. Thereby, pressure oil is discharged to the hydraulic motor. In this hydraulic pump, in place of the shoe structure that slides against the swash plate, the end portions of the pistons fittingly engage with recessed portions formed in the swash plate. Thereby, this hydraulic pump is configured such that the pistons reciprocate in response to the pivot movement of the swash plate.

SUMMARY OF THE INVENTION

In the hydraulic pump disclosed in the above-described article of TOKYO KEIKI INC., the shoe structure is provided at the end portions of the pistons such that the pistons can slide along the swash plate. Accordingly, there is the problem that friction caused between the swash plate and the shoe that slides against the swash plate results in a large energy loss, which leads to a reduction in efficiency. Further, in order to reduce the above-described friction caused between the swash plate and the shoe, the above-described shoe structure is configured such that a portion of the oil in the cylinder chambers is supplied as lubricating oil between the swash plate and the shoe via the holes formed in the pistons. With this configuration, however, there is the problem of an increased oil leakage inside the hydraulic pump, resulting in an increased work load of the hydraulic pump and thus a reduction in efficiency.

Note that the hydraulic pump of the hydrostatic continuously variable transmission disclosed in JP 2008-249099A is configured such that the pistons reciprocate in response to the pivot movement of the swash plate, and therefore, the end portions of the pistons engage with the swash plate, and the hydraulic pump is not provided with a shoe structure that slides against the swash plate. However, this hydraulic pump is used in an application as a transmission configured by being connected with the hydraulic motor via the hydraulic closed circuit. Further, due to the configuration in which the end portions of the pistons engage with the swash plate, there is the problem that a reduction in efficiency tends to occur owing to friction.

In view of the foregoing circumstances, it is an object of the present invention to provide a hydraulic pump that can achieve an increased efficiency for a swash plate type hydraulic pump by suppressing a reduction in efficiency caused by friction and internal oil leakage.

According to a first feature of a hydraulic pump of the present invention for achieving the above-described object, there is provided a hydraulic pump having a swash plate that can be installed obliquely inclined relative to a rotational shaft and a plurality of pistons whose axial displacement is defined by the swash plate and that rotate around the rotational shaft, including: the rotational shaft receiving input of torque that is output from an electric motor; a housing that rotatably supports the rotational shaft; a cylinder block that is installed inside the housing, provided with a plurality of cylinder chambers extending parallel to the rotational shaft, and rotates with the rotational shaft; the pistons being supported relative to the respective cylinder chambers in the cylinder block so as to be slidably displaceable along a direction parallel to the rotational shaft; the swash plate coming into contact with ends of the pistons and being rotatable around the rotational shaft with the pistons, and being rotatable about a rotation centerline that is obliquely inclined relative to the rotational shaft; a case that is installed inside the housing and pivotably supported relative to the housing; and a bearing portion that holds the swash plate relative to the case so as to be rotatable about the rotation centerline, wherein the pistons reciprocate in the cylinder chambers with rotation of the rotational shaft, whereby the pressure of oil sucked into the cylinder chambers is raised and thereafter the oil is discharged.

With this configuration, when the rotational shaft is rotationally driven as a result of the torque from the electric motor being input, the cylinder block rotates with the rotational shaft, and the pistons rotate around the rotational shaft with the cylinder block. Meanwhile, the swash plate is rotatably held via the bearing portion relative to the case that is pivotably supported relative to the housing. Then, with the rotation of the pistons around the rotational shaft, the swash plate with which the end portions of the pistons come into contact rotates about the rotation centerline that is obliquely inclined relative to the rotational shaft. Thereby, the pistons reciprocate in the respective cylinder chambers as a result of rotation of the rotational shaft, whereby the pressure of the oil sucked into the cylinder chambers is raised and thereafter the oil is discharged.

As described above, the hydraulic pump having the above-described configuration, the swash plate rotatably held by the case via the bearing portion rotates with the cylinder block and the pistons. Accordingly, with the hydraulic pump, any shoe structure is not provided between the end portions of the pistons and the swash plate, and therefore a reduction in efficiency as in the case of hydraulic pumps of the related art can be suppressed. That is, the hydraulic pump does not suffer from a reduction in efficiency resulting from an energy loss caused by friction between a shoe and the swash plate, and moreover, it does not suffer from a reduction in efficiency resulting from internal oil leakage caused by part of the oil inside the cylinder chambers being supplied between a shoe and the swash plate as lubricating oil. Therefore, with the hydraulic pump, a shoeless structure different from conventional swash plate type hydraulic pumps can be realized, which makes it possible to suppress a reduction in efficiency caused by friction and internal oil leakage, thus increasing the efficiency. Furthermore, as a result of increasing the efficiency of the hydraulic pump, it is also possible to reduce the heat generation during operation of the hydraulic pump.

Therefore, with the above-described configuration, it is possible to provide a swash plate type hydraulic pump that can suppress a reduction in efficiency caused by friction and internal oil leakage, thus increasing the efficiency. Note that the present inventor analyzed the efficiency of a conventional swash plate type hydraulic pump including a shoe structure and the efficiency of a swash plate type hydraulic pump to which the above-described configuration is applied, and examined the effect of improving the efficiency. As a result, the efficiency, which is the ratio of the effective energy output from the hydraulic pump to the energy that is input to the hydraulic pump, is 75 to 80% for the conventional hydraulic pump including a shoe structure, whereas it was confirmed that a high efficiency of 85 to 90% can be achieved in the case of the hydraulic pump to which the above-described configuration is applied. Accordingly, it was verified that the above-described configuration can realize a significant improvement in efficiency.

According to a second feature of a hydraulic pump of the present invention, in the hydraulic pump of the first feature, an end face of the swash plate that comes into contact with the pistons is flattened, and a curved surface constituting part of a spherical surface having a predetermined size of radius of curvature is formed on an end portion of each of the pistons that comes into contact with the swash plate.

With this configuration, in the pistons and the swash plate that come into contact with each other, the contacting end face of the swash plate is flattened, and the curved surface constituting part of a spherical surface is formed on the contacting end portion of the piston. Accordingly, the swash plate rotatably held relative to the case via the bearing portion can be smoothly rotated with the cylinder block and the pistons. Therefore, it is possible to achieve a further improvement in efficiency.

According to a third feature of a hydraulic pump of the present invention, in the hydraulic pump of the first or second feature, the bearing portion includes a ball-shaped rolling element.

With this configuration, the rolling element of the bearing portion that rotatably supports the swash plate relative to the case is provided in a ball shape, and therefore, the swash plate can be further smoothly rotated with the cylinder block and the pistons. Therefore, it is possible to achieve a further improvement in efficiency. Further, since the rolling element is provided in a ball shape, it is possible to reduce the size of the bearing portion, as compared to the cases where a roller-shaped rolling element is provided. This makes it possible to reduce the size of the hydraulic pump.

According to a fourth feature of a hydraulic pump of the present invention, in the hydraulic pump of any one of the first to third features, the bearing portion includes a rolling element formed of a ceramic material.

With this configuration, the rolling element of the bearing portion is formed of a ceramic material, and it is therefore possible to reduce the contact pressure generated between the rolling element and each of the inner ring and the outer ring in the bearing portion, thus improving the pressure resistance of the bearing portion. This makes it possible to easily provide a configuration adapted to higher pressure for the swash plate type hydraulic pump whose efficiency has been increased by suppressing a reduction in efficiency caused by friction and internal oil leakage.

According to a fifth feature of a hydraulic pump of the present invention, in the hydraulic pump of any one of the first to fourth features, the bearing portion includes: an inner ring to which the swash plate is fixed or that is provided integrally with the swash plate; an outer ring that is fixed to the case; and a rolling element that rolls between the inner ring and the outer ring.

With this configuration, in the bearing portion, the inner ring is fixed to, or integrally provided with the swash plate and the outer ring is fixed to the case. Accordingly, the bearing portion that rotatably holds the swash plate relative to the case pivotably supported relative to the housing can be realized with a simple structure in a compact manner.

According to a sixth feature of a hydraulic pump of the present invention, in the hydraulic pump of the fifth feature, the swash plate is provided with a tubular part that is formed in a tubular shape, and the inner ring is formed separately from the swash plate and is fixed to an outer circumference of the tubular part.

With this configuration, the inner ring of the bearing portion is fixed to the outer circumference of the tubular part provided in the swash plate, and therefore, the bearing portion can be easily replaced at the time of maintenance. This makes it possible to achieve further improvement in the ease of maintenance for the swash plate type hydraulic pump whose efficiency has been increased by suppressing a reduction in efficiency caused by friction and internal oil leakage.

According to a seventh feature of a hydraulic pump of the present invention, the hydraulic pump of any one of the first to sixth features further includes a piston biasing mechanism that is supported relative to the cylinder block and includes a spring that biases the pistons toward the swash plate.

With this configuration, during initial actuation in which the operation of the initial hydraulic pump is started, the pistons are biased toward the swash plate by the biasing force of the spring of the piston biasing mechanism. Accordingly, a state in which the end portions of the pistons are in contact with the swash plate is maintained during initial actuation of the hydraulic pump, and thus a stable starting characteristic is ensured.

According to an eighth feature of a hydraulic pump of the present invention, in the hydraulic pump of the seventh feature, the piston biasing mechanism includes: the spring being supported relative to the cylinder block, directly or via a pedestal portion held by the cylinder block; a retainer that is attached to the spring at an end portion of the spring on a side opposite the cylinder block; and a planar piston biasing plate that is pivotably held relative to the retainer, and transmits biasing force from the spring to bias the pistons toward the swash plate, wherein each of the pistons passes through a hole provided in the piston biasing plate, and can be engaged with the piston biasing plate on a side opposite the cylinder block.

With this configuration, the piston biasing mechanism that can ensure a stable starting characteristic during initial actuation of the hydraulic pump can be constructed in a compact manner with a simple structure including the spring, the retainer attached to the end portion of the spring, and the piston biasing plate that is pivotably held by the retainer and is engaged with the pistons.

It should be appreciated that the above and other objects, and features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiment of the present invention can be widely applied as a swash plate type hydraulic pump including a swash plate that can be installed obliquely inclined relative to a rotational shaft, and a plurality of pistons whose axial displacement is defined by the swash plate and that rotate around the rotational shaft.

FIG. 1is a hydraulic circuit diagram schematically showing a hydraulic circuit including a hydraulic pump1according to an embodiment of the present invention. The present embodiment will be described, taking as an example, a case where the hydraulic pump1is a backup hydraulic pump installed in an aircraft (not shown). In the following description, a description will be first given of a hydraulic circuit to which a hydraulic pump1and a hydraulic system10including the hydraulic pump1are applied, and a description will be then given of the hydraulic pump1and the hydraulic system10.

Note that the application of the hydraulic pump1as a backup hydraulic pump installed in an aircraft and that of the hydraulic system10including the hydraulic pump1are merely examples. The hydraulic pump1and the hydraulic system10of the present embodiment can be widely used as other hydraulic pumps and hydraulic systems for use as backup hydraulic pumps installed in aircrafts, hydraulic pumps and hydraulic systems installed in various vehicles, or hydraulic pumps and hydraulic systems for supplying pressure oil to various hydraulically operated devices.

The hydraulic pump1, which is provided as a backup hydraulic pump in the hydraulic circuit shown inFIG. 1, is provided as a hydraulic pump for supplying pressure oil to an actuator11athat drives a moving surface100of an aircraft (not shown). Also, the moving surface100is provided as a flight control surface of the aircraft, and may be configured as a control surface such as an aileron provided in the main wing, an elevator provided in the tailplane, or a rudder provided in the vertical tail. Alternatively, the moving surface100may be configured as a spoiler provided as a flight spoiler or a ground spoiler, or a flap or the like.

The moving surface100shown inFIG. 1is provided in a fixed wing. When the moving surface100is provided, for example, as an elevator, it is provided on a tailplane serving as a fixed wing. Also, the moving surface100is configured to be driven by a plurality of (for example, two) actuators (11a,11b). Further, the actuators (11a,11b) for driving the moving surface100and the hydraulic pump1configured to supply pressure oil to one of the actuators, namely, the actuator11a, are installed inside the fixed wing on which the moving surface100is installed.

As shown inFIG. 1, each of the actuators (11a,11b) includes a cylinder12, a rod13provided with a piston13a, and so forth. The interior of the cylinder12is divided by the piston13ainto two oil chambers that are not in communication with each other. Also, the oil chambers in the cylinder12of the actuator11aare respectively configured to be in communication with a first aircraft central hydraulic power source101and a reservoir circuit103via a control valve14a. Meanwhile, the oil chambers in the cylinder12of the actuator11bare respectively configured to be in communication with a second aircraft central hydraulic power source102and a reservoir circuit104via a control valve14b.

The first aircraft central hydraulic power source101and the second aircraft central hydraulic power source102are provided as hydraulic power sources each including a hydraulic pump that supplies pressure oil and are installed on the body side (inside the body), which is not shown, as systems that are independent of each other. Then, as a result of the pressure oil being supplied from the first and second aircraft central hydraulic power sources (101,102), the actuators (11a,11b) for driving the moving surface100and actuators (not shown) for driving moving surfaces other than the moving surface100are operated. Note that the hydraulic pump1of the present embodiment may be applied as the hydraulic pump provided in the first aircraft central hydraulic power source101or the second aircraft central hydraulic power source102.

The reservoir circuit103includes a tank (not shown) into which oil (hydraulic fluid) that is supplied as pressure oil to one of the oil chambers of the actuator11aand is thereafter discharged from that oil chamber flows back, and the reservoir circuit103is further configured to be in communication with the first aircraft central hydraulic power source101. The reservoir circuit104that is configured as a system independent of the reservoir circuit103includes a tank (not shown) into which oil (hydraulic fluid) that is supplied as pressure oil to one of the oil chambers of the actuator11band is thereafter discharged from that oil chamber flows back, and the reservoir circuit104is further configured to be in communication with a second aircraft central hydraulic power source102that is configured as a system independent of the first aircraft central hydraulic power source101. Further, the pressure of the oil that has returned to the reservoir circuit103is raised by the first aircraft central hydraulic power source101and is supplied to the actuator11a. Meanwhile, the pressure of oil that has returned to the reservoir circuit104is raised by the second aircraft central hydraulic power source102and is supplied to the actuator11b.

The control valve14ais provided as a valve mechanism that switches the state of connection of the oil chambers of the actuator11awith a supply path101athat is in communication with the first aircraft central hydraulic power source101and an discharge path103athat is in communication with the reservoir circuit103. The control valve14bis provided as a valve mechanism that switches the state of connection of the oil chambers of the actuator11bwith a supply path102athat is in communication with the second aircraft central hydraulic power source102and a discharge path104athat is in communication with the reservoir circuit104. The control valve14amay be configured, for example, as an electrohydraulic servo valve, and may be driven based on a command signal from an actuator controller15athat controls operation of the actuator11a. The control valve14bmay be configured, for example, as an electrohydraulic servo valve, and may be driven in accordance with a command signal from an actuator controller15bthat controls operation of the actuator11b.

The above-described actuator controller15acontrols the actuator11abased on a command signal from a flight controller2, which is a superordinate computer that commands operation of the moving surface100, of the hydraulic system10. The actuator controller15bcontrols the actuator11bbased on a command signal from the flight controller2.

Further, the control valve14adescribed above is switched based on a command from the actuator controller15a, and thereby pressure oil is supplied from the supply path101ato one of the oil chambers of the cylinder12and the oil is discharged from the other of the oil chambers to the discharge path103a. Consequently, the rod13is displaced relative to the cylinder12, thus driving the moving surface100. Note that the control valve14bis configured in the same manner as the control valve14adescribed above, and therefore the description thereof is omitted.

The hydraulic pump1, which will be described below, is provided as a backup hydraulic pump that is installed inside a fixed wing (not shown) on which the moving surface100is provided, and supplies pressure oil to the hydraulically operated actuator11afor driving the moving surface100. The suction side of the hydraulic pump1is connected in communication with the discharge path103a, and its discharge side is connected in communication with the supply path101avia a check valve16so as to be able to supply pressure oil to the supply path101a. Also, the hydraulic pump1is configured to be able to supply pressure oil to the actuator11aat the occurrence of a loss or degradation of the function (pressure oil supply function) of the first aircraft central hydraulic power source101due to a failure of the hydraulic pump, an oil leakage, or the like in the first aircraft central hydraulic power source101. Note that a pressure sensor21is connected between the hydraulic pump1and the check valve16. The pressure of the pressure oil on the discharge side of the hydraulic pump1is detected by the pressure sensor21.

A check valve17for permitting flow of pressure oil into the actuator11aand preventing flow of the oil in the opposite direction is provided upstream (on the first aircraft central hydraulic power source101side) of a location of the supply path101awhere the discharge side of the hydraulic pump1is connected. Further, a relief valve18for discharging pressure oil into the reservoir circuit103when the pressure of the oil discharged from the actuator11arises is provided downstream (on the reservoir circuit103side) of a location of the discharge path103awhere the suction side of the hydraulic pump1is connected. Also, the relief valve18is provided with a pilot pressure chamber that is in communication with the supply path101aand in which a spring is disposed. When the pressure of the pressure oil supplied from the supply path101adecreases below a predetermined pressure value, the pressure of the pressure oil being supplied as a pilot pressure oil to the pilot pressure chamber (pilot pressure) from the supply path101aalso decreases below the predetermined pressure value, as a result of which the discharge path103ais blocked by the relief valve18. In the case of a loss or degradation of the function of the first aircraft central hydraulic power source101, the provision of the above-described check valves (16,17) and the relief valve18allows the pressure of the oil discharged from the actuator11ato be raised by the hydraulic pump1without returning the oil to the reservoir circuit103, and the pressure oil is supplied to the actuator11awith an increased pressure.

The electric motor19is installed inside the fixed wing (not shown) on which the moving surface100is provided, together with the hydraulic pump1. Also, the electric motor19is coupled to the hydraulic pump1via a coupling or a gear mechanism, and is configured to drive the hydraulic pump1. The operational status of the electric motor19is controlled via the driver20, in accordance with a command signal from the flight controller2. Note that the driver20is provided as a circuit board or the like that drives the electric motor19by controlling the current supplied to the electric motor19and the running speed (rotational speed) of the electric motor19in accordance with a command signal from the flight controller2.

Next, the hydraulic pump1of the present embodiment will be described in detail.FIG. 2is a cross-sectional view of the hydraulic pump1.FIG. 3is a cross-sectional view showing a cross section of the hydraulic pump1that is different from the cross section shown inFIG. 2.FIG. 4is an enlarged cross-sectional view showing part ofFIG. 2.FIG. 5is an enlarged cross-sectional view showing part ofFIG. 3. The hydraulic pump1is provided as a swash plate type hydraulic pump. The hydraulic pump1includes a rotational shaft22, a housing23, a cylinder block24, a plurality of pistons25, a swash plate26, a case27, a bearing portion28, a piston biasing mechanism29, a pivot drive mechanism30, and so forth.

The rotational shaft22is provided as a round-bar-shaped shaft member that receives input of torque output from the electric motor19. Also, the rotational shaft22is, at one longitudinal end portion22athereof, directly coupled to the electric motor19by a coupling (not shown), or coupled to the electric motor19via a gear mechanism (not shown).

The housing23is provided as a structure that rotatably holds the rotational shaft22via a pair of rotational shaft bearings (33,34) and contains the cylinder block24, the swash plate26, and so forth. Also, the housing23is configured by a first housing member31and a second housing member32that are assembled and fixed together.

The first housing member31is provided with a substantially cylindrically shaped tubular portion31aand a disk portion31bthat is provided integrally with one end portion of the tubular portion31aand is formed as a disk-like portion. A recessed portion into which the rotational shaft bearing33is fitted is formed at the central part of the disk portion31b. Also, the disk portion31brotatably holds the rotational shaft22, which passes through its central part, via the rotational shaft bearing33on the end portion22aside.

The second housing member32is provided as a disk-like member that closes the tubular portion31aof the first housing member31. The second housing member32is fixed to the first housing member31at the end portion of the tubular portion31aon the side opposite the disk portion31b. Also, a recessed portion into which the rotational shaft bearing34is fitted is formed at the central part of the second housing member32. The second housing member32rotatably holds the rotational shaft22, which passes through its central part, at the other end portion22bvia the rotational shaft bearing34.

Further, the second housing member32is provided with a suction port35a, a suction oil path35b, a suction communication path35c, a discharge port36a, a discharge oil path36b, and a discharge communication path36c.

The suction port35ais open toward the outside of the second housing member32, and is connected to the discharge path103aso as to be in communication therewith. The suction communication path35cis formed as a space area extending in an arc shape in the circumferential direction around the rotational shaft22. Also, the suction communication path35cis provided so as to be in communication with half of the plurality of cylinder chambers24aof the cylinder block24, which will be described below, that rotate with the rotational shaft22. The suction oil path35bis provided as an oil path that provides communication between the suction port35aand the suction communication path35c.

Upon rotation of the cylinder block24, the oil flowing through the discharge path103ais sucked, via the suction port35a, the suction oil path35b, and the suction communication path35c, into the cylinder chambers24ain communication with the suction communication path35c. Note that, as the cylinder block24rotates, the half of the cylinder chambers24ain communication with the suction communication path35care sequentially switched on a portion-by-portion basis.

The discharge port36ais open toward the outside of the second housing member32, and is connected to the supply path101aso as to be in communication therewith. The discharge communication path36cis formed as a space area extending in an arc shape in the circumferential direction around the rotational shaft22. Also, the discharge communication path36cis provided so as to be in communication with half of the plurality of cylinder chambers24aof the cylinder block24that rotates with the rotational shaft22. The discharge oil path36bis provided as an oil path that provides communication between the discharge port36aand the discharge communication path36c.

Upon rotation of the cylinder block24, the pressure oil is discharged, via the discharge communication path36c, the discharge oil path36b, and the discharge port36a, from the cylinder chamber24ain communication with the discharge communication path36cto the supply path101a. Note that, as the cylinder block24rotates, the half of the cylinder chambers24ain communication with the discharge communication path36care sequentially switched on a portion-by-portion basis.

The cylinder block24is configured as a member provided with the plurality of cylinder chambers24a, and is installed inside the housing23. The cylinder chambers24aare provided such that they are disposed with an equiangular interval along the circumferential direction about the center axis C1(the center axis C1indicated by the dash-dotted lines inFIGS. 2 to 4) of the rotational shaft22, and each extend along a direction parallel to the rotational shaft22. The pistons25, which will be described below, are disposed in the respective cylinder chambers24a.

Further, a through hole provided with spline grooves is formed at the center of the cylinder block24. Meanwhile, the rotational shaft22, which passes through the through hole at the center of the cylinder block24, is provided with spline teeth. Then, the cylinder block24and the rotational shaft22are spline-coupled to each other via meshing between the spline grooves of the cylinder block24and the spline teeth of the rotational shaft22. Thereby, the cylinder block24is configured to rotate with the rotational shaft22about the center axis C1as a result of rotation of the rotational shaft22.

A plurality of pistons25are provided, and are supported relative to the respective cylinder chambers24aof the cylinder block24so as to be slidably displaceable in a direction parallel to the rotational shaft22. Also, the axial displacement of the pistons25is defined by the swash plate26, which will be described below, and the pistons25are installed so as to rotate around the rotational shaft22.

Each of the pistons25is provided with a piston shaft portion25aand a piston head portion25b. The piston shaft portion25ais provided as a columnar portion, and is supported in the cylinder chamber24aso as to be axially slidable against the inner wall thereof. Note that the axial direction of the piston shaft portions25aof the pistons25whose axial direction coincides with the axial direction of the cylinder chambers24aextends parallel to the center axis C1of the rotational shaft22. Further, the circumferential displacement of the pistons25relative to the inner walls of the cylinder chambers24ais not restrained, and the pistons25are supported inside the cylinder chambers24aso as to be slidable against and relatively rotatable with the inner walls in the circumferential direction.

The piston head portions25bare provided as end portions of the respective pistons25that come into contact with the swash plate26, which will be described below. The piston head portions25bare disposed protruding from the respective cylinder chambers24aof the cylinder block24, and are installed so as to abut against and come into contact with the swash plate26. Further, each of the piston head portions25bis provided with a curved surface25cconstituting part of a spherical surface having a predetermined size of a radius of curvature (seeFIG. 5).

The surface of each of the pistons25, or in other words, the surface of the piston shaft portion25aand the surface of the piston head portion25bare subjected to a coating treatment for providing a diamond like carbon (DLC) coating, and thereby a coating of diamond like carbon is formed thereon. Note that the inner walls of the cylinder chambers24amay also be subjected to a coating treatment for providing a diamond like carbon coating.

The swash plate26is rotatably held relative to the case27, which will be described below, via the bearing portion28. Also, the swash plate26comes into contact with the pistons25at the piston head portions25b, which are the end portions of the pistons25, and are installed so as to able to rotate with the pistons25around the rotational shaft22. Further, the swash plate26is configured so as to be able to be installed obliquely inclined relative to the rotational shaft22. That is, by being supported relative to the case27via the bearing portion28, the swash plate26is installed so as to be able to rotate about the rotation centerline C2(the rotation centerline C2indicated by the dash-dotted lines inFIGS. 3 and 5), which is obliquely inclined relative to the center axis C1of the rotational shaft22, as shown inFIGS. 3 and 5.

Further, the swash plate26includes a planar part26aand a tubular part26b. The planar part26ais provided as a planar portion having a disk-like outer shape and a through hole formed at the center. Also, the rotational shaft22is disposed passing through the through hole at the center of the planar part26a. Further, an end face26cof the planar part26athat faces the cylinder block24is flattened, and constitutes the end face of the swash plate26that comes into contact with the plurality of pistons25. The end face26cof the planar part26ais subjected to a coating treatment for providing a diamond like carbon coating, and a coating of diamond like carbon is formed thereon.

The tubular part26bis formed as a cylindrical portion extending from an edge portion of the through hole at the center of the planar part26a, parallel to a direction perpendicular to the planar part26a. In the present embodiment, the tubular part26bis formed integrally with the planar part26a, and the end portion of the tubular part26band the edge portion of the through hole of the planar part26aare provided integrally. Further, the rotational shaft22, which passes through the through hole of the planar part26a, is disposed passing through the inside of the tubular part26bas well. Note that the edge portion of the through hole of the planar part26aand the inner circumference of the tubular part26bare spaced away from the outer circumference of the rotational shaft22with a space therebetween, without coming into contact with the rotational shaft22.

The case27is installed inside the housing23, and is configured to be pivotably supported relative to the housing23and to pivot relative to the housing23by being driven by the pivot drive mechanism30. Also, the case27is provided with a case main body portion27a, pivot shaft portions (27b,27c), and a pivot end portion27d.

The case main body portion27ais formed as a cup-shaped portion composed of a cylindrical portion and a bottom plate-like portion that are integrally provided. Further, the case main body portion27ainternally holds the bearing portion28, which will be described below. Also, the bottom plate-like portion of the case main body portion27ais provided with a through hole at the center, and the rotational shaft22is disposed passing through this through hole via a gap.

The pivot shaft portions (27b,27c) are provided as columnar portions that are attached to the housing23via pivot axis bearings (37,38). The pivot shaft portions (27b,27c) are provided in pairs. Also, the pivot shaft portions (27b,27c) are provided integrally with the cylindrical portion of the case main body portion27aon both sides in the diametral direction, and also are provided protruding radially outward in a cantilevered manner.

The pivot shaft portions (27b,27c) are rotatably attached to the housing23via the pivot axis bearings (37,38) on both sides in the diametral direction of the tubular portion31aof the first housing member31. That is, relative to the first housing member31, the pivot shaft portion27bis pivotably held via the pivot axis bearing37, and the pivot shaft portion27cis pivotably held via the pivot axis bearing38.

With the above-described configuration, the case27is supported at the pivot shaft portions (27b,27c) via the pivot axis bearings (37,38) so as to be pivotable relative to the housing23. Further, as described above, the case27is configured to pivot relative to the housing23in a direction in which it rotates about the center axis C3(the center axis C3indicated by the dash-dotted lines inFIGS. 2 and 4) of the pivot shaft portions (27b,27c).

The pivot end portion27dis provided as a portion of the case27that is driven by the pivot drive mechanism30, which will be described below. Also, the pivot end portion27dis provided as a portion that protrudes in a cantilevered manner from the cylindrical portion of the case main body portion27a, radially outward thereof. A single pivot end portion27dis provided so as to protrude outward from a single location on the outer circumference of the cylindrical portion of the case main body portion27a. Also, the pivot end portion27dis provided so as to protrude in a direction perpendicular to the direction in which the paired pivot shaft portions (27b,27c) are arranged and along the radial direction of the cylindrical portion of the case main body portion27a, relative to the cylindrical portion of the case main body portion27a. Further, a tip portion of the pivot end portion27dis provided with a curved surface constituting part of a spherical surface.

The bearing portion28is attached to the case27, and is provided as a bearing mechanism that holds the swash plate26. Also, the bearing portion28is configured to hold the swash plate26relative to the case27such that the swash plate26can rotate about the rotation centerline C2that is obliquely inclined relative to the center axis C1of the rotational shaft22.

The bearing portion28includes an inner ring28a, an outer ring28b, and a plurality of rolling elements28c. The tubular part26bof the swash plate26is fitted and fixed to the inner ring28aserving as a ring-shaped member on the inner circumference side thereof. That is, the inner ring28ais formed separately from the swash plate26, and fixed to the outer circumference of the tubular part26b. Further, the outer ring28bserving as a ring-shaped member disposed on the outside of the inner ring28aand the rolling elements28cis fitted and fixed inside the case main body portion27aof the case27.

The rolling elements28care provided as members that roll between the outer circumference of the inner ring28aand the inner circumference of the outer ring28b, and a plurality of rolling elements28care aligned along the circumferential direction of the inner ring28aand the outer ring28b. Each of the rolling elements28cis provided as a ball-shaped rolling element. That is, the bearing portion28is configured as a ball bearing in the present embodiment. Further, the ball-shaped rolling elements28care formed of a ceramic material. Note that the inner ring28aand the outer ring28bare formed of a ceramic material or a metallic material.

The piston biasing mechanism29is provided as a mechanism for biasing the plurality of pistons25toward the swash plate26. The provision of this piston biasing mechanism29ensures a state in which the pistons25are abutted against the swash plate26at the start of operation of the hydraulic pump1. The piston biasing mechanism29includes a pedestal portion29a, a spring29b, a retainer29c, and a piston biasing plate29d.

The pedestal portion29ais formed in the shape of a plate that is fitted into the recessed portion formed in the shape of a hole at the center of the cylinder block24, and is provided as a member that supports the spring29brelative to the cylinder block24. An indentation into which the end portion of the spring29bis fitted is formed on the side of the pedestal portion29aopposite the end face that abuts the recessed portion of the cylinder block24. Further, a through hole in which the rotational shaft22is disposed in a state of passing therethrough is formed at the center of the pedestal portion29a.

The spring29bis supported relative to the cylinder block24, and is provided as an elastic member that generates biasing force for biasing the plurality of pistons25toward the swash plate26. In the present embodiment, the spring29bis provided as a coil spring, and is installed in a compressed state. The rotational shaft22is disposed inside the spring29bserving as the coil spring in the state of passing therethrough. Also, the spring29bis supported relative to the cylinder block24via the pedestal portion29aheld by the cylinder block24.

The retainer29cis attached to the spring29bat an end portion of the spring29bon the side opposite the cylinder block24. This retainer29cis provided as a cup-shaped member that is provided, at the center, with a through hole in which the rotational shaft22is disposed in a state of passing therethrough. Also, the retainer29cis attached to the end portion of the spring29bin a state in which the end portion of the spring29binserted inside the retainer29cis abutted against the peripheral edge portion the above-described through hole. Further, a curved surface29ethat is formed so as to be tapered, with its outer dimension decreasing toward the tip, is provided on the outer surface of the retainer29c.

The piston biasing plate29dis provided as a planar member that transmits the biasing force from the spring29bto bias the plurality of pistons25toward the swash plate26. Further, a through hole is provided at the center of the piston biasing plate29d, and the piston biasing plate29dis held in the through hole at the center so as to be pivotable relative to the retainer29c. Note that a curved surface29fcapable of sliding against the outer curved surface29eof the retainer29cis formed on the inner circumference of the through hole at the center of the piston biasing plate29d. That is, the piston biasing plate29dis installed so as to be pivotable relative to the retainer29cby sliding, with the curved surface29fon the inner circumference of the through hole at the center, against the outer curved surface29eof the retainer29c. Further, the curved surface29fon the inner circumference of the through hole at the center of the piston biasing plate29dis formed as the curved surface29fthat is tapered toward the swash plate26. Thereby, in the curved surface29ethat is tapered toward the tip on the outer side thereof, the retainer29cis abutted against the curved surface29fon the inner circumference of the through hole at the center of the piston biasing plate29d, thus biasing the piston biasing plate29dtoward the swash plate26.

Around the through hole at the center, the piston biasing plate29dis provided with a plurality of holes29galong the circumferential direction of the piston biasing plate29d. Each of the plurality of holes29gis formed so as to pass through the piston biasing plate29d. The holes29gare provided at positions corresponding to the respective pistons25. Also, each of the plurality of pistons25is disposed in a state in which it passes through the hole29gprovided in the piston biasing plate29dat the piston shaft portion25a. Further, each piston head portion25bis disposed on the swash plate26side relative to the piston biasing plate29d, and each piston shaft portion25apassing through the corresponding hole29gis disposed on the cylinder block24side relative to the piston biasing plate29d. Thereby, each of the pistons25is installed so as to be able to engage with the piston biasing plate29dat the edge portion of the corresponding hole29gon the side opposite the cylinder block24with the corresponding piston head portion25b.

The pivot drive mechanism30is provided as a mechanism capable of driving the case27in which the swash plate26is held via the bearing portion28such that the case27pivots relative to the housing23. This pivot drive mechanism30includes a pivot biasing spring30a, a spring piston30b, and a hydraulic piston30c.

The pivot biasing spring30ais provided as a coil spring that biases the pivot end portion27dof the case27. Also, the pivot biasing spring30ais installed such that one end thereof is supported inside the disk portion31bof the first housing member31and the pivot end portion27dis biased at the other end via the spring piston30b.

The spring piston30bis provided as a member that transmits the biasing force of the pivot biasing spring30ato bias the pivot end portion27dof the case27. Alto, the spring piston30bis provided as a cup-shaped member, and is attached to the pivot biasing spring30aso as to cover the other end of the pivot biasing spring30a. Further, the spring piston30bis installed inside the first housing member31so as to be able to reciprocate in a direction parallel to the center axis C1of the rotational shaft22. Further, the spring piston30bis abutted against the curved surface at the tip portion of the pivot end portion27dof the case27on the side opposite the side on which it covers the pivot biasing spring30a.

In the tubular portion31aof the first housing member31, a pressure chamber30dis defined in which pressure oil is introduced that allows the pivot end portion27dof the case27to be biased by the hydraulic piston30ctoward the opposite direction from the direction in which the pivot biasing spring30ais biased, against the biasing force of the pivot biasing spring30a. Furthermore, the first housing member31is provided with an oil path that is in communication with the interior of the pressure chamber30d. Then, this oil path is in communication with the supply path101avia a valve mechanism, which is not shown.

The hydraulic piston30cis installed slidably against the inner wall of the pressure chamber30d, and is supported so as to be freely reciprocate relative to the pressure chamber30d. Also, the end portion of the hydraulic piston30cthat protrudes from the pressure chamber30dis abutted against the curved surface at the tip portion of the pivot end portion27dof the case27. The end of the hydraulic piston30cis abutted against the tip portion of the pivot end portion27don the side opposite the side on which the spring piston30bis abutted against (the opposite side in a direction parallel to the center axis C1of the rotational shaft22).

The above-described valve mechanism provided between the oil path in communication with the interior of the pressure chamber30dand the supply path101ais configured to control the pivot of the swash plate26by achieving a balance between the load generated via the hydraulic piston30cby the pressure oil from the supply path101aand the load generated from the pivot biasing spring30a, thus adjusting the discharge amount of the hydraulic pump1.

As a result of the pressure oil whose pressure is controlled by the above-described valve mechanism being introduced into the pressure chamber30d, the hydraulic piston30cbiases the pivot end portion27dof the case27against the biasing force of the pivot biasing spring30a. This achieves a state in which the swash plate26is inclined relative to the rotational shaft22at an inclination angle that has been adjusted by the operation of the above-described valve mechanism. That is, the case27pivots about the pivot shaft portions (27b,27c), and stops at an inclination angle that has been adjusted by the operation of the above-described valve mechanism. Thereby, the inclination angle of the swash plate26is controlled such that the inclination angle of the swash plate26, which is held relative to the case27via the bearing portion28, relative to the center axis C1of the rotation centerline C2is a inclination angle that has been adjusted by the operation of the above-described valve mechanism.

Next, the operation of the hydraulic pump1will be described. The operation of the hydraulic pump1is started by operating the electric motor19. Note that in a state before the start of the electric motor19, the piston biasing mechanism29maintains a state in which the plurality of pistons25are abutted against and in contact with the swash plate26. That is, the pistons25are biased toward the swash plate26via the retainer29cand the piston biasing plate29by the biasing force of the spring29d. Then, a state in which the curved surface25cof each of the piston head portions25bis abutted against the end face26cof the planar part26aof the swash plate26is maintained.

Upon start of the operation of the electric motor19, the rotational shaft22rotates about the center axis C1, and the cylinder block24rotates with the rotational shaft22. Upon rotation of the cylinder block24, the plurality of pistons25supported by the cylinder block24also rotate around the rotational shaft22about the center axis C1.

In the above-described state, the piston head portion25bof each of the pistons25is abutted against the end face26cof the swash plate26, and rotates around the rotational shaft22while being abutted against the end face26cat substantially the same position. Since the plurality of pistons25are pressed against the swash plate26, the swash plate26is driven by the frictional force acting from the piston head portions25b, and rotates about the rotation centerline C2with the pistons25. That is, the swash plate26, which is rotatably held relative to the case27via the bearing portion28, rotates within the case27about the rotation centerline C2.

In the above-described state, when the case27has an inclined angle relative to the center axis C1, the swash plate26rotates about the rotation centerline C2obliquely inclined relative to the center axis C1. Consequently, while the rotational shaft22makes one rotation about the center axis C1, the pistons25move by a stroke of one reciprocation cycle in the respective cylinder chambers24a. Then, as a result of the pistons25reciprocating in the respective cylinder chambers24awith the rotation of the rotational shaft22, the pressure of the oil sucked into the cylinder chambers24ais raised and the oil is thereafter discharged.

Note that when a piston25is displaced in a direction protruding from the corresponding cylinder chamber24aas a result of rotation of the cylinder block24rotating with the rotational shaft22, oil is sucked into that cylinder chamber24avia the suction port35a, the suction oil path35b, and the suction communication path35c. On the other hand, when a piston25is displaced in a direction returning to the corresponding cylinder chamber24aas a result of rotation of the cylinder block24, the pressure oil is discharged from that cylinder chamber24aas the oil whose pressure has been raised, and the pressure oil is discharged to the outside via the discharge communication path36c, the discharge oil path36b, and the discharge port36a.

Note that when the cylinder block24rotates, the piston head portions25bof the pistons25rotate around the rotational shaft22while they are abutted against the end face26cof the swash plate26at substantially the same positions, as described above. Accordingly, while the cylinder block24rotates around the rotational shaft22, the pistons25relatively rotate and slide against the inner walls of the cylinder chambers24ain the circumferential direction in the respective cylinder chambers24a.

The flight controller2is provided as a superordinate computer of the actuator controllers (15a,15b), and is configured as a controller that commands operation of the moving surface100and controls operation of the hydraulic pump1. Note that the flight controller2includes, for example, a central processing unit (CPU), a memory, an interface, and so forth, which are not shown.

In the hydraulic system10, the operational status of the electric motor19is controlled by the driver20based on a command signal from the flight controller2. Furthermore, as described above, the pivot drive mechanism30is operated and thereby the inclination angle of the swash plate26of the hydraulic pump1is controlled. Also, a cylinder stroke is adjusted in which the pistons25are displaced within the respective cylinder chambers24awhile the rotational shaft22makes one rotation. Thereby, the pressure of the pressure oil discharged from the hydraulic pump1is controlled. Thus, the hydraulic pump1is configured as a variable displacement hydraulic pump.

Further, the flight controller2is configured to be able to receive a discharge pressure signal for the value of the pressure, detected by the pressure sensor21, of the pressure oil discharged from the hydraulic pump1. Also, the flight controller2is configured to be able to monitor the operating state of the hydraulic pump1and detect an abnormality of the operating state of the hydraulic pump1, based on the above-described discharge pressure signal. For example, the flight controller2determines whether the pressure of the pressure oil discharged from the hydraulic pump1is greater than or equal to a predetermined threshold value, base on the above-described discharge pressure signal.

If it is determined that the pressure of the pressure oil discharged from the hydraulic pump1is less than a predetermined threshold value, the flight controller2determines that the predetermined discharge pressure is not secured in the hydraulic pump1and thus an abnormality has occurred. If it is determined that an abnormality has occurred in the operating state of the hydraulic pump1, the flight controller2issues a warning to provide a notification to a manager that manages the operation of the hydraulic system10. This warning is displayed, for example, on an operation monitoring monitor that is checked by the manager. In the present embodiment, the warning is displayed, for example, on an operation monitoring monitor that is checked by a manager serving as a pilot of an aircraft.

As described thus far, with the hydraulic pump1, when the rotational shaft22is rotationally driven as a result of the torque from the electric motor19being input, the cylinder block24rotates with the rotational shaft22, and the pistons25rotate around the rotational shaft22with the cylinder block24. Meanwhile, the swash plate26is rotatably held via the bearing portion28relative to the case27that is pivotably supported relative to the housing23. Then, with the rotation of the pistons25around the rotational shaft22, the swash plate26with which the end portions of the pistons25(the piston head portions25b) come into contact rotates about the rotation centerline C2that is obliquely inclined relative to the rotational shaft22. Thereby, the pistons25reciprocate in the respective cylinder chambers24aas a result of rotation of the rotational shaft22, whereby the pressure of the oil sucked into the cylinder chambers24ais raised and thereafter the oil is discharged.

As described above, with the hydraulic pump1, the swash plate26rotatably held by the case27via the bearing portion28rotates with the cylinder block24and the pistons25. Accordingly, with the hydraulic pump1, any shoe structure is not provided between the end portions of the pistons25(piston head portions25b) and the swash plate26, and therefore a reduction in efficiency as in the case of hydraulic pumps of the related art can be suppressed. That is, the hydraulic pump1does not suffer from a reduction in efficiency resulting from an energy loss caused by friction between a shoe and the swash plate, and moreover, it does not suffer from a reduction in efficiency resulting from internal oil leakage caused by part of the oil inside the cylinder chambers being supplied between a shoe and the swash plate as lubricating oil. Therefore, with the hydraulic pump1, a shoeless structure different from conventional swash plate type hydraulic pumps can be realized, which makes it possible to suppress a reduction in efficiency caused by friction and internal oil leakage, thus increasing the efficiency. Furthermore, as a result of increasing the efficiency of the hydraulic pump1, it is also possible to reduce the heat generation during operation of the hydraulic pump1.

Accordingly, with the present embodiment, it is possible to provide a swash plate type hydraulic pump1that can suppress a reduction in efficiency caused by friction and internal oil leakage, thus increasing the efficiency.

Furthermore, with the hydraulic pump1, in the pistons25and the swash plate26that come into contact with each other, the contacting end face26cof the swash plate26is flattened, and the curved surface25cconstituting part of a spherical surface is formed on the contacting end portion of the piston25. Accordingly, the swash plate26rotatably held relative to the case27via the bearing portion28can be smoothly rotated with the cylinder block24and the pistons25. Therefore, it is possible to achieve a further improvement in efficiency.

With the hydraulic pump1, the rolling elements28cof the bearing portion28that rotatably supports the swash plate26relative to the case27are provided in a ball shape, and therefore, the swash plate26can be further smoothly rotated with the cylinder block24and the pistons25. Therefore, it is possible to achieve a further improvement in efficiency. Further, since the rolling elements28care provided in a ball shape, it is possible to reduce the size of the bearing portion28, as compared to the cases where roller-shaped rolling elements are provided. This makes it possible to reduce the size of the hydraulic pump1.

With the hydraulic pump1, the rolling elements28cof the bearing portion28aare formed of a ceramic material, and it is therefore possible to reduce the contact pressure generated between the rolling elements28cand each of the inner ring28aand the outer ring28bin the bearing portion28, thus improving the pressure resistance of the bearing portion28. This makes it possible to easily provide a configuration adapted to higher pressure for the swash plate type hydraulic pump1whose efficiency has been increased by suppressing a reduction in efficiency caused by friction and internal oil leakage.

With the hydraulic pump1, in the bearing portion28, the inner ring28ais fixed to the swash plate26and the outer ring28bis fixed to the case27. Accordingly, the bearing portion28that rotatably holds the swash plate26relative to the case27pivotably supported relative to the housing23can be realized with a simple structure in a compact manner.

With the hydraulic pump1, the inner ring28aof the bearing portion28is fixed to the outer circumference of the tubular part26bprovided in the swash plate26, and therefore, the bearing portion28can be easily replaced at the time of maintenance. This makes it possible to achieve further improvement in the ease of maintenance for the swash plate type hydraulic pump1whose efficiency has been increased by suppressing a reduction in efficiency caused by friction and internal oil leakage.

With the hydraulic pump1, during initial actuation in which the operation of the initial hydraulic pump1is started, the pistons25are biased toward the swash plate26by the biasing force of the spring29bof the piston biasing mechanism29. Accordingly, a state in which the end portions of the pistons25(piston head portions25b) are in contact with the swash plate26is maintained during initial actuation of the hydraulic pump1, and thus a stable starting characteristic is ensured.

With the hydraulic pump1, the piston biasing mechanism29that can ensure a stable starting characteristic during initial actuation of the hydraulic pump1can be constructed in a compact manner with a simple structure including the spring29b, the retainer29cattached to the end portion of the spring29b, and the piston biasing plate29dthat is pivotably held by the retainer29cand is engaged with the pistons25.

With the hydraulic pump1, the surface of the pistons25and the end face26cof the planar part26aof the swash plate26are subjected to a coating treatment for providing a diamond like carbon coating, and a coating of diamond like carbon is formed thereon. That is, a coating of diamond like carbon, which is hard and has excellent wear resistance, self-lubricating property, and seizure resistance, is formed on the portions of pistons25and the swash plate26that come into contact with each other. Therefore, even if an abnormality such as prying or jamming of the bearing portion28occurs, the piston head portions25bof the pistons25slide against the end face26cof the swash plate26, thus making it possible to continue the operation of the hydraulic pump1for a short period of time. Accordingly, even at the time of occurrence of an abnormality of the bearing portion28, it is possible to prevent the hydraulic pump1from becoming instantly inoperable.

Although an embodiment of the present invention has been described thus far, the present invention is not limited to the embodiment described above, and various modifications may be made within the scope recited in the claims. For example, the following modifications are possible.

(1) Although the above-described embodiment was described taking, as an example, a backup hydraulic pump installed in an aircraft, this need not be the case. The present invention can be widely applied to general swash plate type hydraulic pumps. That is, the present invention can be widely used as hydraulic pumps other than those for use as backup hydraulic pumps installed in aircrafts, hydraulic pumps installed in various vehicles, or hydraulic pumps for supplying pressure oil to various hydraulically operated devices.

(2) The shapes of the pistons and the swash plate are not limited to those illustrated in the above-described embodiment, and various modifications may be made. Also, the configuration of the bearing portion that rotatably holds the swash plate relative to the case is not limited to the shapes described in the above embodiment, and various modifications may be made. Although the above-described embodiment was described taking, as an example, a configuration in which the inner ring of the bearing portion is provided separately from the swash plate and is fixed to the swash plate, this need not be the case. It is possible to implement a configuration in which the inner ring of the bearing portion is provided integrally with the swash plate.

(3) The configuration of the piston biasing mechanism is not limited to the configurations illustrated in the above-described embodiment, and various modifications may be made. For example, it is possible to implement a configuration in which the spring is directly supported relative to the cylinder block, without providing the pedestal portion. The configurations of the spring, the retainer, and the piston biasing plate of the piston biasing mechanism are also not limited to the configurations illustrated in the above-described embodiment, and various modifications may be made.

(4) The configuration in which the case is pivotably supported relative to the housing is not limited to the configurations illustrated in the above-described embodiment, and various modifications may be made. For example, it is possible to implement a configuration in which the case is pivotably supported relative to the housing via a pivot axis provided separately from the case.

The present invention can be widely applied to a swash plate type hydraulic pump including a swash plate that can be installed obliquely inclined relative to a rotational shaft and a plurality of pistons whose axial displacement is defined by the swash plate and that rotate around the rotational shaft. The present invention is not limited to the above-described embodiment, and all modifications, applications and equivalents thereof that fall within the claims, for which modifications and applications would become apparent by reading and understanding the present specification, are intended to be embraced therein.