JP3188863U - Hydraulic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the amount of protrusion of a tooth tip from an outer diameter of a bearing member substantially equal during a break-in operation and an actual operation, and to remove an excess inner peripheral surface of a hydraulic chamber during the actual operation. Provided is a hydraulic pressure device capable of preventing a decrease in sealing property and preventing a decrease in volumetric efficiency. SOLUTION: A pair of helical gears 20 and 23, a main body 3 in which these are housed, bushes 40 and 45 for supporting rotating shafts 21 and 24 of the helical gear, and each helical gear and a bush. It is composed of side plates 30 and 33 arranged between them, partition seals 43 and 48 interposed between the bush and the side plates, and cover plates 7 and 8 fixed on both end surfaces of the main body in a liquid-tight manner. .. Each helical gear and bush is made of a metal material containing iron as a main component, and the main body is made of a metal material having a hardness lower than that of aluminum as a main component. [Selection diagram] Fig. 1

Description

  The present invention relates to a hydraulic device including a pair of gears whose tooth surfaces mesh with each other, and more specifically, the pair of gears has tooth shapes each including an arc portion at a tooth tip and a tooth bottom, and the meshing portion. The present invention relates to a hydraulic device using a helical gear in which a continuous contact line is formed from one end portion in the tooth width direction to the other end portion.

  In the hydraulic device, a pair of gears are appropriately rotated by a drive motor, and a hydraulic pump that pressurizes and discharges the working liquid by a rotating operation of the gears, or a pre-pressurized working liquid is introduced to the gears. There are hydraulic motors that rotate and use the rotational force of the rotating shaft as power.

  Conventionally, various types of gears have been used for the pair of gears. Among them, there is a hydraulic device using helical gears whose teeth are inclined obliquely. As such a hydraulic device using a helical gear, for example, a gear pump disclosed in US Pat. No. 6,888,055 (Patent Document 1) has been proposed.

  As shown in FIG. 8, the gear pump 100 includes a main body 101 in which a hydraulic chamber 101a is formed, and a pair of helical shafts inserted into the hydraulic chamber 101a in a state where teeth are engaged with each other. Gears 115 and 120 are provided. The pair of gears 115 and 120 includes a gear 115 as a driving gear and a gear 120 as a driven gear, and a rotating shaft 116 by bushes 110a, 110b, 110c, and 110d that are bearing members inserted into the hydraulic pressure chamber 101a. , 121 are rotatably supported.

  Further, a front cover 102 is fixed on the front end surface of the main body 101 in a liquid-tight manner by a seal, while an intermediate plate 106 is fixed on the rear end surface of the main body 101 in a liquid-tight manner by a seal. A rear cover 104 is fixed to the rear end surface of the intermediate plate 106 in a liquid-tight manner by a seal. The main body 101, the front cover 102, the intermediate plate 106, and the rear cover 104 constitute a housing in which the hydraulic chamber 101a is sealed. Note that the rotating shaft 116 inserted through the through hole 102a of the front cover 102 and extending outwardly is interposed between an outer peripheral surface of the rotating shaft 116 and an inner peripheral surface of the through hole 102a by a seal (not shown). Is sealed.

  The hydraulic chamber 101a is divided into a high pressure side and a low pressure side with the meshing portion of the pair of gears 115 and 120 as a boundary. The gear pump 100 appropriately rotates the drive gear 115 by a drive source, When the pair of gears 115 and 120 are rotated, the working liquid is introduced from the intake port (not shown) to the low pressure side, and the introduced working liquid is guided to the high pressure side while being pressurized by the action of the pair of gears 115 and 120. The high-pressure working liquid is discharged from a discharge port (not shown).

US Pat. No. 6,888,055

  By the way, in the hydraulic device such as the gear pump 100, the running-in operation is performed in advance before starting the normal operation. This break-in operation is performed when the hydraulic device is assembled, and the clearance between the outer surface of the tooth tip of the pair of gears and the inner peripheral surface of the hydraulic chamber is made as small as possible so that they slide in contact with each other. In this way, it is performed in order to prevent leakage of the working liquid from the same part. In this break-in operation, a pair of gears are rotated, and the inner peripheral surface of the housing is scraped or worn by the outer surface of the gear tip (hereinafter referred to as “removal processing”). Keep the hydraulic chamber in close contact with the inner peripheral surface.

  However, in general, in the hydraulic device, a metal material mainly composed of aluminum is used for the main body constituting the housing, and a metal material mainly composed of aluminum is similarly used for the bearing member. Since a metal material mainly composed of iron is used, there is a difference in the material constituting the pair of gears and the bearing member, which results in a difference in the coefficient of thermal expansion. Therefore, for example, after running-in at normal temperature and then operating at a temperature lower than normal temperature (under low temperature), the outer diameter of the bearing member is greater during actual operation than during running-in. Therefore, the amount of protrusion of the tooth tip from the top is remarkably increased, and the inner peripheral surface of the hydraulic chamber is removed and removed by an amount corresponding to that amount. As a result, there arises a problem that the sealing performance between the outer surface of the tooth tip of the gear and the inner peripheral surface of the hydraulic chamber is lowered, and the volumetric efficiency is lowered.

  The present invention has been made in view of the above circumstances, and the tooth tip and the bottom of the tooth include an arc portion, and a continuous contact line is formed from one end portion to the other end portion in the tooth width direction at the meshing portion. In a hydraulic device using a helical gear having a tooth profile, the amount of protrusion of the tooth tip from the outer diameter of the bearing member during the break-in operation and the actual operation is approximately equal, and the hydraulic pressure during the actual operation is An object of the present invention is to provide a hydraulic device that can prevent the inner peripheral surface of the chamber from being excessively removed and suppress a decrease in sealing performance and a decrease in volumetric efficiency.

The present invention for solving the above problems
A pair of helical gears each having a rotation shaft provided so as to extend outward from both end faces and in which the tooth portions mesh with each other, each including a circular arc portion at the tooth tip and the tooth bottom A pair of helical gears that form a continuous contact line from one end in the tooth width direction to the other end at the meshing portion,
Both ends are open, and a hydraulic chamber is housed in a state in which the pair of gears are engaged with each other, and the hydraulic chamber has an arc-shaped inner peripheral surface with which the outer surface of the gear tip slides. A body having;
A pair of bearing members disposed on both sides of each gear in the hydraulic chamber of the main body and rotatably supporting the rotation shaft of each gear;
At least a pair of cover plates that are fixed in a liquid-tight manner to both end faces of the main body and seal the hydraulic chamber, respectively.
The pair of gears and the pair of bearing members are made of a metal material mainly composed of iron,
The said main body is comprised from the metal material whose hardness is smaller than the metal material which has the said iron as a main component, It concerns on the hydraulic device.

  According to the hydraulic device according to the present invention, the pair of gears is composed of a metal material mainly composed of iron, and the main body is composed of a metal material whose hardness is smaller than that of a metal material mainly composed of iron. By performing the break-in operation, the inner peripheral surface of the hydraulic chamber can be removed by the outer surfaces of the tooth tips of the pair of gears. As a result, the clearance between the outer surface of the tooth tip of the gear and the inner peripheral surface of the hydraulic chamber is minimized, and the outer surface of the gear tip is in close contact with the inner peripheral surface of the hydraulic chamber.

  In the hydraulic device, since the pair of gears and the bearing member are both made of a metal material mainly composed of iron, the thermal expansion coefficients of the two gears are almost equal. As a result, when the hydraulic device is used in a lower temperature environment than during the break-in operation, there is almost no difference in the amount of protrusion of the tooth tip from the outer diameter of the bearing member due to the difference in the coefficient of thermal expansion. The problem that the inner peripheral surface of the chamber is excessively removed is less likely to occur.

  Examples of the metal material containing iron as a main component include gray cast iron, carbon steel, chrome molybdenum steel, and nickel chrome molybdenum steel. A high mechanical strength is required because a thrust force, a pressure of the working liquid, and the like act on the tooth surfaces of the pair of gears. Therefore, it is preferable to use nickel chrome molybdenum steel having high quench hardenability and toughness for the pair of gears. In addition, it is preferable to use gray cast iron for the bearing member from the viewpoint of cost-effectiveness that has sufficient mechanical strength to support the gear and is manufactured at low cost.

  In addition, the metal material whose hardness is smaller than that of the metal material mainly composed of iron is a metal material mainly composed of aluminum from the viewpoint of reducing the weight of the hydraulic device while satisfying a certain mechanical strength. Preferably, the metal material mainly composed of aluminum can be exemplified by an aluminum magnesium silicon alloy, an aluminum silicon copper alloy, or the like.

  Each tooth tip and bottom of the tooth includes a circular arc portion, and a gear having a tooth profile (hereinafter referred to as a helical gear) in which a continuous contact line is formed from one end portion to the other end portion in the tooth width direction at the meshing portion. Examples of the cogwheel are “continuous contact wire meshing gear”) include involute gears, sine curve gears, segmented gears, parabolic gears, and the like.

  As described above, according to the hydraulic device according to the present invention, even when the actual operating temperature is lower than the running-in temperature, there is a difference in the amount of protrusion of the tooth tip from the outer diameter of the bearing member. Therefore, the inner peripheral surface of the hydraulic chamber is not excessively removed by the outer surface of the tooth tip, resulting in a sealing property between the outer surface of the gear tip and the inner peripheral surface of the hydraulic chamber. Can be ensured, and a decrease in volumetric efficiency can be prevented.

It is a plane sectional view showing a hydraulic pump concerning one embodiment of the present invention. It is a front sectional view of the arrow AA direction in FIG. It is a top view which shows the side plate of the hydraulic pump which concerns on this embodiment. It is a top view which shows the bush of the hydraulic pump which concerns on this embodiment. It is a side view of the arrow B direction in FIG. It is a side view which shows the state which attached the division seal to the bush. It is an expanded sectional view of the arrow CC direction in FIG. It is a plane sectional view showing a conventional gear pump.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. In addition, the hydraulic apparatus of this example is a hydraulic pump, and uses hydraulic oil as the hydraulic fluid.

  As shown in FIGS. 1 and 2, the hydraulic pump 1 includes a housing 2 in which a hydraulic chamber 4 is formed, and a pair of helical gears disposed in the hydraulic chamber 4. A helical gear having a tooth shape in which a continuous contact line is formed from one end portion in the tooth width direction to the other end portion in the tooth width direction at the tooth tip and the tooth bottom, respectively, “Continuous contact line meshing gears” (hereinafter simply referred to as “gears”) 20 and 23, bushes 40 and 45 as a pair of bearing members, and a pair of side plates 30 and 33.

  The housing 2 includes a main body 3 in which the hydraulic chamber 4 having a space whose cross-sectional shape is similar to a figure of an Arabic numeral 8 is formed from one end face toward the other end face. 3 is fixed to the one end surface (front end surface) of the body 3 in a liquid-tight manner via a seal 12, and similarly fixed to the other end surface (rear end surface) of the main body 3 in a liquid-tight manner via a seal 13. The hydraulic pressure chamber 4 is closed by the front cover 7 and the end cover 8. The main body 3, the front cover 7 and the end cover 8 are made of a metal material mainly composed of aluminum. Examples of the metal material mainly composed of aluminum include aluminum magnesium silicon alloy and aluminum silicon. A copper alloy etc. can be illustrated.

  The pair of gears 20 and 23 is made of a metal material mainly composed of iron, one of which is a drive gear 20 and the other is a driven gear 23. When the rotation direction of the drive gear 20 is used in the right direction when viewed from the front cover 7, the teeth of the drive gear 20 are right-handed, and the teeth of the driven gear 23 are left-handed. Examples of the metal material mainly composed of iron include carbon steel, chrome molybdenum steel, and nickel chrome molybdenum steel, but the gears 20 and 23 are required to have considerable mechanical strength. The gears 20 and 23 are preferably made of nickel chrome molybdenum steel having high quench hardenability and toughness.

  Further, the gears 20 and 23 are respectively provided with rotating shafts 21 and 24 extending in the axial direction from both end faces thereof, and the pair of gears 20 and 23 are engaged with each other in the hydraulic chamber. 4, the outer surface of the tooth tip is in sliding contact with the inner peripheral surface 3 a of the hydraulic chamber 4, and the hydraulic chamber 4 borders the meshing portion of the pair of gears 20 and 23. Then, it is divided into a high pressure side and a low pressure side. Further, the end portion of the rotary shaft 21 on the front side of the drive gear 20 is formed in a tapered shape, and further, a screw portion 22 is formed at the tip thereof, and this portion is a through-hole formed in the front cover 7. It extends outward through the hole 7a, and the oil seal 10 seals between the outer peripheral surface of the rotating shaft 21 and the inner peripheral surface of the through hole 7a.

  The main body 3 is formed with an intake hole (intake channel) 5 that communicates with the low pressure side of the hydraulic pressure chamber 4 on one side surface, and the hydraulic pressure chamber 4 is also formed on the other side surface opposite to this. A discharge hole (discharge flow path) 6 leading to the high pressure side is formed. The intake hole 5 and the discharge hole 6 are provided such that their respective axes are positioned at the center between the rotation shafts 21 and 24 of the pair of gears 20 and 23.

  As shown in FIG. 3, the pair of side plates 30 and 33 are plate-like members each having two through holes 31 and 34 and having a cross-sectional shape resembling an approximate Arabic numeral 8. There are disposed on both sides of the gears 20 and 23 in a state in which the rotary shafts 21 and 24 of the gears 20 and 23 are inserted into the through holes 31 and 34, respectively, and one end face thereof is a tooth of the gears 20 and 23. It is in the state which contact | abutted to the whole end surface including a part, respectively. The pair of side plates 30 and 33 are formed with lubricating grooves 32 and 35 that open to the inner peripheral surfaces of the two through holes 31 and 34 and communicate with the front and back of the side plates 30 and 33. When the gears 20 and 23 rotate, the roots of the gears 20 and 23 are cooled by guiding the hydraulic oil in the lubrication grooves 32 and 35 to the end surfaces and the tooth bottoms of the gears 20 and 23. In addition, it is possible to improve the lubrication between the gears 20, 23 and the side plates 30, 33 to reduce the friction between them.

  The bushes 40 and 45 are made of a metal material mainly composed of iron, and have two support holes 41 and 46, respectively, as shown in FIG. 4 and FIG. It is a metal bearing made of a member having a similar shape, and bearings 42 and 47 are provided in the respective support holes 41 and 46. The bushes 40 and 45 are disposed outside the pair of side plates 30 and 33 in a state where the rotation shafts 21 and 24 of the gears 20 and 23 are inserted into the support holes 41 and 46, respectively. 21 and 24 are rotatably supported. As described above, examples of the metal material mainly composed of iron include gray cast iron and carbon steel, but the material of the bushes 40 and 45 is gray cast iron from the viewpoint of cost effectiveness. It is preferable to adopt.

  Further, grooves 40a and 45a having a shape imitating a substantially Arabic numeral 3 in side view are formed on end surfaces of the bushes 40 and 45 facing the side plates 30 and 33, respectively. 6 and 7, the grooves 40a and 45a are provided with elastic partition seals 43 and 48 and the partition seals 43 and 48, and the partition seals 43 and 48 protrude. Are provided with backup rings 44 and 49, respectively. The partition seals 43 and 48 partition the gaps 50 and 51 between the bushes 40 and 45 and the side plates 30 and 33 into a high-pressure side and a low-pressure side. The hydraulic oil on the high pressure side of the hydraulic pressure chamber 4 is guided through the flow path, and the side plates 30 and 33 are guided by the high pressure hydraulic oil guided to the gaps 50 and 51, respectively. On the other hand, the end face is pressed against the end face of each of the gears 20, 23, thereby preventing the hydraulic oil on the high pressure side from leaking to the low pressure side. Note that high pressure hydraulic oil in the hydraulic chamber 4 also acts on the side plates 30 and 33 on the end surfaces on the gears 20 and 23 side, but the pressure receiving area in the gaps 50 and 51 is on the gears 20 and 23 side. As a result, the side plates 30 and 33 are pressed against the end faces of the gears 20 and 23 due to the difference in their acting forces.

  Further, as shown in FIG. 7, the partition seals 43 and 48 are formed with folded portions 43a and 48a whose both end portions are folded outward, and the folded portions 43a and 48a have a high-pressure side. The hydraulic fluid is retained, and the pressure of the retained hydraulic fluid acts on the side plates 30 and 33, whereby the side plates 30 and 33 move along the end surfaces of the gears 20 and 23. The partition seals 43, 48 are pressed against the inner peripheral surface 3 a of the hydraulic chamber 4 by holding the hydraulic oil on the high pressure side in the folded portions 43 a, 48 a, so that the gap 50 , 51 can effectively prevent the hydraulic oil from leaking from the high pressure side to the low pressure side.

  Further, the other end surfaces of the bushes 40 and 45 are in contact with the end surfaces of the front cover 7 and the end cover 8, respectively, whereby the end surfaces of the gears 20 and 23 and the one end surface of the side plates 30 and 33 are in contact with each other. And the other end surfaces of the side plates 30 and 33 and the partition seals 43 and 48 provided on the bushes 40 and 45 are in contact with each other, and the gears 20 and 23, the side plates 30 and 33 and the bush 40, 45 is in a state where a preload is applied.

  When the distance between the bushes 40 and 45 is increased, the distortion of the main body 3 caused by the pressure difference between the high pressure side and the low pressure side during the operation of the hydraulic pump 1 and the deflection of the rotary shafts 21 and 24 increase. Since the gap between the tooth tips 20 and 23 and the inner peripheral surface 3a of the hydraulic chamber 4 is increased, the volumetric efficiency is lowered. Therefore, in order to make the distance between the bushes 40 and 45 as small as possible and to increase the volumetric efficiency of the hydraulic pump 1, the side plates 30 and 33 have their mechanical strengths kept moderately and the thickness thereof is set. It is preferable to make it as thin as possible.

  A cylinder hole 8a is formed in the end cover 8 at a portion facing the end surface of the rotary shaft 21 on the rear side of the gear 20, and a piston 9 is fitted into the cylinder hole 8a. Further, the hydraulic oil on the high pressure side in the hydraulic pressure chamber 4 is supplied to the rear portion of the cylinder hole 8a through a flow path (not shown), and the back surface (rear end surface) of the piston 9 is The hydraulic oil on the high pressure side works. The inner peripheral surface of the cylinder hole 8a is alumite impregnated with molybdenum disulfide by applying alumite treatment and then lubricating with molybdenum disulfide in order to improve wear resistance. The film is covered.

As described above, the tooth portion of the gear 20 of this example is right-handed and the tooth portion of the gear 23 is left-handed. Therefore, when the rotation direction of the gear 20 is rotated to the right when viewed from the front cover 7, a pressure receiving thrust force _Fpa directed to the rear generated by the high pressure hydraulic oil acting on the tooth portion of the gear 20; also it acts as a thrust force F _ma meshing toward the rear due meshing gears 20, 23, synthetic thrust force acts as a resultant force of the thrust force F _ma meshing with these pressure receiving thrust force F _pa.

  The piston 9 of this example has a cross-sectional area (pressure-receiving area) so that a thrust force that counteracts the synthetic thrust force acting on the gear 20 is substantially balanced by the action of high-pressure hydraulic oil on the back surface thereof. ) Is set.

On the other hand, the gear 23, a pressure receiving thrust force F _pa towards the rear caused by acting high pressure hydraulic fluid to the teeth, meshing with the thrust force F _ma toward the front caused by meshing gears 20, 23 The resultant force acts. However, theoretically, the magnitudes of the pressure-receiving thrust force F _pa and the meshing thrust force F _ma are equal to each other. Therefore, in the gear 23, these forces interfere with each other and cancel each other, and the thrust force does not act.

  In the hydraulic pump 1 of the present example having the above-described configuration, a break-in operation is performed before actual use.

  In the running-in operation, first, an appropriate pipe connected to an appropriate tank for storing hydraulic oil is connected to the intake hole 5 and the discharge hole 6 of the housing 2, and the screw of the rotary shaft 21 of the drive gear 20 is connected. A drive motor is appropriately connected to the portion 22 and the drive motor 20 is operated to rotate the drive gear 20.

  As a result, the driven gear 23 meshed with the drive gear 20 rotates, and the hydraulic oil in the space sandwiched between the inner peripheral surface 3a of the hydraulic chamber 4 and the tooth portions of the gears 20, 23 is transferred to the gears 20, 23. Is rotated to the discharge hole 6 side, and the discharge hole 6 side becomes the high pressure side and the intake hole 5 side becomes the low pressure side with the meshing part of the pair of gears 20 and 23 as a boundary.

  Then, when the hydraulic oil is discharged to the discharge hole 6 side and the intake hole 5 side becomes negative pressure, the hydraulic oil in the tank is sucked into the hydraulic chamber 4 on the low pressure side through the pipe and the intake hole 5. Similarly, the hydraulic fluid in the space sandwiched between the inner peripheral surface of the hydraulic chamber 4 and the tooth portions of the gears 20 and 23 is transferred to the discharge hole 6 side by the rotation of the gears 20 and 23, and the high pressure And is sent into the tank through the discharge hole 6 and the piping.

  As described above, the discharge hole 6 side becomes the high pressure side and the intake hole 5 side becomes the low pressure side, whereby a differential pressure is generated between the discharge hole 6 side and the intake hole 5 side. Moves to the low pressure side, the outer surface of the tooth tip of each gear 20, 23 is pressed against the inner peripheral surface 3 a on the low pressure side of the main body 3, and the inner peripheral surface 3 a is removed by the rotation of each gear 20, 23. .

  As a result, the hydraulic pump 1 is in a state where the outer surfaces of the tooth tips of the pair of gears 20 and 23 are in sliding contact with the inner peripheral surface 3a of the hydraulic chamber 4, and leakage of hydraulic oil from between the two is prevented.

  And since the hydraulic pump 1 of this example comprises both the pair of gears 20 and 23 and the bushes 40 and 45 from a metal material mainly composed of iron, the thermal expansion coefficients of the two are close to each other. Yes. As a result, even when used in an environment at a temperature lower than the temperature during the break-in operation, there is no significant difference in the amount of protrusion of the outer surfaces of the tooth tips of the gears 20, 23 from the outer diameter of the bushes 40, 45. , 23, the inner peripheral surface 3a of the hydraulic chamber 4 is not removed. Therefore, even when the hydraulic pump 1 is used in an environment at a temperature lower than the temperature during the break-in operation, the sealing performance between the outer surfaces of the gear tips 20 and 23 and the inner peripheral surface 3a of the hydraulic chamber 4 is good. Is ensured, and a decrease in volumetric efficiency can be prevented.

  As mentioned above, although one Embodiment of this invention was described, the specific aspect which this invention can take is not limited to this at all.

  For example, in the hydraulic pump of the above example, the rotation direction of the drive gear 20 is clockwise when viewed from the front cover 7 side, a right-handed helical gear is used for the drive gear 20, and a left-handed twist is applied to the driven gear 23. A helical gear is used, but the rotational direction of the drive gear 20 is left-handed when viewed from the front cover 7, the left-handed helical gear is used as the driving gear, and the right-handed helical gear is used as the driven gear. You may make it use.

  In the above example, the hydraulic device according to the present invention is embodied as a hydraulic pump. However, the present invention is not limited to this. For example, the hydraulic device may be embodied as a hydraulic motor. Further, the working liquid is not limited to working oil, and for example, a cutting fluid may be used as the working liquid. In this case, the hydraulic device according to the present invention is embodied as a coolant pump.

  Although not particularly mentioned in the above example, a key groove is formed in the taper portion of the rotary shaft 21 and a key is inserted into the key groove, and the taper of the rotary shaft 21 is formed by the key groove and the key. You may make it connect a rotary body to a part suitably.

  In the above example, the intake hole 5 and the discharge hole 6 are formed as through-holes in the main body 3. However, the intake hole 5 and the discharge hole 6 are respectively connected to the hydraulic chamber 4. Therefore, the main body of the intake hole 5 and the discharge hole 6 are configured so that one of them forms a flow path (an intake flow path and a discharge flow path) that leads to the outside through an opening formed in the main body 3. , And the front cover 7 and / or the end cover 8 may be formed.

DESCRIPTION OF SYMBOLS 1 Hydraulic pump 2 Housing 3 Main body 4 Hydraulic chamber 7 Front cover 8 End cover 8a Cylinder hole 9 Piston 20 Drive gear 21 Rotating shaft 23 Driven gear 24 Rotating shaft 30, 33 Side plate 32, 35 Lubricating groove 40, 45 Bush 43, 48 Partition seal 43a, 48a Folded part 50, 51 Clearance

Claims (2)

A pair of helical gears each having a rotation shaft provided so as to extend outward from both end faces and in which the tooth portions mesh with each other, each including a circular arc portion at the tooth tip and the tooth bottom A pair of helical gears that form a continuous contact line from one end in the tooth width direction to the other end at the meshing portion,
Both ends are open, and a hydraulic chamber is housed in a state in which the pair of gears are engaged with each other, and the hydraulic chamber has an arc-shaped inner peripheral surface with which the outer surface of the gear tip slides. A body having;
A pair of bearing members disposed on both sides of each gear in the hydraulic chamber of the main body and rotatably supporting the rotation shaft of each gear;
At least a pair of cover plates that are fixed in a liquid-tight manner to both end faces of the main body and seal the hydraulic chamber, respectively.
The pair of gears and the pair of bearing members are made of a metal material mainly composed of iron,
The said main body is comprised from the metal material whose hardness is smaller than the metal material which has the said iron as a main component, The hydraulic apparatus characterized by the above-mentioned. 2. The hydraulic apparatus according to claim 1, wherein the main body is made of a metal material mainly composed of aluminum.

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