JP2003139071A - Gear pump and power steering device using this gear pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance lubricatability between a side surface of a gear chamber and a side surface of gears, and to equalize pressure of a plurality of oil reservoir parts arranged for enhancing this lubricatability. SOLUTION: The side surface of the two gears 1 and 2 rotated by mutually meshing in the gear chamber 31 has the plurality of oil reservoir parts 15 and 25 recessed by separating in the circumferential direction, and communicating grooves 16 and 26 for communicating the respective oil reservoir parts 15 and 25. When the gears 1 and 2 rotate, a hydraulic fluid of the gear chamber 31 is introduced to the oil reservoir parts 15 and 25 from clearance between the side surface of the gear chamber 31 and the side surface of the gears 1 and 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gear pump that performs a pumping action by the rotation of two gears and a power steering device that assists steering of steering means using the gear pump.

[0002]

2. Description of the Related Art FIG. 7 is a vertical sectional front view showing the structure of a conventional gear pump. A gear pump that supplies hydraulic oil to a hydraulically operated device such as an actuator arranged in a steering mechanism of a vehicle includes two gears 102 and 103 that rotate around axes that are parallel to each other in a gear chamber 101 inside a housing 100. The gears 102 and 103 are meshed with each other, and a suction chamber and a discharge chamber are formed on both sides of the meshed position, and the working oil in the suction chamber is received between the teeth of the two gears 102 and 103. It acts as a pump that seals between the inner peripheral surface of the gear chamber 101 and sends it to the discharge chamber.

The gear of the gear pump is formed by machining a bar material. This machining process is formed through processes such as a turning process, a gear cutting process, a quenching process, a shaving process, a polishing process, and a barrel process.

In the gear pump configured as described above, there is a slight gap between the side surface of the gear chamber 101 and the side surfaces of the gears 102, 103 so that the gears 102, 103 can rotate smoothly. When is rotated, part of the hydraulic oil in the suction chamber and the discharge chamber is attracted to the gap, and an oil film is generated in the gap.

[0005]

However, in the conventional gear pump configured as described above, the pressure oil boosted in the discharge chamber causes a gap between the side surface of the gear chamber 101 and the side surfaces of the gears 102 and 103. Since the gap is made small in order to prevent backflow from the suction chamber to the suction chamber, the amount of the oil film formed in the gap is very small. As a result, when the gear rotates, oil film breakage is likely to occur, and when the gear is rotated with this oil film breakage, seizure occurs on the side surface of the gear, and improvement measures have been demanded.

Further, since the gear of this gear pump is formed by machining a bar material, the number of steps from the turning step to the final step is large, and a large amount of money is required when a new production line is set up. Investment is needed and also
Gear processing costs increased, and improvement measures were required.

The present invention has been made in view of the above circumstances, and it is possible to enhance the lubricity between the side surface of the gear chamber and the side surface of the gear, and further reduce the number of gear processing steps. , And a power steering device including the gear pump.

[0008]

A gear pump according to a first aspect of the present invention includes two gears that are meshed with each other and rotated, and a gear chamber that accommodates the gears. In a gear pump in which the gear chamber is divided into a suction chamber and a discharge chamber, a side surface of the gear communicates with a plurality of oil retaining portions that are provided in a circumferentially spaced and recessed manner and each of the oil retaining portions. It is characterized by having a groove.

In the first aspect of the invention, the operating oil in the gear chamber is rotated by the gear while the pump is operating, so that the working oil in the gear chamber has a gap between the side faces of the gear chamber and the side faces of the gear, and all oil retaining parts on the side faces of the gear. To improve the lubricity between the side surface of the gear chamber and the side surface of the gear. At this time, since the oil pressure in the discharge chamber is higher than the oil pressure in the suction chamber, a pressure difference is generated between the oil retaining portion communicating with the discharge chamber and the oil retaining portion communicating with the suction chamber. Since all the oil retention parts are always communicated by the communication groove, the pressure of all the oil retention parts can be instantly equalized, and the force applied to the side surface of the gear can be instantly equalized over the entire circumference. The rotatability of the gear can be improved.

A gear pump according to a second aspect of the invention is characterized in that the communication groove is shallower than the depth of the oil retaining portion.

According to the second aspect of the present invention, since the operating oil that has entered the oil retaining portions can be retained and retained in the respective oil retaining portions, the pressure-increasing operating oil in the discharge chamber can be the side surface of the gear chamber and the gear. It is possible to suppress the reverse flow from the gap between the side surfaces of the side walls to the suction chamber side, and reduce the decrease in the discharge flow rate.

A gear pump according to a third aspect of the invention is characterized in that the gear is made of a metal powder injection molding. In the third invention, the metal powder is used as the molding material,
Since the gear is formed by injection-molding the metal powder, the oil retaining portion and the communication groove can be obtained by a gear forming die, and processing for obtaining the oil retaining portion and the communication groove Gears can be obtained without going through the steps.

A gear pump according to a fourth aspect of the present invention includes two gears that are meshed with each other and rotated, and a gear chamber that accommodates the gears. The gear chamber is a suction chamber with the meshing portion of the gears as a boundary. In the gear pump divided into the discharge chamber, the side surface of the gear has a plurality of oil retaining portions that are provided in a circumferentially spaced apart manner, and the gear is made of a metal powder injection molded body. Characterize.

In the fourth aspect of the present invention, the metal powder is used as the molding material, and the gear is formed by injection molding the metal powder. Therefore, a plurality of recesses are provided on the side surfaces of the gear. The oil retaining portion can be obtained by the gear forming mold, and the gear can be obtained without a processing step for obtaining the oil retaining portion. In addition, since a plurality of oil retaining portions are provided on the side surface of the gear, the operating oil in the gear chamber is moved by the rotation of the gear during pump operation, and the gap between the side surface of the gear chamber and the side surface of the gear, and It is possible to improve the lubricity between the side surface of the gear chamber and the side surface of the gear by entering the oil retaining portion. At this time, since the oil pressure in the discharge chamber is higher than the oil pressure in the suction chamber, a pressure difference is generated between the oil retaining portion communicating with the discharge chamber and the oil retaining portion communicating with the suction chamber. As the gear rotates, each of the oil retaining portions repeatedly communicates with the discharge chamber and the suction chamber through the gap, so that the pressure in the oil retaining portion can be equalized.

In a gear pump according to a fifth aspect of the present invention, the gear has a shaft portion fitted in a bearing hole formed in a housing having the gear chamber, and a cavity elongated in the axial direction from an end edge of the shaft portion. It is characterized by having and.

According to the fifth aspect of the invention, since a cavity that is long in the axial direction can be obtained from the end edge of the shaft portion by the gear forming mold, a lightweight gear can be obtained without a machining step for obtaining the cavity. Can be obtained.

6. A power steering apparatus according to a sixth aspect of the present invention, wherein the power steering apparatus is driven based on a steering means, an actuator for assisting the steering of the steering means, and a steering angle of the steering means. And a hydraulic control valve for switching the pressure oil feed passage from the gear pump to feed the pressure oil to the actuator. The sixth invention is the same as any one of the first invention to the fifth invention.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. Embodiment 1 FIG. 1 is a longitudinal sectional view showing the configuration of a gear pump according to the present invention,
2 is an enlarged sectional view of a part of the gear pump, and FIG. 3 is FIG.
III-III line enlarged sectional view, FIG. 4 is an enlarged part of the gear, (a) is a sectional view and (b) is a side view.

The gear pump GP (see FIG. 5) shown in FIGS. 1 and 2 includes a drive gear 1 which is interlocked with an output shaft of a motor M (see FIG. 5) via a transmission means such as a shaft coupling. Gear 1
A driven gear 2 that meshes with a gear chamber 1, a gear chamber 31 accommodating the gears 1 and 2, and a housing 3 having bearing holes 32, 33, 34 and 35 in which shaft portions of the gears 1 and 2 are fitted. ,
A support body 4 for supporting the housing 3, a damper container 5 attached to the housing 3 for reducing pulsation during pressure oil discharge, and an operating oil such as oil surrounding the damper container 5 and the housing 3. And a tank 6 for storing

The gears 1 and 2 are made of a metal powder injection molded body in which metal powder is injection molded. The gear 1 has a plurality of teeth 11a on its peripheral surface.
11 having a tooth and a tooth 11 corresponding to the side surface of the gear 1.
The shaft portions 12 and 13 that are continuous on both sides of the shaft, a cavity 14 that is long in the axial direction from the end edge of the one shaft portion 12 to the vicinity of the end edge of the other shaft portion 13, and is circumferentially separated from the side surface. It has a plurality of recessed oil retaining portions 15 and a communication groove 16 that communicates with each of the oil retaining portions 15. Also, the shaft portion 12,
At the end edge of 13, tapered center holes 17 and 18 having a large diameter from the center of rotation are provided.

The oil retaining portions 15 are recessed at the side surface positions of the teeth 11a at a pitch of approximately 1/2 of the number of teeth, and more specifically, six oil retaining portions are provided for the gear 1 having 12 teeth. The portion 15 is recessed. In addition, the oil retaining portion 15 is provided so as to be recessed on the rotation center side of the tooth bottom and beyond the tooth bottom.

The communication groove 16 is recessed so as to form an arc on the rotation center side with respect to the tooth bottom. The communication groove 16 is shallower than the depth of the oil retaining portion 15.

The gear 2 has a tooth portion 21 having a plurality of teeth 21a on its peripheral surface, shaft portions 22 and 23 connected to both sides of the tooth portion 21 corresponding to the side surface of the gear 2, and an end edge of one shaft portion 22. Cavity 24 penetrating in the axial direction over the edge of the other shaft 23
And a plurality of oil retaining portions 25 provided on the side surface so as to be spaced apart from each other in the circumferential direction, and a communication groove 26 for communicating each of the oil retaining portions 25. Further, at the end edges of the shaft portions 22 and 23, a tapered center hole 27 having a large diameter from the center of rotation,
28 is provided.

The oil retaining portions 25 are recessed at the end face positions of the teeth 21a at a pitch of 1/2 of the number of teeth, which is approximately equal to six, and more specifically, six oil retaining portions are provided for the gear 2 having 12 teeth. The portion 25 is recessed. Further, the oil retaining portion 25 is recessed in a position beyond the tooth bottom on the rotation center side with respect to the tooth bottom.

The communication groove 26 is recessed so as to form an arc on the rotation center side with respect to the tooth bottom. Further, the communication groove 26 is shallower than the depth of the oil retaining portion 25.

The gears 1 and 2 configured as described above are molded as follows. 1) As a molding material, ultrafine metal powder and a binder in which wax is added to synthetic resin are used, and the metal powder and the binder are kneaded by a kneader. 2) This kneaded product is processed into pellets by a granulator,
Moldability is enhanced. 3) Using a molding die having cavities corresponding to the gears 1 and 2, and an injection molding machine, the pellets supplied to the hopper of the injection molding machine are melted and filled into the cavity of the molding die. And molded into a gear body. This gear body has a structure in which metal powders are bound by a binder. 4) The gear body is supplied to a degreasing furnace, the binder is dissolved and removed from the gear body by heating in the degreasing furnace,
It becomes a degreased gear body. 5) The degreased gear element body is sintered in a sintering furnace and has a high-density metal structure with a relative density of 95% or more.
It becomes a highly accurate gear, and it is possible to obtain the same strength as an existing gear formed by processing a bar material. In this state, the tooth portions 11, 21, the shaft portions 12, 13, 22, 23, the cavities 14, 24, the oil retaining portions 15, 25, the communication grooves 16, 2
6, center holes 17, 18, 27, 28 are formed.

The housing 3 is open to both side surfaces and has an elliptical hole 36 and a pair of arcuate surfaces 36a, 36a corresponding to the outer diameters of the tooth portions 11, 21 of the gears 1, 2 and the elliptical hole 36. A cylindrical housing body 3a having a plurality of insertion holes 37 formed around the hole 36, and the housing body 3a.
The two side plates 3b and 3c, which are fitted into both ends of the elliptical hole 36 and have the elliptical hole 36 as the gear chamber 31, and the lid 3d for preventing the side plates 3b and 3c from falling off. The inside of the side plates 3b and 3c is the side surface of the gear chamber 31.

With the housing body 3a positioned by the positioning pin 7, a plurality of tightening screws 8 are inserted into the insertion holes 37 through holes (not shown) formed in the lid 3d. It is detachably attached to the support 4 together with the lid 3d. Further, the housing main body 3a penetrates between the arcuate surfaces 36a, 36a of the gear chamber 31, and a suction passage 38 communicating with the inside of the tank 6 through the suction pipe 9 and a discharge communicating with the inside of the damper container 5. Road 39
And are provided.

The gear chamber 31 includes gears 1 and 2 housed inside.
The meshing portion of the teeth 11a and 21a is defined as a suction chamber 31a in which the suction passage 38 opens and a discharge chamber 31b in which the discharge passage 39 opens.

The side plate 3b has a through hole 32 for supporting the shaft portions 12, 22 of the gears 1, 2.
33 is provided, and the shaft portions 12 and 22 are fitted into the bearing holes 32 and 33 via the bushes 40 and 41. Further, the side plate 3c has through bearing holes 34, 3 for supporting the shaft portions 13, 23 of the gears 1, 2.
5 are provided, and the shaft portions 13 and 23 are fitted into the bearing holes 34 and 35 via the bushes 42 and 43. Further, the teeth 11a and 21a of the gears 1 and 2 and the gear chamber 31
Between the circular arc surfaces 36a, 36a of the oil trap portion 1a, 2a
Is provided.

The lid 3d of the housing 3 has a bottomed tubular shape in which a tubular portion is connected to the peripheral edge of the bottom portion, and the bottom portion is attached to the support body 4 by the tightening screw 8.

The damper container 5 has a bottomed tubular shape in which a tubular portion is connected to the peripheral edge of the bottom portion, and the tubular portion is fitted in the tubular portion of the lid 3d. The inside of the damper container 5 is the discharge chamber 31.
It has a larger volume than b. Further, the inside of the damper container 5 communicates with the discharge chamber 31b through the through hole formed in the bottom of the lid 3d and the discharge passage 39, and further through the discharge hole formed in the bottom. It communicates with the feed pipe 10.

The tank 6 has a bottomed tubular shape in which a tubular portion is connected to the peripheral edge of the bottom portion, and the end edge of the tubular portion is detachably attached to the support 4.

Reference numeral 20 in FIG. 1 denotes a sealing material for preventing the hydraulic oil from leaking to the outside from around the shaft portion 13 of the driving gear 1.

Gear pump GP configured as described above
The driving gear 1 and the driven gear 2 meshing with the gear 1 are rotated in the direction of the arrow in FIG. 3 by the driving of the motor through the transmission means, and the working oil stored in the tank 6 is sucked into the suction pipe. 9 and the suction passage 38 to be sucked into the suction chamber 31a of the gear chamber 31 and further confined in the oil confining portions 1a and 2a of the gears 1 and 2, and the hydraulic oil in these oil confining portions 1a and 2a is The pressure is increased with the rotation of the first and second parts and is discharged into the discharge chamber 31b, and the damper container 5 is discharged from the discharge chamber 31b through the discharge passage 39.
After being supplied to the inside of the damper container 5 and the oil veins are reduced in the damper container 5, the oil is supplied to the feed pipe 10.

When the gears 1 and 2 rotate, the gear chamber 3
The hydraulic oil of No. 1 enters the gaps K1 and K2 between the side surfaces of the gear chamber 31 and the side surfaces of the gears 1 and 2, and all the oil retaining portions 15 and 25 on the side surfaces of the gears 1 and 2, 31
The lubricity between the side surface of the gear and the side surfaces of the gears 1 and 2 can be improved. At this time, the hydraulic pressure of the discharge chamber 31b is the same as that of the suction chamber 3
Since the oil pressure is higher than that of 1a, a pressure difference is generated between the oil retaining portions 15 and 25 communicating with the discharge chamber 31b and the oil retaining portions 15 and 25 communicating with the suction chamber 31a. Since the oil retaining portions 15 and 25 of are always communicated with each other by the communication grooves 16 and 26, all the oil retaining portions 15 and 25
The pressure of 25 can be instantly equalized, the force applied to the side surfaces of the gears 1 and 2 can be equalized over the entire circumference, and the rotatability of the gears 1 and 2 can be improved.

The gears 1 and 2 are made of metal powder injection molding, and when the gears 1 and 2 are injection molded, the cavity 1 is formed.
4, 24, oil retaining portions 15 and 25, communication grooves 16 and 26,
Since the center holes 17, 18, 27, 28 can be obtained by the forming die, the cavities 14, 24, the oil retaining portions 15, 25, the communication grooves 16, 26, the center holes 17, 18,
The gears 1 and 2 can be obtained without going through the processing steps for obtaining 27 and 28, the number of processing steps of the gears 1 and 2 can be reduced, and the processing cost of the gears 1 and 2 can be reduced. Also,
Since waste materials such as spool runners generated when the gears 1 and 2 are molded can be crushed and reused to mold the gears 1 and 2, the waste materials can be reduced and the cost can be further reduced.

FIG. 5 is a schematic diagram of a power steering apparatus constructed by using a gear pump according to the present invention in a vehicle equipped with a rack and pinion type steering mechanism. In the rack and pinion type steering mechanism, a pinion 52 is fixedly provided at the lower end of a steering shaft 51 whose upper end is connected to the steered wheels 50, and the pinion 52 is provided at the front of the vehicle body and extends in the left-right direction.
Steering wheel 50 for steering to mesh with rack teeth of No. 3
Is converted into sliding in the axial direction of the rack shaft 53, and the pair of left and right front wheels 54, 54 respectively connected to both ends of the rack shaft 53 are changed in direction for steering. There is. The steered wheels 50 and the steering shaft 51 constitute a steering means.

The power steering device according to the present invention is
The steering assist actuator (hydraulic cylinder) 55 is provided in the middle of the rack shaft 53, and the rotary hydraulic control valve 56 is provided in the middle of the steering shaft 51. By operating the hydraulic control valve 56, the feed passage from the gear pump GP is switched to feed pressure oil to the actuator 55, and the hydraulic pressure generated by the actuator 55 is applied to the rack shaft 53 in response to this feed, It is configured to assist the sliding of the rack shaft 53.

The gear pump GP according to the present invention comprises a motor M
Is used as a source of oil to be fed to the actuator 55. The hydraulic oil sucked from the tank 6 into the gear chamber 31 is pressurized by the rotation of the gears 1 and 2 in the gear chamber 31. The pressure oil whose pressure is increased is supplied to the actuator 55 via the supply pipe 10 and the hydraulic control valve 56.

The motor M for driving the gear pump GP includes
The output of the drive control unit 57 using a microprocessor is given through a drive circuit (not shown), and the motor M is drive-controlled including ON / OFF according to a command from the drive control unit 57. It has been done. On the input side of the drive control unit 57, a steering angle sensor 58 provided in the middle of the steering shaft 51 receives a steering angle detection signal of the steered wheels 50, and a vehicle speed sensor 59 receives a traveling speed detection signal. Has been given.

The drive control unit 57 controls the rotation speed by which the rotation speed of the motor M is reduced according to the increase in the detected vehicle speed in response to the input from the vehicle speed sensor 59. As a result, the actuator 5 is transmitted from the gear pump GP via the hydraulic control valve 56.
The pressure oil supplied to the vehicle 5 has a pressure that becomes high or low in accordance with the slow speed of the vehicle, and a large steering force is exerted during low speed running or when the road surface reaction force acting on the front wheels 54, 54 is large. While the assisting force is obtained and the force required to steer the steered wheels 50 for steering is greatly reduced, the steering assist becomes small during high-speed traveling when the road surface reaction force is small.
It is possible to improve the straight running stability by imparting appropriate rigidity to the.

Second Embodiment FIG. 6 is an enlarged view of a part of the gear according to the second embodiment.
(a) is a sectional view and (b) is a side view. This Embodiment 2
The gear pump GP of does not have the communication grooves 16 and 26,
The gears 1A and 2A having the oil retaining portions 15 and 25 on the side surfaces are made of a metal powder injection molded body.

In the second embodiment, a molding die having a cavity corresponding to the gears 1A and 2A having the oil retaining portions 15 and 25 on the side surface and an injection molding machine are used, and a hopper of the injection molding machine is used. The pellets supplied are filled in a molten state in the cavity of the molding die,
It is molded into a gear body, and this gear body is manufactured through the steps 4) and 5) of the first embodiment. In this state, tooth 1
1, 21, shaft portions 12, 13, 22, 23, cavities 14, 2
4, oil retaining portions 15, 25, center holes 17, 18, 2
7, 28 are molded.

Since other configurations and operations are the same as those of the first embodiment, the same parts are designated by the same reference numerals,
The detailed explanation and the explanation of the action and effect are omitted.

[0046]

According to the first aspect of the present invention, the lubricity between the side surface of the gear chamber and the side surface of the gear can be enhanced by the oil retaining portions, and the pressures of all the oil retaining portions are instantly equalized. Therefore, the force applied to the side surface of the gear can be instantly equalized over the entire circumference, and the rotatability of the gear can be improved.

According to the second aspect of the present invention, it is possible to prevent the hydraulic oil whose pressure has been boosted in the discharge chamber from flowing back to the suction chamber side through the gap between the side surface of the gear chamber and the side surface of the gear, thereby reducing the discharge flow rate. Can prevent a decrease.

According to the third aspect of the invention, the oil retaining portion required to enhance the lubricity between the side surface of the gear chamber and the side surface of the gear,
It is possible to obtain a gear without going through a machining step for obtaining a communication groove, and easily obtain an oil retention portion having a shape that is unlikely to cause oil film breakage in the gap between the side surface of the gear chamber and the side surface of the gear. You can Further, compared with the existing gear formed by machining the bar material, at least the turning step and the gear cutting step can be eliminated, the number of gear processing steps can be reduced, and the gear processing cost can be reduced. .

According to the fourth aspect of the present invention, the lubricity between the side surface of the gear chamber and the side surface of the gear can be enhanced by the oil retaining portion, and further, the gear step can be performed without a processing step for obtaining the oil retaining portion. Can be obtained. Moreover, it is possible to easily obtain an oil retaining portion having a shape in which an oil film is unlikely to run out in the gap between the side surface of the gear chamber and the side surface of the gear. Further, compared with the existing gear formed by machining the bar material, at least the turning step and the gear cutting step can be eliminated, the number of gear processing steps can be reduced, and the gear processing cost can be reduced. .

According to the fifth aspect of the invention, a lightweight gear can be obtained without going through a processing step for obtaining a cavity necessary for making a lightweight gear, and further, the material cost can be reduced and the gear cost can be reduced. Can be further reduced.

According to the sixth invention, the same effect as any of the first to fifth inventions can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a configuration of a gear pump according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing a configuration of a main part of a gear pump according to the present invention.

FIG. 3 is an enlarged sectional view taken along line III-III in FIG.

FIG. 4 is an enlarged view of a part of a gear of a gear pump according to the present invention, in which (a) is a sectional view and (b) is a side view.

FIG. 5 is a schematic diagram of a power steering device configured using a gear pump according to the present invention.

FIG. 6 is an enlarged view of a part of the gear of the second embodiment of the gear pump according to the present invention, in which (a) is a sectional view and (b) is a side view.

FIG. 7 is a vertical sectional front view of a gear pump showing a conventional example.

[Explanation of symbols]

1,1A gear 12,13 Shaft 14 cavities 15 Oil retention part 16 communication groove 2,2A gear 22,23 Shaft 24 cavities 25 Oil retention part 26 communication groove 3 housing 31 gear chamber 40 steering wheel 41 Steering axis 45 actuator 46 Hydraulic control valve GP gear pump

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 3D033 EB02                 3H041 AA02 BB02 CC03 CC07 DD05                       DD07 DD15 DD31 DD33 DD38                 3H044 AA02 BB02 CC03 CC07 DD05                       DD06 DD11 DD21 DD23 DD28

Claims (6)

[Claims] 1. A gear comprising: two gears that are meshed with each other and rotated; and a gear chamber that accommodates the gears. The gear chamber is divided into a suction chamber and a discharge chamber with a meshing portion of the gears as a boundary. In the gear pump, the side surface of the gear is
A gear pump comprising: a plurality of oil retaining portions that are spaced apart in the circumferential direction and are recessed; and a communication groove that communicates with each of the oil retaining portions. 2. The gear pump according to claim 1, wherein the communication groove is shallower than the depth of the oil retaining portion. 3. The gear pump according to claim 1, wherein the gear is made of a metal powder injection molded body. 4. A gear, comprising: two gears that are meshed with each other and rotated; and a gear chamber that accommodates the gears. The gear chamber is divided into a suction chamber and a discharge chamber with a meshing portion of the gears as a boundary. In the gear pump, the side surface of the gear is
A gear pump having a plurality of oil retaining portions that are provided in a circumferentially spaced manner so as to be recessed, and the gear is made of a metal powder injection molded body. 5. The gear has a shaft portion fitted into a bearing hole formed in a housing having the gear chamber, and a cavity elongated in the axial direction from an end edge of the shaft portion. Claim 3
Alternatively, the gear pump according to item 4. 6. A steering means, an actuator for assisting steering of the steering means, a gear pump according to claim 1, which is driven based on a steering angle of the steering means, and a gear pump from the gear pump. A power steering device comprising: a hydraulic control valve that switches a pressure oil supply path to supply pressure oil to the actuator.