JP2024035808A - external gear pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the trade-off problem between clearance and friction at the tips of gear teeth in an external gear pump.

SOLUTION: An external gear pump comprises a movable casing 2 having an inner surface, to which the tooth tips of a pair of gears 3 are close, and an internal space accommodating the gears 3; and an outer casing 1 having an inner surface, which faces the outer surface of the movable casing 2, and an accommodation part accommodating the movable casing 2. The internal space of the movable casing 2 includes a low pressure region 2A on a suction port side and a high pressure region 2B on a discharge port side. Within the accommodation part of the outer casing 1, the movable casing 2 is movable in a direction away from the tooth tips in response to movement of the tooth tips due to eccentricity of the gears caused by a fluid pressure difference in the internal space of the movable casing 2.

SELECTED DRAWING: Figure 4

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an external gear pump, and more particularly to a hydraulic machine, a hydraulic pump, a hydraulic actuator, a robot actuator, and the like.

In external gear pumps, the gap between the rotating gear and the casing is important. The internal clearances of a gear pump include an axial clearance, which is the clearance between the axial gear and the casing, and a tooth tip clearance, which is the clearance between the gear tooth tip and the casing (Figure 1). In an external gear pump, when high pressure is generated, internal leakage occurs in the axial gap and tooth tip gap between the gear and the casing, causing a pressure drop. On the other hand, if the pump is designed to eliminate gaps, friction will occur between the gear and the casing, reducing pump efficiency.

In an external gear pump, eccentric force acts on the shaft of the gear from the high pressure side to the low pressure side, so there is a risk that the tips of the teeth will be slightly displaced and come into contact with the casing, as shown in Figure 2. This is caused by the clearance between the gear shaft (drive shaft, driven shaft) and the bearing, or by the deflection of the shaft due to the pressure difference (see Figure 3). On the other hand, if the gap between the tooth tips is made larger, this will cause an increase in internal leakage. Therefore, it is important to reduce friction while reducing the tooth tip clearance. That is, it is important to solve the trade-off problem between clearance and friction at the tips of gear teeth.

Regarding the axial gap, proposed methods include a method of reducing the gap using a movable side plate (Non-patent Document 1), and a method of preventing the gap from expanding due to deformation of the fixed side plate by reinforcing high-rigidity ceramics (Non-Patent Document 2). has been done. However, in a fixed side plate type gear pump, if reinforcement means for the fixed side plate is not adopted, the casing may expand due to internal pressure within the casing, increasing the axial gap between the gear and the casing, and increasing internal leakage. There is.

As described above, in the structure of a conventional external gear pump, if the gap between the tooth tips is small, the tooth tips come into contact with the casing due to eccentricity due to a pressure difference, and large friction occurs. On the other hand, if the gap between the tooth tips is large, friction at the tooth tips can be avoided, but internal leakage may increase. Further, in an external gear pump that employs a fixed side plate, the casing may expand due to internal pressure, increasing the gap between the gear and the casing, and increasing internal leakage.

In addition, hydraulic actuators equipped with external gear pumps are widely used in large construction machinery because they are difficult to break down, but it is difficult to reduce the size and weight to a size that can be mounted on robots without compromising the power-to-weight ratio. there were. Solving the above-mentioned problem regarding the gap between the gear and the casing is also important in realizing a smaller and lighter hydraulic pump.

E. Koc, C. J. Hooke, “An experimental investigation into the design and performance of hydrostatically loaded floating wear plates in gear pumps,” Wear, Vol. 209, pp. 184-192, 1997. M. Komagata, T. Ko, Y. Nakamura, “Design and Development of Compact Ceramics Reinforced Pump with Low Internal Leakage for Electro-Hydrostatic Actuated Robots,” Advances in Mechanism and Machine Science, Vol. 73, pp. 2439-2448, 2019.

An object of the present invention is to provide an external gear pump with an appropriate gap between the gear and the casing.

The technical means adopted by the present invention are:
a casing having a fluid inlet and a fluid outlet;
a pair of gears housed in the casing;
In an external gear pump with
The casing is
a movable casing including an inner surface where the tips of the teeth of the pair of gears are close to each other, and an internal space that accommodates the pair of gears;
an outer casing comprising an inner surface facing the outer surface of the movable casing and a housing portion for accommodating the movable casing;
In the internal space of the movable casing, when the gear rotates, a low pressure region is formed on the suction port side and a high pressure region is formed on the discharge port side,
The movable casing is movable within the housing portion of the outer casing in a direction escaping from the tooth tip in response to movement of the tooth tip due to eccentricity of the gear caused by a pressure difference of fluid in the internal space of the movable casing. ,
It is an external gear pump.
Typically, the fluid is hydraulic oil.

In one aspect, a gap between the outer surface of the movable casing and the inner surface of the outer casing is filled with fluid,
The movable casing has a first force generated by a pressure difference between the low pressure area and the high pressure area in the internal space of the movable casing, and a first force generated by a pressure difference of fluid in the gap between the movable casing and the outer casing. 2 forces act,
The second force is adapted to at least partially cancel the first force.

In one aspect, a high-pressure chamber filled with high-pressure fluid is formed on the outside of the movable casing, and is located outside of the high-pressure region in the internal space and communicates with the high-pressure region. , the second force is generated by utilizing the pressure of the fluid within the high pressure chamber.

In one aspect, the internal space of the movable casing includes a low pressure region on the suction port side and a high pressure region on the discharge port side,
A gap between the outer surface of the movable casing and the inner surface of the outer casing includes a low-pressure first chamber located outside the low-pressure region in the internal space and communicating with the low-pressure region, and a low-pressure first chamber located outside the high-pressure region. and a second chamber that forms the high pressure chamber by communicating with the high pressure region, and an intermediate pressure section filled with intermediate pressure fluid, and includes the first chamber, the second chamber, and the intermediate pressure chamber. The sections are separated by sealing material,
The second force is generated by a pressure difference between the first chamber and the second chamber.
In one aspect, an intermediate pressure region is formed in the internal space of the movable casing, located between the low pressure region and the high pressure region,
The intermediate pressure portion of the gap between the outer surface of the movable casing and the inner surface of the outer casing communicates with the intermediate pressure portion of the internal space of the movable casing.
In the embodiments described below, the external gear pump is a hydraulic pump employed in a closed hydraulic circuit used in an electrostatic hydraulic actuator (EHA), etc. However, if the external gear pump is equipped with an open hydraulic circuit, A fluid pressurized in advance to an intermediate pressure (for example, charge pressure) may be sealed in the intermediate pressure region.

In one aspect, the first force is estimated based on a pressure distribution in the interior space of the movable casing.

In one aspect, the first chamber includes a first surface forming an outer surface of the low pressure region of the movable casing,
The second chamber includes a second surface forming an outer surface of the high pressure region of the movable casing,
The second force can be adjusted by the areas of the first surface and the second surface.

In one aspect, the external gear pump includes a pair of side plates whose inner surfaces are close to the side surfaces of the gear,
The pair of side plates are integrated with the movable casing and are movable together with the movable casing.
In one aspect, the outer surface of the side plate is close to the outer casing via the gap,
The gap is filled with intermediate pressure fluid.
In one aspect, the gap between the outer surface of the side plate and the inner surface of the outer casing is part of the intermediate pressure section.

The technical means adopted by the present invention are:
an inner movable casing having an internal space in which a pair of gears is housed;
an outer casing having a housing portion in which the movable casing is housed;
Consisting of
The movable casing is formed into a box shape, and includes a peripheral wall having an inner surface adjacent to the tips of the teeth of the pair of gears, and a pair of side walls having an inner surface adjacent to the side surfaces of the gears,
In the internal space of the movable casing, when the gear rotates, a low pressure region is formed on the suction port side and a high pressure region is formed on the discharge port side,
A gap between the outer surface of the side plate of the movable casing and the inner surface of the outer casing is filled with intermediate pressure fluid.
It is an external gear pump.
In one aspect, an intermediate pressure region is formed in the internal space of the movable casing, located between the low pressure region and the high pressure region,
The intermediate pressure portion of the gap between the outer surface of the movable casing and the inner surface of the outer casing communicates with the intermediate pressure portion of the internal space of the movable casing.

In one aspect, a gap between the outer surface of the movable casing and the inner surface of the outer casing is located outside of the low-pressure region in the internal space and communicates with the low-pressure first chamber, and the high-pressure a second chamber located outside the section and communicating with the high pressure section to form the high pressure chamber; and an intermediate pressure section communicating with the intermediate pressure section within the internal space, the first chamber , the second chamber and the intermediate pressure section are partitioned by a sealing material,
The movable casing has a first force generated by a pressure difference between the low pressure area and the high pressure area in the internal space of the movable casing, and a second force generated by the pressure difference between the first chamber and the second chamber. force acts,
The movable casing is movable within the housing portion of the outer casing in a direction escaping from the tooth tip in response to movement of the tooth tip due to eccentricity of the gear caused by a pressure difference of fluid in the internal space of the movable casing. .

The present invention makes the casing adjacent to the gear of an external gear pump movable in the direction of the tooth tip, and balances the eccentric force acting on the movable casing by the pressure difference in the internal space of the movable casing. To solve the trade-off problem between tooth tip clearance and friction and provide a structure that reduces the friction and gap at the tooth tip.
In the present invention, by filling the space between the movable casing and the outer casing with intermediate pressure fluid, the side plate of the movable casing is prevented from expanding excessively and the axial gap is expanded, and leakage in the axial gap is prevented. reduce

FIG. 2 is a diagram showing internal clearances in a general external gear pump, where (a) represents the axial clearance and (b) represents the tooth tip clearance. It is a sectional view of a general external gear pump, showing how the gear shaft is eccentric when a pressure difference occurs, and the tips of the teeth come into contact with the inner surface of the casing. FIG. 3 is a diagram illustrating eccentricity of a gear shaft caused by differential pressure. It is a figure showing an external gear pump concerning this embodiment. It is a view taken along arrow A in FIG. 4. It is a view taken along arrow B in FIG. 4. It is a figure explaining the force which acts on the inside of a movable casing. It is a figure explaining the force which acts on the movable casing outer side. Only the forces in the vertical direction are shown, and the forces in the left and right directions are omitted. FIG. 2 is a conceptual diagram of a structure for balancing pressure acting on a movable casing. FIG. 6 is a diagram showing the estimated distribution of pressure acting on the inner surface of the movable casing. It is a sectional view of the external gear pump concerning this embodiment. It is a figure showing a unit consisting of a movable casing and a pair of gears concerning this embodiment. The upper figure is a cross-sectional view of the outer casing according to the present embodiment along a plane perpendicular to the gear axis, and the lower figure is a cross-sectional view of the same outer casing along the gear axis. FIG. 2 is a cross-sectional view (a plane perpendicular to the gear axis) of an external gear pump including an outer casing and a movable casing according to the present embodiment. It is a figure explaining prevention of expansion by introduction of intermediate pressure. It is a figure explaining the determination of the axial direction clearance gap concerning this embodiment. It is a figure showing the measurement result of the maximum pressure of the external gear pump concerning this embodiment.

[A] Overall configuration of external gear pump according to the present embodiment The external gear pump according to the present embodiment is a hydraulic pump employed in a closed hydraulic circuit used in an electrostatic hydraulic actuator (EHA) or the like. Note that the present invention can also be applied to open hydraulic circuits. Referring to FIGS. 4 to 6, the casing of the external gear pump according to the present embodiment includes an outer casing 1 and an inner movable casing 2. The movable casing 2 accommodates a pair of gears 3 consisting of a first gear 3A, which is a driving gear, and a second gear 3B, which is a driven gear. In a state where the movable casing 2 is accommodated in the housing part of the outer casing 1, a space (gap) is formed between the outer surface of the movable casing 2 and the inner surface of the outer casing 1, and the movable casing 2 It is movable within one housing part. In this embodiment, the gear 3 is an involute gear. The outer casing 1 and the movable casing 2 are made of aluminum alloy. The movable casing 2 is coated with Teflon-containing electroless nickel plating which has excellent slip properties.

The external gear pump according to this embodiment is a hydraulic pump, and the working fluid is hydraulic oil. In the internal space of the movable casing 2, a low pressure region 2A is formed on the hydraulic oil suction side and a high pressure region 2B is formed on the hydraulic oil discharge side by the rotation of the pair of gears 3. An intermediate pressure region 2C is formed at the location. When the gear 3 rotates, the intermediate pressure, which is the pressure of the hydraulic oil in the intermediate pressure section 2C, is lower than the pressure of the hydraulic oil in the high pressure section 2B, and higher than the pressure of the hydraulic oil in the low pressure section 2A. In one aspect, the intermediate pressure is a pressure equivalent to the charge pressure. Note that the pressure of the intermediate pressure hydraulic oil does not necessarily have to exactly match the charge pressure or the average value of the high pressure part pressure and the low pressure part pressure.

The space between the outer surface of the movable casing 2 and the inner surface of the outer casing 1 includes a low-pressure part 4 formed on the outer side of the movable casing 2 (hydraulic oil suction side) and a low-pressure part 4 formed on the outer side of the movable casing 2 (hydraulic oil discharge side). ), and an intermediate pressure section 6 which is a gap excluding the low pressure section 4 and the high pressure section 5, and the low pressure section 4 and the intermediate pressure section 6 are separated by an O ring 7 as a sealing material. The high pressure section 5 and the intermediate pressure section 6 are separated by an O-ring 7 as a sealing material. The low pressure section 4 communicates with a low pressure section 2A in the interior space of the movable casing 2, and the high pressure section 5 communicates with a high pressure section 2B in the interior space of the movable casing 2. The intermediate pressure portion 6 communicates with the intermediate pressure portion 2C of the internal space of the movable casing 2 through a communication hole 8 formed at a predetermined portion of the movable casing 2, and the intermediate pressure portion 6 is supplied with intermediate pressure hydraulic oil. Filled. Although the drawings specify the high-pressure side and the low-pressure side for convenience of explanation, it should be noted that the external gear pump according to this embodiment is reversible, and the high-pressure side and low-pressure side can be interchanged. That is, when the pump reverses, the suction side (suction port) and the discharge side (discharge port) are swapped, the low-pressure part and high-pressure part on the outside of the movable casing 2 are swapped, and the high-pressure part and low-pressure part on the inside of the movable casing 2 are swapped. .

As shown in FIG. 12, the movable casing 2 according to the present embodiment is formed into a box shape including a peripheral wall portion 20 having four peripheral walls and a pair of side plates 21. The peripheral wall portion 20 includes an internal space that accommodates the pair of gears 3 and an inner surface where the tips of the teeth of the pair of gears 3 are close to each other. A pair of side plates 21 are fixed to the peripheral wall 20 so as to close the internal space of the peripheral wall 20 . The internal space of the movable casing 2 is a space surrounded by the inner surface of the peripheral wall portion 20 and the inner surface of the pair of side plates 21.

As shown in FIGS. 11 and 13, the outer casing 1 according to the present embodiment includes a main body portion 1A, a first side portion 1B, and a second side portion 1C. The main body portion 1A includes an internal space that accommodates the movable casing 2 and an inner surface that is close to the outer surface of the peripheral wall portion 20 of the movable casing 2. The first side part 1B and the second side part 1C are fixed to the main body part 1A so as to enclose the movable casing 2 accommodated in the internal space of the main body part 1A.

The drive shaft 30A of the first gear 3A passes through the pair of side plates 21 and is rotatably supported by a needle bearing 31 on the first side 1B and the second side 1C, and one end of the drive shaft 30A is , protrudes to the outside of the outer casing 1 (first side portion 1B). The driven shaft 30B of the second gear 3B passes through the pair of side plates 21 as shown in FIG. 12, and is rotatable by needle bearings 31 on the first side 1B and second side 1C as shown in FIG. Supported. The drive shaft 30A of the first gear 3A and the drive shaft 30B of the second gear 3B are rotatably supported by bearing balls 32 in the movable casing 1 (side plate 21). In the figure, 33 is a packing, and 34 is a gasket. As shown in FIG. 12, in the box-shaped movable casing 2 according to this embodiment, a drive shaft 30A and a driven shaft 30B each protrude from one side plate 21, and the other side plate (not shown in FIG. 12) A drive shaft 30A and a driven shaft 30B each protrude from the shaft.

The peripheral wall portion 20 of the movable casing 2 includes a first wall 200 located on the hydraulic oil suction side and having a first inner surface close to the tooth tips of the first gear 3A and the second gear 3B, and a hydraulic oil discharge side. The second wall 201 has a second inner surface located at the top of the first gear 3A and the second gear 3B, and a third inner surface near the top of the teeth of the first gear 3A (the movement locus of the top of the tooth). a third wall 202 with an arcuate surface or a curved surface along the tooth tip of the second gear 3B; and a fourth inner surface (an arcuate surface or a curved surface along the movement locus of the tooth tip) close to the tooth tip of the second gear 3B. It has four walls 203. The first wall 200 and the second wall 201 face each other. The third wall 202 and the fourth wall 203 face each other.

Two circular recesses 204 are formed on the outer surface of the first wall 200, and a hole 205 is formed on the bottom surface 2040 of the recess 204. It communicates with a low pressure region 2A of the internal space. When the movable casing 2 is housed in the storage section of the outer casing 1, the space within the recess 204 is closed by the O-ring 7, forming the low pressure section 4 as a first chamber. The bottom surface 2040 of the recess 204 forms the pressurizing surface 40 of the low pressure section 4 formed on the outside (suction side) of the movable casing 2 .

Two circular recesses 206 are formed on the outer surface of the second wall 201, and a hole 207 is formed on the bottom surface 2060 of the recess 206. It communicates with a high pressure region 2B in the internal space. When the movable casing 2 is housed in the storage section of the outer casing 1, the space within the recess 206 is closed by the O-ring 7, forming the high pressure section 5 as a second chamber. A bottom surface 2060 of the recess 206 forms a pressurizing surface 50 of the high pressure section 5 formed on the outside (discharge side) of the movable casing 2 .

A hole 208 is formed in the third wall 202 and the fourth wall 203 of the peripheral wall 20, and when the movable casing 2 is stored in the storage part of the outer casing 1, the peripheral wall The external space (intermediate pressure section 6) and internal space (intermediate pressure section 2C) of the section 20 communicate with each other. The hole 208 forms a communication hole 8 (see FIGS. 4, 5, and 8).

In this embodiment, the outer casing 1 is assembled by fixing the side plate 21 to the peripheral wall portion 20 with a plurality of hexagon socket head bolts 209. The side plate 21 includes an inner surface 210 (see FIGS. 11, 15, and 16) that is close to the side surfaces of the first gear 3A and the second gear 3B, and an outer surface 211 that forms part of the outer surface of the movable casing 2. ing. A hole 212 is formed in the side plate 21 at a position close to the third wall 202 and the fourth wall 203 of the peripheral wall 20, and the internal space and the external space of the movable casing 2 are connected through the hole 212. It is designed to communicate. The hole 212 forms a communication hole 8 (see FIGS. 4, 5, and 8).

As shown in FIG. 13, the outer casing 1 includes an accommodating portion that accommodates the movable casing 2, and this accommodating portion includes an inner surface (first surface 10, first surface 10, 2 surfaces 11, 3rd surfaces 12, and 4th surfaces 13), an inner surface 14 of the first side portion 1B, and an inner surface 15 of the second side portion 1C.

In a state in which the movable casing 2 is accommodated in the housing portion of the outer casing 1, the inner surface of the main body portion 1A is close to the outer surface of the peripheral wall portion 20 of the movable casing 2. The inner surface of the main body 1A includes a first surface 10 facing the outer surface of the first wall 200 of the peripheral wall 20 of the movable casing 2 and a second surface facing the outer surface of the second wall 201 of the peripheral wall 20 of the movable casing 2. 11, a third surface 12 facing the outer surface of the third wall 202 of the peripheral wall 20 of the movable casing 2, and a fourth surface 13 facing the outer surface of the fourth wall 203 of the peripheral wall 20 of the movable casing 2. We are prepared. The inner surface 14 of the first side 1B of the outer casing 1 is close to the outer surface 211 of one side plate 21, and the inner surface 15 of the first side 1C is close to the outer surface 211 of the other side plate 21.

In this embodiment, two cylindrical flow path elements 16 are provided on the first wall forming the first surface 10 of the main body portion 1A of the outer casing 1, and the second wall forming the second surface 11 is provided with two cylindrical flow path elements 16. is provided with two cylindrical flow path elements 17. The flow path element 16 forms an inlet for hydraulic oil, extends through the first wall forming the first surface 10 of the main body 1A, and has a conical shape whose diameter increases toward the internal space. The inner end of the channel element 16 protrudes further into the internal space than the first surface 10. The flow path element 17 forms a discharge port for hydraulic oil, extends through the second wall forming the second surface 11 of the main body portion 1A, and has a conical shape whose diameter increases toward the internal space. The inner end of the channel element 17 protrudes further into the internal space than the second surface 11.

In a state in which the movable casing 2 is housed in the housing portion of the outer casing 1, the first surface 10 of the main body portion 1A and the outer surface of the first wall 200 of the peripheral wall portion 20 are close to each other, and the inner end of the flow path element 16 is located within a circular recess 204 formed in the first wall 200. The second surface 11 of the main body portion 1A and the outer surface of the second wall 201 of the peripheral wall portion 20 are close to each other, and the inner end of the channel element 17 is located within the circular recess 206 formed in the second wall 201. are doing.

In this embodiment, the outer casing 1 is formed by assembling a main body portion 1A, a first side portion 1B, a second side portion 1C, two flow path elements 16, and two flow path elements 17. The movable casing 2 only needs to be movable at least in the Y direction (see FIG. 14) in the housing part of the outer casing 1, but when the movable casing 2 is housed in the housing part of the outer casing 1, the channel element 16 For example, a gap (for example, around 0.15 mm) that prevents the O-ring 7 from getting caught is formed at the fitting portion of the flow path element 17 and the movable casing 2 to prevent over-restriction of the movable casing 2. It is prevented. Due to this gap, the movable casing 2 has a slight play in the XZ directions as well. 14 and 16, the straight line connecting the centers of the two shafts 30A and 30B of the pair of gears 3 is the X direction, and the direction perpendicular to the plane passing through the centers of the two shafts is the Y direction. Let the direction of the center of the book's axis be the Z direction.

As described above, in this embodiment, when the movable casing 2 is housed in the housing part of the outer casing 1, the outer surface of the movable casing 2 and the inner surface of the outer casing 1 are close to each other, and there is a space (gap) between them. This space is formed from a low pressure section 4, a high pressure section 5, and an intermediate pressure section 6.

The low pressure section 4 is a space formed between the circular recess 204 on the outer surface of the first wall 200 of the peripheral wall section 20 of the movable casing 2 and the internal space of the flow path element 16 . When the inner end of the channel element 16 is located in the recess 204, an O-ring 7 is provided between the inner end and the recess 204 to partition the recess 204 and the intermediate pressure section 6, thereby forming a low pressure section. A first chamber as number 4 is formed.

The high pressure section 5 is a space formed between the circular recess 206 on the outer surface of the second wall 201 of the peripheral wall section 20 of the movable casing 2 and the internal space of the flow path element 17 . When the inner end of the channel element 17 is located in the recess 206, an O-ring 7 is provided between the inner end and the recess 206, and by partitioning the recess 206 and the intermediate pressure part 6, the high pressure part A second chamber as 5 is formed.

The intermediate pressure section 6 is a gap between the outer surface of the movable casing 2 and the inner surface of the outer casing 1, excluding the low pressure section 4 and the high pressure section 5. The high pressure section 5 and the intermediate pressure section 6 are separated by an O-ring 7. The intermediate pressure section 6 is movable via holes 208 formed in the third wall 202 and fourth wall 203 of the peripheral wall section 20 of the movable casing 2 and holes 212 formed in the side plate 21 of the movable casing 2. It communicates with the intermediate pressure region 2C of the internal space of the casing 2.

More specifically, the intermediate pressure section 6 is located between the outer surface (first plane) of the first wall 200 of the peripheral wall section 20 of the movable casing 2 and the first surface 10 of the main body section 1A of the outer casing 1 (the recess 204 , the gap between the outer surface (second plane) of the second wall 201 of the peripheral wall portion 20 of the movable casing 2 and the main body portion 1A of the outer casing 1 The gap between the second surface 11 (excluding the second chamber formed by the recess 206, the cylindrical member 17, and the O-ring 7), the outer surface of the third wall 202 of the peripheral wall 20 of the movable casing 2 (the third surface ) and the third surface 12 of the main body 1A of the outer casing 1, the outer surface (fourth surface) of the fourth wall 203 of the peripheral wall 20 of the movable casing 2, and the fourth surface of the main body 1A of the outer casing 1. a gap between the outer surface 211 of one side plate 21 of the movable casing 2 and the inner surface 14 of the first side 1B of the outer casing 1; and a gap between the outer surface 211 of the other side plate 21 of the movable casing 2 The second side portion 1C of the outer casing 1 includes a gap between the second side portion 1C and the inner surface 15, and these gaps communicate with each other and are filled with intermediate pressure hydraulic oil.

[B] Structure that solves the problem of trade-off between clearance and friction at gear tips In an external gear pump, when the gear 3 rotates, the internal space of the movable casing 2 has a low pressure region 2A on the suction port side and a discharge region 2A. A high pressure region 2B on the exit side and an intermediate pressure region 2C between the low pressure region 2A and the pressing region 2B are formed. The larger the pressure difference between the high-pressure side and the low-pressure side caused by the rotation of the gear 3, the greater the eccentric force acting on the rotating shafts (drive shaft 30A, driven shaft 30B) that support the gear 3 from the high-pressure side to the low-pressure side. In conventional mechanisms, the casing that houses the gears is fixed, and the eccentricity of the gears causes the tips of the teeth to press against the casing on the low-pressure side, causing friction (see Figures 2 and 3).

If the structure is such that when the gear is eccentric, the casing adjacent to the tooth tip is pushed by the gear and can move without resistance, it is thought that friction will be reduced and the gap between the tooth tips can be reduced. Therefore, we propose a design method that balances the pressure by making the casing in contact with the gear teeth movable. For pressure balancing, the load inside the casing is estimated based on the pressure distribution at the tooth tip, and the counterbalancing force outside the casing is determined.

In this embodiment, the casing housing the pair of gears is placed in the hydraulic oil flow path to allow movement in the tooth tip direction, and the casing moves in accordance with the amount of tooth tip movement due to the eccentricity of the gears. This reduces tooth tip friction. Here, when the casing housing the pair of gears is made movable, the pressure in the internal space of the movable casing 2 is divided by the pair of gears into a high-pressure region 2B and a low-pressure region 2A when the gear pump is driven, and this pressure difference causes the movable casing to move. Eccentric force acts on the casing 2 in the direction from the low pressure region 2A to the high pressure region 2B. This may cause the inner surface of the movable casing to be pressed against the tips of the gear teeth, causing friction.

When driving an external gear pump, in order to reduce tooth tip friction or ideally make it zero, if the load applied to the movable casing 2 can be made to appear to be zero, when contact with the tooth tips occurs, the movable casing 2 It is possible to realize a mechanism that moves by that amount. Separate the casing of an external gear pump into an outer casing and an inner casing, and float the inner casing in oil. By doing this, the inner casing is placed in a virtual unloaded state, allowing it to move along with the displacement of the gear (in the Y direction), and friction at the tips of the teeth can be avoided when the gaps between the tips of the teeth are narrow.

In order to achieve a virtual no-load state, a structure is adopted that balances the pressure inside and outside the inner casing. The movable casing 2 has a first force (indicated by an arrow in FIG. 7) caused by a pressure difference inside the casing, and a second force (indicated by an arrow in FIG. 8) caused by a pressure difference outside the casing in the opposite direction. ) are acting, and if the magnitude of the first force and the second force can be made equal, it is possible to cancel out the effects of the two forces and realize an apparent no-load state.

The first force is determined by the pressure distribution on the tooth tips inside the casing. The optimal second force can be obtained by designing the area where the outer surface of the movable casing 2 contacts the hydraulic oil (the area of the pressure surface 40 and the area of the pressure surface 50) based on the estimated value of the first force. , a virtual no-load state of the movable casing 2 can be realized.

In the embodiment shown in FIG. 12, the area of the pressure surface 40 is the sum of the areas of the bottom surfaces 2040 of the two circular recesses 204, and the area of the pressure surface 50 is the sum of the areas of the bottom surfaces 2060 of the two circular recesses 206. It is. In the external gear pump according to this embodiment, since the suction side and the discharge side can be changed arbitrarily, the area of the pressurizing surface 40 and the area of the pressurizing surface 50 are the same.

In the embodiment shown in FIGS. 12 and 13, the movable casing 2 of the external gear pump is provided with two suction ports and two discharge ports. Each inlet consists of a flow path element 16 and a set of holes 205 formed in the bottom surface 2040 of the recess 204, and each outlet consists of a flow path element 17 and a set of holes 207 formed in the bottom surface 2060 of the recess 206. The movable casing 2 has two sets of suction ports and two sets of discharge ports. In the external gear pump according to this embodiment, the two flow path elements 16 communicate with the suction port of one common outer casing 2, and the two flow path elements 17 communicate with the inlet of one common outer casing 2. It communicates with the discharge port.

In this embodiment, by providing two circular recesses 204, two flow path elements 16, two circular recesses 206, and two flow path elements 17, the area of the pressurizing surface 40 (bottom surface 2040) is sufficient. , the area of the pressurizing surface 50 (bottom surface 2060) is ensured. In this embodiment, the pressure surfaces 40 and 50 are formed from a plurality of surfaces, but the pressure surfaces 40 and 50 may be formed from a single surface as long as they can generate a predetermined second force. Alternatively, the pressure surfaces 40, 50 may be formed from three or more surfaces.

As shown in FIG. 10, by applying a force (second force) that counteracts the eccentric force F (first force) acting on the movable casing to the outside of the movable casing 2, the resultant force acting on the movable casing 2 and the resulting Reduce friction torque to zero. Specifically, as shown in FIG. 9, hydraulic oil is introduced into the space outside the movable casing (low pressure section 4, high pressure section 5). In FIG. 9, the internal space of the movable casing 2 is divided into a low pressure region 2A and a high pressure region 2B by a pair of gears 3. The hydraulic fluid in the high pressure section 2B is introduced into the high pressure section 5 (second chamber) outside the movable casing 2. The hydraulic fluid introduced into the low pressure section 4 and the high pressure section 5 acts to counteract the force exerted by the hydraulic fluid in the low pressure section 2A and high pressure section 2B. However, it is assumed that the pressure in the area outside the movable casing 2 (intermediate pressure section 6) is constant.

As shown in FIG. 12, the outer surface of the movable casing 2 according to the present embodiment includes an outer surface of the peripheral wall portion 20 and an outer surface 211 of the pair of side plates 21. The outer surface of the peripheral wall portion 20 includes the outer surface (first surface) of the first wall 200, the outer surface (second surface) of the second wall 201, the outer surface (third surface) of the third wall 202, and the fourth wall 203. It consists of an outer surface (fourth surface). The outer surface (first surface) of the first wall 200 consists of a first plane and a bottom surface 2040 (low-pressure pressurizing surface 40) of the circular recess 204. The outer surface (second surface) of the second wall 201 consists of a second plane and a bottom surface 2060 (high pressure pressurizing surface 50) of the circular recess 206. The outer surface (first plane, second plane, third surface, fourth surface) of the peripheral wall section 20 and the outer surface 211 of the side plate 21 are surfaces on which intermediate pressure acts (facing the intermediate pressure section 6). The inner surface of the internal space of the movable casing 2 includes a low pressure surface corresponding to the bottom surface 2040 of the recess 204, a high pressure surface corresponding to the bottom surface 2060 of the recess 206, and an arcuate or curved surface located between the low pressure surface and the high pressure surface. The curved surface is a surface that follows the tooth tip pressure distribution.

ここで低圧側の圧力をP₀、高圧側の圧力はP₀+ΔPとした。P(θ)は歯先の圧力分布を表す。圧力分布が高圧から低圧にかけて一定の勾配で減少すると仮定すると、

となる。歯先圧力分布の実験結果（A.Corvaglia, M. Rundo, P. Casoli and A. Lettini,“Evaluation of Tooth Space Pressure and Incomplete Filling in External Gear Pumps by Means of Three-Dimensional CFD Simulations,”Energies, Vol. 14, No.2, 342, 2021.）では圧力上昇部の勾配がほぼ一定であるためこのような仮定をおいた。このとき低圧側の歯先がケーシング内面に押し付けられる力は

と表せる。ただしlは歯車間距離、dは歯車の厚み、rはケーシング内径を表す。この偏心力に拮抗する力を外側から与える設計とする。 Estimation of eccentric force due to internal pressure acting on the movable casing will be explained. Assume a situation where a gear rotates and generates a differential pressure ΔP in an oval movable casing as shown in FIG. Calculate the eccentric force from the pressure acting on the inner surface of the movable casing. The pressure distribution P _r on the inner surface of the movable casing adjacent to the tooth tip of the gear is expressed as a function of the angle θ as follows.

Here, the pressure on the low pressure side was P ₀ and the pressure on the high pressure side was P ₀ +ΔP. P(θ) represents the pressure distribution at the tooth tip. Assuming that the pressure distribution decreases with a constant slope from high pressure to low pressure,

becomes. Experimental results of tooth tip pressure distribution (A. Corvaglia, M. Rundo, P. Casoli and A. Lettini, “Evaluation of Tooth Space Pressure and Incomplete Filling in External Gear Pumps by Means of Three-Dimensional CFD Simulations,” Energys, Vol. 14, No. 2, 342, 2021.), this assumption was made because the slope of the pressure rise section is almost constant. At this time, the force with which the tips of the teeth on the low pressure side are pressed against the inner surface of the casing is

It can be expressed as However, l represents the distance between gears, d represents the thickness of the gear, and r represents the inner diameter of the casing. The design is such that a force that counteracts this eccentric force is applied from the outside.

従って、式(3)より、Sは以下のように求められる。

The design is based on the expectation that the pressure balance as shown in FIGS. 7 and 8 will work. The force pushing the movable casing 2 by the hydraulic oil introduced into the low pressure part 4 (first chamber) and the high pressure part 5 (second chamber) is balanced with the force acting on the movable casing 2 by the hydraulic oil inside the movable casing. The areas of the bottom surfaces 2040 and 2060 of the circular recesses 204 and 206 are designed. Specifically, assuming that the area of the bottom surfaces 2040 and 2060 is S, the conditional expression for balance is as follows.

Therefore, from equation (3), S can be obtained as follows.

[C] Structure that solves the problem of gap expansion due to internal pressure in fixed side plate type gear pumps In this embodiment, by filling the space between the movable casing 2 and the outer casing 1 with intermediate pressure hydraulic oil, Also realizes a floating state of the movable casing 2. This prevents the axial gap from expanding excessively, and at the same time, lubricates the space between the outer casing 1 and the movable casing 2 with intermediate pressure hydraulic oil, thereby reducing friction. In a typical fixed side plate type pump, the casing expands as the internal pressure increases, increasing the gap between the gear and the casing. This increases internal leakage. In this embodiment, the outer peripheral portion of the inner casing is filled with intermediate-pressure hydraulic oil to reduce the pressure difference between the inside and outside of the inner casing and prevent expansion and deformation. On the other hand, the outer casing can expand due to internal pressure, but this does not affect internal leakage. In addition, if only to solve the problem of trade-off between clearance and friction at the gear tooth tips, filling the gap between the inner surface of the outer casing 1 and the outer surface of the movable casing 2 (excluding the low pressure part 4 and high pressure part 5) is necessary. The fluid may be a fluid other than intermediate pressure hydraulic oil, for example a gas (eg air at atmospheric pressure).

Determination of the axial clearance, which is the clearance between the axial gear and the casing, will be explained with reference to FIG. 16. The gear shafts (drive shaft 30A, driven shaft 30B) of the pair of gears are supported by needle bearings 31 on the first side 1B and second side 1C of the outer casing 1. The displacement of the gear shaft in the XY direction with respect to the casing 1 is restricted. The bearing balls 32 inside the movable casing play the role of a thrust bearing, and restrain the displacement of the movable casing 2 in the Z direction with respect to the gear shaft. On the other hand, there is play in the radial direction (XY direction). A ring-shaped groove is formed on the inner surface 210 of the side plate 21 of the movable casing 2 adjacent to the insertion portion of the gear shaft, and the depth of this groove is indicated by D in FIG. Further, the axial clearance is indicated by G1, and the diameter of the bearing ball 32 is indicated by d.
Axial clearance G1 = diameter d of bearing ball 32 - depth D of groove,
The dimension of the axial gap can be determined by the tolerance of the two parts, and it is possible to precisely determine the optimum axial gap in microns.

[D] Evaluation of friction and internal leakage The frictional torque and internal leakage resistance of the external gear pump according to this embodiment at a differential pressure of about 13 MPa were measured and compared with a conventional fixed casing type external gear pump. The results are shown in Table 1.
Compared to the fixed casing type, the friction was lower, but internal leakage was greater.

内部漏れ損失は、

で計算される。Δp=14MPaの時でも内部漏れ抵抗がΔp=13MPaのときとほとんど同じ値であるとみなせると仮定した場合、損失は約123Wと見積もられるが、これはモータ定格出力（2,310W）の5％程度になる。このレベルの内部漏れは、本実施形態に係る外接歯車ポンプがEHAモジュールの要素として採用される場合において許容範囲であると考えられる。 The loss due to internal leakage of the external gear pump according to this embodiment will be supplemented. For internal leakage flow rate q [m3/s] when differential pressure Δp=13×10 ^-6 [Pa], internal leakage resistance k _L =1.6×10 ¹² [Pa・s/m ³ ] is defined by the following formula. be done.

Internal leakage loss is

It is calculated by Assuming that the internal leakage resistance is almost the same value when Δp=14MPa as when Δp=13MPa, the loss is estimated to be about 123W, which is about 5% of the motor rated output (2,310W). become. This level of internal leakage is considered to be within an acceptable range when the external gear pump according to the present embodiment is employed as an element of an EHA module.

The maximum pressure was measured for the external gear pump according to this embodiment. The results are shown in FIG. It was confirmed that the target maximum pressure of 14MP can be fully achieved.

1 Outer casing 2 Movable casing (inner casing)
20 Peripheral wall section (peripheral wall)
204 Circular recess 2040 Bottom surface of recess (pressure surface)
206 Circular recess 2060 Bottom surface of recess (pressure surface)
208 Hole (insertion hole)
212 Hole (insertion hole)
21 Side plate (side wall)
3 Gear 3A Drive gear 3B Driven gear 4 Low pressure section 40 Pressure surface 5 High pressure section 50 Pressure surface 6 Intermediate pressure section 7 O-ring (sealing member)
8 Communication hole

Claims (13)

a casing having a fluid inlet and a fluid outlet;
a pair of gears housed in the casing;
In an external gear pump with
The casing is
a movable casing including an inner surface where the tips of the teeth of the pair of gears are close to each other, and an internal space that accommodates the pair of gears;
an outer casing comprising an inner surface facing the outer surface of the movable casing and a housing portion for accommodating the movable casing;
In the internal space of the movable casing, when the gear rotates, a low pressure region is formed on the suction port side and a high pressure region is formed on the discharge port side,
The movable casing is movable within the housing portion of the outer casing in a direction escaping from the tooth tip in response to movement of the tooth tip due to eccentricity of the gear caused by a pressure difference of fluid in the internal space of the movable casing. ,
External gear pump. A gap between the outer surface of the movable casing and the inner surface of the outer casing is filled with fluid;
The movable casing has a first force generated by a pressure difference between the low pressure area and the high pressure area in the internal space of the movable casing, and a first force generated by a pressure difference of fluid in the gap between the movable casing and the outer casing. 2 forces act,
the second force is adapted to at least partially cancel the first force;
The external gear pump according to claim 1. A high-pressure chamber filled with high-pressure fluid is formed on the outside of the movable casing, and is located outside of the high-pressure part in the internal space and communicates with the high-pressure part, and is filled with high-pressure fluid. The second force is generated by using fluid pressure.
The external gear pump according to claim 2. The internal space of the movable casing includes a low pressure region on the suction port side and a high pressure region on the discharge port side,
A gap between the outer surface of the movable casing and the inner surface of the outer casing includes a low-pressure first chamber located outside the low-pressure region in the internal space and communicating with the low-pressure region, and a low-pressure first chamber located outside the high-pressure region. and a second chamber that forms the high pressure chamber by communicating with the high pressure region, and an intermediate pressure section filled with intermediate pressure fluid, and includes the first chamber, the second chamber, and the intermediate pressure chamber. The sections are separated by sealing material,
the second force is generated by a pressure difference between the first chamber and the second chamber;
The external gear pump according to claim 3. An intermediate pressure region is formed in the internal space of the movable casing, located between the low pressure region and the high pressure region,
The intermediate pressure portion in the gap between the outer surface of the movable casing and the inner surface of the outer casing communicates with the intermediate pressure portion of the internal space of the movable casing.
The external gear pump according to claim 4. The first force is estimated based on the pressure distribution in the internal space of the movable casing.
The external gear pump according to claim 2. The first chamber includes a first surface forming an outer surface of the low pressure region of the movable casing,
The second chamber includes a second surface forming an outer surface of the high pressure region of the movable casing,
The second force is adjustable by the areas of the first surface and the second surface.
The external gear pump according to claim 4. The external gear pump includes a pair of side plates whose inner surfaces are close to the side surfaces of the gear,
The pair of side plates are integrated with the movable casing, and are movable integrally with the movable casing.
The external gear pump according to any one of claims 1 to 7. The outer surface of the side plate is close to the outer casing via the gap,
the gap is filled with intermediate pressure fluid;
The external gear pump according to claim 8. The external gear pump includes a pair of side plates whose inner surfaces are close to the side surfaces of the gear,
The pair of side plates are integrated with the movable casing,
The intermediate pressure portion includes a gap between the outer surface of the side plate and the inner surface of the outer casing.
The external gear pump according to claim 5. an inner movable casing having an internal space in which a pair of gears is housed;
an outer casing having a housing portion in which the movable casing is housed;
Consisting of
The movable casing is formed into a box shape, and includes a peripheral wall having an inner surface adjacent to the tips of the teeth of the pair of gears, and a pair of side walls having an inner surface adjacent to the side surfaces of the gears,
In the internal space of the movable casing, when the gear rotates, a low pressure region is formed on the suction port side and a high pressure region is formed on the discharge port side,
A gap between the outer surface of the side plate of the movable casing and the inner surface of the outer casing is filled with intermediate pressure fluid.
External gear pump. An intermediate pressure region is formed in the internal space of the movable casing, located between the low pressure region and the high pressure region,
The intermediate pressure portion of the gap between the outer surface of the movable casing and the inner surface of the outer casing communicates with the intermediate pressure portion of the internal space of the movable casing.
The external gear pump according to claim 11. A gap between the outer surface of the movable casing and the inner surface of the outer casing includes a low-pressure first chamber located outside the low-pressure region in the internal space and communicating with the low-pressure region, and a low-pressure first chamber located outside the high-pressure region. and a second chamber that communicates with the high pressure section to form the high pressure chamber, and an intermediate pressure section that communicates with the intermediate pressure section in the internal space, the first chamber and the second chamber. , the intermediate pressure section is partitioned by a sealing material,
The movable casing has a first force generated by a pressure difference between the low pressure area and the high pressure area in the internal space of the movable casing, and a second force generated by the pressure difference between the first chamber and the second chamber. force acts,
The movable casing is movable within the housing portion of the outer casing in a direction escaping from the tooth tip in response to movement of the tooth tip due to eccentricity of the gear caused by a pressure difference of fluid in the internal space of the movable casing. ,
The external gear pump according to claim 12.

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