JP7572904B2 - Parallel Pump - Google Patents

Description

The present invention relates to a parallel pump that includes a pair of piston pump mechanisms arranged in parallel with each other.

Parallel pumps that include a pair of piston pump mechanisms arranged in parallel with each other have been known. For example, Patent Document 1 discloses a parallel pump 100 as shown in FIG. 5.

Specifically, in the parallel pump 100, a first piston pump mechanism 120 and a second piston pump mechanism 130 are arranged in parallel to each other within a casing 110. A pump chamber 111 that houses the first piston pump mechanism 120 and the second piston pump mechanism 130 is formed in the casing 110.

The first piston pump mechanism 120 is driven by a drive shaft 140, and the second piston pump mechanism 130 is driven by a driven shaft 150. One end of the drive shaft 140 is located outside the casing 110 and is connected to a prime mover such as an engine or an electric motor.

A drive gear 160 is fixed to the drive shaft 140 between the one end and the first piston pump mechanism 120. A driven gear 170 that meshes with the drive gear 160 is fixed to the driven shaft 150. A gear chamber 112 that houses the drive gear 160 and the driven gear 170 is also formed in the casing 110.

In the parallel pump 100 of Patent Document 1, the first piston pump mechanism 120 and the second piston pump mechanism 130 are variable displacement swash plate pumps. In each of the first piston pump mechanism 120 and the second piston pump mechanism 130, a portion of the hydraulic oil is supplied between the shoe plate fixed to the swash plate and the shoe, and is used as lubricating oil. The oil is stored in the pump chamber 111.

The oil stored in the pump chamber 111 is also supplied to the gear chamber 112 and stored there. Therefore, in the gear chamber 112, the oil is stirred as the drive gear 160 and the driven gear 170 rotate. More specifically, around the drive gear 160, the oil flows in the rotational direction of the drive gear 160, and around the driven gear 170, the oil flows in the rotational direction of the driven gear 170.

Furthermore, in the parallel pump 100 of Patent Document 1, a linear groove 180 (a linear groove perpendicular to the paper in FIG. 5) is formed on each of a pair of opposing surfaces 113, 114 in the gear chamber 112 that face each other across the drive gear 160 and driven gear 170 and that extends along the meshing region between the drive gear 160 and driven gear 170.

JP 2000-220566 A

In the first half of the meshing process between the drive gear 160 and the driven gear 170, the tooth of one gear enters the tooth space of the other gear, reducing the volume of the tooth space. As a result, the oil in the tooth space overflows in the axial direction of the gears. In contrast, if groove 180 is present as described above, the oil that overflows from the tooth space flows into groove 180. This reduces the compression work (so-called mixing loss) that the gears do to compress the oil. On the other hand, in the second half of the meshing process between the drive gear 160 and the driven gear 170, the tooth of the other gear comes out of the tooth space of the one gear, increasing the volume of the tooth space. As a result, oil enters the tooth space from groove 180.

In this way, in the parallel pump 100 of Patent Document 1, the compression work done by the gears is reduced, and the efficiency of the parallel pump 100 (the ratio of the work done by the pump to the work provided by the prime mover) is improved. However, further efficiency improvements are desired for parallel pumps.

Therefore, the present invention aims to provide a parallel pump that can improve efficiency compared to conventional pumps.

In order to solve the above problem, the inventors of the present invention conducted extensive research and discovered that when a linear groove is formed on at least one of a pair of opposing surfaces that face each other across the drive gear and driven gear in the gear chamber as in the conventional case, oil flows only along the linear shape of the groove within the groove, and therefore acceleration work is required to accelerate the oil that has entered the tooth groove in the circumferential direction of the gear in the latter half of the meshing process. The present invention was made from this perspective.

That is, the parallel pump of the present invention comprises a drive shaft to which a drive gear is fixed, a driven shaft to which a driven gear that meshes with the drive gear is fixed, and a gear chamber in which oil is stored and which houses the drive gear and the driven gear, and at least one of a pair of opposing surfaces in the gear chamber that face each other with the drive gear and the driven gear in between is formed with a groove that extends along the meshing area of the drive gear and the driven gear, and the end of the groove facing the rotation direction of the drive gear and the driven gear is bifurcated along the rotation direction of the drive gear and the driven gear.

According to the above configuration, the ends of the grooves formed on the opposing surfaces of the gear chamber facing the rotation direction of the drive gear and driven gear are bifurcated along the rotation direction of the drive gear and driven gear, so the oil flow in the grooves is also bifurcated. Therefore, in the latter half of the meshing process, oil with a circumferential velocity can be made to enter the tooth grooves from the grooves. This makes it possible to reduce the acceleration work and improve the efficiency of the parallel pump compared to conventional methods.

The present invention provides a parallel pump that can improve efficiency compared to conventional pumps.

FIG. 1 is a cross-sectional view of a parallel pump according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 2 is a perspective view of a portion of a casing body. FIG. 4 is an enlarged view of the meshing region between the drive gear and the driven gear. FIG. 1 is a cross-sectional view of a conventional parallel pump.

Figure 1 shows a parallel pump 1 according to one embodiment of the present invention. This parallel pump 1 includes a casing 2, and a first piston pump mechanism 3A and a second piston pump mechanism 3B arranged in parallel to each other within the casing 2. For example, the first piston pump mechanism 3A and the second piston pump mechanism 3B are arranged horizontally.

The first piston pump mechanism 3A is driven by a drive shaft 4, and the second piston pump mechanism 3B is driven by a driven shaft 5. The drive shaft 4 and the driven shaft 5 are parallel to each other. For ease of explanation, one of the axial directions of the drive shaft 4 and the driven shaft 5 (the left side in FIG. 1) will be referred to as the front, and the other (the right side in FIG. 1) will be referred to as the rear.

The casing 2 includes a casing body 22, and a front cover 21 and a rear cover 23 attached to the casing body 22. The casing body 22 includes a cylindrical peripheral wall 24 extending in the front-rear direction, and a partition wall 25 provided at a position toward the front within the peripheral wall 24. The front cover 21 covers the front space facing the front surface of the partition wall 25, and the rear cover 23 covers the rear space facing the rear surface of the partition wall 25.

A pump chamber 11 is formed between the partition wall 25 and the rear cover 23, and a gear chamber 12 is formed between the partition wall 25 and the front cover 21. A first piston pump mechanism 3A and a second piston pump mechanism 3B are housed in the pump chamber 11.

The drive shaft 4 and the driven shaft 5 both pass through the partition wall 25. The drive shaft 4 also passes through the front cover 21. One end of the drive shaft 4 located outside the casing 2 is connected to a prime mover such as an engine or an electric motor. At least one of the drive shaft 4 and the driven shaft 5 may pass through the rear cover 23.

The drive shaft 4 is rotatably supported by a bearing 41 held by the partition wall 25 and a bearing 42 held by the rear cover 23. The driven shaft 5 is rotatably supported by a bearing 51 held by the partition wall 25 and a bearing 52 held by the rear cover 23.

In this embodiment, the first piston pump mechanism 3A and the second piston pump mechanism 3B are variable displacement swash plate pumps. The first piston pump mechanism 3A and the second piston pump mechanism 3B have the same structure. Below, the structure of the first piston pump mechanism 3A will be described as a representative example.

However, the first piston pump mechanism 3A and the second piston pump mechanism 3B may be variable displacement bent-axis pumps. Alternatively, the first piston pump mechanism 3A and the second piston pump mechanism 3B may be fixed displacement.

The first piston pump mechanism 3A includes a valve plate 31, a cylinder block 32, multiple pistons 33, a swash plate 36, and a support base 37. The valve plate 31 is attached to the rear cover 23. Although not shown, the valve plate 31 is provided with an arc-shaped suction port and discharge port, and the rear cover 23 is provided with an suction passage communicating with the suction port and a discharge passage communicating with the discharge port.

The cylinder block 32 is fixed to the drive shaft 4, and rotates together with the drive shaft 4 to slide against the valve plate 31. The cylinder block 32 has a number of cylinder bores around the drive shaft 4 that open in the opposite direction to the valve plate 31. Pistons 33 are inserted into each of these cylinder bores. Although not shown, the cylinder block 32 has cylinder ports that extend from the bottom of each cylinder bore to the valve plate 31.

A shoe 34 is attached to the head of each piston 33. In this embodiment, the shoe 34 slides on an annular shoe plate 35 fixed to the swash plate 36. However, the shoe plate 35 may be omitted and the shoe 34 may slide on the swash plate 36. The shoe 34 is held down by a pressing member (not shown) so that it remains in contact with the shoe plate 35.

Although not shown in the figure, the piston 33 and the shoe 34 have an oil passage formed from the rear end surface of the piston 33 to the shoe plate 35. Therefore, a portion of the hydraulic oil sucked into the cylinder bore through the above-mentioned suction port and cylinder port is supplied between the shoe plate 35 and the shoe 34 and used as lubricating oil. The oil is stored in the pump chamber 11.

The swash plate 36 is supported from the side opposite the piston 33 by a support base 37 attached to the partition wall 25. The swash plate 36 is supported by the support base 37 so that it can oscillate around an oscillating axis that extends in the direction in which the first piston pump mechanism 3A and the second piston pump mechanism 3B are aligned.

The gear chamber 12 described above houses a drive gear 6 and a driven gear 7 that mesh with each other. The drive gear 6 is fixed to the drive shaft 4, and the driven gear 7 is fixed to the driven shaft 5. The tooth shape (number of teeth, gear pitch, tooth depth, etc.) of the drive gear 6 is the same as the tooth shape of the driven gear 7.

The oil stored in the pump chamber 11 is also supplied to the gear chamber 12 via the through-hole (not shown) and bearings 41, 51 provided in the partition wall 25, and is stored in the gear chamber 12 as well. Therefore, the oil in the gear chamber 12 is stirred as the drive gear 6 and driven gear 7 rotate. More specifically, the oil flows around the drive gear 6 in the rotational direction of the drive gear 6, and the oil flows around the driven gear 7 in the rotational direction of the driven gear 7.

The gear chamber 12 has a pair of opposing surfaces 13, 14 that face each other with the drive gear 6 and driven gear 7 in between. The opposing surface 13 is the rear surface of the front cover 21, and the opposing surface 14 is the front surface of the partition wall 25. The gear chamber 12 also has a peripheral surface 15 that surrounds the drive gear 6 and driven gear 7.

2, the circumferential surface 15 has a first cylindrical surface 15a with a diameter slightly larger than the tip circle 61 of the drive gear 6 (see FIG. 4), and a second cylindrical surface 15b with a diameter slightly larger than the tip circle 71 of the driven gear 7 (see FIG. 4). In other words, the circumferential surface 15 protrudes toward the meshing region between the drive gear 6 and the driven gear 7. Here, the "meshing region" refers to the region surrounded by the tip circle 61 of the drive gear 6 and the tip circle 71 of the driven gear 7 (the biconvex lens-shaped region between the upstream intersection point A and the downstream intersection point B of the tip circles 61, 71) as shown in FIG. 4.

Furthermore, in this embodiment, as shown in Figures 1 and 3, a groove 8 is formed on each of the opposing surfaces 13, 14 of the gear chamber 12, extending along the meshing region of the drive gear 6 and the driven gear 7.

Each groove 8 is Y-shaped, and the end of each groove 8 facing the rotation direction of the drive gear 6 and the driven gear 7 is bifurcated along the rotation direction of the drive gear 6 and the driven gear 7. More specifically, as shown in FIG. 4, each groove 8 includes a straight portion 81, a first branch portion 82, and a second branch portion 83.

The straight portion 81 extends in a direction perpendicular to the arrangement direction of the drive gear 6 and the driven gear 7 (the direction connecting the central axis 40 (see FIG. 2) of the drive shaft 4 and the central axis 50 (see FIG. 2) of the driven shaft 5). The straight portion 81 has an upstream end located on the opposite side to the rotation direction of the drive gear 6 and the driven gear 7, and a downstream end located on the rotation direction side of the drive gear 6 and the driven gear 7.

The first branch portion 82 extends from the downstream end of the straight portion 81 along the rotation direction of the drive gear 6, and the second branch portion 83 extends from the downstream end of the straight portion 81 along the rotation direction of the driven gear 7.

In this embodiment, the upstream end of the straight portion 81 is pointed toward the opposite side to the direction of rotation of the drive gear 6 and the driven gear 7. In other words, the upstream end of the straight portion 81 is bent in a V-shape at the center to form an isosceles triangle. The angle of the bend is, for example, 60 to 120 degrees.

In this embodiment, the tip (center point) of the upstream end of the straight portion 81 coincides with the upstream intersection point A of the tip circles 61, 71. However, the tip of the upstream end of the straight portion 81 does not necessarily have to coincide with the upstream intersection point A of the tip circles 61, 71, and may be located on the side of the upstream intersection point A in the direction of rotation of the drive gear 6 and driven gear 7, or may be located on the opposite side of the upstream intersection point A in the direction of rotation of the drive gear 6 and driven gear 7.

It is desirable that the width W of the straight portion 81 is greater than the minimum distance between the root circle 62 of the drive gear 6 and the root circle 72 of the driven gear 7. For example, the width W of the straight portion 81 is 1.05 to 1.3 times the minimum distance between the root circle 62 of the drive gear 6 and the root circle 72 of the driven gear 7.

The branch point C (the center point of the downstream end of the straight portion 81) between the first branch portion 82 and the second branch portion 83 in the groove 8 is located on the opposite side of the rotation direction of the drive gear 6 and the driven gear 7 with respect to the downstream intersection point B of the tip circles 61, 71. Therefore, the first branch portion 82 and the second branch portion 83 reliably overlap with the meshing region.

The length α of each of the first branch portion 82 and the second branch portion 83 is, for example, about 1/2 the gear pitch P on the tip circles 61, 71 of the drive gear 6 and the driven gear 7. The tip of the first branch portion 82 is linear and perpendicular to the rotation direction of the drive gear 6, and the tip of the second branch portion 83 is linear and perpendicular to the rotation direction of the driven gear 7.

The inner side of the first branch portion 82 is parallel to the tip circle 61 of the drive gear 6 and is located radially inward from the tip circle 61 by a distance β. The outer side of the first branch portion 82 is parallel to the root circle 62 of the drive gear 6 and is located radially inward from the root circle 62 by a distance γ. For example, the distances β and γ are approximately 1/8 of the minimum distance between the root circle 62 of the drive gear 6 and the root circle 72 of the driven gear 7.

Similarly, the inner side of the second branch portion 83 is parallel to the tip circle 71 of the driven gear 7 and is located a distance β radially inward from the tip circle 71. The outer side of the second branch portion 83 is parallel to the root circle 72 of the driven gear 7 and is located a distance γ radially inward from the root circle 72. For example, the distances β and γ are approximately 1/8 of the minimum distance between the root circle 62 of the drive gear 6 and the root circle 72 of the driven gear 7.

As shown in FIG. 3, the depth of groove 8 gradually increases in the rotation direction of drive gear 6 and driven gear 7 at the upstream end of straight portion 81. The depth of groove 8 gradually decreases in the rotation direction of drive gear 6 from the downstream end of straight portion 81 to first branch portion 82, and gradually decreases in the rotation direction of driven gear 7 from the downstream end of straight portion 81 to second branch portion 83. In other words, the bottom of groove 8 is inclined so that it becomes shallower from the center toward both sides. For example, the inclination angle of the inclined portion of the bottom of groove 8 is about 15 degrees on both sides.

Next, the effect of groove 8 will be explained. In the first half of the meshing process between the drive gear 6 and driven gear 7, the teeth of one gear enter the tooth groove of the other gear, reducing the volume of the tooth groove. As a result, the oil in the tooth groove overflows in the axial direction of the gears, and the oil that overflows from the tooth groove flows into groove 8. This reduces the compression work (so-called mixing loss) that the gears do to compress the oil. On the other hand, in the second half of the meshing process between the drive gear 6 and driven gear 7, the teeth of the other gear come out of the tooth groove of the one gear, increasing the volume of the tooth groove. As a result, oil enters the tooth groove from groove 8.

In this embodiment, the end of the groove 8 facing the rotation direction of the drive gear 6 and the driven gear 7 is bifurcated along the rotation direction of the drive gear 6 and the driven gear 7, so the oil flow in the groove 8 is also bifurcated. Therefore, in the latter half of the meshing process, oil with a circumferential velocity can be made to enter the tooth groove from the groove 8. This makes it possible to reduce the acceleration work and improve the efficiency of the parallel pump 1 compared to conventional methods.

In addition, in this embodiment, the tips of the first branch portion 82 and the second branch portion are straight, so the oil in the groove 8 can be guided toward the tooth groove by the blocking effect of these tips.

Furthermore, in this embodiment, the bottom of the groove 8 is inclined so that it becomes shallower from the center toward both sides, so the depth of the groove 8 can be changed in accordance with the change in volume of the tooth gap.

(Modification)
The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

For example, the groove 8 does not necessarily have to be formed on both of the opposing surfaces 13, 14 of the gear chamber 12, but may be formed on only one of the opposing surfaces 13, 14.

The upstream end of the straight portion 81 of the groove 8 may be a straight line parallel to the arrangement direction of the drive gear 6 and the driven gear 7. However, if the upstream end of the straight portion 81 is pointed toward the opposite side to the rotation direction of the drive gear 6 and the driven gear 7 as in the above embodiment, the oil with a circumferential velocity that flows with the rotation of the drive gear 6 and the driven gear 7 can be smoothly introduced into the groove 8.

(summary)
The parallel pump of the present invention comprises a drive shaft to which a drive gear is fixed, a driven shaft to which a driven gear that meshes with the drive gear is fixed, and a gear chamber in which oil is stored and in which the drive gear and the driven gear are housed, and at least one of a pair of opposing surfaces in the gear chamber that face each other across the drive gear and the driven gear is formed with a groove extending along the meshing area of the drive gear and the driven gear, and the end of the groove facing the rotational direction of the drive gear and the driven gear is bifurcated along the rotational direction of the drive gear and the driven gear.

According to the above configuration, the ends of the grooves formed on the opposing surfaces of the gear chamber facing the rotation direction of the drive gear and driven gear are bifurcated along the rotation direction of the drive gear and driven gear, so the oil flow in the grooves is also bifurcated. Therefore, in the latter half of the meshing process, oil with a circumferential velocity can be made to enter the tooth grooves from the grooves. This makes it possible to reduce the acceleration work and improve the efficiency of the parallel pump compared to conventional methods.

For example, the groove may include a straight portion having an upstream end and a downstream end that extends in a direction perpendicular to the arrangement direction of the drive gear and the driven gear, a first branch portion that extends from the downstream end of the straight portion along the rotation direction of the drive gear, and a second branch portion that extends from the downstream end of the straight portion along the rotation direction of the driven gear.

The upstream end of the straight portion may be pointed toward the opposite side to the direction of rotation of the drive gear and the driven gear. With this configuration, oil with a circumferential velocity that flows with the rotation of the drive gear and the driven gear can be smoothly introduced into the groove.

The tip of the first branch may be linear and perpendicular to the rotation direction of the drive gear, and the tip of the second branch may be linear and perpendicular to the rotation direction of the driven gear. With this configuration, the oil in the groove can be guided toward the tooth groove by the blocking effect of the tips of the first branch and the second branch.

The branch point between the first branch portion and the second branch portion in the groove may be located on the opposite side to the rotation direction of the drive gear and the driven gear with respect to the downstream intersection point of the tip circle of the drive gear and the tip circle of the driven gear. With this configuration, the first branch portion and the second branch portion reliably overlap with the meshing region.

The depth of the groove may be deeper in the rotation direction of the drive gear and the driven gear at the upstream end of the straight section, shallower in the rotation direction of the drive gear from the downstream end of the straight section to the first branch section, and shallower in the rotation direction of the driven gear from the downstream end of the straight section to the second branch section. With this configuration, the depth of the groove can be changed in accordance with the change in volume of the tooth gap.

REFERENCE SIGNS LIST 1 Parallel pump 12 Gear chamber 13, 14 Opposing surface 4 Drive shaft 5 Driven shaft 6 Drive gear 61 Tip circle 7 Driven gear 71 Tip circle 8 Groove 81 Straight portion 82 First branch portion 83 Second branch portion A Upstream intersection B Downstream intersection C Branch point

Claims (6)

a first piston pump mechanism and a second piston pump mechanism arranged in parallel with each other;
a drive shaft to which a drive gear is fixed, the drive shaft driving the first piston pump mechanism ;
a driven shaft having a driven gear fixed thereto and meshing with the drive gear, the driven shaft driving the second piston pump mechanism;
a gear chamber containing the drive gear and the driven gear and in which oil is stored;
a groove is formed in at least one of a pair of opposing surfaces in the gear chamber, the opposing surfaces sandwiching the drive gear and the driven gear, the groove extending along an engagement region between the drive gear and the driven gear;
a parallel pump, wherein an end of the groove on the rotation direction side of the drive gear and the driven gear is bifurcated along the rotation direction of the drive gear and the driven gear. The parallel pump according to claim 1, wherein the groove includes a straight portion having an upstream end and a downstream end that extends in a direction perpendicular to the arrangement direction of the drive gear and the driven gear, a first branch portion that extends from the downstream end of the straight portion along the rotation direction of the drive gear, and a second branch portion that extends from the downstream end of the straight portion along the rotation direction of the driven gear. The parallel pump of claim 2, wherein the upstream end of the straight portion is pointed toward the opposite side to the direction of rotation of the drive gear and the driven gear. The parallel pump according to claim 2 or 3, wherein the tip of the first branch is linear and perpendicular to the rotation direction of the drive gear, and the tip of the second branch is linear and perpendicular to the rotation direction of the driven gear. The parallel pump according to any one of claims 2 to 4, wherein the branch point between the first branch portion and the second branch portion in the groove is located on the opposite side of the rotation direction of the drive gear and the driven gear with respect to the downstream intersection point of the tip circle of the drive gear and the tip circle of the driven gear. The parallel pump according to any one of claims 2 to 5, wherein the depth of the groove is deeper in the rotation direction of the drive gear and the driven gear at the upstream end of the straight section, shallower in the rotation direction of the drive gear from the downstream end of the straight section to the first branch section, and shallower in the rotation direction of the driven gear from the downstream end of the straight section to the second branch section.

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