Rotary fluid machine

A rotary fluid machine that reduces fluid leakage from a gear pump or gear motor and achieves improvement in responsiveness is provided. The present invention is configured such that force of pressing a side plate toward gears by a seal member provided between the side plate and a case and performing pressure compartment is partly strong, not uniform along the entire length of the seal member. Specifically, for example, a gear pump comprises an assembly including a pair of gears, a side plate sealing a side surface of the gears, and a seal block sealing tooth tips of the gears, a case housing the pump assembly, and a seal member being arranged between the side plate or the seal block and the case and along a notch portion formed in the side plate or the seal block. The seal member is wider at a portion in a position passing through a place with large pressure fluctuations than at other portions.

TECHNICAL FIELD

The present invention relates to a rotary fluid machine using gears such as a gear pump or a gear motor.

BACKGROUND ART

There is a gear pump used as an oil-pressure source for movable bodies such as construction machines, robots, and automobiles (see JP 10-252589 A (PTL 1)).

In a gear pump disclosed in PTL 1, a pump assembly includes: a pair of gears that have rotary shafts pivotally supported by a gear case and circumscribed and engaged with each other; a pair of side plates that seal side surfaces of the gears; and the pump assembly configured with a seal block that seals tooth tips of the gears in the vicinity of an intake port are housed in the gear cases, and a pressure division seal (seals for dividing pressure into intake pressure on the inside and discharge pressure on the outside) is installed in a groove on end surface of the side plate or the seal block on the gear case side. The pressure division seal is formed from an elastic body such as rubber such that the side plates and the gear side surfaces are brought into light touch with each other by an initial load of the elastic body. The cross section of the pressure division seal is stepped to produce space into which the pressure division seal (rubber) can escape even though the pressure division seal is bulged in the groove.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

The pressure division seal needs to be designed in dimensions such that, taking into account dimensional tolerances for individual components placed in a prescribed position such as a groove or step, the pressure division seal has a margin for crushing and contacts the side plates or the gear cases under contact surface pressure when the gear pump is assembled. In other words, to reliably block a gap between the side plates or the seal block and the gear case, the groove in the side plates or the seal block is designed to be lower than the pressure division seal. Accordingly, after the gear pump is assembled, the pressure division seal is crushed and brought into close contact with the side plates or the seal block while generating a contact surface pressure relative to the inner wall of the gear case.

If the contact surface pressure is insufficient, the pressure division seal is not brought into close contact with the side plates or the gear case, which causes fluid leakage and reduces the volumetric efficiency of the pump. On the other hand, if the margin for crushing of the pressure division seal is increased for secure sealing, the pressure division seal grows in impulsion to increase force of pressing the side plates against the side surfaces of the gears. This also increases a frictional force generated on the side surfaces of the gears, which results in decrease of pressure responsiveness of the pump. Further, since the maximum torque becomes large at driving of the pump, the driving source motor needs to be increased in capacity, which leads to size increase in the entire system.

The gear pump has a section where two gears are engaged. When the two gears contact each other at two places in the section at a rotation angle, there occurs an area that is closed in the section between the tooth grooves in the gears. The closed area varies in volume with rotation of the gears, but the volume of the area is small and large pressure fluctuations take place even with a minor change in volume. Therefore, the side plates provided to sandwich the two gears may be separated from the side surfaces of the gears by force generating from the pressure fluctuations. This may cause a high-pressure area (discharge port side) and a low-pressure area (intake port side) of the pump to communicate with each other to reduce the volumetric efficiency of the pump.

According to the technique of PTL 1, since the cross section of the pressure division seal is stepped, a portion of the pressure division seal to be crushed is thin at the cross section. As a result, it is possible to avoid that force generated by the pressure division seal for pressing the side plates toward the gears after the assembly of the pump is lowered and load torque becomes high due to increase in friction between the side plates and the gears, while securing a sufficient amount of portion of the pressure division seal to be crushed between the side plates or the seal block and the gear case. However, the pressure division seal described in PTL 1 has a cross section uniformly formed along the entire seal length. Accordingly, when the cross section of the pressure division seal is stepped to reduce force of pressing the side plates toward the gears, pressing force becomes weak along the entire seal length. This makes the side plates more prone to be separated from the side surfaces of the gears by force generated from pressure fluctuations, which may further reduce the volumetric efficiency of the pump.

In addition, when the gear pump is configured to seal the tooth tips by the seal block in a relatively short section as described in PTL 1, the high-pressure area varies depending on the rotation angle of the gears. When the high-pressure area is positioned closest to the intake port (low-pressure area), force of separating the side plates from the side surfaces of the gears becomes largest. However, according to the technique described in PTL 1, the cross section of the pressure division seal is uniformly formed along the entire seal length as described above. Thus, when the cross section is stepped to reduce the force of pressing the side plates toward the gears, the force of pressing cannot counteract the force of separating the side plates from the side surfaces of the gears.

When the side plates are to be pressed toward the side surfaces of the gears by force larger than the force of separating the side plates from the side surfaces of the gears to counteract the force of separating, the portion of the pressure division seal to be crushed need to be larger in size. In that case, the force generated by the entire seal becomes large to increase friction, which may cause reduction in responsiveness and efficiency of the pump.

The assembled pump gear may have a gap between the side plates and the gears under influence of a curve or lower surface accuracy of the side plates.

When the side plates are formed of low-rigidity material such as resin, the side plates can be deformed and brought into close contact with the gears by the force generated from the pressure division seal. Meanwhile, when the pressure division seal with a uniform cross section is used, the force of pressing the side plates toward the side surfaces of the gears is generated beyond necessity in places without a gap, thereby increasing friction.

According to the foregoing discussion of the inventors of the present invention, it is difficult with the conventional pressure division seal to reduce fluid leakage from the pump caused by locally acting pressure fluctuations or the like, and improve pressure responsiveness and reduce driving torque while suppressing increase in friction between the side plates or the seal block and the gears. This problem also occurs at gear motors.

An object of the present invention is to provide a rotary fluid machine that reduces fluid leakage from a gear pump or gear motor and achieves improvement in responsiveness.

Solution to Problem

The present invention is configured such that force of pressing a side plate toward gears by a seal member provided between the side plate and a case and performing pressure compartment is partly strong, not uniform along the entire length of the seal member.

Specifically, the foregoing problem is solved by configurations described in the claims.

Advantageous Effects of Invention

According to the present invention, it is possible to reduce fluid leakage from a gear pump or gear motor and achieve improvement in responsiveness.

Problems, configurations, advantages other than those described above will be clarified by the following descriptions of embodiments.

DESCRIPTION OF EMBODIMENTS

Embodiments according to the present invention will be described below with reference to the accompanying drawings. In the following descriptions, the present invention is applied to a gear pump.

First Embodiment

Referring toFIGS. 1 to 5, a gear pump1according to a first embodiment of the present invention will be described.FIG. 1is a cross-sectional view of a basic configuration of the gear pump1with a seal member in the first embodiment of the present invention, which is square to a driving shaft.FIG. 2is a cross-sectional view of the gear pump illustrated inFIG. 1taken along line A-A.FIG. 3is a cross-sectional view of the gear pump illustrated inFIG. 2taken along line E-E.FIG. 4is a cross-sectional view of the gear pump illustrated inFIG. 1taken along line B-B.FIG. 5is a cross-sectional view of the gear pump illustrated inFIG. 1taken along line C-C.FIG. 1is equivalent to a cross-sectional view of the gear pump illustrated inFIG. 2taken along line D-D.

As illustrated inFIGS. 1 and 2, the gear pump1includes a pump assembly10. The pump assembly10includes a drive shaft (driving shaft)2, a driven shaft (following shaft)3, a pair of gears4and4′, drive pins5, a pair of side plates6and6′, and a seal block7.

The drive shaft2is connected to a driving source such as an external electric motor (not illustrated) and is rotated and driven. The driven shaft3is rotated by a rotational force from the drive shaft2via the pair of gears4and4′. The pair of gears4and4′ is supported by the drive shaft2and the driven shaft3, respectively, to engage with each other at tooth tips as illustrated inFIG. 2. The drive pins5are inserted into the two shafts2and3such that the drive shaft2, the driven shaft3, and the gears4and4′ rotate integrally as illustrated inFIG. 3. The pair of side plates6and6′ are arranged adjacent to both side surfaces of the gears4and4′ as illustrated inFIGS. 2 and 4, and have contact surfaces21in contact with the seal block7as illustrated inFIGS. 1 and 3. The seal block7is in contact with the side plates6and6′ by the contact surfaces21as illustrated inFIGS. 1 and 3, and covers circumferential portions of the gears4and4′ as illustrated inFIG. 3(the seal block7is opposed to the tooth tips in the vicinity of the intake port). Specifically, the seal block7is approximate to the tooth tips of the gears4and4′ in a certain circumferential range of the gears4and4′.

As illustrated inFIG. 2, the side plate6is arranged adjacent to a side surface4bof the gear4and a side surface4b′ of the gear4′, and the side plate6′ is arranged adjacent to a side surface4aof the gear4and a side surface4a′ of the gear4′. The side surfaces4band4b′ of the gears4and4′ contact slidably the side plate6, and the side surfaces4aand4a′ of the gears4and4′ contact slidably the side plate6′. Accordingly, the side plates6and6′ seal the both side surfaces of the gears4and4′.

The side plates6and6′ have two each through holes. Inserting the drive shaft2and the driven shaft3into the through holes of the side plates6and6′ allows both the drive shaft2and the driven shaft3to be supported in parallel and with predetermined spacing therebetween.

The side plates6and6′ are formed in the same shape for commonality of components, and have an intake port19as an intake distribution hole as illustrated inFIG. 1. The outer edges of the side plates6and6′ in the vicinity of the intake port19are formed in the shape of an arc almost equal to the outer diameter of circles formed by the tooth tips of the gears4and4′ as illustrated inFIG. 3.

The contact surfaces of the seal block7relative to the side plates6and6′ are shaped in almost the same manner as the arc-shaped portions of the side plates6and6′ as illustrated inFIG. 3. As described above, the seal block7and the side plates6and6′ are in close contact with each other by the contact surfaces21of the side plates6and6′.

The pump assembly10is housed in a case13composed of a front case11and a rear case12as illustrated inFIG. 2. The front case11and the rear case12are formed by members different from that of the seal block7. The rear case12has a concave portion12aas illustrated inFIGS. 1 to 5. The front case11is attached to a free end of the concave portion12ato form a space for sealing a fluid as illustrated inFIGS. 2, 4, and 5.

As illustrated inFIGS. 2, 4, and 5, the pump assembly10has seal members8and8′ arranged at steps6aand6a′ of the side plates on both end surfaces along the longitudinal side of the drive shaft2and at steps7band7b′ of the seal block, and the pump assembly10is sandwiched and supported between the front case11and the rear case12via the seal members8and8′. The front case11and the rear case12are aligned with each other by knock pins9illustrated inFIG. 1, and are tightened by bolts23. The steps6a,6a′,7b, and7b′ are notches at outer peripheral portions of the side plates6and6′ and at an inner peripheral portion of the seal block7. In the present embodiment, notches are formed as the steps6a,6a′,7b, and7b′. Instead of the steps, grooves may be formed in the side plates and the seal block such that the seal members8and8′ are arranged in the grooves. The seal members8and8′ are formed from an elastic body such as rubber.

The concave portion12aof the rear case12is shaped as illustrated inFIGS. 1 and 3, for example, and is configured to house the pump assembly10and the seal members8and8′ as illustrated inFIGS. 1 to 5.

As illustrated inFIGS. 1 and 3, the concave portion12aof the rear case12has a surface12bopposed to the seal block7, and the surface12bconstitutes part of a cylindrical surface (inner peripheral surface of a cylinder extended along the longitudinal side of the drive shaft). The seal block7has a surface7aopposed to the concave portion12aof the rear case12, and the surface7aconstitutes part of a cylindrical surface (cylindrical outer peripheral surface extended along the longitudinal side of the drive shaft). Accordingly, the pump assembly10has a rotational axis as a straight line parallel to the drive shaft2and passing through the center of the arc of the opposed surface12bof concave portion of the rear case as a cylindrical surface, and is rotatably bound around the rotational axis.

The concave portion12aof the rear case12is provided with a protrusion12cat one place of the inner wall as illustrated inFIGS. 1 and 3. Referring toFIGS. 1 and 3, the protrusion12cis located at the side opposite to the rotational axis of the pump assembly10relative to the drive shaft2, that is, at the lower left side of the drive shaft2, in the direction that links the drive shaft2and the driven shaft3(horizontal direction inFIGS. 1 and 3). However, the position of the protrusion12cillustrated inFIGS. 1 and 3is a mere example and is not limited to this.

As illustrated inFIG. 4, the protrusion12ccontacts one of the two side plates6and6′ (the side plate6′ more distant from the front case11inFIG. 4) to suppress rotation of the pump assembly10around the rotational axis described above. In the present embodiment, the side plate6′ contacts the protrusion12cin the concave portion12aof the rear case12on the side opposite to the rotational axis of the pump assembly10relative to the drive shaft2, in the direction that links the drive shaft2and the driven shaft3(horizontal direction inFIGS. 1 and 3).

As illustrated inFIGS. 1, 3, and 5, energizing members14aand14bare provided to press the side plates6and6′ toward the seal block7. The energizing members14aand14bare elastic bodies and are composed of springs and pins, for example. The energizing members14aand14bare arranged between the side plates6,6′ and the inner wall of the rear case concave portion12aas illustrated inFIGS. 1, 3, and 5.

The energizing member14ais arranged to rotate the pump assembly10in the same direction as a rotational direction R1of the drive shaft2and the gear4to press the side plate6′ as illustrated inFIG. 3. Specifically, the energizing member14ais arranged at a position on the side (right side ofFIG. 3) opposite to the position of the protrusion12c(left side inFIG. 3) relative to the rotational axis of the pump assembly10, in the direction that links the drive shaft2and the driven shaft3(horizontal direction inFIG. 3) to press the side plate6′. As described above, the side plate6′ is supported by the protrusion12cin the concave portion12aof the rear case12.

The energizing member14bis arranged at a position on the side (lower side ofFIG. 3) opposite to the position of the seal block7(upper side inFIG. 3) relative to the rotational axis of the pump assembly10, in the direction perpendicular to the direction that links the drive shaft2and the driven shaft3and to the longitudinal side of the drive shaft2(vertical direction inFIG. 3) as illustrated inFIG. 1, and presses the side plate6.

According to the configurations illustrated inFIGS. 1 to 5, the pump assembly10is housed in the concave portion12aof the rear case12in a manner capable of rotation around the rotational axis. The rotation of the pump assembly10is stopped by the energizing member14apressing the side plate6′ against the protrusion12cin the concave portion12aof the rear case12. This allows the pump assembly10to be positioned in the concave portion12aof the rear case12. The side plate6does not contact the concave portion12aof the rear case12but is pressed by the energizing member14band fixed in position in close contact with the seal block7by the contact surface21.

According to the foregoing configuration, the one side plate6′ takes charge of fixing the position of the pump assembly10, and the other side plate6is fixed in contact with the seal block7held by the opposed surface12bof the concave portion12aof the rear case12. Accordingly, even though the contact surfaces21relative to the seal block7are slightly different in shape between the two side plates6and6′ due to processing error, the one side plate does not inhibit the close contact between the other side plate and the seal block7.

As illustrated inFIGS. 2, 4, and 5, the front case11has grooves15on the contact surface relative to the rear case12. Case seals16are arranged in the grooves15. The case seals16are configured to seal a gap possibly produced between the front case11and the rear case12in the assembled state, thereby to prevent leakage of liquid in the rear case12to the outside.

As illustrated inFIGS. 2, 4, and 5, the front case11is provided with a concave17on the surface opposite to the contact surface relative to the rear case12(for example, the lower surface inFIG. 2). An oil seal18is arranged in the concave17. When the oil seal18is pressed and fitted into the concave17of the front case11, the outer peripheral surface of the oil seal18is brought into close contact with the wall surface of the concave17and the outer peripheral surface of the drive shaft2contacts slidably with the inner peripheral surface of the oil seal18. Accordingly, the oil seal18seals the gap between the drive shaft2and the front case11to prevent leakage of the liquid in the pump chamber to the outside at driving of the gear pump.

The intake port19is formed by the side plates6,6′, the seal block7, and the rear case12as illustrated inFIG. 5. In addition, a discharge port20is formed by a flow path in the rear case12. The discharge port20communicates with the concave portion12aof the rear case12as illustrated inFIGS. 1, 3, and 5.

A tank (not illustrated) or the like is connected to upstream of the intake port19to supply liquid to the gear pump1. A valve and cylinder (not illustrated) are connected to downstream of the discharge port20to adjust a pump discharge pressure. A driving source such as a motor (not illustrated) is connected to the drive shaft2.

When the gear pump1is driven, a high-pressure area and a low-pressure area are formed in the concave portion12aof the rear case12. The high-pressure area and the low-pressure area are defined by components described below. Seals by the components will be described. The gear pump1has seal members8and8′ arranged to a seal engaged portion between the gears4and4′, approximate planes between the gears4and4′ and the seal block7, sliding contact surfaces between the side surfaces4a,4b,4a′, and4b′ of the gears4and4′ and the side plates6and6′, contact surfaces between the seal block7and the side plates6and6′, and contact surfaces between the end surface of the pump assembly10and the front case11and the rear case12. The seal members8and8′ are used to define the intake port19and the discharge port20to prevent communication of the liquid between the intake port19and the discharge port20when differential pressure occurs between the periphery of the intake port19and the periphery of the discharge port20. The inside of the seal members8and8′ is a low-pressure area and the outside of the same is a high-pressure area.

Next, the seal members8and8′ for use in the present embodiment will be described. To bring the seal members8and8′ into close contact with the side plates6and6′ and the inner surface of the case13(the front case11or the rear case12) when the gear pump1is assembled, the seal member8and8′ are higher than the gap between the steps6aand6a′ of the side plates and the front case11or the rear case12(vertical direction inFIG. 2). Accordingly, after the assembly of the gear pump1, the seal members8and8′ are crushed in the direction of the drive axis, and are brought into close contact with side plates6and6′, the front case11, and the rear case12with generation of a contact surface pressure.

When the seal member8for use in the present embodiment is seen from the direction illustrated inFIG. 1, a portion81passing through the position corresponding to the engaged portion between the gears4and4′ and a portion82nearer the rotation center of the gear than the section sealed by the side plates6and6′ and the seal block7in contact with each other and passing through the position where the liquid in the intake port19is sent to the high-pressure area, have cross sections that are widened toward the outsides of the steps6aand6a′ of the side plates6and6′ and the outsides of the steps7band7b′ of the seal block, as compared to other portions (portions83and84without or with less pressure fluctuation). The seal member8may be widened not only at the position corresponding to the actually engaged portion between the gears4and4′ as illustrated inFIG. 1but also in the area in which the tooth tips of the gears4and4′ come closer to each other with rotation. The portion82of the seal member8may be widened, as illustrated in the wider portion of the seal member8inFIG. 1, at the position nearer the rotation center of the gear from the contact portion between the seal block7and the side plates6and6′ is widened by a certain length along the outline of the seal member8.

The portions83and84of the seal member8have an L-shaped cross section as illustrated inFIG. 6(equivalent to a section F surrounded by dotted lines in the seal member8ofFIG. 2and the cross section of the portion84of the seal member8), for example, and a thin portion85is provided to reduce force of pressing the side plate6to the gears4and4′ generated by the seal member8when the seal member8is crushed. In the present embodiment, the thin portion of the seal member is formed at the side plate6side and a thick portion86of the same is formed at the front case11side. Alternatively, the thick portion of the seal member may be formed at the side plate6side, and the thin portion86may be formed at the front case11side.

Meanwhile, the seal member8is widened at the portions81and82of the seal member8on the outside of the step6a(the downward direction ofFIG. 7) as illustrated inFIG. 7(a portion G of the seal member8surrounded by the dotted lines inFIG. 5, equivalent to the cross section of the portion81of the seal member8). Accordingly, the portion81has larger force of pressing the side plate6toward the gears4and4′ as compared to the portions83and84. In other words, in the present embodiment, the seal member is made with larger force of pressing the side plate6toward the gears4and4′ at the position (area) equivalent to the portion with larger pressure fluctuations than at the position (area) equivalent to the other portions (without or with smaller pressure fluctuations). This is realized by changing partly the width of the seal member. In the present embodiment, it is important to change partly the width of the seal member to provide the portion with larger force of pressing the side plate6toward the gears4and4′. The range of changing partly the width is decided as appropriate depending on the magnitude of pressure fluctuations. In the present embodiment, as illustrated inFIG. 1, the width of the seal member is decreased gradually from the portion81to the portion84. However, the present invention is not limited to this.

Next, operation of the gear pump1having the seal members8and8′ in the present embodiment will be described. The drive shaft2is driven by a drive source such as a motor (not illustrated) as described above. The gear4rotates integrally with the drive shaft2. Accordingly, when the drive shaft2rotates in the rotational direction R1illustrated inFIG. 3, the gear4also rotates in the rotational direction R1. The gear4′ engages with the gear4at tooth tips, and rotates integrally with the driven shaft3. Accordingly, when the gear4rotates in the rotational direction R1, the gear4′ rotates integrally with the driven shaft3in a rotational direction R2.

When the engaged tooth tips of the gears4and4′ are released from each other due to the rotation, the volume of the space around the intake port19increases and the intake port19takes in liquid. By the rotation of the gears4and4′, the liquid around the intake port19is stored into the tooth grooves in the gears4and4′ and is transferred along the rotational directions R1and R2of the gears4and4′. The transferred liquid flows out from the tooth grooves with the rotation of the gears4and4′.

As described above, the peripheries of the intake port19and the discharge port20in the gear pump1are sealed by the components to avoid communication of the liquid between the intake port19and the discharge port20. Accordingly, the pressure increases around the discharge port20by the liquid flowing out from the tooth grooves, and then the liquid is discharged from the discharge port20.

By performing this operation continuously, the gear pump1is low in pressure only on the inside of the seal members8and8′ and is high in pressure at the other portions.

At the engaged portion between the gears4and4′, the gears may be in contact with each other at two places depending on the rotational angle. In this state, an area (closed area) is surrounded by the tooth tips of the two gears4and4′ and the side plates6and6′. Due to the rotation of the gears4and4′, the volume of the area decreases and then increases. The volume of the closing area is small, and large pressure fluctuations are caused by a small volume change. Under the pressure, the side plates6and6′ are subject to large force in the direction of separation from the side surfaces of the gears4and4′ (vertical direction inFIG. 2). The position of the engaged portion with large pressure change is shifted from the barycenter of the side plates. As illustrated inFIG. 1, the seal member8has an outline asymmetric with respect to the straight lines passing through the center of the drive shaft2and the driven shaft3. Therefore, when the seal member8is configured to have an entirely uniform cross-sectional shape and press the side plates6and6′ toward the gears4and4′ by light force, the side plates6and6′ may separate from the side surfaces of the gears4and4′ while inclining under the pressure of the engaged portions. Thus, the low-pressure area and the high-pressure area of the gear pump1may communicate with each other to reduce the volumetric efficiency.

The tooth tips of the gears4and4′ are partly sealed by the seal block7, but a high-pressure liquid may enters a position near the intake port19depending on the angles of the gears4and4′ as illustrated inFIG. 3. Also in this case, the side plates6and6′ are subjected to force of separation from the side surfaces of the gears4and4′. Accordingly, there are produced a gap between the side plates6and6′ and the gears4and4′, as between the engaged portions of the gears4and4′, which may lead to communication between the high-pressure area and the low-pressure area.

To solve the foregoing issues, the present embodiment is configured such that a portion (portion81) of the seal member8at the position corresponding to the engaged portions between the gears (position just above the place with pressure change) is widened toward the outside of the step6aof the side plate6as compared to the other portions (portions83and84).

The force of the portion81pressing the side plate6is larger than those of the other portions (portions83and84). For example, by designing the force generated from the portion81of the seal member8to be larger than the force resulting from pressure increase in the closed area at the engaged portions between the gears4and4′, the side plates6and6′ are not separated from the gears4and4′ without reduction in volumetric efficiency.

For example, when the seal member8is entirely widened toward the outside of the step in the side plate6, large pressing force acts on the side plate6and thus no gap is produced between the side plate6and the gears4and4′. Nevertheless, increasing partly the pressing force from the seal member8as in the configuration of the present embodiment makes it possible to reduce the force acting on the entire gears4and4′ and minimize torque increase.

As described above, the side plate6is supposed to lift with an inclination under increased pressure at the engaged portion of the gears4and4′. Accordingly, pressing down the portion under the force of lifting makes it possible to prevent more effectively occurrence of a gap between the gears4and4′ and the side plate6.

The gap between the steps in the side plate6or the seal block7and the case13(the front case11or the rear case12) varies among individual pumps depending on manufacturing error of the side plate6, the seal block7, and the case13(the front case11or the rear case12). Accordingly, when the seal member8is entirely widened to increase the entire pressing force of the seal member8, driving torque of the gear pump1may vary among individual pumps. According to the configuration of the present embodiment, however, the seal member8is widened only at a portion to cause small variations in driving torque of the gear pump1.

When the side plates6and6′ are formed from material with low elasticity such as resin and the seal member8is entirely widened to increase the pressing force, the side plates6and6′ may be deformed to cause insufficient force to act on the engaged portions between the gears4and4′. According to the configuration of the present embodiment, however, the periphery of the engaged portions is pressed down to allow effective action of the force.

As illustrated inFIG. 1, as in the case of the engaged portions, a portion (portion82) of the seal member8passing through the area nearer the rotation center of the gears4and4′ than the section of contact between the side plates6and6′ and the seal block7is widened at the cross section on the outsides of the steps in the side plates6and6′. The seal member8is widened at the area nearer the rotation center of the gears4and4′ than the section of contact between the side plates6and6′ and the seal block7because a high-pressure liquid enters the tooth tips of the gears4and4′. Accordingly, it is possible to stop lift of the side plates6and6′ more effectively by causing the pressing force to act on the area near the rotation center equivalent to the portions between the tooth tips and the tooth bottoms.

According to this configuration, as in the case of the engaged portions between the gears4and4′ described above, it is possible to increase the force of the seal member8pressing the side plates6and6′ at the place on which the force of separating the side plates acts. Accordingly, the side plates are not separated during driving of the pump without reduction in volumetric efficiency. In addition, the increase of torque can be minimized as in the case of the closed portion of the gears4and4′.

The portions81and82of the seal member8are widened toward the outside of the groove on the side plate6because the force of separating the side plate6acts by surface and thus the portions81and82of the seal member8are configured to press the side plate6by surface. This reliably prevents lift of the side plate6.

In the present embodiment, the cross section of the seal member8is widened toward the outsides of the steps in the side plates6and6′, at both the portion81corresponding to the engaged portions between the gears4and4′ and the portion82corresponding to the tooth tip seal portion. Alternatively, the cross section may be changed in width (widened) at only either one of the portions. For example, increasing the width of only the portion where larger pressure fluctuations is generated makes it possible to suppress reduction in volumetric efficiency while suppressing increase of driving torque.

The cross section of the portion where the seal member8is widened may not be widened by the same amount at the side plate6side and the front case11side as illustrated inFIG. 7, but may be partly widened between the steps in the side plates6and6′ and the front case11as illustrated inFIGS. 8 and 9(left side), which produces almost the same advantages as described above.

The left side ofFIG. 9illustrates the cross section of the seal member8before the assembly of the front case11and the rear case12, and the right side ofFIG. 9illustrates the cross section of the seal member8after the assembly of the front case11and the rear case12into the case13. As illustrated inFIG. 9, the seal member8is widened toward the outside of the step in the side plate6by the height of the gap between the steps in the side plate6and the case13(dimension A inFIG. 9). According to this configuration, even though the side plate6is slightly lifted from the gears4and4′ at the place on which the force of separating the side plate6acts, force is generated at a widened portion87of the seal member8to minimize the amount of lift. This produces almost the same advantages as those of the configuration described above. In addition, in the configuration ofFIG. 9, it is possible to further suppress increase of driving torque.

Also in the present embodiment, the entire seal member is formed from the same material. Alternatively, the partial material for the seal member8may be altered to change (increase) partly the pressing force. For instance, when the portions81and82widened toward the outsides of the steps in the side plates6and6′ described above in relation to the present embodiment may be formed by highly-elastic material, large force is generated at the portions81and82to press the side plates6and6′ against the gears4and4′, which produces almost the same advantages as described above.

Second Embodiment

A second embodiment of the present invention will be described with reference toFIGS. 10 to 12.FIG. 10is a perspective view of a seal member that is applied to a second embodiment.FIG. 11is an enlarged view of the section G illustrated inFIG. 5in the case where the seal member in the second embodiment is applied, which represents the state of the seal member before assembly of the pump (left side) and the state of the seal member after assembly of the pump (right side).FIG. 12is an enlarged view of the section F illustrated inFIG. 2in the case where the seal member in the second embodiment is applied, which represents the state of the seal member before assembly of the pump (left side) and the state of the seal member after assembly of the pump (right side).

Configuration and operation of the gear pump1in the present embodiment are the same as those in the first embodiment illustrated inFIGS. 1 to 5and descriptions thereof will be omitted. In the present embodiment, a seal member200is used instead of the seal members8and8′ at the steps6aand6a′ of the side plates and the steps7band7b′ of the seal block.

The seal member200for use in the present embodiment is shaped as illustrated inFIG. 10in the state before assembly into the gear pump1. The seal member200has a portion203passing through the seal block7and a portion204passing through the teeth of the gears4and4′ on the side plates6and6′. The seal member200is configured to be higher in the direction of the height of the steps in the side plates6and6′ at the place with pressure change described above in relation to the first embodiment, that is, at a portion201passing though the position corresponding to the engaged portions between the gears4and4′ and a portion202nearer the rotation center of the gears4and4′ than the section sealed by the contact between the side plates6and6′ and the seal block7and passing through the position where the liquid in the intake port19is sent to the high-pressure area (refer to the left side ofFIG. 11).

The portions201and202and the portions203and204are changed in height not discontinuously but gradually as illustrated inFIG. 10, such that the higher portions and the lower portions are smoothly connected. This produces no gap between the seal member200and the step in the side plate6or the case13(the front case11and the rear case12), which causes no leakage of the liquid from the high-pressure area to the low-pressure area.

When the pump assembly10is incorporated into the case13, the portions201and202of the seal member200are crushed at the higher sections as illustrated inFIG. 11to have cross sections widened toward the outside of the step in the side plate6to press the side plate6toward the gear by large force. Meanwhile, the portions203and204are lower even before the crushing as illustrated in the left side ofFIG. 12, and are not widened toward the outside of the side plate6after the crushing (refer to the right side ofFIG. 12) to have smaller force to press the side plate6toward the gear side.

According to this configuration, the seal member200can generate force to prevent separation of the side plates6and6′ from the side surfaces of the gears4and4′ at the place with pressure fluctuations resulting from the rotation of the gears4and4′, as in the case of the seal member8in the first embodiment. Accordingly, there is no gap between the side plate6and the gears4and4′, which makes it possible to obtain almost the same advantages as those of the first embodiment without reduction in volumetric efficiency.

In the present embodiment, as in the first embodiment, the portions201and202of the seal member200are widened toward the outsides of the side plates6and6′ after the assembly of the pump. This reliably prevents the lift of the side plate6against the force of separation acting on the side plate6by surface.

In the present embodiment, as in the first embodiment, since only portions of the seal member200cause large force to act on the side plates6and6′, the increase of driving torque of the gear pump1can be minimized.

Taking the first and second embodiments into account, it can be said that, in the present invention, a portion of the seal member has a cross section of a surface normal to the outline of the seal member and perpendicular to the opposed case and side plate, that is different in shape from those of the other portions of the seal member. In other words, it can be said that, in the present invention, the seal cross section at a portion of the seal member cut along the direction of the height of the step or the depth of the groove (depth of the notch) and the direction perpendicular to the longitudinal side of the seal member, is different in shape from those at the other portions of the seal member.

Third Embodiment

The second embodiment of the present invention will be described with reference toFIGS. 13 to 15.FIG. 13is a perspective view of a seal member that is applied to a third embodiment.FIG. 14is an enlarged view of the section G illustrated inFIG. 5in the case where the seal member in the third embodiment is applied, which represents the state of the seal member before assembly of the pump (left side) and the state of the seal member after assembly of the pump (right side).FIG. 15is an enlarged view of the section F illustrated inFIG. 2in the case where the seal member in the third embodiment is applied, which represents the state of the seal member before assembly of the pump (left side) and the state of the seal member after assembly of the pump (right side).

Configuration and operation of the gear pump1in the present embodiment are the same as those in the first embodiment illustrated inFIGS. 1 to 5and descriptions thereof will be omitted. In the present embodiment, a seal member300is used instead of the seal members8and8′ at the steps6aand6a′ of the side plates and the steps7band7b′ of the seal block. In addition, the steps6aand6a′ of the side plates and the steps7band7b′ of the seal block are partly changed (reduced) in height.

The seal member300in the present embodiment is formed to have a cross section made uniform in the axial direction of the pump as illustrated inFIG. 13. Meanwhile, in the present embodiment, the steps6aand6a′ of the side plates are partly changed in height. The steps in the side plates6and6′ or the seal block7in contact with portions of the seal member passing through the place with pressure change, that is, a portion301passing through the position corresponding to the engaged portions between the gear4and4′ and a portion302nearer the rotation center of the gears4and4′ than the section sealed by contact between the side plates6and6′ and the seal block7and passing through the position where the liquid in the intake port19is sent to the high-pressure area, are decreased in height.

Also in this case, no gap is produced between the seal member300, and the steps in the side plates6and6′ or the seal block7and the case13(the front case11and the rear case12) by connecting smoothly the portions with lower steps where the portions301and302of the seal member are placed and the portions with higher steps where the portions303and304of the seal member are placed to prevent leakage of the liquid.

As illustrated inFIG. 14, the steps in the side plate6are lower at the portions301and302of the seal member300and a large amount of the seal member300is crushed at these portions. As illustrated in the right side ofFIG. 14, the portions301and302are widened toward the outsides of the steps in the side plate6while pressing the side plate6toward the gear by larger force. Meanwhile, as illustrated inFIG. 15, the steps in the side plate6are higher at the portions303and304of the seal member and a small amount of the seal member300is crushed at these portions. The portions303and304of the seal member300are hardly widened toward the outsides of the steps in the side plate6. Accordingly, the portions303and304of the seal member press the side plate6toward the gear by smaller force.

According to this configuration, as with the seal member8in the first embodiment, it is possible to generate force of preventing the side plates6and6′ from being separated from the side surfaces of the gears4and4′ at the place with pressure fluctuations resulting from the rotation of the gears4and4′. Accordingly, there is produced no gap between the side plate6and the gears4and4′ without reduction in volumetric efficiency, which makes it possible to produce almost the same advantages as those of the first embodiment.

In the present embodiment, as in the first embodiment, after the assembly of the pump, the portions301and302of the seal member300are widened toward the outsides of the side plates6and6′, which makes it possible to stop reliably the lift of the side plate6against the force of separation acting on the side plate6by surface.

In the present embodiment, as in the first embodiment, since only portions of the seal member300cause large force to act on the side plates6and6′, the increase of driving torque of the gear pump1can be minimized.

In the present embodiment, the seal member is uniformly shaped to facilitate the formation of the seal member.

Fourth Embodiment

A fourth embodiment of the present invention will be described with reference toFIGS. 16 and 17. Configuration and operation of the gear pump1in the present embodiment are the same as those in the first embodiment illustrated inFIGS. 1 to 5and descriptions thereof will be omitted. In the present embodiment, a seal member400is used instead of the seal members8and8′ at the steps6aand6a′ of the side plates and the steps7band7b′ of the seal block.

The side plates6and6′ constituting the gear pump1in the present embodiment have thin cross sections or are formed from low-rigidity material such as resin. In the case of these side plates6and6′, even though the side plates6and6′ are fabricated with high precision, the surfaces of the side plates6and6′ to be in contact with the gears4and4′ may not be perfectly flat or the side plates6and6′ may be curved after the processing due to processing limitation. Accordingly, when the gear pump1is assembled, the side plates6and6′ and the gears4and4′ may not perfectly contact each other by the contact surfaces. In this state, when the gear pump1is driven, the high-pressure area and the low-pressure area communicate each other through the gap to reduce the volumetric efficiency.

It is assumed in the present embodiment that the gear pump is configured as illustrated inFIG. 17, for instance, such that side plates406and406′ are curved in U shape to have contact surfaces relative to the gears4and4′ lifted at the right and left ends of the side plates406and406′. The curves in the side plates result from the used manufacturing method, and thus almost the same curves would be generated with the use of the same manufacturing method.

In this case, as illustrated inFIG. 16, portions (portions401) of the seal member passing through the positions corresponding to the gaps resulting from the curve between the contact surfaces between the side plates406and406′ and the gears4and4′, has a cross section widened toward the outsides of the side plate steps. For example, as illustrated inFIG. 16, the seal member400is widened toward the outsides of the steps in the side plates406and406′ at most lifted right and left ends of the side plates406and406′.

As described above, in the gear pump1of the present embodiment, portions (portions401) of the seal member400in the same positions as the portions of the side plates406and406′ lifted from the gears4and4′ provide large force to the side plates406and406′. Accordingly, the side plates406and406′ are deformed to come into close contact with the side surfaces of the gears4and4′. As a result, it is possible to reduce liquid leakage during operation of the gear pump1.

As with the seal member in the first embodiment, changing the cross section of the portions partly in the present embodiment makes it possible to reduce the force of pressing the side plates406and406′ and minimize increase of frictional force as compared with the case where the cross section of the seal member400is entirely widened toward the outsides of the steps or the grooves in the side plates as in the portions401.

When the entire seal member400is made the same in width as the portions401to eliminate a warp in the side plate6by deformation, the heights of the steps in the side plates406and406′, the height of the case13, and the like vary among individual pumps due to manufacturing error or the like, and the force of the seal member400pressing the side plates also varies among individual pumps due to the height variations among individual pumps. Accordingly, high friction may occur in some pumps. In the present embodiment, however, the seal member400is widened only at portions (portions401), and there occurs fewer variations in friction even with manufacturing error in the pump components.

In the present embodiment, portions (portions401) of the seal member are widened toward the outsides of the steps in the side plates406and406′ to increase partly the pressing force. Alternatively, the same advantages can be obtained by extending the portions401of the seal member400along the heights of the steps in the side plates406and406′ as described above in relation to the second embodiment or by changing the heights of the steps in the side plates406and406′ at which the portions401of the seal member400are placed as described above in relation to the third embodiment.

The present embodiment and the first embodiment may be combined with each other. Specifically, in addition to the portions401illustrated inFIG. 16, a portion (portion81inFIG. 1) passing through the place corresponding to the engaged portions between the gears may be widened.

Fifth Embodiment

A fifth embodiment relating to an actuator to which the gear pump1of the present invention is applied will be described with reference toFIGS. 18 and 19.

The gear pump1in the present embodiment is used, for instance, as an oil-pressure source for driving a cylinder503attached to one end of an arm502in construction machinery as illustrated inFIG. 18. The cylinder503includes an oil-pressure control unit504to control a supplied oil pressure. The oil-pressure control unit504is supported by a boom501.

The oil-pressure control unit504is composed of at least the gear pump1, an electric motor505, a tank506, a valve unit507, and a control unit508as illustrated inFIG. 19. Under an instruction from the operator, the electric motor505drives the gear pump1to increase the pressure of an operating oil, and the valve unit507decides a route for supplying the operating oil to the cylinder503. Accordingly, the oil-pressure cylinder503is operated to move the arm502.

The use of the gear pump1in the present invention realizes a high-volumetric efficiency pump without increasing torque, which eliminates the need to use a large-sized electric motor. Accordingly, the oil-pressure control unit504to be attached to the cylinder503can be reduced in size and easy to install.

Sixth Embodiment

A sixth embodiment relating to an actuator to which the gear pump1of the present invention is applied will be described with reference toFIGS. 20 and 21.

The gear pump1of the present invention can be used as an oil pressure source for an actuator to steer a wheel601of a robot illustrated inFIG. 20, for example. As illustrated inFIG. 20, a steering unit600for the wheel601of the robot includes a cylinder603that extends or contracts a rod602by oil-pressure force to adjust a steering angle of the wheel601, an oil-pressure control unit604that supplies the oil-pressure force to the cylinder603, a control unit605that controls the oil-pressure control unit604, an input device606, and a sensor607. The oil-pressure control unit604is composed of an electric motor608, the gear pump1, a tank609that supplies oil to the pump, and a valve unit610as illustrated inFIG. 21.

The thus configured steering unit600generates a control order value at the control unit605based on the operator's input or information from the sensor607, and drives the electric motor608according to the order value to increase the pressure of the working oil by the gear pump1. Then, the valve unit610is operated to decide a route for supplying the operating oil to the cylinder603. Accordingly, the cylinder603is extended or contracted to adjust the steering angle of the wheel601attached to an end of the rod602.

The use of the gear pump1in the present invention eliminates the need for a large-sized electric motor as in the present embodiment. Accordingly, the oil-pressure control unit604attached to the cylinder603can be reduced in size and easy to install.

The configuration with the use of the gear pump1in the present invention can be used as an oil-pressure source for actuators in various kinds of machinery such as robots, construction machines, and automobiles.

As described above, the present invention includes a wide variety of solutions. Configuration examples of the present invention applied to a gear pump are as follows:(1) A gear pump includes: a pump assembly having gears that engage with each other and are rotated and driven by a driving source, side plates arranged adjacent to side surfaces of the gear, and a seal block that is in contact with the side plates and circumferential portions of the gears; a case that houses the pump assembly; and a seal member that is arranged along notches (steps or grooves) formed in the side plates and the seal block on sides opposite to the gears, and is in close contact with the case to define a high-pressure portion and a low-pressure portion in the case, wherein, when the pump assembly is incorporated into the case, the cross-sectional shape of a portion of the seal member normal to the outline of the seal member and perpendicular to the opposed case and side plates is different from the cross-sectional shape of another portion of the seal member.(2) The gear pump according to (1) is configured such that the portion of the seal member with the different cross-sectional shape is situated at a position corresponding to engaged portions between the gears.(3) The gear pump according to (1) is configured such that the portion of the seal member with the different cross-sectional shape passes through an area near the rotation centers of the gears in a section where the seal block is in contact with the side plates (also where the seal block covers circumferential portions of the gears).(4) The gear pump according to (1) is configured such that the portion of the seal member with the different cross-sectional shape is situated at a position corresponding to a gap between the gear side surfaces and the side plates resulting from a curve in the side surfaces.(5) The gear pump according to any of (1) to (4) is configured such that the portion of the seal member with the different cross-sectional shape has a cross section that is more widened toward the outsides of grooves or steps in the side plates or in the seal block than the other portion.(6) The gear pump according to any of (1) to (4) is configured such that the portion of the seal member with the different cross-sectional shape has a cross section that is larger other than the other portion along the depth of the grooves or the height of the steps in the side plates.(7) The gear pump according to any of (1) to (4) is configured such that a portion of the seal member is formed from a material with different elasticity, instead of the portion of the seal member with the different cross-sectional shape. Otherwise, a portion of the seal member has the portion of the seal member with the different cross-section shape formed from a material with further different elasticity.(8) The gear pump according to any of (1) to (4) is configured such that, instead of the seal member, a seal member formed in an almost entirely uniform shape is used, and the grooves or steps in the side plates corresponding to the portion of the seal member with the different cross-sectional shape are formed to be shallower than the other portion.

In addition, advantages of the configuration examples of the present invention are as follows:(1) A portion of the seal member causes a large load on the place where force of separating the side plates from the gear side surfaces acts during driving of the pump, which makes it possible to prevent the side plates from being separated from the gear side surfaces without reduction in volumetric efficiency of the pump. The force generated by the seal member is increased at a limited necessary place under influence of local pressure fluctuations of the pump, which makes it possible to prevent lift of the side plates only by causing requisite minimum force to act on the side plates. Even though the notches (steps or grooves) in the seal block or the side plates are different in height due to manufacturing error, smaller differences occur in force generated by the seal member pressing the side plates and small differences occur in driving torque among individual gear pumps, as compared to the case where the seal member is entirely changed in width of the cross section to increase the force.(2) The present invention is particularly effective on a small-sized pump in which a small gap may result in a large reduction in volumetric efficiency and a gear pump composed of side plates as low-rigidity members such as resin, and realizes a high-efficiency gear pump. The gear pump to which the present invention is applied can be driven by a small-scale motor in a high-responsive manner and under a high pressure. This allows size reduction of the entire system including an actuator with the gear pump.

The present invention is not limited to the foregoing embodiments but includes various modifications. For instance, the foregoing embodiments described above are intended to make the present invention easy to understand, and do not necessarily include all of the configurations described above. The configuration of one embodiment may be partly replaced with the configuration of another embodiment, or the configuration of one embodiment may be added to the configuration of another embodiment. Part of the configuration of each of the embodiments may be added to the configuration of another embodiment, or may be deleted or replaced with the configuration of another embodiment.

For instance, in addition to the shapes of the seal members in the first to fourth embodiments, the portion of the seal member corresponding to the place with large pressure fluctuations may be formed from a high-elasticity material to further increase partly the pressing force. Alternatively, the seal member may have a shape in combination of the first and second embodiments. Otherwise, the shape of the seal member in the first, second, or fourth embodiments and the shape of the steps in the side plates or the like in the third embodiment may be combined together.

For instance, the present invention can be applied to a gear motor that moves gears inversely by flow of a liquid. In the foregoing embodiments, the circumscribed gear pump has a combination of two external gears. The present invention is also applicable to an inscribed gear pump with a combination of an internal gear and an external gear. Also in these cases, the same advantages as those of the foregoing embodiments can be obtained by widening the seal member at the place with pressure fluctuations, that is, at the portion corresponding to the engaged portions between the gears to increase partly the force of pressing the side plates toward the gears.

REFERENCE SIGNS LIST