JP2019196724A - Gear pump - Google Patents

Abstract

To reduce loss torque at a gear pump operation.SOLUTION: In a gear pump in which a first gear 22 and a second gear 26 rotate while being engaged with each other, the first gear 22 is pressed to a first pressing direction by a pressure difference which occurs between an intake port side and a discharge port side when the gear pump is operated at a prescribed discharge pattern, and a running-in operation for cutting a pump chamber internal peripheral face 18 by a tooth tip at a contact part 18a is performed. A length of a first initial clearance being a clearance between a first shaft 24 and a first insertion hole 16b at the first pressing direction side when the tooth tip contacts with the contact part 18a immediately after the running-in operation is started when the first gear 22 is pressed to the first pressing direction P1 at a time point before the pump chamber internal peripheral face 18 is cut is set so that final stress which is generated at the tooth tip of the first gear 22 when the number of teeth at which the first gear 22 contacts with the contact part 18a becomes maximum after the running-in operation is progressed becomes higher than the housing hardness of the contact part 18a.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a circumscribed gear pump that discharges fluid by rotating gears that mesh with each other in a housing.

  Conventionally, a gear pump has been used as a hydraulic source of a hydraulic system mounted on an automobile or the like. This gear pump is an external gear pump, and includes a drive gear, a driven gear meshing with the drive gear, and a housing provided with a housing space for housing these two gears. The accommodation space includes a drive shaft insertion hole that rotatably accommodates the drive shaft of the drive gear, a driven shaft insertion hole that rotatably accommodates the driven shaft of the driven gear, a pump chamber that accommodates the drive gear and the driven gear, Have The housing is provided with a suction port and a discharge port communicating with the pump chamber. When the drive gear and the driven gear are engaged and rotated by the rotation of the drive shaft, the fluid is sucked into the suction port and discharged from the discharge port.

  During operation of the gear pump, the drive gear and the driven gear are pressed to the suction port side by the differential pressure between the suction port side and the discharge port side, and the tooth tips of these gears contact the inner peripheral surface of the pump chamber in the pressing direction (hereinafter referred to as the following). The inner peripheral surface of the contacted portion is referred to as a “contact portion”). When the drive gear and the driven gear are rotated, these tooth tips slide on the inner peripheral surface of the pump chamber at the contact portion, whereby the fluid is efficiently transferred.

  Here, when a gap is generated between the tooth tips of these gears and the inner peripheral surface of the pump chamber during the gear pump operation, the fluid leaks from the gap, so that the sealing performance is deteriorated. For this reason, it is necessary to precisely machine the dimensions and shapes of these gears, pump chambers, and the like so that gaps do not occur as much as possible. However, there is a limit to managing the gap accuracy only by machining.

  Therefore, conventionally, when assembling the gear pump, a so-called running-in operation is performed to manage the accuracy of the clearance between the tooth tips of the driving and driven gears and the inner peripheral surface of the pump chamber. Here, the running-in operation means that the gear pump is operated at a discharge pressure higher than the normal discharge pressure for a certain period of time, the driving and driven gears are pressed in the pressing direction, and the inner peripheral surface of the pump chamber is cut at the contact portion by the tooth tip. It is the driving | operation aiming at doing (refer patent document 1). By performing the running-in operation, it is possible to reduce the gap between the tooth tips of the driving and driven gears and the inner peripheral surface of the pump chamber during the gear pump operation and improve the sealing performance.

JP 2009-36160 A

  By the way, before the running-in operation is started, the drive shaft is arranged concentrically with the drive shaft insertion hole, and a gap is generated between them. This gap is made larger than the gap on the pressing direction side between the tooth tip of the drive gear and the inner peripheral surface of the pump chamber. The inner peripheral surface can be cut. For this reason, immediately after the start of the break-in operation and before the start of cutting, the drive gear moves in the pressing direction until the tooth tip contacts the inner peripheral surface (contact portion) of the pump chamber, and at the same time The drive shaft is also moved in the pressing direction by the same distance as the movement distance of the drive gear. At this time, a gap smaller than the gap before the start of the break-in operation remains between the drive shaft and the drive shaft insertion hole. Hereinafter, the gap is defined as an “initial gap”.

  While the discharge pressure is increasing during the running-in operation, a force that presses the drive gear in the pressing direction always acts on the drive gear. For this reason, when the tooth tip of the drive gear cuts the inner peripheral surface of the pump chamber at the contact portion, the drive gear is pressed by the amount of cutting (that is, the length by which the inner peripheral surface of the pump chamber is cut in the pressing direction). At the same time, the drive shaft further moves in the pressing direction by the amount of cutting, and approaches the drive shaft insertion hole (the inner peripheral surface thereof). When the cutting amount increases and the cutting amount reaches a length equal to the initial gap, the drive shaft comes into contact with the drive shaft insertion hole. It will not be cut. That is, the maximum value of the cutting amount is equal to the length of the initial gap.

  Here, the break-in operation is performed by repeating a predetermined discharge pressure pattern a predetermined number of times. If the initial gap is relatively large, cutting by the drive gear is performed before the drive shaft contacts the drive shaft insertion hole. It may end. In this case, the cutting amount does not increase any more even if the running-in operation is continued thereafter. That is, the break-in operation may end before the cutting amount reaches the length of the initial gap.

  In recent years, it has been desired to develop a technique for improving the mechanical efficiency of the gear pump and further increasing the discharge pressure. As a result of investigation by the inventors of the present application, when the amount of cutting by the break-in operation is less than the length of the initial gap, the loss torque during the gear pump operation is larger than when the amount of cutting is equal to the length of the initial gap. It has been found that the mechanical efficiency decreases. That is, when the cutting amount is equal to the length of the initial gap, the drive shaft and the drive shaft insertion hole (the inner peripheral surface thereof) are in close contact during gear pump operation. It is a value obtained by multiplying “the force acting on the contact point with the insertion hole” by “the length in the pressing direction from the center of the drive gear to the drive shaft insertion hole”. On the other hand, when the cutting amount is less than the length of the initial gap, a gap is generated between the drive shaft and the drive shaft insertion hole during gear pump operation, and the tooth tip of the drive gear closely contacts the inner peripheral surface of the pump chamber. Therefore, the loss torque due to the friction is a value obtained by multiplying “the force acting on the contact portion between the tooth tip of the drive gear and the inner peripheral surface of the pump chamber” by “the radius of the drive gear”. Since the “drive gear radius” is longer than the “length in the pressing direction from the center of the drive gear to the drive shaft insertion hole”, if the applied force is equal, the loss torque is less than the length of the initial gap. The case is bigger. Therefore, it is desirable that the running-in operation is performed until the cutting amount matches the length of the initial gap (that is, until the gap in the pressing direction between the drive shaft and the drive shaft insertion hole becomes zero at the end of the running-in operation).

  The present invention has been made to solve the above-described problems, and one of its purposes is to perform a running-in operation until the amount of cutting by the drive gear matches the length of the initial gap, thereby operating the gear pump. An object of the present invention is to provide a gear pump capable of reducing loss torque.

The gear pump (10) of the present invention comprises:
A first gear (22) to which the first shaft (24) is fixed or integrated;
A second gear (26) in which a second shaft (28) arranged in parallel with the first shaft (24) is fixed or integrated, and meshes with the first gear (22);
A first insertion hole (16b) that rotatably accommodates the first shaft (24), a second insertion hole (16c) that rotatably accommodates the second shaft (28), the first and second An accommodation space (16) having a pump chamber (16a) communicating with the insertion holes (16b, 16c) and accommodating the first gear (22) and the second gear (26); and the pump chamber A housing (12) provided with a suction port (30) and a discharge port (32) communicating with (16a).
In the gear pump (10), the first gear (22) and the second gear (26) are engaged with each other and rotated by the rotation of the first shaft (24), so that fluid flows into the suction port (30). Inhaled and discharged from the discharge port (32). In addition, the direction in which the first gear (22) is pressed toward the suction port (30) by the differential pressure between the suction port (30) and the discharge port (32) when the gear pump (10) is operated. Is defined as the first pressing direction (P1), the gear pump (10) is operated with a predetermined discharge pressure pattern, and the first gear (22) is pressed in the first pressing direction (P1) to add the tooth tip. A break-in operation for cutting the contact portion (18a) with the inner peripheral surface (18) of the pump chamber (16a) is performed.
Immediately after the start-up operation is started and before the inner peripheral surface (18) of the pump chamber (16a) is cut, the first gear (22) is pressed in the first pressing direction (P1). The first pressing direction (between the first shaft (24) and the first insertion hole (16b) when the tooth tip is in contact with the contact portion (18a) of the pump chamber (16a) ( When the gap on the P1) side is defined as the first initial gap (gi),
When the running-in operation proceeds and the number of teeth with which the first gear (22) contacts the contact portion (18a) becomes maximum, the final stress generated at the tooth tip of the first gear (22) is the first stress. 1 correlates with the length of the initial gap (gi),
The length of the first initial gap (gi) is set so that the final stress is greater than the hardness of the housing (12) at the contact portion (18a).

  When the first initial clearance is relatively large, the amount of cutting by the first gear (the tooth tip) increases as the running-in operation proceeds. As the amount of cutting increases, the cutting angle (that is, the circumferential length of the inner circumferential surface of the pump chamber) increases accordingly. As the cutting angle increases, the number of teeth of the first gear that contacts the inner peripheral surface of the pump chamber at the contact portion increases. A pressing force due to a differential pressure between the suction port side and the discharge port side acts on the first gear, and a stress based on the pressing force is applied to the tooth tip where the first gear is in contact with the inner peripheral surface of the pump chamber. Has occurred. As the cutting angle increases and the number of teeth in contact with the inner peripheral surface of the pump chamber increases, the stress disperses and the stress per tooth decreases. That is, “the final stress generated at the tooth tip of the first gear when the running-in operation proceeds and the number of teeth with which the first gear contacts the inner peripheral surface of the pump chamber at the contact portion becomes maximum” This final stress tends to be smaller as the length of the first initial gap is longer.

  If the final stress falls below the hardness of the housing at the contact portion (i.e., the portion to be cut) of the pump chamber inner peripheral surface, the inner peripheral surface of the pump chamber will not be cut any further even if the running-in operation is continued thereafter. In the gear pump of the present invention, paying attention to the above correlation, the length of the first initial gap is set so that the final stress generated at the tooth tip of the first gear is greater than the hardness of the housing at the contact portion of the pump chamber. . According to this configuration, even if the running-in operation proceeds and the number of teeth of the first gear contacting the contact portion of the pump chamber increases, the stress per tooth does not become less than the hardness of the housing at the contact portion. Therefore, the cutting of the inner circumferential surface of the pump chamber by the first gear is performed until the first shaft comes into contact with the first insertion hole (the inner circumferential surface thereof). Therefore, according to the gear pump of the present invention, the running-in operation can be performed until the cutting amount by the first gear surely matches the length of the first initial gap, and the loss torque during the gear pump operation can be greatly reduced. it can.

  In addition, when the first initial gap is relatively large, the cutting angle increases as the amount of cutting increases, and as a result, the cutting volume increases and the volume efficiency may decrease (the discharge pressure decreases). is there. According to the configuration of the present invention, until the break-in operation is completed, the relationship between the stress generated in the tooth tip of the first gear and the hardness of the housing at the contact portion of the pump chamber is maintained. For this reason, the cutting angle is not so large (specifically, the final stress generated at the tooth tip of the first gear becomes less than the hardness of the housing at the contact portion of the pump chamber). For this reason, the cutting volume does not become so large, and as a result, the possibility that the volume efficiency is lowered can be reduced.

  The same applies to the second gear. That is, immediately after the running-in operation is started and before the inner peripheral surface of the pump chamber is cut, the second gear is pressed in a predetermined pressing direction (hereinafter referred to as “second pressing direction”) and its teeth. When the gap on the second pressing direction side that occurs between the second shaft and the second insertion hole when the tip is in contact with the contact portion of the pump chamber is defined as the second initial gap, the tooth tip of the second gear is The resulting final stress is correlated with the length of the second initial gap, and the length of the second initial gap may be set such that the final stress is greater than the hardness of the housing at the contact portion of the pump chamber. According to this configuration, the cutting of the inner circumferential surface of the pump chamber by the second gear is performed until the second shaft comes into contact with the second insertion hole (the inner circumferential surface thereof). Therefore, the running-in operation can be performed until the amount of cutting by the second gear also reliably matches the length of the second initial gap, and the loss torque during the gear pump operation can be further reduced.

  In the above description, in order to help the understanding of the invention, the reference numerals used in the embodiments are attached to the configuration of the invention corresponding to the embodiment in parentheses, but each constituent element of the invention is the reference numeral. It is not limited to the embodiment defined by.

1 is a schematic cross-sectional view of a gear pump according to an embodiment of the present invention. It is a schematic sectional drawing of the pump chamber of a gear pump. It is a figure which shows a mode that the tooth tip of a drive and a driven gear cuts the internal peripheral surface by the side of the suction port of a pump chamber by running-in operation. It is a fragmentary sectional view of the gear pump when the gear pump at the time immediately after the start of the break-in operation and before the inner peripheral surface of the pump chamber is cut is cut along a plane including the central axis of the drive shaft and the pressing direction. It is a figure which shows the discharge pressure pattern of a running-in operation. It is a figure which shows the shape of the internal peripheral surface of the pump chamber immediately after the start of a break-in operation and the end when an initial clearance is set to a comparatively large value. It is the elements on larger scale of the area | region enclosed with the broken line A of FIG. 6, and is a figure which shows the cutting angle and the number of contact teeth when a cutting amount is comparatively small. It is the elements on larger scale of the area | region enclosed by the broken line A of FIG. 6, and is a figure which shows the cutting angle and the number of contact teeth when the cutting amount increases from the cutting amount of FIG. 7A. It is the elements on larger scale of the area | region enclosed with the broken line A of FIG. 6, and is a figure which shows the cutting angle and the number of contact teeth when the cutting amount increases from the cutting amount of FIG. 7B. It is a graph which shows correlation with an initial stage clearance gap and the final stress which arises in the tooth-tip of a drive gear when a running-in operation advances and the number of contact teeth becomes the maximum. It is a fragmentary sectional view when the gear pump as a comparative example after the running-in operation is cut along a plane including the central axis of the drive shaft and the pressing direction. It is a fragmentary sectional view when the gear pump which concerns on embodiment of this invention after the end of a break-in operation is cut | disconnected by the plane containing the center axis | shaft of a drive shaft and a press direction.

  Hereinafter, a gear pump 10 according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIGS. 1 and 2, the gear pump 10 is an external gear pump, and includes a housing 12, a drive gear 22, a drive shaft 24 that is fixed to the drive gear 22 and rotates integrally with the drive gear 22, and a driven gear. A gear 26 (see FIG. 2) and a driven shaft 28 (see FIG. 2) that are arranged in parallel with the drive shaft 24 and are fixed to the driven gear 26 and rotate integrally with the driven gear 26. The drive gear 22 and the driven gear 26 are examples of “first gear” and “second gear”, respectively. The drive shaft 24 and the driven shaft 28 are examples of “first axis” and “second axis”, respectively. It corresponds to.

  The housing 12 has a substantially bottomed cylindrical housing body 14 that is open on one side, and a rear cover 20 that covers an opening portion of the housing body 14. The housing body 14 is provided with an accommodation space 16 for accommodating the drive gear 22, the drive shaft 24, the driven gear 26 and the driven shaft 28. The accommodation space 16 includes a pump chamber 16a that accommodates the drive gear 22 and the driven gear 26, an insertion hole 16b that accommodates the drive shaft 24, and an insertion hole 16c (see FIG. 2) that accommodates the driven shaft 28. The pump chamber 16a communicates with the insertion holes 16b and 16c. The insertion hole 16b and the insertion hole 16 correspond to examples of “first insertion hole” and “second insertion hole”, respectively.

  The housing body 14 has a side plate 15. Inside the housing main body 14, a cylindrical concave portion that opens to the opening portion is provided. The pump chamber 16a is a space provided by fitting the side plate 15 liquid-tightly into the recess from the opening. For this reason, the length of the arbitrary radial direction of the pump chamber 16a is substantially equal to the length of the side plate 15 in the same direction. The side plate 15 can slide along the axial direction, and the sliding portion between the side plate 15 and the rear cover 20 is sealed by an O-ring 36 and a backup ring 38.

  The housing body 14 is made of aluminum, and the inner peripheral surface of the insertion hole 16b and the inner peripheral surface of the insertion hole 16c function as a bearing. For this reason, the drive shaft 24 is rotatably supported by the insertion hole 16b, and the driven shaft 28 is rotatably supported by the insertion hole 16c. One end portion of the drive shaft 24 opposite to the side plate 15 side with respect to the drive gear 22 extends through the housing main body 14 to the outside, and is connected to the motor 40 via the connection portion 40a.

  The housing body 14 is provided with a suction port 30 and a discharge port 32 that communicate with the pump chamber 16a at a position where the drive gear 22 and the driven gear 26 mesh (see FIG. 2). The suction port 30 and the discharge port 32 are provided at positions opposite to each other with respect to the pump chamber 16a (see FIG. 2). A pressure chamber 34 is provided between the side plate 15 and the rear cover 20. The discharge port 32 communicates with the pressure chamber 34 via a passage 36 provided in the housing body 14 and a passage 37 provided between the housing body 14 and the rear cover 20.

  The operation of the gear pump 10 will be described. When the motor 40 is driven and the drive shaft 24 rotates, the drive gear 22 rotates in the direction indicated by the arrow in FIG. 2 (clockwise), and the driven gear 26 meshes with the drive gear 22 and is indicated by the arrow in FIG. Rotate in the direction (counterclockwise). As a result, on the suction port 30 side, the meshing between the drive gear 22 and the driven gear 26 is released and a negative pressure is generated, so that fluid is sucked. The sucked fluid moves along the inner peripheral surface 18 of the pump chamber 16a with the rotation of the drive gear 22 and the driven gear 26, and the fluid is brought into contact with the drive gear 22 and the driven gear 26 on the discharge port 32 side. Extruded and discharged.

  At this time, since the pressure in the pressure chamber 34 is equal to the pressure (discharge pressure) on the discharge port 32 side through the passages 36 and 37, the side plate 15 is on the drive and driven gears 22 and 26 side (paper surface in FIG. 1). Left side) and pressed against the wide surfaces of the drive and driven gears 22,26. This enhances the sealing performance between the wide surfaces of the drive and driven gears 22 and 26 and the housing body 14 in contact with the wide surfaces.

  In addition, the drive and driven gears 22 and 26 are pressed against the suction port 30 side in the pump chamber 16a by the differential pressure between the pressure on the discharge port 32 side (discharge pressure) and the pressure on the suction port 30 side (suction pressure). . Thereby, the sealing performance by the side of the suction port 30 with the drive and driven gears 22 and 26 and the inner peripheral surface 18 of the pump chamber 16a is ensured.

  However, even if the driving and driven gears 22 and 26 are pressed against the suction port 30 side in the pump chamber 16a due to the differential pressure between the discharge pressure and the suction pressure, the inner peripheral surface 18 on the suction port 30 side of the pump chamber 16a in the first place. Is not in good agreement with the tooth tips of the drive and driven gears 22 and 26, a gap is created between the tooth tips of the drive and driven gears 22 and 26 and the inner peripheral surface 18 of the pump chamber 16a. Since the fluid leaks from there, the sealing performance is lowered. For this reason, it is necessary to precisely machine the dimensions and shape of the drive and driven gears 22 and 26 and the pump chamber 16a so that the gap is not generated as much as possible, but to manage the accuracy of the gap only by machining. There are limits.

  Therefore, when assembling the gear pump 10, a known operation called a running-in operation is performed to manage the accuracy of the clearance between the tooth tips of the drive and driven gears 22 and 26 and the inner peripheral surface 18 of the pump chamber 16a. FIG. 3 shows a state in which the tooth tips of the driving and driven gears 22 and 26 cut the inner peripheral surface 18 on the suction port 30 side of the pump chamber 16a by the running-in operation. In the running-in operation, the gear pump 10 is operated for a certain period of time at a discharge pressure (described later) higher than the normal discharge pressure. At this time, the drive gear 22 is pressed in the pressing direction P1 due to the differential pressure between the discharge pressure and the suction pressure, and the tooth tip contacts the inner peripheral surface 18 of the pump chamber 16a at the contact portion 18a. In this state, when the drive gear 22 rotates clockwise, the tooth tip of the drive gear 22 cuts the contact portion 18a. Similarly, the driven gear 26 is pressed in the pressing direction P2 by the differential pressure between the discharge pressure and the suction pressure, and the tooth tip thereof contacts the inner peripheral surface 18 of the pump chamber 16a at the contact portion 18b. In this state, the driven gear 26 rotates counterclockwise, whereby the tooth tip of the driven gear 26 cuts the contact portion 18b. 3 indicates a cutting region (cutting volume) of the inner peripheral surface 18 of the pump chamber 16a cut by the tooth tips of the driving and driven gears 22 and 26. By performing the running-in operation, it is possible to reduce the clearance between the tooth tips of the driving and driven gears 22 and 26 and the inner peripheral surface 18 (strictly speaking, the contact portions 18a and 18b) of the pump chamber 16 during the gear pump operation. Can be improved. The pressing direction P1 corresponds to an example of a “first pressing direction”.

  FIG. 4 shows the gear pump 10 cut at “a plane including the central axis of the drive shaft 24 and the pressing direction P1” “at the time immediately after the start of the break-in operation and before the inner peripheral surface 18 of the pump chamber 16a is cut”. The fragmentary sectional view of the gear pump 10 when doing is shown. The right side of FIG. 4 corresponds to the pressing direction P1. Hereinafter, the above time point is simply referred to as “immediately after the start of the break-in operation”. As shown in FIG. 4, the insertion hole 16 b provided in the side plate 15 is formed so that the diameter D <b> 1 is larger than the diameter d <b> 1 of the drive shaft 24. In addition, the pump chamber 16a is formed such that the diameter D2 in the pressing direction P1 (that is, the length of the side plate 15 in the pressing direction P1) is larger than the diameter d2 of the drive gear 22. Further, the drive gear 22, the drive shaft 24, the pump chamber 16a, and the insertion hole 16b are formed in advance so that the relationship D1-d1> D2-d2 is established. For this reason, when the drive gear 22 and the drive shaft 24 are pressed in the pressing direction P1 immediately after the start of the break-in operation, the tooth tips of the drive gear 22 first come into contact with the inner peripheral surface 18 of the pump chamber 16a at the contact portion 18a. . Accordingly, a gap gi is generated between the drive shaft 24 and the insertion hole 16b of the side plate 15 on the pressing direction P1 side. Since the gap gi is a gap generated immediately after the start of the break-in operation, the gap gi is hereinafter referred to as “initial gap gi”. The following relationship is established between the initial gap gi and each of the diameters D1, d1, D2, and d2, that is, gi = (d2-d1) / 2- (D2-D1) / 2. In the present embodiment, the dimensions of the diameters D1, d1, D2, and d2 are designed so that the initial gap gi of the gear pump 10 is less than 4.5 μm. The initial gap gi corresponds to an example of “first initial gap”.

  The grounds for setting the initial gap gi to less than 4.5 μm will be described with reference to FIGS. FIG. 5 shows a discharge pressure pattern of the running-in operation. In the running-in operation, a pressure regulating valve and a pressure sensor (not shown) are connected to the discharge port 32. The pressure regulating valve adjusts the discharge pressure of the discharge port 32 to a predetermined pressure. The pressure sensor detects the discharge pressure of the discharge port 32. The discharge pressure pattern shown in FIG. 5 is realized by the pressure regulating valve and the pressure sensor. This discharge pressure pattern is a triangular wave pattern in which the pressure is increased to a maximum pressure (typically 15 Mpa) at a constant pressure increase speed and then repeatedly depressurized at a constant speed. Over a certain period of time (typically 10 cycles). Done.

  FIG. 6 shows the shape of the inner peripheral surface 18 of the pump chamber 16a immediately after the start of the break-in operation and after the end when the initial gap gi is set to a relatively large value (for example, 6 μm). As shown in FIG. 6, when the running-in operation is performed, the driving and driven gears 22 and 26 are pressed in the pressing direction P1 and the pressing direction P2, respectively, and the tooth tips are contact portions with the inner peripheral surface 18 of the pump chamber 16a. Each of 18a and contact portion 18b is cut.

  7A to 7C are partial enlarged views of a region surrounded by a broken line A in FIG. 6 and show a process in which the cutting amount T (cutting length in the pressing direction P1) is increased by the break-in operation. As shown in FIGS. 7A to 7C, when the running-in operation proceeds and the cutting amount T by the drive gear 22 gradually increases (T1 <T2 <T3), the cutting range in the circumferential direction is widened, so the cutting angle θ Gradually increases. Then, the number of teeth with which the drive gear 22 comes into contact with the inner peripheral surface 18 (contact portion 18a) of the pump chamber 16a also increases from one tooth to three teeth. This indicates that the cutting amount T and the cutting angle θ are likely to increase as the initial gap gi increases, so that the number of teeth with which the drive gear 22 contacts the inner peripheral surface 18 of the pump chamber 16a is likely to increase.

  A pressing force due to a differential pressure between the discharge pressure and the suction pressure acts on the driving gear 22, and a stress based on the pressing force is applied to the tooth tip where the driving gear 22 is in contact with the inner peripheral surface 18 of the pump chamber 16 a. Has occurred. As the cutting angle θ increases and the number of teeth in contact with the inner peripheral surface 18 of the pump chamber 16a increases, the stress is dispersed and the stress per tooth decreases. This indicates that as the initial clearance gi is larger, the stress generated at the tooth tip of the drive gear 22 that is in contact with the inner peripheral surface 18 of the pump chamber 16a is more likely to decrease when the break-in operation proceeds. The inventors of the present application pay attention to this relationship, and “when the running-in operation proceeds and the number of teeth with which the drive gear 22 comes into contact with the inner peripheral surface 18 of the pump chamber 16a reaches the maximum, it occurs at the tooth tip of the drive gear 22. An experiment was conducted on how the stress (hereinafter, also simply referred to as “final stress”) changes depending on the value of the initial gap gi. FIG. 8 is a graph showing the experimental results. FIG. 8 shows the following information, that is, the hardness [Mpa] of the housing 12 (housing body 14) in the contact portion 18a (that is, the portion to be cut) of the pump chamber 16a, and the gear pump 10 of the initial gap gi. The machine efficiency index during normal operation after running-in is also shown. Hereinafter, the hardness of the housing 12 in the contact portion 18a of the pump chamber 16a is also simply referred to as “housing hardness”.

  As shown in FIG. 8, the final stress generated at the tooth tip of the drive gear 22 decreases in a stepped manner as the initial gap gi increases. Specifically, when the initial gap gi is 0 <gi <gi1, the number of teeth with which the drive gear 22 contacts the inner peripheral surface 18 of the pump chamber 16a (hereinafter also simply referred to as “contact tooth number”) is one tooth. The final stress is the largest. When the initial gap gi is gi1 ≦ gi <gi2 (= 4.5 μm), the number of contact teeth is two, and the final stress is decreased by the amount of one tooth. When the initial gap gi is gi2 ≦ gi, the number of contact teeth is three, and the final stress is reduced by the amount of one more tooth increase. As a result, when the number of contact teeth is one or two, the final stress exceeds the housing hardness, whereas when the number of contact teeth is three, the final stress is significantly lower than the housing hardness. In the gear pump 10 of the present embodiment, the initial gap gi is set so that the final stress is greater than the housing hardness. According to the graph of FIG. 8, this condition is satisfied when the initial gap gi is set within the range of 0 <gi <4.5 μm. The above is the basis for setting the initial gap gi to less than 4.5 μm. In other words, in the gear pump 10 of this embodiment, the relationship of (d2-d1) / 2- (D2-D1) / 2 <4.5 μm is established.

  In the above description, the initial gap gi in the drive gear 22 has been described, but the same can be said for the driven gear 26. That is, immediately after the start of the running-in operation, when the driven gear 26 is pressed in the pressing direction P2 and the tooth tip comes into contact with the inner peripheral surface 18 of the pump chamber 16a and the contact portion 18b, the insertion hole of the driven shaft 28 and the side plate 15 is inserted. If the gap generated on the pressing direction P2 side with respect to 16c is defined as the initial gap gdi, the driven gear 26, the driven shaft 28, the pump chamber 16a, and the insertion are made so that the initial gap gdi is also less than 4.5 μm. The dimensions of the holes 16c are designed.

  The effect of the gear pump 10 of this embodiment is demonstrated. In the gear pump of FIG. 9, the initial gap gi is set to 6 μm. In this case, according to the graph of FIG. 8, when the running-in operation proceeds, the number of teeth with which the drive gear 22 contacts the inner peripheral surface 18 of the pump chamber 16a becomes 3, so that the final stress is less than the housing hardness at that time. After that, even if the running-in operation is continued, the inner peripheral surface 18 of the pump chamber 16a is no longer cut. Therefore, the cutting amount T becomes less than the initial gap gi (T <gi), and a gap r remains between the drive shaft 24 and the insertion hole 16b of the side plate 15 (r = gi−T). Accordingly, the loss torque due to friction when the gear pump is normally operated is expressed by “the force F1 acting on the contact portion 18a between the tooth tip of the drive gear 22 and the inner peripheral surface 18 of the pump chamber 16a” “the radius of the drive gear 22”. (D2 / 2) ". The gap r becomes larger as the initial gap gi is larger. For this reason, as shown in FIG. 8, when gi2 ≦ gi (that is, in a range where the number of contact teeth is 3 and the final stress is lower than the housing hardness), the mechanical efficiency decreases due to an increase in loss torque.

  On the other hand, in the gear pump 10 of this embodiment, paying attention to the correlation between the initial gap gi and the final stress, the length of the initial gap gi is set so that the final stress is larger than the housing hardness. According to this configuration, even if the running-in operation proceeds and the number of teeth of the drive gear 22 that contacts the contact portion 18a of the pump chamber 16a increases, the stress per tooth becomes less than the housing hardness in the contact portion 18a. There is no. For this reason, as shown in FIG. 10, the cutting of the pump chamber circumferential surface 18 by the drive gear 22 is performed until the drive shaft 24 comes into contact with the insertion hole 16 b of the side plate 15. That is, the process is performed until the cutting amount T becomes equal to the initial gap gi (T = gi). The running-in time is set to be sufficiently long so that it does not end when the cutting amount T is less than the initial gap gi, although the final stress is greater than the housing hardness. Therefore, the loss torque due to friction when the gear pump 10 is normally operated is “force F2 acting on the contact point between the drive shaft 24 and the insertion hole 16b of the side plate 15” and “from the center of the drive gear 22 to the side plate 15. This is a value obtained by multiplying the length in the pressing direction P1 to the insertion hole 16b (that is, the radius (d1 / 2) of the drive shaft 24). Here, since d1 <d2, if F1 = F2, the loss torque of the gear pump 10 is smaller. As a result of experiments by the present inventors, in the gear pump in which the length of the initial gap gi is set so that the final stress is larger than the housing hardness, the length of the initial gap gi is set so that the final stress is less than the housing hardness. The loss torque was reduced by about 30% compared to the gear pump. As described above, according to the gear pump 10 of the present embodiment, the running-in operation can be performed until the cutting amount T by the drive gear 22 surely matches the length of the initial gap gi, and the loss torque during the gear pump operation is greatly reduced. can do.

  In addition, when the initial gap gi is relatively large, the cutting angle θ increases as the cutting amount T increases, and as a result, the cutting volume increases and the volumetric efficiency decreases (the discharge pressure decreases). There is. According to the gear pump 10 of the present embodiment, the relationship between the final stress and the housing hardness is maintained until the break-in operation is completed. For this reason, the cutting angle θ does not become so large (specifically, the final stress becomes less than the housing hardness). For this reason, the cutting volume does not become so large, and as a result, the possibility that the volume efficiency is lowered can be reduced.

  Although the gear pump of the embodiment has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the object of the present invention.

10: gear pump, 12: housing, 14: housing main body, 15: side plate, 16: housing space, 16a: pump chamber, 16b, 16c: insertion hole, 18: inner peripheral surface, 18a: contact portion, 20: rear cover, 22: drive gear, 24: drive shaft, 26: driven gear, 28: driven shaft, 30: suction port, 32: discharge port

Claims (1)

A first gear having a first shaft fixed or integrated;
A second gear which is fixed or integrated with a second shaft arranged in parallel with the first shaft and meshes with the first gear;
A first insertion hole that rotatably accommodates the first shaft; a second insertion hole that rotatably accommodates the second shaft; and the first gear that communicates with the first and second insertion holes. A housing having a pump chamber for housing the second gear, and a housing provided with a suction port and a discharge port communicating with the pump chamber,
A gear pump in which fluid is sucked into the suction port and discharged from the discharge port when the first gear and the second gear are engaged and rotated by the rotation of the first shaft, and the operation of the gear pump When the direction in which the first gear is pressed toward the suction port side is defined as the first pressing direction by the pressure difference between the suction port side and the discharge port side, the gear pump is operated with a predetermined discharge pressure pattern. In a gear pump that performs a break-in operation that presses the first gear in the first pressing direction and cuts the contact portion with the inner peripheral surface of the pump chamber at the tooth tip,
Immediately after starting the break-in operation and before the inner peripheral surface of the pump chamber is cut, the first gear is pressed in the first pressing direction, and the tooth tip contacts the contact portion of the pump chamber. When the gap on the first pressing direction side generated between the first shaft and the first insertion hole is defined as a first initial gap when
The final stress generated at the tooth tip of the first gear when the running-in operation proceeds and the number of teeth with which the first gear contacts the contact portion becomes maximum correlates with the length of the first initial gap. And
The length of the first initial gap is set so that the final stress is greater than the hardness of the housing at the contact portion,
Gear pump.

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