US20080240955A1

US20080240955A1 - Hydraulic pump

Info

Publication number: US20080240955A1
Application number: US12/079,628
Authority: US
Inventors: Yasuhiro Takeuchi; Kazuhide Utida; Keiichi Uno
Original assignee: Denso Corp; Nippon Soken Inc
Current assignee: Denso Corp; Soken Inc
Priority date: 2007-03-30
Filing date: 2008-03-27
Publication date: 2008-10-02
Also published as: DE102008015843A1; JP2008248800A

Abstract

A hydraulic pump includes a cylinder block having a cylinder, a rotor rotatable in the cylinder, and a vane movable in a radial direction of the rotor and biased to the rotor. The vane, the cylinder, and the rotor thereamong define an operation chamber. The rotor draws fluid into the operation chamber and sends the fluid outside the operation chamber. The vane is urged to the rotor according to differential pressure between pressure of fluid at high-pressure in the operation chamber and pressure of fluid at low-pressure in the operation chamber. The vane and the rotor define a hardness ratio being calculated by dividing hardness of the vane by hardness of the rotor, and the hardness ratio is greater than or equal to 1.6.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and incorporates herein by reference Japanese Patent Application No. 2007-91582 filed on Mar. 30, 2007.

FIELD OF THE INVENTION

The present invention relates to a hydraulic pump. In particular, the present invention may relate to a refrigerant pump for pumping refrigerant fluid to a heater in a waste heat recovery system such as a Rankine cycle system.

BACKGROUND OF THE INVENTION

For example, JP-A-63-277883 discloses a rotary compressor configured to be provided to an airconditioner, a refrigerator, or the like. In the present rotary compressor, a vane is provided to a cylinder accommodating a rotor. The vane is movable in a vane groove provided in the cylinder. The vane has a tip end urged to a rotor and the tip end of the vane is formed from a material being excellent in wear resistance compared with that of a body portion of the vane. In the present structure, the tip end of the vane is enhanced in wear resistance, and abrasion caused in a wall surface, which defines the vane groove, is reduced.
The rotary compressor is configured to compress vapor-phase refrigerant in a refrigeration cycle of, for example, an airconditioner. In the present structure, the vane and the rotor are capable of therebetween sufficiently forming an oil film in a steady operation, thereby maintaining therebetween a state of fluid lubrication. In the present structure, only in a transitional operation at the time of starting or stopping of the operation of the rotary compressor, the vane and the rotor are in a state of boundary lubrication where the vane and the rotor therebetween do not sufficiently form an oil film. Therefore, as indicated by a dashed line in FIG. 6, development in abrasion accompanying time progress is not so significant in the rotary compressor. Therefore, in the rotary compressor, wear resistance needs to be considered only in the state of boundary lubrication.
However, in a hydraulic pump, which pumps low-viscosity fluid, a vane and a rotor are regularly in the state of boundary lubrication at any operations. Therefore, as indicated by a solid line in FIG. 6, the vane and the rotor are apt to therebetween significantly develop abrasion accompanying time progress. Accordingly, only the above structure of the rotary compressor, in which the tip end of the vane is formed from the wear-resistive material, may not be practical for reducing abreaction in the hydraulic pump configured to pump low-viscosity fluid.
As follows, an exemplified premise for calculating a minimum oil film thickness t and an oil film parameter Λ is described with reference to FIG. 7. In the present premise, fluid fed by the hydraulic pump has viscosity of 1 [mPa·s], a vane 151 has a tip radius Rv of 20 [mm], the vane 151 exerts load F of 4000 [N/m] per unit length to a rotor 141, the vane 151 has surface roughness Rzv of 0.8, the rotor 141 has radius Rr of 20 [mm], the rotor 141 slides at sliding speed v of 1 [mm/s], and the rotor 141 has surface roughness Rzr of 0.32.
According to the premise and the elastohydrodynamic lubrication theory, the minimum oil film thickness t between the vane 151 and the rotor 141 and the oil film parameter Λ are calculated such that the minimum oil film thickness=0.03 [μm] and the oil film parameter Λ<1. According to the calculation, the vane 151 and the rotor 141 are obviously in the state of boundary lubrication in the hydraulic pump. Therefore, abrasion between the vane 151 and the rotor 141 in the hydraulic pump needs to be steadily suppressed so as to enhance product lives of both the vane and the rotor and maintain a performance of the hydraulic pump for a long period.

SUMMARY OF THE INVENTION

In view of the foregoing and other problems, it is an object of the present invention to produce a hydraulic pump having a vane and a rotor for pumping liquid-phase fluid, the hydraulic pump being capable of restricting ablation between the vane and the rotor and capable of maintaining a performance thereof.
According to one aspect of the present invention, a hydraulic pump comprises a cylinder block having a cylinder. The hydraulic pump further comprises a rotor rotatable in the cylinder. The hydraulic pump further comprises a vane movable substantially in a radial direction of the rotor and configured to be biased to the rotor. The vane, the cylinder, and the rotor thereamong define an operation chamber. The rotor is configured to draw fluid into the operation chamber and configured to send the fluid outside the operation chamber. The vane is configured to be urged to the rotor according to differential pressure between pressure of fluid at high-pressure in the operation chamber and pressure of fluid at low-pressure in the operation chamber. The vane and the rotor define a hardness ratio being calculated by dividing hardness of the vane by hardness of the rotor. The hardness ratio is greater than or equal to 1.6.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a sectional view showing a hydraulic pump according to a first embodiment;

FIG. 2 is a sectional view taken along the line II-II in FIG. 1;

FIG. 3 is an enlarged sectional view showing a vane, a rotor, and peripheral components of the hydraulic pump;

FIG. 4 is a schematic view showing an ablation developed in the vane;

FIG. 5 is a table showing specific wear rates of both the vane and the rotor of the hydraulic pump;

FIG. 6 is a graph showing a relationship between ablation, which is developed in each of a rotary compressor and a hydraulic pump, and an operation period; and

FIG. 7 is a schematic view showing a vane and a rotor being in contact with each other.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Embodiment

In the present embodiment, a refrigerant pump 100 is provided to pump liquid-phase refrigerant as fluid in a Rankine cycle for recovery of waste heat. The Rankine cycle as a waste heat recovery cycle is, for example, provided to a vehicle. Next, a structure of the refrigerant pump 100 is described with reference to FIGS. 1, 2. The waste-heat recovery Rankine cycle is constructed by combining the refrigerant pump 100, a heater, an expansion device, and a condenser to define an annual circuit. The condenser condenses therein liquid-phase refrigerant, and the refrigerant pump 100 feeds the condensed refrigerant to the heater. The heater heats the liquid-phase refrigerant using waste heat of an internal combustion engine of the vehicle. The liquid-phase refrigerant in the heater is heated to be superheated steam refrigerant. The superheated steam refrigerant is fed into the expansion device, whereby the expansion device recovers kinetic energy caused by expansion of the superheated steam refrigerant. The refrigerant used in the present waste-heat recovery Rankine cycle is preferably used for a refrigeration cycle of an airconditioner of the vehicle.
The refrigerant pump 100 is a rotary-vane pump having a cylinder, which accommodates a rotor and a vane. In the present embodiment, the refrigerant pump 100 is a two-cylinder pump having two cylinders 121, two rotors 141, and two vanes 151.
The refrigerant pump 100 has a body portion, which is constructed by combining a side plate 111, one cylinder plate 120, an intermediate plate 112, another cylinder plate 120, a side plate 113, and a bearing holder 114 in order. Each of the components of the body portion of the refrigerant pump 100 is substantially in a flat cylinder shape.
The side plate 111 has one-end side on the left side in FIG. 1, and the one-end side has a large opening being configured to be mounted with an additional device such as an electric motor as a driving source of the refrigerant pump 100. The opening in the one-end side of the side plate 111 is reduced in diameter stepwise toward the other-end side on the right side in FIG. 1, whereby the opening is communicated with the other-end side of the side plate 111. The other-end side of the side plate 111 has a communication hole having an inner diameter, which is less than an inner diameter of the cylinder 121 of the cylinder plate 120. The communication hole of the other-end side of the side plate 111 is inserted with a shaft 131. The other-end side of the side plate 111 has a center portion fixed with a bearing 133. The bearing 133 rotatably supports one-end of the shaft 131.
The intermediate plate 112 and the side plate 113 are disc-shaped members respectively having center portions defining insertion holes. The insertion holes of the intermediate plate 112 and the side plate 113 are substantially the same as the opening of the side plate 111 on the other-end side in inner diameter. The bearing holder 114 is a bottomed cylindrical member having a center portion defining a recess on the one-end side. The recess of the bearing holder 114 is provided with a bearing 134, which rotatably supports the other-end side of the shaft 131.
Each cylinder plate 120 is a cylinder block member being in a disc shape. The cylinder plate 120 has a center portion defining the cylinder 121 being in a circular shape. One of the cylinder plates 120 is interposed between the side plate 111 and the intermediate plate 112. The other cylinder plate 120 is interposed between the intermediate plate 112 and the side plate 113. The side plate 111, the one cylinder plate 120, the intermediate plate 112, the other cylinder plate 120, the side plate 113, and the bearing holder 114 are communicated with each other through the insertion hole and the cylinders 121.
Each cylinder plate 120 has an inlet port 122, an outlet port 123, a vane groove 124, and a backpressure feed port 125, in addition to the cylinder 121. In the present structure, the inlet port 122 as one communicating portion is provided for communicating an exterior of the cylinder plate 120 with an interior of the cylinder 121. The outlet port 123 as another communicating portion is provided for communicating the interior of the cylinder 121 with the exterior of the cylinder plate 120. The outlet port 123 is adjacent to the inlet port 122 with respect to a circumferential direction of the cylinder plate 120. The vane groove 124 extends from the cylinder 121 radially outward in the cylinder plate 120. The vane groove 124 is located circumferentially between the inlet port 122 and the outlet port 123. The backpressure feed port 125 as another communicating portion is provided for communicating an interior of the vane groove 124 with a high-pressure chamber in an operation chamber V.
The shaft 131 has two portions correspondingly to the two cylinders 121, and each of the two portions of the shaft 131 is provided with a circular cam portion 132. The circular cam portion 132 is eccentric relative to an axis of the shaft 131.
The rotor 141 is a flat cylindrical member and rotatably equipped to an outer circumferential periphery of the cam portion 132 via a bearing (not shown) for feeding liquid-phase refrigerant. An outer diameter of the rotor 141 is smaller than an inner diameter of the cylinder 121. The rotor 141 is inserted into the cylinder 121 such that the rotor 141 is configured to revolve around the cam portion 132 in the cylinder 121.
The vane 151 is a plate-shaped member and accommodated in the vane groove 124 such that the vane 151 is movable in the vane groove 124. A spring 152 is interposed between a recess in a bottom of the vane groove 124 and the vane 151. The spring 152 biases the vane 151 toward the rotor 141 such that a tip end of the vane 151 is in contact with an outer circumferential periphery of the rotor 141 mainly in a condition where the refrigerant pump 100 stops. The rotor 141 and the vane 151 define the operation chamber V in the cylinder 121.
Here, hardness of a material of each of the vane 151 and the rotor 141 is predetermined by selecting a material of each of the vane 151 and the rotor 141 and selecting heat treatment applied to the material. More specifically, a hardness ratio Hr between hardness Hvv of the vane 151 and hardness Hvr of the rotor 141 is predetermined to be greater than or equal to 1.6. Here, the hardness ratio Hr is defined by dividing the hardness Hvv of the vane 151 by the hardness Hvr of the rotor 141.
The refrigerant pump 100 with the structure described above has the inlet port 122 and the outlet port 123. The inlet port 122 is connected with an outlet of the condenser, and the outlet port 123 is connected with an inlet side of the heater. When an electric motor (not shown) as a driving source drives the shaft 131, each rotor 141 revolves around the cam portion 132 in the cylinder 121, whereby the rotor 141 draws liquid-phase refrigerant from the condenser into the operation chamber V and pumps the liquid-phase refrigerant to the heater.
In this operation, the high-pressure chamber in the operation chamber V is communicated with the vane groove 124 through the backpressure feed port 125, so that urging force is exerted to the vane 151 to urge the vane 151 onto the rotor 141 correspondingly to differential pressure between pressure in the low-pressure chamber and pressure in the high-pressure chamber. The urging force is steadily applied to the vane 151 to bias the vane 151 toward the rotor 141, so that a tip end of the vane 151 is steadily maintained in contact with the outer circumferential periphery of the rotor 141. In the present structure, the vane 151 is maintained in contact with the rotor 141, whereby liquid-phase refrigerant in the high-pressure chamber can be restricted from leaking into the low-pressure chamber.
Next, the urging force exerted to the vane 151 is further specifically described with reference to FIG. 3. Here, the spring 152 is provided in the vane groove 124. The spring 152 exerts biasing force to the vane 151 to maintain the state where the vane 151 is in contact with the rotor 141 mainly in a state where the refrigerant pump 100 stops. In this structure, the spring 152 biases the vane 151 to restrict liquid-phase refrigerant in the high-pressure chamber from leaking into the low-pressure chamber when the refrigerant pump 100 starts operation. The biasing force of the spring 152 is significantly small and negligible compared with the urging force, which correlates with the differential pressure between the high-pressure chamber and the low-pressure chamber. Therefore, in the following description, the biasing force of the spring 152 is disregarded.
In FIG. 3, a thickness direction of the vane 151 is defined as a horizontal direction (left and right direction), and a direction perpendicular to the sheet of FIG. 3 is defined as a depth direction of the vane 151. The operation chamber V on the right side of the vane 151 is a low-pressure chamber directly communicating with the inlet port 122. The operation chamber V on the left side of the vane 151 is a high-pressure chamber directly communicating with the outlet port 123.
In an initial state, the tip end of the vane 151 is substantially in convex. The tip end has a center portion with respect to the thickness direction, and the center portion has the maximum projected portion relative to the rotor 141. The tip end of the vane 151 and the rotor 141 therebetween have a contact portion in which the tip end of the vane 151 defines a contact point 151 a. The contact point 151 a is at a distance Lhigh from an end of the vane 151 on the high-pressure side, i.e., on the side of the high-pressure chamber. The contact point 151 a is at a distance Llow from an end of the vane 151 on the low-pressure side, i.e., on the side of the low-pressure chamber. Backpressure Pb is applied to the vane 151 toward the rotor 141. The high-pressure chamber is at pressure Phigh. The low-pressure chamber is at pressure Plow.
The vane 151 has a depth DP with respect to the depth direction orthogonal to the page of FIG. 3. The vane 151 is exerted with back pressure force Fb, which is calculated by the following equation 1.
Fb=Pb×(Lhigh+Llow)×DP (1)
The vane 151 is also exerted with pushback force Fhigh from the high-pressure chamber.
Fhigh=Phigh×Lhigh×DP (2)
The vane 151 is further exerted with pushback force Flow from the low-pressure chamber.
Flow=Plow×Llow×DP (3)
Here, the backpressure Pb is equal to the pressure Phigh, and according to the above equations (1) to (3), urging force Fu, with which the vane 151 is exerted toward the rotor 141, can be calculated by the following equation (4).
Fu=Fb−(Fhigh+Flow)=(Phigh−Plow)×Llow×DP (4)
Thus, the urging force Fu is determined correspondingly to the difference between the pressure Phigh in the high-pressure chamber and pressure Plow in the low-pressure chamber. The urging force Fu becomes large as the distance Llow increases.
As an operation period of the refrigerant pump 100 increases, abrasion between the vane 151 and the rotor 141 develops. Specifically, as shown in FIG. 4, the convex portion of the tip end of the vane 151 is scraped substantially to be a flat surface extending along an envelope defined by revolution of the rotor 141. In the initial state, the tip end of the vane 151 is in contact with the rotor 141 via a contact surface of a contact width A. As the vane 151 is scraped and worn out as the rotor 141 revolves, the contact width A increases to a contact width B. Therefore, at a time point in the operation of the refrigerant pump 100, the contact point 151 a largely moves toward the low-pressure chamber, and the distance Llow decreases. As a result, the urging force Fu exerted to the vane 151 decreases. Consequently, liquid-phase refrigerant may leak from the high-pressure chamber into the low-pressure chamber, and such leakage results in decrease in a pump performance of the refrigerant pump 100. In addition, the vane 151 may fluctuates to cause further ablation, breakage in the components, and abnormal noise between components.
Therefore, in the present embodiment, the hardness ratio Hr is defined by the value of: (hardness Hvv of the vane 151)/(the hardness Hvr of the rotor 141), and the hardness ratio Hr is determined to be greater than or equal to 1.6. In the present structure, ablation between the vane 151 and the rotor 141 can be steadily reduced.
Specifically in the present embodiment, as shown in FIG. 5, the base material of the vane 151 is selected from four kinds of tool steel including chrome molybdenum steel (SCM415), high-speed tool steel (SKH51), and alloy tool steel (SKD11). The surface of the vane 151 is applied with heat treatment including carburizing, quenching, and tempering (GC), softnitriding (TFG) with quenching and tempering (QT), chromium nitride coating (CrN), and titanium nitride coating (TiN). Surface roughness Rz of the vane 151 is predetermined to 3.2 or 0.3.
Here, the surface roughness Rz is, for example, a ten points average height as mean roughness depth calculated by measuring distances between highest five peaks and lowest five bottoms, then averaging the distances.
In the present embodiment, the base material of the rotor 141 is chrome molybdenum steel (SCM415) as case-hardened steel. The surface of the rotor 141 is applied with carburizing, quenching, and tempering (GC). Surface roughness Rz of the rotor 141 is predetermined to 3.2.
Vickers hardness (Hv) of each material applied with heat-treating is obtained. The hardness ratio Hr is defined by the following equation (5) using hardness Hvv of the vane 151 and hardness Hvr of the rotor 141.
Hr=Hvv/Hvr (5)
A specific wear rate WR [m2/N] of each of the vane 151 and the rotor 141 is defined by the following equation (6) using abrasion ABR [m3], load L [N], and sliding distance D [m].
WR[m2/N]=ABR[m3]/L[N]×D[m] (6)
As shown in FIG. 5, a result indicating the specific wear rate WR of each of the vane 151 and the rotor 141 relative to each hardness ratios Hr is obtained by combining relations between the materials, the heat treatment, and the surface roughness Rz of the vane 151 and the rotor 141 at four levels. According to the result, as the hardness ratio Hr increases, the specific wear rate WR of the vane 151 substantially decreases, and the specific wear rate WR of the rotor 141 substantially increases. It suffice to determine the hardness ratio Hr to be greater than or equal to 1.6 so as to restrict the specific wear rate WR of the vane 151 to be less than the specific wear rate WR of the rotor 141.
It is confirmed in advance that it suffices to restrict the specific wear rate WR of each of the vane 151 and the rotor 141 to be less than or equal to about 10 to the minus 16th power [m2/N] so as to restrict leakage of liquid-phase refrigerant. To satisfy the present condition of the specific wear rate WR, it suffice to restrict the hardness ratio Hr to be less than or equal to about 2.5. Thus, according to the result shown in FIG. 5, both the levels 2, 3 are determined to be preferable.
As described above, the specific wear rate WR of the vane 151 relative to the rotor 141 can be steadily suppressed by determining the hardness ratio Hr between the vane 151 and the rotor 141 to be greater than or equal to 1.6. Therefore, by determining the hardness ratio Hr to be greater than or equal to 1.6, the contact width of the vane 151 relative to the rotor 141 can be restricted from increasing. Thereby, the contact point between the vane 151 and the rotor 141 can be restricted from moving toward the low-pressure chamber as described above with reference to FIG. 4. Thus, the pump performance of the refrigerant pump 100 can be maintained for a long period. The specific wear rate WR of, in particular, the rotor 141 can be suppressed by determining the hardness ratio Hr to be less than or equal to 2.5, and the pump performance of the refrigerant pump 100 can be significantly maintained.

Second Embodiment

The specific wear rates WR of the vane 151 and the rotor 141 can be further reduced by appropriately determining the surface roughness Rz of the vane 151 and the rotor 141, in addition to the determination in the first embodiment.
According to the first embodiment, when the surface roughness Rz of the rotor 141 is reduced from 3.2 to 0.08 in the level 2 in FIG. 5, the specific wear rate WR of the vane 151 can be reduced to a value of 8.63×10 to the minus 19th power [m2/N], and the specific wear rate WR of the rotor 141 can be reduced to 2.22×10 to the minus 18th power [m2/N]. In the present determination of the surface roughness Rz of the rotor 141, the specific wear rate WR of the vane 151 is reduced by two orders of magnitude, and the specific wear rate WR of the rotor 141 is reduced by one order of magnitude. The specific wear rate WR is considered to be presently reduced, since abrasion between the vane 151 and the rotor 141 is reduced by the determination of the surface roughness Rz of the rotor 141.
Therefore, it suffices to determine the surface roughness Rz of the vane 151 to be less than or equal to 0.3 and the surface roughness Rz of the rotor 141 to be less than or equal to 0.1 so as to reduce the specific wear rates WR of both the vane 151 and the rotor 141 to be less than or equal to 10 to the minus 18th power [m2/N].

Other Embodiments

In the first embodiment, the above structure is applied to the refrigerant pump 100 for the waste-heat recovery Rankine cycle provided to the vehicle. Alternatively, the above structure may be applied to various hydraulic pumps for pumping fluid. For example, the above structure may be applied to a hydraulic pump for a Rankine cycle provided to a stationary power generator or the like.
Various modifications and alternations may be diversely made to the above embodiments without departing from the spirit of the present invention.

Claims

1. A hydraulic pump comprising:

a cylinder block having a cylinder;

a rotor rotatable in the cylinder; and

a vane movable substantially in a radial direction of the rotor and configured to be biased to the rotor;

wherein the vane, the cylinder, and the rotor thereamong define an operation chamber,

the rotor is configured to draw fluid into the operation chamber and configured to send the fluid outside the operation chamber,

the vane is configured to be urged to the rotor according to differential pressure between pressure of fluid at high-pressure in the operation chamber and pressure of fluid at low-pressure in the operation chamber,

the vane and the rotor define a hardness ratio being calculated by dividing hardness of the vane by hardness of the rotor, and

the hardness ratio is greater than or equal to 1.6.

2. The hydraulic pump according to claim 1, wherein the hardness ratio is less than or equal to 2.5.

3. The hydraulic pump according to claim 1,

wherein the vane is formed from tool steel being quenched and tempered, and

the rotor is formed from case-hardened steel being carburized, quenched, and tempered.

4. The hydraulic pump according to claim 3, wherein the vane is formed from the tool steel nitrided after being carburized, quenched, and tempered.

5. The hydraulic pump according to claim 1, wherein the vane and the rotor therebetween define a sliding portion, in which:

a surface roughness Rz of the vane is equal to or less than 0.3, and

a surface roughness Rz of the rotor is equal to or less than 0.1.

6. The hydraulic pump according to claim 1, the hydraulic pump being used for a vehicle.

7. The hydraulic pump according to claim 6, the hydraulic pump being used for a waste heat recovery cycle for the vehicle.

8. The hydraulic pump according to claim 7, wherein the waste heat recovery cycle is a Rankine cycle.