Roots type fluid machine |
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申请号 | EP10158762.4 | 申请日 | 2010-03-31 | 公开(公告)号 | EP2236830B1 | 公开(公告)日 | 2017-08-02 |
申请人 | Kabushiki Kaisha Toyota Jidoshokki; | 发明人 | Hirano, Takayuki; Yamada, Kazuho; Sowa, Masato; Fujii, Toshiro; Nasuda, Tsutomu; Shiromaru, Katsutoshi; Suzuki, Fumihiro; | ||||
摘要 | |||||||
权利要求 | |||||||
说明书全文 | The present invention relates to a roots type fluid machine. A roots type fluid machine is known which includes a housing, a pair of rotary shafts, a pair of rotors and a rotor chamber. The housing has a suction port and a discharge port formed therein, and the paired rotary shafts are rotatably arranged in parallel to each other in the rotor chamber. The rotors respectively including lobe and valley portions are rotatably mounted on the respective rotary shafts and engaged with each other in the rotor chamber. Fluid chambers are formed between the rotors and the inner surface of the rotor chamber. During the rotation of the rotors, the fluid chamber firstly communicates with the suction port, then is closed from the suction and discharge ports, and communicates with the discharge port. The volume of the fluid chamber is gradually increased while the fluid chamber is in communication with the suction port, and gradually decreased while the fluid chamber is closed or in communication with the discharge port, thus performing a pumping operation. That is, fluid is flowed in through the suction port, then compressed and discharged out through the discharge port. As shown in In the conventional roots type fluid machine wherein the shape of the lobe portion 92 of the rotor 98 is narrowed toward the apex end T thereof, the moment of inertia of the rotor 98 is relatively small and, therefore, the rotor 98 may be driven easily to rotate at a high speed. The space for the rotor 98 in the rotor chamber 73 may be reduced, so that the volume of the fluid chamber 96 may be increased and the displacement by the rotor 98 may be increased for a small size of the roots type fluid machine. However, in this conventional roots type fluid machine shown in For this reason, a roots type fluid machine has been disclosed in As shown in International patent application publication no. Therefore, it is desirable to provide a roots type fluid machine according to which power loss and noise development may be further reduced and stable volumetric efficiency ηV and a reliable and excellent overall thermal efficiency ηtad may be achieved. The invention provides a roots type fluid machine, comprising: a housing; a rotor chamber formed by the housing; a suction port formed in the housing; a discharge port formed in the housing; a pair of rotary shafts rotatably arranged in parallel to each other in the rotor chamber; a pair of rotors, plane symmetrical to each other, each rotor being fixed on one of the rotary shafts for rotation therewith in the rotor chamber, the rotors respectively having a number n of lobe portions with an apex end and valley portions with a bottom end for engaging each other, wherein the lobe portions of each rotor are located on imaginary lines extending radially from an axis of the associated rotary shaft at an angular spacing apart from each other; and a fluid chamber defined by the outer surfaces of the rotors and the inner surface of the rotor chamber, and in which fluid is caused to flow in through the suction port and discharged out through the discharge port by rotating the rotors, wherein: the outer surface of each one of the rotors is generated by rotating an outline of the rotor around and moving the outline in the direction of the axis of the associated rotary shaft, the outline of the rotor extending from each apex end of the lobe portion to the bottom end of the valley portion through a first transition point and a second transition point thereon, the outline of the rotor including an arc extending from the apex end of the lobe portion to the first transition point and having a radius R and a center located on the imaginary line, an involute curve extending continuously from the first transition point to the second transition point and formed by an imaginary base circle having a radius r and a center located on the axis of the rotary shaft, and an envelope curve with an arc having a radius R extending continuously from the second transition point to the bottom end of the valley portion; the number n of the lobe portions is four or more; and a torsional angle β of the lobe portions is over 360/n degrees, characterized in that the axes of the rotary shafts are spaced away from each other at a distance L, and the radius r of the circle meets a condition of r<nL/(π2+4n2)1/2 and the radius R of the arc meets the condition R<πr/2n. In order that the invention will be more readily understood, embodiments thereof and comparative examples will now be described, given by way of example only, with reference to the drawings, and in which:-
The following will describe a roots type fluid machine embodied in a roots type compressor according to a first preferred embodiment of the present invention with reference to Referring to The end plate 2 is fixed to the rotor housing 1 by means of a plurality of bolts 6. A rotor chamber 1A of a cocoon shape ( A suction port 1B and a discharge port 1C are formed in the rotor housing 1. As shown in As shown in In the rotor chamber 1A, a rotor 13 is fixed on the rotary shaft 9 for rotation therewith and, a rotor 14 is fixed on the rotary shaft 12 for rotation therewith. The rotor 13 includes a lobe portion 13A and a valley portion 13B, and the rotor 14 includes a lobe portion 14A and a valley portion 14B. The lobe portions 13A, 14A are engaged with their mating valley portions 14B, 13B, respectively. The roots type compressor is a six-lobe configuration in which each lobe number n of the rotors 13, 14 is six and each number of the lobe portions 13A, 14A and the valley portions 13B, 14B is six. Coating is applied on the surface of each of the rotors 13, 14 for adjusting the clearance therebetween. As shown in The gear housing 3 has a hole 3B formed therethrough for communication with the gear chamber 3A. A shaft seal 16 is arranged in the hole 3B. The rotary shaft 12 extends from the rotor chamber 1A to the motor chamber 4A through the gear chamber 3A and the shaft seal 16 and is driven to rotate by a motor 17 disposed in the motor chamber 4A. A drive gear 18 is fixed on the rotary shaft 12 in the gear chamber 3A. The rotary shaft 9 extends from the rotor chamber 1 A to the gear chamber 3A. A driven gear 19 is fixed on the rotary shaft 9 in the gear chamber 3A. The drive gear 18 and the driven gear 19 are engaged with each other and cooperate to form a gear train for driving the rotors 13, 14. As shown in The following will describe the shape of the rotors 13, 14 in detail. The rotors 13, 14 are plane symmetrical to each other and, therefore, only one of the rotors, i.e. the rotor 13, will be described and the description of the rotor 13 is also applicable to the rotor 14. The shape of the rotor 13 is defined by the axis 01 of the rotary shaft 9, a plurality of imaginary lines Li, curved outlines Le and outer surfaces F. The number n of the imaginary lines Li corresponds to the number of lobe portions 13A, i.e. six. The imaginary lines Li extend radially from the axis 01 toward the respective top end of the lobe portions 13A at an angularly spaced interval of 60 degrees. In other words, the lobe portions 13A are located on the imaginary lines Li, respectively. The outline Le extends from the apex end T of the lobe portion 13A to the bottom end B of the valley portion 13B through a first transition point C1 and a second transition point C2. The outer surface F is formed by the outline Le rotated and moved in the direction of the axis 01 ( The outline Le of the rotor 13 is formed by an arc 21 A, an involute curve 22A and an envelope curve 23. The arc 21 A, which forms a part of a circle 21 having its center at Q1 located on the imaginary line Li and a radius R, extends from the apex end T of the outline Le to the first transition point C1 which is located between the arc 21A and the involute curve 22A. Reference symbol R1 indicates the distance from the axis 01 to the center Q1 of the circle 21. The involute curve 22A, which is formed by an imaginary base circle 22 having a center Q2 located at the axis 01 and a radius r, extends continuously from the first transition point C1 to the second transition point C2 which is located between the involute curve 22A and the envelope curve 23 and on the imaginary base circle 22. As shown in The radius R of the circle 21 and the radius r of the imaginary base circle 22 which are used for drawing the arc 21A, the involute curve 22A and the envelope curve 23 are determined as follows. Firstly, a line L3 that is tangential to the arc 21 A of the mating rotor 14 is drawn from the axis 01, as shown in Therefore, the following equation 1-1 is obtained. Then, the equation 1-1 is changed to the following equations 1-2 and 1-3. As shown in Therefore, the following equations 1-4 and 1-5 are obtained. The following equation 1-6 is obtained from the equations 1-4 and 1-5. In the case that the number of the lobe portions is n and the rotors are bilaterally symmetrical with each other, condition of continuity is expressed by the following equation 1-7. Thus, the following equation 1-8 is obtained from the equations 1-4 and 1-7. The following equation 1-9 is obtained from the equations 1-2, 1-3 and 1-8. The following equation 1-10 is obtained from the equation 1-9 and a equation sin2 α + cos2 α = 1. Thus, the rotor 13 used in a comparative example is formed such that the radius r of the imaginary base circle 22 is nL / (π2 + 4n2)1/2 and the radius R of the circle 21 is πr / 2n. Therefore, in the case of the comparative example, in which the radius meets the condition of nL / (π2 + 4n2)1/2 < r < L / 2 and the radius R meets the condition πr / 2n < R, the shape of the envelope curve 23 of the rotor 13 is substantially the same as that of the arc 21 A of the rotor 14. In this case, the dead volume 30 shown in On the other hand, in the case of an embodiment of the invention, in which the radius r meets a condition r < nL / (π2 + 4n2)1/2 and the radius R meets a condition R < πr / 2n, the dead volume 30 is increased, but the volumetric efficiency of the roots type compressor is improved and the roots type compressor becomes smaller in size as compared to the case in the comparative example, in which the radius r meets a condition nL / (π2 + 4n2)1/2 < r < L / 2 and the radius R meets a condition πr / 2n < R. In the roots type compressor of the present embodiment, when the outer surface F of the rotor 13 is defined by the outline Le rotated and moved in the direction of the axis 01, a torsional angle β is set larger than 60 degrees, which will be described as follows. When defining the outer surface F of the rotor 13 by the outline Le rotated and moved in the direction of the axis 01 for an axial distance m, as shown in Referring to The following equation 2 is obtained from the equations 1-2, 1-3 and 1-8. If the rotors are of three-lobe configuration (n=3), according to a comparative example, the compression ratio does not exceed 1.0 unless the torsional angle β is over 120 degrees. The maximum torsional angle βmax in the case of rotors of three-lobe configuration is 140 degrees because x = 50 and n = 3 in the above equation 2. If the torsional angle β is 140 degrees, the compression ratio is approximately 1.0 and it is difficult to form the suction port 1B and the discharge port 1C appropriately in the rotor housing 1. Additionally, if the torsional angle β is over 140 degrees, the suction port 1B and the discharge port 1C communicate with each other through the backflow port 40 and the fluid chambers 20, so that overall thermal efficiency ηtad is not sufficiently improved. Meanwhile, in the case, according to an embodiment of the invention, when the rotors of four-lobe configuration (n = 4), the compression ratio will not exceed 1.0 unless the torsional angle β is over 90 degrees. Because x = 50 and n = 4 in the above equation 2, the torsional angle β is 170 degrees. If the torsional angle β is 170 degrees, the compression ratio is approximately 1.4 and the suction port 1B and the discharge port 1C may be formed appropriately in the rotor housing 1. If the rotors of five-lobe configuration (n = 5), the compression ratio will not exceed 1.0 unless the torsional angle β is over 75 degrees. Because x =50 and n = 5 in the above equation 2, the maximum torsional angle βmax is 188 degrees. If the torsional angle β is 188 degrees, the compression ratio is approximately 1.7 and the suction port 1B and the discharge port 1C may be formed easily in the rotor housing 1. In the roots type compressor constructed as described above, when the motor 17 drives the rotary shaft 12 to rotate, the engagement of the drive gear 18 and the driven gear 19 causes the rotary shaft 9 to rotate. Thus, the rotors 13, 14 engaged with each other are rotated in the rotor chamber 1A. During the rotation of the rotors 13, 14, the fluid chamber 20 firstly communicates with the suction port 1B, then closed from the suction port 1B and the discharge port 1C, and finally communicates with the discharge port 1C. The volume of the fluid chamber 20 is gradually increased while the fluid chamber 20 is in communication with the suction port 1 B, and gradually decreased while the fluid chamber 20 is closed and in communication with the discharge port 1C, thereby performing pumping operation. In the roots type compressor, fluid flowed in through the suction port 1B in to the fluid chamber 20 is compressed and then discharged out through the discharge port 1C. During the operation of the roots type compressor according to the preferred embodiment of the present invention, the fluid chambers 20 formed between the any two adjacent lobe portions 13A, which are shown in In addition, the dead volume 30 shown in Meanwhile, in the conventional roots type compressor of In the roots type compressor according to the preferred embodiment of the present invention, where a part of the outline Le extending from the second transition point C2 to the bottom end B is formed by the envelope curve 23, as shown in In the roots type compressor of the preferred embodiment, the torsional angle β may be set in the range between 60 and 200 degrees. Thus, fluid is compressed by the outer surface F in the fluid chamber 20 with a relatively large compression force. The section of the rotors 13, 14 overlapped with each other is shown in Meanwhile, in the roots type compressor according to a comparative example 3 of Therefore, in the roots type compressor according to the preferred embodiment of the present invention, power loss and noise development may be reduced and stabilized volume efficiency and reliable and excellent overall thermal efficiency ηtad may be achieved. The present invention is not limited to the above-described preferred embodiment, but it may be modified in various ways as exemplified below. The roots type fluid machine according to the preferred embodiment of the present invention may be embodied into not only a roots type compressor but also a roots type pump or roots type blower. The present invention may be applied to an air conditioner, a turbo charger or a fuel cell system. |