Method for adjusting engaged clearance between rotors of screw compressor and apparatus therefor

Abstract: The present invention relates to a method of adjusting engaged clearance between rotors (2,3) of a screw compressor comprising a male rotor (2) and a female rotor (3) inside a casing (1), both of the rotors being rotated while maintaining a required very small clearance by timing gears (10,11) fixed individually to the rotors through shrinking, wherein the very small clearance between the both rotors is set to a required value by loosing the shrinking between one of the timing gears (10) and the rotor (2) fixing the one of the timing gears while the other of the timing gears is being restricted; and intermittently applying torques to the rotor fixing the one of the timing gears through a servo motor (24). According to the present invention, it is possible to obtain a screw compressor in which the very small clearance between the rotors can be set to a required value in a short time, and which is high in the reliability of symmetrizing adjustment and high in the compressing performance.

Description: BACKGROUND OF THE INVENTION The present invention relates to a method and an apparatus for adjusting engaged clearance between rotors of a screw compressor comprising a male rotor and a female rotor inside a casing, both of the rotors being rotated while maintaining a required very small clearance by timing gears fixed individually to the rotors through shrinking, and more particularly relates to a method and an apparatus for adjusting engaged clearance between rotors of a screw compressor capable of setting the very small clearance between the both rotors to a desired value in a short time. A conventional method of adjusting clearance between rotors of a screw compressor is disclosed in Japanese Patent Application Laid-Open No. 1-155089 where the very small clearance between both of rotors is set using a rotating phase difference of a male and a female rotors measured by an encoder or the like under a rotating condition in which one of the rotors is rotated forward and backward while the other of the rotors is being applied braking under a state in which at least one of timing gears is removed, which is called as timing adjustment or symmetrizing adjustment. The setting of clearance is performed under the assembling process of the screw compressor. Oil-hydraulic pressure is applied between one of the timing gears and the rotor fixing the one of the timing gears thereto to loosen the shrinking between the both while the other of the timing gears is being restricted. Then, relative positional displacement is produced between the one of the timing gears and the rotor fixing the one of the timing gears thereto by hitting the tooth surface of the one of the timing gears using a hammer, a shim (thickness gage) is inserted between the both rotors to confirm whether the clearance between the both rotors is in a required value (shim measurement), and the hammer hitting and the shim measurement are repeated to set the clearance between the both rotors to the required value. In the conventional technology described above, there has been a problem in that not only the shim measurement takes a long time since the setting of clearance between the both rotors (symmetrizing adjustment) is performed by hand, but also reliability of the symmetrizing adjustment is low since accuracy of the symmetrizing adjustment is disturbed by hammering which depends on skill of a worker, which causes rotor hitting or low performance of the compressor as a result. SUMMARY OF THE INVENTION An object of the present invention is to provide a method of a screw compressor and an apparatus for adjusting clearance between rotors of a screw compressor in which the very small clearance between the rotors can be set to a required value in a short time, and which is high in the reliability of symmetrizing adjustment and high in the compressing performance. The above object of the present invention can be attained by providing a method of adjusting engaged clearance between rotors of a screw compressor comprising a male rotor and a female rotor inside a casing, both of the rotors being rotated while maintaining a required very small clearance by timing gears fixed individually to the rotors through shrinking, the method comprising the steps of loosing the shrinking between the one of the timing gears and the rotor fixing the one of the timing gears while the other of the timing gears is being restricted; and intermittently applying torques to the rotor fixing the one of the timing gears through a servo motor to set the very small clearance between the both rotors to a required value. Further, the above object of the present invention can be attained by providing a method of adjusting engaged clearance between rotors of a screw compressor comprising a male rotor and a female rotor inside a casing, both of the rotors being rotated while maintaining a required very small clearance by timing gears fixed individually to the rotors through shrinking, the method comprising the steps of loosing the shrinking between the one of the timing gears and the rotor fixing the one of the timing gears while the other of the timing gears is being restricted; intermittently applying torques to the rotor fixing the one of the timing gears through a servo motor; applying torques forward and backward to the rotor during the intermittent torque application, each of the torques being larger than a static friction force of the driving system of the servo motor and smaller than each torque intermittently applied; calculating a median value of relative positions of the rotors during applying the forward and backward torques; and calculating a command value of an intermittent torque to be applied next from a difference between the median value and the required value for the very small clearance between the both rotors. Furthermore, the above object of the present invention can be attained by providing an apparatus for adjusting engaged clearance between rotors of a screw compressor comprising a male rotor and a female rotor inside a casing, both of the rotors being rotated while maintaining a required very small clearance by timing gears fixed individually to the rotors through shrinking, which further comprises an intermittent torque applying means for loosing the shrinking between the one of the timing gears and the rotor fixing the one of the timing gears while the other of the timing gears is being restricted and intermittently applying torques based on command values to the rotor having the one of the timing gears through a servo motor; a forward and backward torque applying means for applying torques forward and backward to the rotor during the intermittent torque application, each of the torques being larger than a static friction force of the driving system of the servo motor and smaller than each torque intermittently applied; a relative position median value calculating means for calculating a median value of relative positions of the rotors during applying the forward and backward torques; and an intermittent torque calculating means for calculating the command value of an intermittent torque to be applied next from a difference between the median value and the required value for the very small clearance between the both rotors. It was confirmed from a study conducted by the present inventors that a screw compressor could not assembled in a required value. That is, in assembling a screw compressor, when shrinking between the one of the timing gears and the rotor fixing the one of the timing gears was loosed by applying oil-hydraulic pressure between them while the other of the timing gears was being restricted and a torque was applied to the rotor having the one of the timing gears through a servo motor in order to set the very small clearance between the both rotors to a required value, the rotors were positioned at the target position under a condition that the servo motor was being operated (the very small clearance was in the required value), but the very small clearance between the both rotors was moved from the target position when the servo motor was stopped and consequently the screw compressor could not assembled in the required value. The reason considered is as follows. That is, even though the shrinking between the one of the timing gears and the rotor fixing the one of the timing gears is loosed by applying oil-hydraulic pressure between them, there still exists a friction, accordingly high shrinking force, between the one of the timing gears and the rotor fixing the one of the timing gears. Therefore, the rotor fixing the one of the timing gears is elastically deformed under the condition of applying the torque by the servo motor. Consequently, when the servo motor was stopped, the elastic deformation is released, the rotor is returned to its natural shape and the very small clearance between the both rotors is moved from the target position. The following method was employed in order solve the problem. That is, torques were intermittently applied to the rotor fixing the one of the timing gears through the servo motor, and the rotor was returned to its natural shape without applying the torque, and then a torque value to be applied next time was determined based on a position in that time. In that case, it was confirmed that the rotor was not completely returned to its natural shape because the static friction force of the servo motor system became restriction force against the rotor returning to the natural shape, and an error was caused between the target value of a required very small clearance between the both rotors and the actual value of a very small clearance between the both rotors after being adjusted. Therefore, by applying torques, each of which is larger than a static friction force of the driving system of the servo motor and smaller than each of the torques intermittently applied, forward and backward to the rotor during the intermittent torque application, a median value of relative positions of the both rotors is calculated during applying the forward and backward torques. The median value corresponds to a median value of residual stresses in the forward and the backward directions caused in the rotor by the static friction force of the servo motor which can be considered as a position of the rotor under a condition without elastic deformation. Therefore, by calculating a command value of an intermittent torque to be applied next from a difference between the median value and the required value for the very small clearance between the both rotors (a preset value), the very small clearance between the both rotors is adjusted to the target position as if the rotor having the one of the timing gears is in a state without elastic deformation. Accordingly, it is possible to obtain a screw compressor in which the very small clearance between the rotors can be set to a required value in a short time, and which is high in the reliability of symmetrizing adjustment and high in the compressing performance. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an apparatus for adjusting clearance between rotors of a screw compressor in accordance with the present invention. FIG. 2 is schematic views showing small clearances of rotors and timing gears in the screw compressor shown in FIG. 1. FIG. 3 is a diagram showing a state setting the small clearances of the rotors and the timing gears to a required symmetrizing adjusting position in the screw compressor shown in FIG. 1. FIG. 4 is a software flow-chart showing the process of adjusting clearance between rotors of a screw compressor in accordance with the present invention. FIG. 5 is a view showing the state loosing the shrunk fitting of the other of the timing gears with the rotor in the software flow-chart shown in FIG. 4. FIG. 6 is a graph explaining the state loosing the shrunk fitting of the other of the timing gears with the rotor in the software flow-chart shown in FIG. 5. FIG. 7 is a graph explaining a state intermittently applying torques to the rotor having the other of the timing gears through a servo motor in the software flow-chart of FIG. 4. FIG. 8 is a graph showing the relationship between position of the rotor having the other of the timing gears and the target position in the intermittent torque applying shown in FIG. 7. FIG. 9 is a graph showing the relationship between position of the rotor having the other of the timing gears and the target position in a case where torques are intermittently applied to the rotor through a servo motor in the software flow-chart of FIG. 4 in a different way from that of the embodiment shown in FIG. 7. FIG. 10 is an enlarged view of the timing gear portion showing an embodiment of press-fitting of an M-timing gear of the screw compressor shown in FIG. 1. FIG. 11 is views showing a rotating state of the timing gear portion of the screw compressor shown in FIG. 10; (a) is a partially sectional view, (b) is a view showing an engaging state of the timing gears, and (c) is a view showing an engaging state of the M-timing gear and an outer gear. FIG. 12 is views showing a rotating state of the rotor portion of the screw compressor shown in FIG. 10; (a) is a schematic view, (b) is a view showing an engaging state of the rotors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below, referring to an embodiment shown by the accompanying drawings. FIG. 1 is a block diagram showing a screw compressor and an apparatus for adjusting clearance between rotors of a screw compressor in accordance with the present invention. Referring to the figure, the reference character 1 is a casing of the screw compressor in which a male rotor 2 and female rotor 3 are supported in the thrust direction and in the radial direction through ball bearings 4, 5 and roller bearings 6A, 6B, 7A, 7B. The reference characters 8A, 8B, 9A, 9B are seal rings, the reference character 10 is an M-timing gear of helical gear fixed by shrinking to an axle end portion (upper end in FIG. 1) in the delivery side of the male rotor 2, the reference character 11 is an F-timing gear of helical gear fixed by shrinking to an axle end portion (similarly, upper end in FIG. 1) in the delivery side of the female rotor 3, and the reference character 12 is a pinion gear fixed by shrinking to an axle end portion (lower end in FIG. 1) in the suction side of the male rotor 2. During normal operation of the screw compressor, by driving the pinion gear 12 using some means the male rotor 2 and the M-timing gear 10 are rotated, and at the same time the F-timing gear 11 is driven by the M-timing gear 10 to rotate the female rotor 3 in the opposite direction to the rotation of the male rotor 2. In the end surface portion of the casing 1 having the both timing gears 10, 11 there is attached a bracket for receiving a thrust force applied to the ball bearing 4. Further, although the screw compressor is generally installed horizontally, the longitudinal direction is shown in vertical direction in FIG. 1 because of convenience of illustration. FIG. 2 schematically shows a state of small clearances in the rotors and in the timing gears of the screw compressor shown in FIG. 1. An engaging portion (a portion surrounded by a chain line circle aa) of the M-timing gear 10 and the F-timing gear 11 is shown by an enlarged view in a circle AA, and an engaging portion (a portion surrounded by a chain line circle bb) of the male rotor 2 and the female rotor 3 is shown by an enlarged view in a circle BB. There is little clearance B1 of the both gears 10, 11 in the forward side, and there is clearance B2 in the backward side. Very small clearances G1, G2 are set in the forward side and the backward side of the both rotors 2, 3, respectively. The very small clearances G1, G2 are varied by shifting the fixing position of the M-timing gear 10 to the male rotor 2. What position the timing gear should be fixed at is described in Japanese Patent Application Laid-Open No. 1-155089 as follows. As an example, the M-timing gear 10 is removed from the male rotor 2, the male rotor 2 is rotated forward and backward while the female rotor 3 is being applied braking through the F-timing gear 11, and rotating phase difference of each of the rotors 2, 3 is measured using encoders 21, 22 connected to the rotors 2, 3 respectively during the rotating period (hereinafter, this work is referred to as "measuring work"). Then, by calculating very small clearances G1, G2 for the forward side and the backward side of the both rotors using the measured result by which desired compressing performance may attain, the M-timing gear 10 is fixed to the male rotor 2 through shrinking so as to be set to the target position (hereinafter, this work is referred to as "adjusting work"). FIG. 3 shows a state setting the small clearances of the rotors and the timing gears to a required symmetrizing adjusting position in the screw compressor. Referring to FIG. 1, the reference character 23 is a gear to drive the pinion gear 12, and the drive gear 23 is driven by a servo motor of a direct drive motor (hereinafter referred to as "DD motor") 24. The DD motor 24 is arranged in the bottom end side of the male rotor 2 where the M-timing gear is not arranged, and applies intermittent torques to the male rotor through the pinion gear 12. The reference character 25 is a servo motor for restricting or applying braking to the F-timing gear 11 through a gear 25. The apparatus for adjusting engaged clearance between rotors in accordance with the present invention is composed of a plurality of means having the following functions. (1) an intermittent torque applying means for loosing the shrinking between one of the timing gears and the rotor fixing the one of the timing gears while the other of the timing gears is being restricted and intermittently applying torques based on command values to the rotor having the one of timing gears through the servo motor. (2) a forward and backward torque applying means for applying torques forward and backward to the rotor during the intermittent torque application, each of the torques being larger than a static friction force of the driving system of the servo motor and smaller than each torque intermittently applied. (3) a relative position median value calculating means for calculating a median value of relative positions of the rotors during applying the forward and backward torques. (4) an intermittent torque calculating means for calculating the command value of an intermittent torque to be applied next from a difference between the median value and the required value for the very small clearance between the both rotors. The plurality of means having the above-mentioned functions may be realized by a central control unit (hereinafter referred to as "MPU") 30 and a program for adjusting engaged clearance between rotors stored in a memory unit in the MPU. According to the program for adjusting engaged clearance between rotors, output pulses of the encoders 21, 22 individually connected to the rotors 2, 3 enter to a counter 33 through interpolators 31, 32 for splitting each of them, and difference of rotating phases of the rotors 2, 3 each is calculated in the MPU 30. The reference character 34 is a controller for rotating the DD motor 24 forward and backward directions through a servo-amplifier 35 during measuring work, and the reference character 36 is a D/A converter for converting a positional command output from the MPU 30 during adjusting work and for driving the DD motor 24 through the servo-amplifier 35 to drive the male rotor 2 so that the male rotor 2 has a required clearance to the female rotor 3, and the reference character 37 is a D/A converter for converting a torque command output from the MPU 30 during measuring work or during adjusting work and for driving the servo motor 25 through a servo-amplifier 38. The reference character 41 is a monitor for displaying a state of processing in the MPU 30, and the reference character 42 is a printer for output various kinds of data during measuring work and adjusting work. The reference character 51 is a press-fitting jig for loosing shrinking of the M-timing gear 10 fixed to the male rotor 2 using oil-hydraulic pressure supplied from an oil-hydraulic pressure pump 53 during measuring work or during adjusting work, and the reference character 54 is a jig for fixing (restricting) the M-timing gear 10 to the casing 1 during adjusting work so that the M-timing gear 10 is not rotated to the male rotor 2. Description will be made below on a method of adjusting clearance between the rotors of a screw compressor using the apparatus for adjusting engaged clearance of rotors shown in FIG. 1, referring to the flow of an embodiment of software (a program of adjusting clearance between rotors) in accordance with the present invention shown in FIG. 4. Initially, in Step (hereinafter referred to as "S") 1, the various electric units such as the encoders 21, 22 and the servo motors 24, 25 are connected to the main body of the compressor in which the M-timing gear 10 is not fixed to the male rotor 2. Next, the following work is performed in S2. The measuring work is performed by positioning control of the servo motor 24 using the controller 34. The explanation will be omitted here since the details are disclosed in Japanese Patent Application Laid-Open No. 1-155089. Next, after temporarily fixing the M-timing gear 10 to the male rotor 2 through shrinking, the press-fitting jig 51 is attached to the axle end portion in the delivery side of the male rotor 2 (S3). FIG. 5 shows a state in which the press-fitting jig 51 is attached to the male rotor 2. The process to get the state of FIG. 5 is as follows. The lower end screw portion of a piston 51a in the press-fitting jig 51 is fastened to the upper end portion of the male rotor 2 using screw. A cylinder 51b of the press-fitting jig 51 is fixed to the M-timing gear 51 using screw. Then, a pipe 52 is fixed to the upper end portion of the piston 51a using screw. Thereby, an oil-pressure chamber 51c is partitioned by the M-timing gear 10, the piston 51a and the cylinder 51b. There is an inlet hole 51d communicating from the upper end portion of the piston 51a to the oil-pressure chamber 51c, and pressurized oil is supplied to the oil-pressure chamber 51 from the oil pressure pump 53 shown in FIG. 1. The supplying of oil-hydraulic pressure corresponds to S4 in FIG. 4. In this step, the oil hydraulic pressure in the oil-pressure chamber 51c expands the inner diameter of the shrunk portion of the M-timing gear 10 to the male rotor 2, and the M-timing gear 10 and the cylinder 51b are moved downward to the male rotor 2 by pressure difference between the oil-hydraulic pressure in the downward direction applied onto the end surface of the M-timing gear 10 in the oil-pressure chamber 51c and the oil-hydraulic pressure in the upward direction applied onto the end surface of the cylinder 51b. Then, the M-timing gear 10 is stopped to be moved by being blocked by the ball bearing 4, and the state shown in FIG. 5 can be formed as a result. Therein, since the M-timing gear 10 and the F-timing gear 11 are helical gears, they must rotate together along the helical teeth when the M-timing gear is moved to form the state of FIG. 5. However, when the M-timing gear 10 is rotated, the male and the female rotors 2, 3 are in contact to each other and rotation of the F-timing gear is stopped since the F-timing gear 11 is fixed to the female rotor 3. Therefore, the M-timing gear 10 is about to rotate around the male rotor 2, but there occurs torsion between the contact point of the both timing gears 10, 11 and the contact point of the both rotors 2, 3. The portion (strain) is not released due to friction force and the strain remains even in the state of FIG. 5. Next, in S5 of FIG. 4, backlash, that is, clearance between the timing gears 10, 11 is measured. In the measurement, the timing gear 11 is slightly driven using the servo motor 25 while the male rotor 2 is being restricted using the servo motor 24, and a phase difference between output pulses of the encoders 21, 22, and the backlash to the timing gear 10 is calculated in the MPU 30 using the phase difference. As the clearances between the both rotors 2, 3 and between the both timing gears 10, 11 are measured in S2 and S4, a required symmetrizing position shown in FIG. 3, that is, G1, G2 are given from a desired compressing performance. Thus, the adjusting work to set the positional relation of the both rotors 2,3 to clearances G1 and G2 is started. As preparation of the adjusting work, in S6, the timing gear 10 is fixed to the casing 1 using the fixing jig 54 shown in FIG. 1. This adjusting work performs torque control of the servo motor 24 through the A/D converter 36 in S7. At that time, the F-timing gear 11 is restricted so as to be not rotated within the backlash range of the timing gears by applying a torque toward one direction using the servo motor 25 to keep the timing gears in contact with each other. The torque control of the servo motor 24 will be described in detail below. FIG. 6 shows the state loosing the shrunk fitting between the M-timing gear 10 and the male rotor 2, which is obtained from an experiment conducted by the present inventors. In FIG. 6, the abscissa is oil-hydraulic pressure applied from the oil-pressure pump 53 to the oil-pressure chamber 51c shown in FIG. 5 and the ordinate is mutual rotating torque indicating at how large torque the M-timing gear 10 begins to be rotated against the friction force with the male rotor 2 to the oil-hydraulic pressure when the rotating torque is applied to the male rotor 2 using the DD motor 24 shown in FIG. 1. In other words, even though the shrinking between the M-timing gear 10 and the male rotor 2 is loosed by applying oil-hydraulic pressure to the oil-pressure chamber 51c, there still exists a friction, accordingly, a high shrinking force, between the M-timing gear 10 and the male rotor 2. It can be understood that by the shrinking force the male rotor 2 is restricted to be rotated and elastically deformed. Further, there are static friction forces between the ball bearing 4, the roller bearings 6A, 6B and the male rotor 2, and the male rotor 2 and the DD motor 24. Based on the fact, in S7 of FIG. 4 in the present invention, intermittent (step-shape) torques are applied to the male rotor 2 by the DD motor 24 as shown in FIG. 7. The torque command value V is determined by the MPU 30 calculating a symmetrizing target of clearance between the both rotors 2, 3 (target position) in each screw compressor, a median value of relative positions of the both rotors during applying forward and backward torques ((b) and (c) in FIG. 7) which are larger than a static friction force of the driving system of the servo motor and smaller than each of the torques ((a) in FIG. 7) intermittently applied during the intermittent torque application and the characteristic curve shown in FIG. 6. FIG. 8 shows the rotational movement (displacement) of the male rotor 2 when the torques shown in FIG. 7 are intermittently applied. In the figure, the curve 1 is difference between detected results of the encoder 21 and the encoder 22, and the curve 2 is an envelope of displacement of the male rotor 2 in the state in which rotation is returned by releasing of elastic deformation in the male rotor 2. In FIG. 8, the portion (d) is a rotational movement (displacement) of the male rotor 2 corresponding to the intermittently applied torque (a), the portions (e) and (f) are rotational movements of the male rotor 2 corresponding to the forward and the backward torques (b) and (c), respectively. The portion (i) is a median value of rotational movements (e) and (f) of the male rotor 2. After intermittently applying torques, in S8 of FIG. 4, the MPU 30 calculates a median value (i) from outputs of the encoders 21, 22, and confirms using displacement of the male rotor 2 obtained from the curve 2 whether the median value is in the symmetrizing target position. If the median value is not in the symmetrizing target position, a torque command value to be applied next is calculated based on the median value (i), that is, from difference between the position of the male rotor 2 and the target position. Then, the processing is returned to S7 to apply the next intermittent torque. Therefore, as shown by curve 2, the male rotor 2 is driven toward the target position through the intermittently applied torque and the forward and the backward torques, as shown by the curve 2. The dotted lines in FIG. 8 indicate tolerance to the target position. If it is judged in S8 that the position of the male rotor 2 is within the tolerance and in the symmetrizing target position, the processing advances to S9. By repeating the processes of S7 and S8, the clearance B1+B2 of FIG. 3 falls in the clearance G1+G2. As a result, all the strains produced between the both rotors 2, 3, between the both timing gears 10, 11 and between the male rotor 2 and the M-timing gear 10 are released. It may be acceptable that in S7 the torque command to be applied next is calculated based on the displacement when the median value is not in the symmetrizing target position, and in S8 it is only confirmed using displacement of the male rotor 2 whether the median value is in the symmetrizing target position. In this case, since it is empirically known that how many times intermittent torque applications are required to bring the median value in the tolerance, an operator can pre-define the time that the processing advances to S8. In addition to this, it should be programmed that the processing advances to S8 ever time executing process of S7 if the processing returns from S8 to S7. In S9 the press-fitting jig 51 and the fixing jig 54 are removed, and the processing advances to S10 to measure the clearance (backlash) of the timing gears again. The strains possibly produced during fixing the M-timing gear in S4 between the M-timing gear 10 and the F-timing gear 11, and the male rotor 2 are released in S5 and S7, and the M-timing gear 10 and the F-timing gear 11 are in a free state between them by symmetrizing the both rotors to the target position. Therefore, in this measurement, clearance between the M- and F-timing gears 10, 11 is measured through the same method as the measuring method in S5. In S11, the MPU 30 re-determines a final symmetrizing target position from the measured values of S2, S10. In S12 the press-fitting jig 51 is installed again, and in S13 oil-hydraulic pressure is supplied to the M-timing gear 10 through the press-fitting jig 51 to loose the shrinking to the male rotor 2, as similar to S4. Then, timing gear backlash is measured and the M-timing gear 10 is fixed to the casing 1 using the fixing jig 54 as the same way as in S5 and S6 though these processes are not shown in the figure. After that, in S14 and S15, the same processes of S7 and S8 are performed to set the both rotors 2, 3 to the final symmetrizing target position determined in S11. In the last, in S16, the press-fitting jig 51 and the fixing jig 54 are removed, the M-timing gear 10 is fixed to the male rotor 2 by shrinking, and in S17 clearance between the M- and the F-timing gears is measured for the purpose of confirmation. In S18 a hard copy is formed using the printer 42, if necessary, and in S19 the adjusting units such as the encoders 21, 22 are removed. Thus, the series of processes are completed. As having been described above, the clearance between the rotors can be adjusted using the MPU 54 automatically except attaching and detaching of the press-fitting jig 51 and the fixing jig 54, and under a state without elastic deformation. In FIG. 7, the forward and the back ward torque application is performed by applying the forward torque (b) first and then applying the backward torque (c) in S7 and S14 of FIG. 4. However, since this process is to obtain the median value (i) of the rotational movements (e) and (f) of the male rotor 2 shown in FIG. 8, it is possible to apply the backward torque (c) first and then apply the forward torque (b). Further, in S7 and S14, although the forward torque (b) and the backward torque (c) are applied during a period between the intermittent torque (a) applications, the forward torque (b) and the backward torque (c) can be omitted in a case of a screw compressor of which the rotor can be returned to its natural shape only the intermittent torque application. FIG. 9 shows rotational movement (displacement) of the male rotor 2 in a case where only the intermittent torques are applied and the forward and the backward torques are omitted. In FIG. 9, the curve 1 is difference between detected results of the encoder 21 and the encoder 22, and the curve 2 is an envelope of displacement of the male rotor 2 in the state in which rotation is returned by releasing of elastic deformation in the male rotor 2. In this case, in S8 and S15 of FIG. 4, using displacement of the male rotor 2 obtained from the curve  2 under a condition where the torque is not applied to the male rotor 2, it is confirmed whether the median value is in the symmetrizing target position. If the median value is not in the symmetrizing target position, a torque command value to be applied next is calculated based on the median value, that is, from difference between the position of the male rotor 2 and the target position. Then, the processing is returned to S7 in the case of S8, and to S14 in the case of S15 to apply the next intermittent torque. Thereby, the male rotor 2 is driven toward the target position. The other processes will be omitted here since they are the same as those in FIG. 4. Press-fitting of the M-timing gear shown by S4 of FIG. 4 will be described below. In a case where the M-timing gear 10 is press-fit to the male rotor 2 after press-fitting (inserting) the F-timing gear 11 to the female rotor 3, since the timing gears 10, 11 are helical gears, both of the timing gears 10, 11 are rotated counterclockwise together while sliding along the helical teeth. Therefore, the male rotor 2 and the female rotor 3, which cannot be moved in the axial direction, are sometime in contact with each other (hereinafter, referred to as "clash") and the rotors 2, 3 are twisted. When the clash occurs, excessive large forces act between the rotors 2, 3 and between the timing gears 10, 11. Therefore, there is possibility to cause problems that damage may occur in the rotors 2, 3 and in the timing gears 10, 11, that damage may occur in each of the bearings shown in FIG. 1 and in the other bearings not shown, and that the axial span between the rotors 2, 3 is expanded. When the symmetrizing adjustment is performed under a condition that shrinking between the male rotor 2 and the M-timing gear 10 is loosed by applying oil pressure and the M-timing gear 10 is fixed to the casing 1 with the jig 54, the M-timing gear 10 is sometime tilted in the conventional technology. That is, when the screw of the jig 54 is fastened, a force acts onto the male rotor 2 in the direction intersecting at right angle to the axial direction of the rotors 2, 3 to tilt the M-timing gear 10, and the M-timing gear is, thereby, displaced in the radial direction and in the thrust direction at the engaging position of the timing gears 10, 11. As the result, the F-timing gear 11 is rotated. Since the female rotor 3 is also rotated with the rotation of the F-timing gear, the rotors 2, 3 are in contact with each other depending on the magnitude of rotation. Since the gap (backlash) between the rotors 2, 3 is as very small as several tens micro-meters (equivalent to 0.15° in rotational angle), even a very small tilting affects bad effect on the accuracy of the symmetrizing adjustment. FIG. 10 shows an embodiment of press-fitting of an M-timing gear. Referring to FIG. 10, the reference character 61 is an outer gear which is an alternative jig of the jig 54 shown in FIG. 1, and the reference character 62 is a DD motor for driving the outer gear 61. Process of fixing of the M-timing gear 10, the piston 51a and the cylinder 51b of the press-fitting jig 51 is the same as the process to the state of FIG. 5. That is, the lower end screw portion of a piston 51a in the press-fitting jig 51 is fastened to the upper end portion of the male rotor 2 using screw. A cylinder 51b of the press-fitting jig 51 is fixed to the M-timing gear 51 using screw. Then, a pipe 52 is fixed to the upper end portion of the piston 51a using screw. Thereby, an oil-pressure chamber 51c is partitioned by the M-timing gear 10, the piston 51a and the cylinder 51b. On the other hand, the outer gear 61 is engaged with the M-timing gear 10. Next, oil hydraulic pressure is applied to the M-timing gear 10 as the same as in the conventional press-fitting to loose the shrinking by expanding the inner diameter, and at the same time a thrust force is applied in the direction of inserting (press-fitting) as shown by the arrow A in FIG. 11. Thereby, the M-timing gear 10 is engaged with the helical teeth of the F-timing gear 11. At that time, the M-timing gear 10 is rotated using the outer gear 61 as shown by the arrow D of FIG. 11. Then, the M-timing gear 10 is rotated as shown by the arrow E and is moved and twisted in the tilting direction of the helical teeth of the F-timing gear 11. The DD motor 62 and the outer gear 61 are moved in matching with the moving speed of the M-timing gear 10 as shown by the arrow F so that the rotating force is sufficiently transmitted from the outer gear 61 to the M-timing gear 10. By doing so, the M-timing gear 10 is press-fit to the male rotor 2 by being pushed by the outer gear 61 as shown in FIG. 11 (c) while the both timing gears 10, 11 are keeping a gap as shown in FIG. 11 (b). Further, the male rotor 2 is about to rotate as the M-timing gear 10 is being press-fit to the male rotor 2, but the rotors 2, 3 are not in contact with each other as shown in FIG. 12 (b) by applying torque in the direction shown by the arrow G opposite to the rotating direction of the M-timing gear 10 using the DD motor 24, as schematically shown in FIG. 12 (a). In order to matching the moving speed of the M-timing gear 10 in the direction A with the moving speed of the outer gear 61 in the direction F, a position sensor is arranged in the oil pressure cylinder 51b and the movements of the outer gear 61 and the DD motor 62 are controlled using the detected result. The rotating angle of the outer gear 61 toward the direction D, that is, the control amount of the DD motor 62 may be determined from the moving speed of the outer gear 61 toward the direction F based the skew angle of the M-timing gear 10. Although the encoder 21 detecting rotation of the male rotor is not shown in FIG. 12 (a), the two values of rotating angles 1 and 2 detected by the encoders 21, 22 are measured, and the difference of the two values is calculated. When the calculated result is larger than the backlash between the gear 26 and the F-timing gear 11, it is judged that the clash occurs. It is also possible from positive or negative sign of the calculated result to judge the direction of clash. Instead of detecting the rotating angle 2 using the encoder 22, it is possible to provide an encoder in the servo motor 25 and use the output. The symmetrizing adjustment of the both rotors 2, 3 will be described below. In the symmetrizing adjustment, the female rotor 3 is applied braking by the servo motor 25 not to be rotated, and the male rotor 2 is rotated by the DD motor 24. In this case, the M-timing gear 10 is applied braking by the DD motor 62 through the outer gear 61 not to be rotated. That is, by keeping the DD motor 62 to be stopped by applying braking during symmetrizing adjusting, the M-timing gear 10 engaging with the outer gear 61 is also restricted in the rotating direction so that engaging problem of the M-timing gear 10 and the F-timing gear 11 does not occur. In this clamping, no additional external force to change the distance between axles is applied onto the M-timing gear 10, and accordingly no bad effect affects on the accuracy of symmetrizing adjustment. Although the F-timing gear 11 is press-fit to the female rotor 3 in prior to press-fitting the M-timing gear 10 in the above-mentioned embodiments, the M-timing gear 10 may be press-fit to the male rotor 2 in prior to fitting the f-timing gear 11 to the female rotor 3. Further, the symmetrizing adjustment may be performed by restricting the male rotor 2 using the DD motor 24 and applying torque to the female rotor 3 using the servo motor 25 or the DD motor 62. As having been described above, according to the present invention, it is possible to adjust clearance of rotors of a screw compressor without causing problems such as occurrence of flaws in the timing gears, damage of the bearings and expanding axle distance between the rotors. Further, according to the present invention, it is possible to adjust clearance of rotors of a screw compressor without affecting bad effect on the accuracy of the symmetrizing adjustment. Furthermore, according to the present invention, it is possible to set the very small clearance between the both rotors to a desired value within a short time and to provide a screw compressor having high reliability in symmetrizing adjustment and high compression performance.

Claims: A method of adjusting an engaged clearance (G1 G2) between rotors (2, 3) of a screw compressor having a male rotor (2) and a female rotor (3) inside a casing (1), both of the rotors (2, 3) being rotated while maintaining a required very small clearance therebetween using timing gears (10, 11) fixed individually to the rotors (2, 3) through shrink fitting, comprising the step of applying torques to said rotor (2) to set the very small clearance between the rotors (2, 3) to a required value characterized in that the torques are applied under loosening the shrink fit between one of said timing gears (10) and the rotor (2) on which the one of said timing gears (10) is mounted but still leaving a friction between the one of said timing gears (10) and the rotor (2) on which the one of said timing gears (10) is mounted, while movement of the other of said timing gear (11) is being restricted, whereas said torques are step-shaped torques applied at intervals using a servo motor (24). A method of adjusting an engaged clearance (G1 G2) between rotors (2, 3) of a screw compressor according to claim 1, characterized in that during the application of said step-shaped torques to said rotor (2) on which the one of said timing gears (10) is mounted, a torque value to be applied next time is determined from a difference between a position of said rotor (2) without applying the torque and a target position to set the very small clearance (G1, G2) between the rotors (2, 3) to the required value. A method of adjusting an engaged clearance (G1 G2) between rotors (2, 3) of a screw compressor according to claim 1, the method further comprising the steps of: applying torques (Fig. 7(b), (c)) in forward and backward directions to said rotor (2) during application of said step-shaped torques, said torques (Fig. 7(b), 7(c)) being larger than a static friction force of the driving system of said servo motor (24) and smaller than each of the applied step-shaped torques (Fig. 7 (a)); calculating a median value of relative positions of said rotors (2, 3) during the application of said forward and backward applied torques; and calculating a command value of an step-shaped torque to be applied next from a difference between said median value and said required value for the very small clearance (G1 G2) between the rotors (2, 3). A method of adjusting an engaged clearance (G1 G2) between rotors (2, 3) of a screw compressor according to claim 3, characterized in that the application of said forward applied torque is performed after the application of said backward applied torque. A method of adjusting an engaged clearance (G1 G2) between rotors (2, 3) of a screw compressor according to claim 1, where each of the timing gears (10, 11) is a helical gear, the method further comprising the steps of: fixing a first timing gear (11) which has been precedingly press-fit so that it cannot be rotated; engaging a second timing gear (10) to be press-fit later than said first timing gear (11), with helical teeth of an outer gear (61); rotating said second timing gear (10) toward the direction in which the first and second timing gears (10, 11) engage each other using said outer gear; and at the same time, fixing the rotor (2) to be press-fit in the second timing gear (10) so that it is not rotated. A method of adjusting an engaged clearance (G1, G2) between rotors (2, 3) of a screw compressor according to claim 5, the method further comprising the steps of: providing a direct drive motor (24, 25) and an encoder (21, 22) to each of the rotors (2, 3) which has been press-fit with the first timing gear (11) with the rotor (3) and to be press-fit with the second timing gear (10) later; fixing the rotors (2, 3), so that they cannot be rotated by controlling each of the direct drive motors (24, 25) using output power from each of the encoders (21, 22). A method of adjusting an engaged clearance (G1 G2) between rotors (2, 3) of a screw compressor according to claim 5, the method further comprising the steps of: loosening the shrink fit between said second timing gear (10) and the rotor (2) on which the second timing gear (10) is mounted; stopping rotation of said second timing gear (10) using the outer gear engaging with said second timing gear (10); and adjusting the small clearance (G1 G2) between the male and the female rotors (2, 3) using the direct drive motor (24) coupled to said rotor (2). An apparatus for carrying out the method according to claims 1 to 7 for adjusting an engaged clearance (G1 G2) between rotors (2, 3) of a screw compressor having a male rotor (2) and a female rotor (3) inside a casing (1), both of the rotors (2, 3) being rotated while maintaining a required very small clearance (G1 G2) therebetween using timing gears (10, 11) fixed individually to the rotors (2, 3) through shrink fitting, characterized by step-shaped torque applying means (30) connected to that rotor (2) for applying step-shaped torques to said rotor (2) on which the one of said timing gears (10) is mounted based on command values on a servo motor (24). An apparatus of adjusting an engaged clearance (G1, G2) between rotors (2, 3) of a screw compressor according to claim 8, characterized in that the step-shaped torque applying means (30) comprises step-shaped torque calculating means for calculating said command value of the step-shaped torque to be applied next time from a difference between a position of said rotor (2) without applying the torque and a target position to set the very small clearance between the rotors (2, 3) to a required value. An apparatus of adjusting an engaged clearance (G1 G2) between rotors (2, 3) of a screw compressor according to claim 8, characterized in that the step-shaped torque applying means (30) comprises forward and backward torque applying means for applying torques in forward and backward directions to said rotor (2) during said step-shaped torque application, each of said forward and backward applied torques being larger than a static friction force of the driving system of said servo motor (24) and smaller than each applied step-shaped torque; relative position median value calculating means for calculating a median value of relative positions of said rotors (2, 3) during the application said forward and backward applied torques; and step-shaped torque calculating means for calculating said command value of a step-shaped torque to be applied next from a difference between said median value and a required value for the very small clearance between the rotors (2, 3). An apparatus of adjusting an engaged clearance (G1, G2) between rotors (2, 3) of a screw compressor according to claim 8, characterized in that said rotor (2) comprises an end portion opposite to an end portion at which the one of said timing gears (10) is attached, onto which the step-shaped torques and the forward and backward torques are applied.

Inventors: HIROYASU OBATA, HIROYUKI MATSUNO, KENICHI TAKAHASHI, MEGUMI KAWAI, HIROYASU, OBATA, HIROYUKI, MATSUNO, KENICHI, TAKAHASHI, MEGUMI, KAWAI
Applicants: HITACHI IND CO LTD, HITACHI INDUSTRIES CO., LTD.
Application year: 1997
Main classification: F04C18
IPC codes: F01C21