Ceramic turbo charger rotor

Abstract: A ceramic turbo charger rotor (11) having a bearing structure in which an inner lathe or sleeve (14) of an annular ball bearing race and a spacer (15) are assembled to a journal shaft (13a) as one unit in such manner that one end of the spacer (15) is assembled to a turbine-side connecting portion (13b) of the journal shaft (13a) in a pressure inserting manner and the other end of the spacer (15) is assembled to a compressor-side connecting portion (13c) of the journal shaft (13a) in a clearance fitting manner. Therefore, the deviation between a center axis and a rotational axis of the rotor (11) caused by the pressure insertion of the spacer (15) is released at the compressor side and the amount of the unbalance before correcting of the rotor (11) is remarkably reduced.

Description: The present invention relates to a ceramic turbo charger rotor having a ball bearing structure, particularly to a ceramic turbo charger rotor in which an annular ball bearing race and a spacer are assembled to an outer surface of a journal shaft of the ceramic turbo charger rotor as one unit. US-A-4,652,219 discloses a turbocharger having a metal shaft with a journal shaft portion formed between two connecting portions, a spacer fitted on the metal shaft to enclose the journal shaft portion, two bearing assemblies each fitted on one of the connecting portions to abut one end of the spacer, a turbine rotor assembled to one end of the shaft and a compressor assembled to the other end of the shaft. A ceramic turbo charger rotor having a ceramic turbine rotor and a metal compressor rotor connected by a metal shaft is generally used for assembling to a bearing housing which is supported by a floating metal or a ball bearing. The balance of such a ceramic turbo charger rotor is corrected in such manner that the unbalance of the ceramic turbine rotor is firstly corrected under the condition that the metal shaft is assembled to the ceramic turbine rotor, and then the balance of the turbo charger rotor as a whole is corrected after the metal compressor rotor has been assembled to the metal shaft by means of a nut. Fig. 1 is a schematic view showing a ceramic turbo charger rotor having a ball bearing structure. The ceramic turbo charger rotor 11 comprises a ceramic turbine rotor 12 and a metal shaft 13 comprising a journal shaft 13a, and an inner sleeve 14 and a spacer 15 which are assembled to an outer surface of the journal shaft 13a as one unit. Hitherto, there have been suggested two ways, i.e press fit and clearance fit, to assemble the spacer 15 to connecting portions 13b and 13c of the journal shaft 13a. If the spacer 15 is assembled to the connecting portions 13b and 13c of the journal shaft 13a by a press fit, the balance of the turbo charger rotor 11 is corrected under the condition that the inner sleeve 14 and the spacer 15 have been assembled to the journal shaft 13, as shown in Fig. 1. On the other hand, in case the spacer 15 is assembled to the connecting portions 13b and 13c of the journal shaft 13 by a clearance fit, the balance of the rotor 11 is corrected before assembling the inner lathe 14 and the spacer 15 to the journal shaft 13. However, if the spacer 15 is assembled to the journal shaft 13 with a press fit, a deviation occurs between the center axis and the rotation axis of the ceramic turbo charger rotor, and therefore the amount of unbalance of the ceramic turbo charger rotor tends to become large due to the deviation. Thus a lot of working time is necessary to correct the unbalance of the ceramic turbo charger rotor, so that the balance of ceramic turbo charger rotor to which the metal compressor rotor has been assembled is not maintained due to the influence of the deviation. While, if the spacer 15 is assembled to the journal shaft 13 by a clearance fit, a precise processing and inspecting are required to make a clearance in the spacer 15, because the clearance between the journal shaft 13 and the spacer 15 should be about several µm or less. The present invention has for its object to provide a ceramic turbo charger rotor in which the amount of the unbalance of the ceramic turbo charger rotor is small when the inner sleeve of the annular ball bearing race and the spacer are assembled to the metal journal shaft, and the unbalance can be easily corrected, and further the requirement for highly precise processing is reduced. The ceramic turbo charger rotor of the invention is specified in claim 1. According to the invention, since one end of the spacer is assembled to the turbine-side connecting portion of the journal shaft by a press fit and the other end of the spacer is assembled to the compressor-side connecting portion of the journal shaft by a clearance fit, the deviation between the center axis and a rotation axis of the ceramic turbo charger rotor caused by the press fitting of the spacer to the journal shaft is released when the other end of the spacer is assembled to the compressor-side connecting portion of the journal shaft by a clearance fit. Therefore, the amount of the unbalance of the ceramic turbo charger rotor is reduced, and thus the working time for adjusting the unbalance of the ceramic turbo charger rotor can be shortened. Further, the variation of the unbalance, which is caused when the ceramic turbo charger rotor, to which a metal compressor rotor has been assembled, is rotated due to the deviation, can be effectively prevented. Furthermore, according to the invention, highly precise processing is not required for the clearance of the spacer at both sides. Preferably the ceramic turbo charger rotor satisfies the following condition: 0.25 ≦ L/D ≦ 1.5 wherein: D represents the diameter of the turbine-side connecting portion of the journal shaft, and L represents the press fit length of the spacer to the turbine-side connecting portion of the journal shaft. When the ceramic turbo charger rotor satisfies the above mentioned condition, the deviation caused by the press fit of the spacer becomes smaller and the amount of the unbalance of the ceramic turbo charger rotor is more reduced. Embodiments of the invention will now be described in detail with reference to the accompanying drawings, wherein: Fig. 1 is a schematic view showing an embodiment of a ceramic turbo charger rotor according to the invention; and Fig. 2 is a schematic view showing the ceramic turbo charger rotor shown in Fig. 1 to which a metal compressor rotor is assembled. Fig. 2 is a schematic view showing an embodiment of a ceramic turbo charger rotor according to the present invention. In Fig. 2, reference number 1 denotes a ceramic turbine rotor; 2 a metal compressor rotor; 3 a metal shaft which connects the ceramic turbine rotor and the metal compressor rotor, and the metal shaft 3 comprises a journal shaft 4 having connecting portions 4a at a turbine side and 4b at a compressor side; 3a a nut for assembling the metal compressor rotor 2 to the metal shaft 3; 5 an inner sleeve of an annular ball bearing which is assembled to the outer surface of the journal shaft 4 at a turbine side by a press fit or a clearance fit ; 6 a spacer the top end of which is assembled to the turbine-side connecting portion 4a of the journal shaft by a press fit and the bottom end of which is assembled to the compressor-side connecting portion 4b by a clearance fit, 7 an inner sleeve which is assembled to the compressor-side of the outer surface of the journal shaft 4 by a press fit; and 8 denotes a thrust spacer which is arranged between the inner sleeve 7 and the metal compressor rotor 2. It should be noted that the inner sleeve 5, the spacer 6 and the sleeve 7 are assembled to the journal shaft 4 so as to be arranged between the ceramic turbine rotor 1 and the metal compressor rotor 2 via the thrust spacer 8 and these assemblies are fixed to the metal shaft 3 by means of the nut 3a. In this embodiment, the diameter of the journal shaft 4 is made large at both ends, i.e. connecting portions 4a and 4b, in order to make easy the assembling the inner sleeves 5 and 7 and the spacer 6. It should be noted that the press fit dimension varies in accordance with the diameter of the journal shaft 4, and therefore the press fit dimensions are not particularly limited. Experiment 1 Seven ceramic turbo charger rotors (sample No. 1∼7) made of Si₃N₄ were prepared. The diameter of turbine blade of each rotor is 55 mm and the diameter of the connecting portions of the metal shaft is 8 mm. The top end of the spacer 6 was assembled to the turbine-side connecting portion 4a of the journal shaft 4 by a press fit and the bottom end of the spacer 6 was assembled to the compressor-side connecting portion 4b of the journal shaft 4 by a clearance fit; the insertion clearances (positive or negative) of the inner sleeve of the annular ball bearing and the spacer 6 are varied in accordance with the numeral data shown in Table 1, and the press fit length L of the spacer 6 to the turbine-side connecting portion of the journal shaft 4 was 3 mm (L/D=0.375). On the other hand, seven comparative ceramic turbo charger rotors (sample No. 8∼14), which are the same as the rotors according to the invention mentioned above in material and size, but in which both the ends of the spacer 6 are assembled to the connecting portions 4a, 4b of the journal shaft 4 by a press fit were prepared. Then the amount of the unbalance before correcting was measured for each sample on the correcting surfaces I and II. The correcting surfaces I and II are shown in Fig. 1 by lines I-I and II-II. It is clear from Table 1 that the amounts of the unbalance of the correcting surfaces I and II of sample number 1∼7 (rotors according to the present invention) are clearly improved in comparison with those of the rotors of sample numbers 8∼14 (conventional rotors). Experiment 2 The ceramic turbo charger rotor which is the same as the rotors of sample numbers 1∼7 in Table 1 in material and size but the insertion clearance of the ball bearing inner sleeve at the compressor side is arranged to be -2 µm, the the insertion clearance of the spacer at the turbine side 6 µm, and the press fit length L of the spacer to the turbine-side connecting portion 4a 5 mm (L/D=0.625) was prepared. After correcting the unbalance of this ceramic turbo charger rotor, the rotor was assembled to an engine and rotated to be tested in a rotational speed of 130,000 r.p.m. for 15 minutes at a temperature of 900°C and thereafter 80,000 r.p.m. for 15 minutes at 900°C. And the cycle was repeated 300 times. However, no accident occurred in the ceramic turbo charger rotor. Further, a vibration detector was set at an oil exit of a turbo charger center housing to detect the vibration of the engine. However, the vibration was generated in synthesized with the rotation of the ceramic turbo charger rotor and it was stabilized. This test proves that the ceramic turbo charger rotor according to the invention has the same or better performance than the conventional rotors. Experiment 3 In order to find a range of a pressure insertion length L preferred to make the unbalance before correcting small, the relation between the diameter D of the turbine-side connecting portion 4a of the journal shaft and the press fit length L of the spacer 6 to the turbine-side connecting portion was examined for the ceramic turbo charger rotors according to the invention. That is to say, ten turbo charger rotors (sample Nos. 15∼24) made of Si₃N₄ were prepared. The diameter of the blade of each rotors is 55 mm and the diameter of the turbine-side connecting portion of the journal shaft thereof 8 mm. And the top end of the spacer is assembled to the turbine-side connecting portion of the journal shaft by a press fit and the bottom end of the spacer is assembled to the compressor-side connecting portion of the journal shaft by a clearance fit, but the insertion clearance of the spacer at the turbine side, the diameter D of the connecting portion of the journal shaft, and the press fit length L of the spacer to the turbine-side connecting portion of the journal shaft were varied according to the data shown in Table 2. Then, for each sample (sample Nos. 15∼34), the amount of the unbalance was measured on the correcting surfaces I and II in the same manner as Experiment 1. As clear from Table 2, it is proved that the amount of the unbalance before correcting becomes small in the range of 0.25∼1.5 of L/D and that it is impossible to make the amount of the unbalance before correcting small only by making the press fit clearance large. Experiment 4 The ceramic turbo charger rotor according to the present invention was made in which the diameter of the connecting portions of journal shaft is 8 mm, press fit length of the spacer to the turbine-side connecting portion is 4 mm (L/D=0.5), and the amount of the unbalance before correcting is 0.3 g/mm at the surface I and 0.5 g/mm at the surface II was prepared. The unbalance was corrected at a predetermined value. Thereafter the rotor was assembled in an engine, and the engine was rotated to be tested at a rotational speed of 125,000 r.p.m. for 20 minutes at a temperature of 880°C and 90,000 r.p.m. for 10 minutes at 880°C and then the engine was stopped for 5 minutes. And this cycle was repeated 200 times. However, no accident was found in the rotor. As in Experiment 2, a vibration detector was set on a surface of a turbo charger center housing to detect the vibration of the engine. The vibration was generated synchronously with the rotation of the turbo charger rotor and it was stabilized. As clear from the explanation of the experiments, in the ceramic turbo charger rotor having ball bearing structure according to the present invention, since the top end of the spacer is assembled to the turbine-side connecting portion of the journal shaft by a press fit and the bottom end of the spacer is assembled to the compressor-side connecting portion of the journal shaft by a clearance fit, the amount of the unbalance before correcting of the rotor is decreased. Therefore, the working time for balancing the rotor can be shortened and the variation of the unbalance caused by the deviation between the rotating shaft and the center shaft of the rotor can be effectively prevented. Furthermore, since the processing accuracy of the spacer of the rotor is not required so severely , the processing of the spacer becomes easier. Moreover, when the ratio of the diameter of the turbine-side connecting portion of the journal shaft D and the press fit length L of the spacer to the turbine-side connecting portion of the journal shaft satisfied the condition of 0.25≦L/D≦1.5, it is possible to reduce the amount of the unbalance before correcting of the ceramic turbo charger rotor. In such rotor, the working time for correcting the unbalance can be remarkably shortened.

Claims: A turbo charger rotor (11) comprising: a turbine rotor (12;1); a metal shaft (13;3) comprising a journal shaft (13a;4) assembled to said turbine rotor (12;1); an inner sleeve (14;5) of an annular ball bearing race; and a spacer (15;6); said inner sleeve (14;5) and said spacer (15;6) being assembled to an outer surface of said journal shaft (13a;4); said journal shaft (13a;4) comprising connecting portions (13b,13c;4a,4b) at both turbine side and compressor side thereof for fitting to said spacer (15;6); characterized in that said turbine rotor (12;1) is a ceramic rotor; and one end of said spacer (15;6) is assembled to said turbine-side connecting portion (13b;4a) of said journal shaft with a press fit and the other end of said spacer (6) is assembled to said compressor-side connecting portion (13c;4b) of said journal shaft with a clearance fit. A turbo charger rotor according to claim 1, further comprising: a metal compressor rotor (2); and a thrust spacer (8); said compressor rotor (2) being assembled to said metal shaft (3) and said thrust spacer (8) being assembled on said metal shaft between said spacer (15;6) and said compressor rotor. A turbo charger rotor according to one of claims 1 and 2, wherein: the ratio of the diameter (D) of said turbine-side connecting portion (4a) of the journal shaft (4) and the press fit length (L) of said spacer (6) to the turbine-side connection portion (4a) of the journal shaft (4) satisfies the following condition: 0.25 ≦ L/D ≦ 1.5.

Inventors: ADACHI KENJI, ASAMI SEIICHI, KAWASE HIROYUKI, MIZUNO TAKEYUKI, ADACHI, KENJI, ASAMI, SEIICHI, KAWASE, HIROYUKI, MIZUNO, TAKEYUKI
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1990
Main classification: F04D29
IPC codes: F01D5, F04D29, F02B39