Patent Document

BACKGROUND OF THE INVENTION 
     The present invention relates to the field of turbomachines and relates more particularly to multibody gas turbine engines. It relates to engine assembly operations and in particular to the fitting of the low pressure turbine module to a high pressure body. 
     DESCRIPTION OF THE PRIOR ART 
     A turbojet with a front turbofan and a double body, for example, comprises a low pressure (LP) body and a high pressure (HP) body. The LP body rotates at a first speed and the LP turbine drives the fan. The HP body rotates at a speed different from that of the LP turbine. The shafts of the two bodies are concentric, the low pressure shaft is guided in rotation in bearings supported by the fixed structure of the engine, respectively situated downstream of the turbine and upstream of the high pressure compressor. The shaft of the high pressure body is guided in rotation by bearings supported by the fixed structure of the engine upstream and by the shaft of the low pressure body by means of downstream inter-shaft bearings. The latter are of the roller bearing type and situated, at least according to a known engine, between the high pressure turbine and the low pressure turbine. The bearing comprises an inner ring equipped with rollers held by a cage on the LP shaft and an outer ring shrink fitted in the HP shaft. The fitting of this bearing, that is to say the assembly of the outer ring with the assembly formed by the rollers, of the cage and of the inner ring, is carried out at the same time as the mating of the low pressure turbine where the shaft, previously fitted to the low pressure turbine, is guided into the high pressure body. The term “mating” here refers to all or part of the translational movement of the LP turbine module until the flange of the outer casing of the latter comes into contact with the corresponding flange of the HP module. 
     It follows that the assembly of the inter-shaft bearing is carried out blind. The operator has no visibility for monitoring, in particular, the engagement of the rollers in the HP rotor and then in the outer ring. This operation comprises high risks of damage to the bearing if the conditions are not controlled. The highest risk for the bearing is a hard contact between the rollers and the retaining nut of the outer ring and the ring itself. 
     At present, the means used do not make it possible to fit the LP turbine without negative impact for this inter-shaft bearing, because of the heating method used and of the imprecise positioning of the LP turbine. In particular, the heating of the HP part (equipped with the outer ring) is carried out from the inside of the journal by means of a diffuser fed by a heater. The temperature measurement is carried out manually using a probe applied against the outside of the HP part. The investigations carried out on this operating method have revealed several disadvantages:
         a relatively high heterogeneity, of the order of 20° C., of the temperature levels of the heated parts,   a high risk of adding pollution by the ambient air taken for the heating and the heating device itself, and   a high risk of damage of the outer ring of the bearing by contact with the diffuser. This risk is particularly high as the clearance between the diffuser and the outer ring is only a few millimeters, and the assembly is installed on rollers and therefore presenting a risk of being moved inadvertently by the operators.       

     SUMMARY OF THE INVENTION 
     The objective of the invention is to improve the device for heating the journal and, more generally, to produce a device for heating a cylindrical component. 
     According to the invention, these objectives are achieved with a device for heating a cylindrical component of given diameter, by means of hot gas, characterized in that it comprises at least two heaters each delivering a stream of hot gas and emerging in an annular chamber, the inside diameter of which is slightly greater than said given diameter. 
     Preferably, the heaters are equidistant from one another, and the enclosure includes a perforated inner wall. 
     Advantageously, the heaters are electrical heaters. The temperature may be continuously regulated. 
     More particularly, the invention relates to the use of such a device for heating a metal journal in which a bearing ring for a bearing is mounted. More particularly, the temperature at the surface of the journal is measured and the supply of hot gas is controlled according to said temperature. 
     The invention applies in particular to the assembling of an inter-shaft bearing in a double-body turbomachine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages will emerge on reading the following description of a non-limiting embodiment of the invention, applied to the fitting of a low pressure turbine module in the high pressure body of a double-body gas turbine, given with reference to the appended drawings in which: 
         FIG. 1  shows an engine in the process of assembly; 
         FIG. 2  shows a detail of the inter-shaft bearing before assembly; 
         FIG. 3  shows the same zone as  FIG. 2 , after assembly; 
         FIGS. 4 to 6  show an equipment supporting a heating device, in the position of use and in a retracted position respectively; 
         FIG. 7  shows a detail of the heating device in the position of use; 
         FIG. 8  is an axial cross-sectional view of the device shown in  FIG. 7  in position; 
         FIG. 9  illustrates a detail of the device showing a temperature sensor. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows an engine in the process of assembly in which only the outer casings are seen. In this case it is a double-body bypass turbojet such as the CFM56. It comprises a front fan  3  and a module  5 , called the first module, constituted by the HP body with its shaft, called the first shaft. These components are already assembled. In this view the LP turbine module  7 , called the second module, whose shaft  9 , called the second shaft, is already engaged in the HP body, is in the process of being fitted. The critical zone is situated in zone  8  of the inter-shaft bearing whose visibility is zero. 
     In the continuation of the description, the fitting of this second module, the low pressure module, into the first module, the high pressure module, is therefore described. 
     In  FIG. 2 , this zone is seen in cross-section and in greater detail. The shaft  101 , the second shaft of the second module, the LP turbine, is housed in the shaft  103 , the first shaft, of the first module, the HP body. The shaft  101  comprises at its end, on the right of the figure, a journal  104  for the fitting of a bearing. A radial flange  105  allows the fitting of the various components constituting the LP turbine  110 , which is partly visible. 
     The shaft  103  of the HP body is extended by a journal  111  at its downstream end. Only a part of the turbine  112  of the HP body can be seen. 
     The inner-shaft bearing  120 , known per se, comprises an inner ring  121 , fixed to the shaft  101  with the rolling elements, such as rollers  122 , whose cage  122 ′ is crimped on the ring  121 . The outer ring  123  is shrink fitted inside the journal  111 . It is locked in position by a nut  125 .  FIG. 3  shows the same components after assembly. The assembly is carried out by translational displacement of the LP turbine module  110  with the shaft  101  towards the left with respect to  FIG. 2 , after expansion of the journal together with the outer ring, by heating, the HP module being fixed. It is understood that because of low tolerances, there is a great risk of contact between the rolling parts. This contact can be the cause of scratches, grooves or spalling initiators which are able to result in the fracture of the bearing. 
     The applicant company has developed a piece of equipment allowing a secure fitting of the LP module in this environment. 
     The equipment  200  comprises a mobile frame  210 , from which is suspended a means of heating the HP body journal. This assembly is shown in  FIGS. 4 ,  5  and  6  in several positions. 
     The frame  210  comprises a carriage  211 , mounted on rollers, with a vertical frame member  212 . A support beam  220  is mounted on this frame member provided with rails in order to be able to slide between a first low, active or operating, position, shown in  FIG. 4 , and a second high, retracted position, which is seen in  FIG. 6 . 
     A support  230  in the form of an inverted T is fixed to the end of the horizontal arm  222  of the support beam  220 . 
     The support  230  comprises a vertical arm  232  rigidly fixed with respect to the horizontal arm  222  of the support beam, and two horizontal branches  233  and  234 . The latter are designed to support two sliders  233 C and  234 C each supporting one half of the annular heating device  300 ,  300 A and  300 B respectively, as seen in  FIG. 7 . 
     The equipment is shown in the active position in  FIG. 4 . The support  230  is bearing against the flange  51  of the casing of the HP body module. Starting from this position, the heating device is released by separating the two halves  300 A and  300 B which move in direction parallel with the two branches  233  and  234  with their respective slider  233 C and  234 C. Once the heating device is open, it is distanced in the upward direction by causing the support beam  220  to slide in the rails of the frame member  212 . The equipment is shown in the high retracted position in  FIG. 6 . 
     The heating device is put into position using the reverse sequence. 
     The heating device is described in more detail with reference to  FIGS. 7 ,  8  and  9 .  FIG. 7 , which is an enlarged view of  FIG. 4 , shows the heating device with three heaters  310 ,  312  and  314 , in dotted line, disposed substantially tangentially with respect to an annular enclosure  316  forming a diffuser and air distributor. They are equidistant from each other and deliver a gas heated to a controlled temperature, air in particular, along at least one tangential component. In  FIG. 9  it can be seen that the heaters, because of the bulk of the suspension cannot be disposed strictly tangentially with respect to the annular chamber  316 . The latter is delimited by a cylindrical casing  317  and two walls  318  and  319 , perpendicular to the axis of the engine. An inner cylindrical wall  320  is perforated and forms a space with the journal  111 . The casing comprises a thermally insulating material as can be seen on the walls  317  and  318 . 
     Deflectors  321  are disposed inside the annular enclosure between two consecutive heaters. These deflectors are arched and inclined towards the axis of the engine. The end receiving the gaseous flow from an adjacent heater is at a greater distance from the axis than is the other end. In this way the gas flows emerging into the enclosure are simultaneously driven in a rotational movement about the axis of the engine with a centripetal component towards the perforated wall  320 . 
     The wall  318  towards the end of the journal comes into contact with the latter. The wall  319  on the other side forms a space or openings for the passage of the gasses which will heat up the thicker mass at that place of the journal. The components of the jacket  317 ,  318 ,  319  defining the annular enclosure  316  are made of two parts attached to their respective supports  320  A and B. These supports are themselves each suspended from a slider  233 C and  234 C respectively. 
     The support  230  bears against the flange  51  by stops, one of which is visible in  FIG. 8 . It is the stop  232 B integral with the vertical arm  232  of the support. The arm  233  and  234  also comprise chocking means  234 B and  233 B which can be seen in  FIG. 7 . The chocks are retractable and become positioned behind the flange  51  in order to ensure the immobilization of the support on the flange  51 . 
     The device serves as a support for three thermocouples  340  distributed equidistant from each other.  FIG. 9  is a partial cross-sectional view of the heating device  300  at the level of one of the thermocouples  340 . The latter is bearing against the downstream surface of the journal in order to sense the temperature. A cable  341  connects the sensor to the control unit which, in particular, comprises the function of controlling the heaters according to the temperature to be reached. In this example, it is seen that the thermocouple is attached to the wall  318  by means of a bracket  342 . 
     The device also supports three instruments  350  for measuring the distance between the journal  111  and the LP shaft inside the latter. They are distributed equidistant from each other, for example at three o&#39;clock, six o&#39;clock and nine o&#39;clock, as seen from the rear of the engine. The alignment of the LP shaft is carried out by comparing the differences in measurements of distances at these three points and by correlatively acting on the transverse positioning of the shaft in the handling system. The distance measuring instruments  350  are of the laser type for example. They have been shown diagrammatically in  FIGS. 7 and 8 . They are mounted on support arms  351  fixed on the horizontal arms of the supports  230 . They can move between two positions as seen in  FIG. 8  which shows a measuring instrument positioned high with respect to the axis of the engine. When they are in position  350  of the figure, they aim at the journal; by shifting them into the position  350 ′, they aim at the low pressure shaft. It is thus possible to derive from this the clearance between the shaft and the journal. The three together distributed around the journal make it possible to know the relative position of the two axes accurately. The correction is carried out by moving the turbine module in space using the appropriate control means. 
     A control console is mounted on the frame. It receives the signals from the temperature sensors and the distance measurements. It also comprises means for providing alarm signals, for example of the green light/red light type, to inform the operator of the situation and of the state of preparation of the journal before mating. 
     The sequence of operations is as follows. 
     The engine is partially assembled. The fan  3  and the HP body  5  are assembled. The LP module  7  is waiting. 
     a) For fitting the outer ring  123  in the journal,
         the device is put into position as shown in  FIG. 7 , and   the journal  111  is heated up to the temperature specified for the fitting; the obtaining of this temperature authorizes the putting into the retracted position, as shown in  FIG. 6 , the fitting of the ring  123 , and the tightening of the nut  125 ;       

     b) For the centering of the turbine shaft,
         the equipment is put into the operating position,   the LP shaft  101  is inserted into the HP body, and   the distance measuring system  350  is activated. The measurements taken by the instruments  350  allow the centering of the shaft  101 , within the limits specified, with respect to the journal.       

     c) For the heating of the journal/outer ring assembly,
         the equipment is put into the operating position, and   the heating is started. The heating is controlled according to the temperatures measured by the thermocouples  340  until the commanded temperature is reached, to within the specified limits. The obtaining of the temperature within the specified range authorizes the putting of the equipment into the retracted position.       

     The assembly is completed by proceeding with the final mating. 
     The device of the invention provides everything with the simultaneous control of the two major assembly conditions in order to ensure risk-free assembly of the bearing. 
     It is furthermore understood that the invention is not limited to the fitting of the LP turbine in an HP body of a gas turbine engine. It is applicable to all equivalent situations of fitting a second module assembled by a bearing in a first module.

Technology Category: 2