Abstract:
A turbocharger with an improved suspension mechanism for the actuation ring of a variable nozzle mechanism, for improved maintenance of the geometry of the suspension mechanism in the case of higher temperature oscillations. The suspension mechanism includes a number of guide rollers ( 48 ) provided between a housing part ( 24, 26 ) and nozzle ring ( 38 ) with circumferential grooves ( 59 ) in which the inner circumference of the actuating ring rides. The rollers are freely rotatable on pins ( 55′, 55″ ), and these pins are inserted in bores ( 55   a  or  55   b ) either in a housing part ( 24, 26 ) or in the nozzle ring ( 38 ), but not both.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention concerns a turbocharger of the type set forth in the precharacterizing portion of claim 1.  
           [0003]    2. Description of the Related Art  
           [0004]    In turbomachinery in which the turbine is intended to drive a compressor or the like, it is often desirable to control the flow of motive gas to the turbine to improve its efficiency or operational range. In order to accomplish this, the nozzle passages leading to the turbine wheel may be of variable geometry. These variable geometry nozzle passages can be provided by means of a plurality of blades which are pivotable so as to alter the configuration of the passages therebetween. The design of the suspension system used in association with the pivoting blade design is critical to prevent binding of either the suspension system or the blades.  
           [0005]    U.S. Pat. Nos. 2,860,827 and 4,179,247 disclose designs to prevent binding of the pivoting blade actuation mechanism. However, none of the above-mentioned designs are suspension systems for an actuation system which accommodates the thermal cycling experienced by the turbine housing as well as the components of the actuation system.  
           [0006]    U.S. Pat. No. 2,860,827, the content of which is to be considered as incorporated by reference herein, describes a turbocharger with variable turbine geometry. Exhaust gasses flow radially past nozzles in a ring-shaped passage situated between the housing part of the turbine housing and the nozzle ring, which nozzles are defined by the intermediate space between nozzle blades which are arranged in a ring and mounted pivotably along the nozzle ring, and operate in such a manner that the nozzles are maximally opened when the nozzle blades are radial, and maximally closed when the nozzle blades are essentially oriented tangential.  
           [0007]    The nozzle blades are mounted to the nozzle ring by means of pins, which extend through the nozzle ring, and which carry actuating arms on their opposite ends.  
           [0008]    Provided on the same plane as the circularly arranged actuating arms there is a second ring, the so-called actuating ring, for simultaneous actuation of all actuating arms, for which the actuating ring on its inner edge includes engagement means which cooperate with corresponding engagement means on each of the actuating arms, so that with limited coaxial pivoting of the actuating ring with respect to the nozzle ring all actuating arms, and the therewith associated nozzle blades, can be pivoted.  
           [0009]    Associated with the actuating ring is an actuating means which extends through the turbine housing in order to control the actuating ring from outside the housing.  
           [0010]    The actuating ring is carried by a certain number of rollers each of which is provided with a groove, and guided for limited rotation, which rollers can be arranged in a circular pattern corresponding to the inner edge of the actuating ring.  
           [0011]    These rollers can rotate freely about pins, which pins can be provided in the same part of the turbine housing as the above described actuating means.  
           [0012]    The pins extend through the wall of the turbine housing and are axially fixed directly outside and inside this wall freely rotatably by means of spring rings.  
           [0013]    This arrangement functions in satisfactory manner as long as no great temperature oscillations occur.  
           [0014]    Turbochargers are however subjected to very strong temperature oscillations as a result of the flowing through of hot exhaust gasses through the turbine part, so that the turbine part and adjacent parts are heated up to 900° C.  
           [0015]    These frequently extreme temperature oscillations, together with the extremely high rotation speed of the turbine wheel and the compressor wheel, produce extreme stresses for all components, which results in an early expenditure and loss of function of the turbocharger.  
           [0016]    It is particularly important that the geometric configuration of all cooperating parts, such as nozzle ring, actuating ring, rollers and pins, etc. remain intact, without thermal misalignment and hysteresis.  
           [0017]    The turbocharger according to U.S. Pat. No. 2,860,827 is not optimally designed in order to maintain the geometry of the described parts in the case of large thermal oscillations.  
           [0018]    U.S. Pat. No. 4,179,247 describes a turbocharger and in particular a suspension mechanism for the actuating ring, which is in the form of a double ball bearing.  
           [0019]    This type of ball bearing is particularly critical in the above-mentioned conditions and is beyond this very complicated in its construction.  
           [0020]    Many attempts have been made in order to solve the above described problem, and in part these problems were solved by the turbocharger according to European Patent 0 226 444 (U.S. Pat. No. 4,804,316).  
           [0021]    This patent describes a suspension mechanism for the actuating ring with pins and rollers, the rollers having circumferential grooves, which can carry and guide the actuating ring in a manner similar to that of U.S. Pat. No. 2,860,827.  
           [0022]    In EP-0226444 the roller pins are however not fixed axially in the housing, but rather they extend freely between bores in the housing on one side to bores in the nozzle ring on the other side, wherein a certain separation is maintained between the inner side of the housing and the opposing side of the nozzle ring in order to produce a second ring gap, and wherein the grooved rollers are provided for free rotation on the pins within this second ring gap.  
           [0023]    Since the ends of the pins engage in the nozzle ring, the effect is to provide an exact co-axiality of nozzle ring and actuating ring.  
           [0024]    In practice however two problems are associated therewith.  
           [0025]    On the one hand the construction of the actuating mechanism according to U.S. Pat. No. 2,860,827 is complicated, and the introduction of the roller pins in the bores first in the nozzle ring or the housing, thereafter the seating of the rollers upon the pins and the actuating ring upon the rollers and then the introduction of the free ends of the pins into the bores in the respective other element (housing or nozzle ring) element is very difficult to accomplish without an exact, axially parallel arrangement of these free ends of the pins.  
           [0026]    This is a true test of finesse, since the orientation of the bores between the two elements is never perfect, and besides this, because of the necessary tolerance between pin and bore, the pins tend to be tilted or askew prior to introduction into the second element.  
           [0027]    On the other hand the bores in the housing and those in the nozzle ring are subjected to different thermal dilations, so that in operation the pins are directed away from their exact axially parallel orientation, which detracts from the friction free operation of the parts.  
         SUMMARY OF THE INVENTION  
         [0028]    The present invention solves the described problems and disadvantages of the state of the art and provides a turbocharger which exhibits the characteristics according to the characterizing portion of claim 1.  
           [0029]    Further tasks and advantages of the invention are seen from the dependent claims.  
           [0030]    It is thus for example one of the tasks of the invention to provide an improved actuating system for a turbine with variable nozzle geometry. It is a further task of the invention to construct an actuating system, in which the actuating ring and the nozzle ring remain precisely coaxial in operation.  
           [0031]    It is further a task to provide a reliable actuating system.  
           [0032]    Finally, it is task to provide a nozzle ring which remains continuously oriented relative to the turbine side wall, in order to produce a ring shaped gap with constant spacing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]    In the following the invention will be described in greater detail on the basis of the figures. Therein:  
         [0034]    FIGS.  1 - 6  show different views of a turbocharger according to the state of the art,  
         [0035]    [0035]FIG. 7 is a view according to FIG. 5 having a first embodiment of the present invention integrated therein,  
         [0036]    [0036]FIG. 8 is likewise a view according to FIG. 5, with a second embodiment of the present invention integrated therein,  
         [0037]    [0037]FIG. 9 is a view according to FIG. 3, with a first embodiment of the present invention integrated therein, and  
         [0038]    [0038]FIG. 10 is a view according to FIG. 3, with a second embodiment of the present invention integrated therein. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]    An engine system as shown in the FIGS.  1  to  3  includes turbomachinery in the form of a turbocharger  10  generally comprising a turbine wheel  12  and a compressor impeller  13  mounted on opposite ends of a common shaft  16 . The turbine wheel  12  is disposed within a turbine housing  18  which includes an inlet  20  for receiving exhaust gas from an engine  14  and an outlet  21  for discharging the exhaust gas. The turbine housing  18  guides the engine exhaust gas into communication with and expansion through the turbine wheel  12  for rotatably driving the turbine wheel. Such driving of the turbine wheel simultaneously and rotatably drives the compressor impeller  13  which is carried within a compressor housing  22 . The compressor housing  22 , including an inlet  23  and outlet  25  and the compressor impeller  13  cooperate to draw in and compress ambient air for supply to the intake of the engine  14 .  
         [0040]    The turbine housing  18  is mounted to a flange member  24  which, in turn, is mounted to center housing  26  and could be a part of it. The compressor housing  22  is mounted on the other side of the center housing  26 . The center housing  26  includes a bearing means  29  for rotatably receiving and supporting the shaft  16 . A thrust bearing assembly  33  is carried about the shaft adjacent the compressor housing for preventing axial excursions of the shaft  16 . A heat shield  44  is positioned about the shaft  16  at the turbine end in order to insulate the center housing  26  from the harmful effects of the exhaust gas.  
         [0041]    Lubricant such as engine oil or the like is supplied via the center housing  26  to the journal bearing means  29  and to the thrust bearing assembly  33 . A lubricant inlet port  37  is formed in the center housing  26  and is adapted for connection to a suitable source of lubricant such as filtered engine oil. The port communicates with a network of internal supply passages which are formed in the center housing  26  to direct the lubricant to the appropriate bearings. The lubricant circulated to the bearings is collected in a suitable sump or drain for passage to appropriate filtering, cooling, and recirculation equipment, all in a well-known manner.  
         [0042]    [0042]FIG. 3 shows the turbine housing  18  forms a generally scroll-shaped volute  28  which accepts the exhaust gas from the engine  14  and directs it onto the blades of the turbine wheel  12  through an annular passage  30 . Thereafter, the exhaust gas flows axially through the turbine shroud  32  and exits the turbocharger through outlet  21  either into a suitable pollution-control device or the atmosphere. Placed within the annular passage way  30  are a plurality of pivotable blades  34  which operate to vary the geometry of the annular passage  30  to control the angle at which the exhaust gas impacts the blades of the turbine wheel  12 . This in turn controls the amount of energy imparted to the compressor wheel and ultimately the amount of air supplied to the engine.  
         [0043]    The flange member  24  and the turbine housing  18  form between them a cavity  27  which houses the hardware used in conjunction with the variable geometry turbine to be described below. The annular passage  30  for the exhaust gas is defined between the inner side wall  31  of the turbine housing  18  and an annular nozzle ring  38 . Located circumferentially around and within the annular passage  30  are a plurality of blades  34 . Each blade  34  is mounted to be capable of pivoting on the nozzle ring  38  on a blade pin  36  which can turn in a bore in the nozzle ring. Attached by welding to the outer end of each blade pin is a blade arm  46 , the shape of which can best be seen in FIG. 6. The nozzle ring is between the blades and the blade arms.  
         [0044]    Located within passage  30  are a plurality of spacers  86 . As shown in FIGS. 4 and 6, spacers  86  are located at the periphery of the plurality of blades. They have an axial length (within the range of 0.005 to 0.015 cm) longer than the blade length. The spacers are press fitted in bores formed in the nozzle ring  38 , though other methods could be used.  
         [0045]    An annular actuating ring  48  has a plurality of slots  51  on its inner radial surface, each of which receives a blade arm  46 . At the inner periphery of the actuating ring  48  are located at least three circumferentially spaced rollers  49 . Rollers  49  are rotatably mounted on pins  55  radially inwardly of the actuating ring and with respective ends inserted in bores in the flange member  24  and the nozzle ring  38 . Pins  55  have some axial clearance within these bores in order to allow nozzle ring  38  slight axial movement. Rollers  49  include an annular groove  59  therearound for acceptance of the inner periphery of the actuating ring  48 . Pins  55  and rollers  49  could be provided additionally at the periphery of the actuating ring  48  if so desired. The pins not only provide a mounting for the actuating ring; they also hold and concentrically locate the nozzle ring  38  and prevent it from rotating.  
         [0046]    The rollers  49  provide for ease of rotation of the actuating ring  48  relative to the flange member  24  and together with pins  55  ensure the concentricity between actuating ring  48  and nozzle ring  38 . The shape of the blade arms  46  as seen in FIG. 6 must be such as to maintain basically a rolling action within slots  51  to avoid binding within actuating ring  48  as it rotates to pivot blades  34 .  
         [0047]    The flange member  24  includes a recessed portion for acceptance of the actuation system as will be described below. Formed in flange member  24  is a shoulder  72  which acts in cooperation with belleville spring  40 . The inboard side of the radially outer edge of spring  40  rests against the shoulder  72 , and when assembled, the opposite side of the radially inner edge of the spring acts against the shoulder portion  39  of the nozzle ring  38  such that it loads the nozzle ring  38  and the spacers  86  against the turbine side wall  31 . Shoulder  72  is continuous about flange  24  with the exception of a break to make room for the bell crank system defined below.  
         [0048]    A tube member  42  which is generally cylindrically shaped with an annular bend therein, is slidably engageable within the inner radial surface of the nozzle ring  38 . The tube member  42  acts as a seal in the event that any exhaust gas leaks behind the nozzle ring  38  and into the cavity  27  formed between the flange  24  and the turbine housing  18 , thereby sealing the turbine housing  18  from the center housing  26 .  
         [0049]    In order to rotate the actuating ring  48  between its two extreme positions which correspond to the limits of the geometry of the annular passage  30 , a bell crank system is used. A pin  50  is rigidly connected to a first linkage member  54  at one end thereof. The pin  50  fits within a corresponding slot  92  within the actuating ring  48  in order to transmit any movement in the bell crank to the actuating ring  48 . The first linkage member  54  is rigidly connected at its other end to a rod member  56 . The rod  56  projects through a bore  57  in the flange member  24  to a point outside the turbocharger assembly. Bushing  58  is used in association with rod  56 . The rod  56  is rigidly connected at its other end to a second linkage member  60  which in turn is connected to an actuator  90 , shown in FIG. 1. The actuator shown is a vacuum boost type which is well known in the art. Furthermore, it is envisioned that other actuator means can be used to control the movement of the blades.  
         [0050]    During operation, movement of the second linkage member  60  is translated into movement of the first linkage member  54  via rod  56 . The existence of pin  50  will translate any movement of the linkage member  54  into rotational movement of actuating ring  48 . In turn, blade arms  46  roll against the side wall of slots  51  to pivot blades  34  while nozzle ring  38  remains stationary. Thus, there is a change in the geometry of the plurality of passageways formed between adjacent blades.  
         [0051]    An alternative embodiment of the invention is shown in FIGS. 5 and 6. FIG. 5 is a partial sectional view of the nozzle and actuating rings,  38  and  48 , respectively.  
         [0052]    In the alternative embodiment the nozzle ring  38  is attached to the turbine housing  18  and defines with it the annular passageway  30 . Specifically, the nozzle ring  38  is bolted directly to the turbine housing  18  by a ring of bolts  60 .  
         [0053]    The blades are mounted on the nozzle ring  38  by blade pins  36 , which can turn in bores in the nozzle ring and are attached at one end to the blades and at the other end to a blade arm  46 . Arm  46  is attached to blade pin  36  by any suitable method of attachment such that the nozzle ring  38  is located between the blade  34  and the blade arm  46 .  
         [0054]    [0054]FIG. 6 shows that actuating ring  48  is an annular ring with a plurality of slots  51  on its inner radial surface. Each slot receives the outer end of a blade arm  46 . Located at the internal periphery of the actuating ring  48  are at least three spaced rollers  49 . Rollers  49  are rotatably mounted on pins  55  spaced radially inwardly of the actuating ring and secured between the nozzle ring  38  and center housing  26 , each of which has bores for acceptance and location of the pins. Rollers  49  include an annular groove  59  therearound for acceptance and guidance of the inner periphery of the actuating ring. Rollers  49  and pins  55  ensure the concentricity between the actuating ring  48  and nozzle ring  38 .  
         [0055]    The alternative embodiment has eliminated several elements of the preferred embodiment, i.e. the flange member  24  and tube member  42 . Center housing  26  is different in that it includes a radially outwardly extending flange portion  27  having a bore  57  therethrough for acceptance of the actuation system. Furthermore, the flange portion  27  includes shoulder  35  shaped to mate with the turbine housing  18  and an annular land  47  above the central bore.  
         [0056]    As shown in FIG. 5, an annular disc  45  is positioned about the turbocharger shaft such that its radially inner edge rests against the land  47  and its radially outer edge rests against a shoulder  39  formed on the inner periphery of nozzle ring  38 . Disc  45  functions as a heat shield and seal to prevent heat and exhaust gas leakage around nozzle ring  38 .  
         [0057]    [0057]FIGS. 7 and 8 show the suspension mechanism according to the present invention in two different embodiments.  
         [0058]    Just as in FIG. 5, in which the same reference numbers designate the same parts as in FIGS. 7 and 8, the nozzle ring  138  carries on its outer edge and in circular arrangement a number of pins  55 ′ (in FIG. 7) and  55 ″ (in FIG. 8), at least however three thereof, distributed about the circumference of the nozzle ring, which pins carry rollers  49  with a groove  59 . The inner edge of the actuation ring  48  is received in these grooves  59  and is guided thereby.  
         [0059]    These pins  55 ′ are seated freely in bores  55   b  in the nozzle ring and the portion of the pin extending out of these bores has a length which corresponds essentially to the axial length of the rollers  49 , so that the free pin end practically aligns with the appropriate axial surface of the respective roller, without engaging in any other bores, for example in the housing.  
         [0060]    At least one end of the pin can be tapered or rounded.  
         [0061]    The two disadvantages of EP-0226444 are therewith overcome. On the one hand the assembly of the turbocharger is substantially simplified, since no pins independent of the rollers exist and since the axial extensions of the rollers need to be introduced respectively in only one bore, namely in the nozzle ring, without the necessity of having other ends having to be introduced into some other, more or less axially oriented bore in the housing, and on the other hand, since the rollers are not in a non-defined manner disoriented by the different thermal expansion of the housing and the nozzle ring, which in the state of the art disturbs the axial orientation of the pins and rollers, since the pins engage in only one bore, the geometry of the actuating ring, the nozzle ring and the guide rollers remains established independent of the temperature oscillations.  
         [0062]    An alternative manner FIG. 8 shows an embodiment in which the pins  55 ″ likewise engage in only respectively one bore  55   a , which bore is however provided in the housing  26 , without the other end of the pin engaging in the nozzle ring.  
         [0063]    In this manner the same advantages are achieved as with the embodiment according to FIG. 7 with respect to the simplified assembly since the pins and rollers as well as the actuating ring and the nozzle ring can first be assembled with the housing part  26 , before the housing part is matted to the turbine housing  18 . Here also it is avoided, that the free ends of the pins need be inserted in more or less aligned bores.  
         [0064]    The described effect of the temperature oscillations is likewise unimpaired since there is no longer any necessity to maintain alignment of orientation of boreholes in two different thermally cycling parts.  
         [0065]    [0065]FIGS. 9 and 10 show the inventive turbocharger and in particular a suspension mechanism for the actuating ring according to a first embodiment of EP-0226444, wherein the same reference numbers designate the same parts as in FIG. 3.  
         [0066]    The length of the pins is such that the pin segment extending from the bore exhibits the same length as the axial length of the roller  49 , so that the free end of the pin practically aligns with the appropriate axial surface of the roller.  
         [0067]    Numerous modifications of the described embodiments of the invention would occur to the person of ordinary skill. The present description should thus be considered as exemplary and in no way should be considered to limit the scope of protection of the present invention. This scope of protection should be determined only by the definition of the invention in the following claims, together with their equivalents.  
         [0068]    Thus, for example, the housing part in which the bores  55   a  are incorporated in the second embodiment of the invention, could be a part independent of the turbine housing and thus a construction component to be mounted to the turbine housing, or could together with the turbine housing form a unitary part.