Abstract:
A variable geometry turbocharger employs multiple vanes in the turbine inlet with a unison ring and integral cast wall in the turbine housing forming the nozzle walls. The unison ring incorporates actuation slots receiving tabs on the vanes for opening the closing the nozzle area upon rotation of the unison ring. An integral electrohydraulic actuator rotates the unison ring through a rack and pinion driven crank shaft with direct position feedback to the spring biased variable current solenoid via a cam on the crank shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of application Ser. No. 60/103.063 filed on Oct. 05, 1998 having the same title as the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of turbochargers having variable turbine inlet geometries. More particularly, the present invention provides a simplified structural arrangement for positioning multiple aerodynamic vanes in the inlet nozzle of the turbine housing and an integrated actuator for control of the vane position. 
     2. Description of the Related Art 
     In a turbocharger it is often desirable to control the flow of exhaust gas into the turbine to improve the efficiency or operational range. Various configurations of variable nozzles have been employed to control the exhaust gas flow. Multiple pivoting vanes annularly positioned around the turbine inlet and commonly controlled to alter the throat area of the passages between the vanes is an approach which has been successfully used in prior turbochargers. Various approaches to this method for implementing a variable nozzle are disclosed in U.S. Pat. No. 4,679,984 to Swihart et al. entitled “Actuation System for Variable Nozzle Turbine” and U.S. Pat. No. 4,804,316 to Fleury entitled “Suspension for the Pivoting Vane Actuation Mechanism of a Variable Nozzle Turbocharger” having a common assignee with the present application. 
     While multiple vane variable nozzle turbochargers have significantly increased the overall efficiency and capability of turbochargers, the complexity of support and actuation structures for the vanes have increased manufacturing costs and occasionally created maintenance issues. It is therefore desirable to reduce the complexity and parts count of variable nozzle structural arrangements and improve the actuation systems to increase reliability and reduce manufacturing cost for turbochargers employing them. 
     SUMMARY OF THE INVENTION 
     A variable geometry turbocharger employing the present invention includes a turbine housing having a standard inlet for exhaust gas and an outlet to the exhaust system of the engine. A volute is connected to the inlet and an integral outer nozzle wall is incorporated in the turbine housing casting adjacent the volute. A center housing is attached to the turbine housing . A center bore in the center housing carries a bearing assembly. A compressor housing having an air inlet and a compressed air outlet is attached to the center housing. 
     A turbine wheel is carried within the turbine housing and attached to a shaft extending through the center housing, supported by the bearing assembly. The shaft attached to a compressor impeller carried within the compressor housing. 
     A plurality of vanes having rotation posts extending from a first surface substantially parallel to the outer nozzle wall provide the variable nozzle. The posts are received in circumferentially spaced apertures in the outer nozzle wall. The vanes further have actuation tabs extending from the opposite surface of the vanes. A unison ring is engaged between the center housing and the vanes and has a plurality of profiled slots equal in number to the vanes. The slots are oriented obliquely to a circumference of the unison ring and receive the tabs. The profiled surfaces of the slots engage the substantially flat sides of the tabs on different surfaces during the translation to provide optimum control and wear reduction. 
     Actuation of the unison ring is accomplished by a radial slot and a crank shaft having a pin engaging the radial slot. The crank shaft is movable continuously from a first position to a second position, causing the pin to translate in the radial slot and impart force perpendicular to the radial slot to urge rotational motion of the unison ring. The rotational motion of the unison ring causes the tabs to traverse the actuation slots from a first end of the slots to a second end of the slots. The oblique orientation of the slots causes a continuously variable rotation of the vanes from a first open position to a second closed position. 
     An integral hydraulic actuator provides the actuation mechanism for the crank shaft. Mounted in a boss in the center housing, the actuator uses a piston and piston rod attached by a rack and pinion to the crank shaft for position control of the vanes. Hydraulic pressure to operate the piston is provided by a solenoid operated multiport valve with direct feedback through a cam mounted on the crank shaft adjacent the pinion gear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The details and features of the present invention will be more clearly understood with respect to the detailed description and drawings in which: 
     FIG. 1 is an exploded view of an embodiment of a turbocharger employing the present invention; 
     FIG. 2 is a side section elevation showing the turbine housing, center housing and compressor back plate with the turbine shaft wheel assembly and compressor impeller as supported by the bearing system; 
     FIG. 3 is an end section elevation through the center housing showing an embodiment of an integral actuation valve arrangement according to the invention; 
     FIG. 4 is a partial view of an alternate embodiment of the valve piston arrangement; 
     FIG. 5 a  is a view along line G—G of FIG.  3  and with FIGS. 5b-c provides section views of the crank shaft assembly extending from the actuation valve to the unison ring engaging the nozzle vanes; 
     FIGS. 6 a-e  are end views of the unison ring and nozzle vanes demonstrating the variable vane positions and the actuation structural arrangement; 
     FIG. 7 is a reverse end view of an alternative embodiment of the unison ring showing a blind relief design for pressure compensation; 
     FIG. 8 is a schematic side view of the unison ring of FIG.  7  and vanes as mounted in the turbine housing to demonstrate the pressure compensation for vane tolerance control; and 
     FIGS. 9 a-e  are schematic side views of the actuation valve porting and piston structure for control of the vane position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, the embodiment of the invention shown in FIG. 1 includes a compressor housing  10  which is connected to a backplate  12  using two or more clamps  14  secured by bolts  16 . The backplate is attached to a center housing  18  with multiple bolts  20  and a seal ring  22 . A turbine housing  24  is connected to the center housing using multiple clamps  26  secured by bolts  28 . A turbine wheel and shaft assembly  30  is carried within the turbine housing. Exhaust gas or other high energy gas supplying the turbocharger enters the turbine housing through inlet  32  and is distributed through the volume in the turbine housing for substantially radial entry into the turbine wheel through a circumferential nozzle entry  34 . 
     Multiple vanes  36  are mounted to a nozzle wall  38  machined into the turbine housing using posts  40  extending from the vanes for rotational engagement within holes  42  in the nozzle wall. Actuation tabs  44  extend from the vanes to be engaged by slots  46  in unison ring  48  which acts as the second nozzle wall. The configuration of the tabs, slots and unison ring will be explained in greater detail subsequently. An actuator crank  50  terminates at a first end in a lever arm  52  carrying a pin  54  to engage elliptical slot  56  in the unison ring for rotation of the ring as will be later explained. The crank extends into a boss  58  in the center housing casting through a bushing  60  and a gear  62  which is secured to the crank by a pin  64  and is received into an end bearing  66  which mates with aperture  68  in the crank boss. An O-ring  70  seals the end bearing and a snap ring  72  secures the end bearing into the aperture  68 . 
     A bearing system having two journal bearings  74  and a bearing spacer  76  support the shaft wheel assembly in the center housing center bore  78 . The shaft further extends through a thrust collar  80  which engages a thrust bearing  82  carried between the center housing and compressor back plate. A piston ring  84  seals the thrust collar with the shaft bore in the back plate. The stack up of the shaft wheel assembly within the turbine housing, center housing and back plate is best seen in FIG.  2 . The unison ring and vanes are not shown for clarity. The compressor impeller  86  is attached to the shaft wheel assembly. 
     Referring again to FIG. 1, the integrated actuator for the turbocharger is housed in an actuator boss  83  in the casting of the center housing  18 . A solenoid valve  85  is mounted in an aperture at one end of the boss while the actuating components are mounted in a second aperture at the opposite end of the boss. The actuating components include a piston  87  that incorporates a rod  88  having a rack gear  90  engaging the gear  62  mounted on the crank shaft  50 . A ring seal  92  surrounds the piston circumference sealing the piston in the bore of the actuator boss. Additional ring seals  94  and  96  seal the piston rod to a rod bore of smaller diameter than the piston bore. The piston bore is sealed with a piston end  98  held in the bore with a snap ring  100 . A bolt  102  is inserted into a threaded hole in the piston end for use in manipulating the piston end. An additional ring seal  104  seals the piston end to the bore. Alternatively, a freeze plug  106  is employed as a replacement for the piston end. The solenoid valve is secured to the boss with a bracket  108  held by a bolt  110 . Bore plugs  112  and  114  seal the blind ends of actuation passages in the actuator boss while steel balls  116  are employed to seal other actuation passages, described in greater detail subsequently. 
     FIG. 2 is a side sectional elevation of the turbocharger showing the assembled turbine housing, center housing and compressor back plate with the turbine shaft wheel assembly and compressor impeller supported by the bearing assembly. 
     FIG. 3 is an end sectional view through the actuator boss and assembled actuator components. FIG. 4 shows the alternative freeze plug arrangement for sealing the piston bore. 
     As best seen in FIG. 2, the center housing includes a main casting portion and a turbine housing back plate  120  for attachment of the center housing to the turbine housing using bolts, as previously described. FIG. 5 a  is a sectional view showing the crank shaft assembly with the gear  62  bushing  60  mounted in the main casting portion of the center housing with the crank shaft extending across the air gap between the main casting portion and the turbine housing back plate and into an aperture in the back plate. FIG. 5 b  shows the details of the crank shaft sealing arrangement in the back plate aperture. A first metallic ring seal  122  having a first diameter is employed to seal an inner diameter of the aperture  124 , while a second metallic ring seal  126  is employed in combination with the first seal to seal a second larger diameter  128  of the aperture. This arrangement allows continued sealing during uneven thermal expansion of the main casting portion and the back plate during operation. FIG. 5 b  demonstrates the configuration during operation, with the temperature of the back plate exceed the main portion, with resulting greater expansion while FIG. 5 c , shows the arrangement with nominal tolerance at a common temperature for the main casting portion and the back plate. 
     The nozzle vanes  36  in the turbine inlet nozzle are operated by the unison ring  48 . FIG. 6 a  shows the unison ring engaged by the end pin  54  of the crank shaft  50  in a radial slot  130 . Rotation of the crank shaft causes the offset end pin to traverse the radial slot resulting in rotation of the unison ring. The vanes, mounted for rotation on pins  40  which extend into receiving holes  42  in the nozzle wall of the turbine housing, have actuation tabs  44  which are received in the slots  46  in the unison ring. As the unison ring rotates. The motion of the slots causes the tabs to traverse from one end of the slot to the other resulting in rotation of the vanes from a first fully open position, through a neutral position, shown in FIG. 6 a , to a fully closed position. FIG. 6 b  shows in phantom the fully open, neutral and fully closed positions of the vanes with tab positioning in the slots. FIG. 6 c  is an enlarged view of the unison ring slot with the tab shown in multiple positions. The tab incorporates substantially flat sides  134  and  136  which provide extended engagement of the slot wall by the tab to reduce point wear on the tab. The profile of the slot, not purely oval, is predetermined to provide maximum engagement with the tab, while engaging first side  134  of the tab at the open and closed end points with maximum area and the second side  136  during the intermediate positioning of the vanes. 
     For the embodiment shown in the drawings, FIG. 6 d  shows the fully open and fully closed positions of the vanes. A 22 degree rotation of the vanes is provided. Table 1 shows the related leading edge, trailing edge and throat size in mm for the open, mid and closed positions of the vanes. 
     In certain applications, pressure balancing of the mounting of the vanes in the nozzle is desirable. FIG. 7 shows one embodiment of the unison ring  48  that incorporates blind slots  46  while providing a blind relief  138  on the reverse side of the ring with pressure ports  140  machined into the relief. FIG  8  is a detail side section of the relieved unison ring engagement the vanes in the nozzle. For the arrangement shown, pressure of the exhaust gas entering the nozzle pressurizes the relieved back portion  138  of the unison ring through gap  142  provided by tolerancing of the mounting channel  144  in the back plate  120 , through ports  140 . Alternatively, a feed hole  146  is provided through the back plate into the unison ring mounting channel proximate the location of the ports  144 . Total pressure of the exhaust gas urges the unison ring against the vanes, which are in turn urged against the nozzle surface  38  in the turbine housing. Holes  42  receiving the vane pins  40  are provided with sufficient depth to allow the vanes to be maintained in close contact with the nozzle surface and unison ring for minimum vane leakage. 
     Actuation of the vanes is initiated by the solenoid valve  84  and actuation components previously described. FIGS. 9 a  through  9   e  show the various states of the actuation piston  86  and its piston rod  88  driving gear  62  through rack  90 . The solenoid valve is reacted by a spring  150  having a cap  152  engaging a cam  154  machined into the gear body. Various ports, as will be described are then opened and closed, hydraulically positioning the piston which, through the mechanical closed loop of the rack and gear provides positive control an the position of the crank shaft and, therefore, the unison ring. 
     The solenoid valve is a proportional servo 4-way hydraulic actuator control valve. As shown in FIG. 9 a , if no current is applied to the solenoid, the channeled stem  160  is positioned so port A is open, port B (top of the piston) is connected to drain port D. When oil pressure is applied from the engine on which the turbocharger is mounted, oil pressure is directed from the source  155  through port A into the bottom of the piston through conduit  156 , placing the vanes in a fully open position. As shown in FIG. 9 b  when current is applied to the solenoid, port A is closed, port A (bottom of the piston) is connected to drain, port B opens and oil pressure is directed to the top of the piston through conduit  158 , moving the piston to the left starting to close the vanes. 
     FIG  9   c  shows the condition of the actuation systems with a balanced state low current in the solenoid. Port A is closed, port B is closed and the vanes are positioned as a function of the applied current. If the current is increased, FIG. 9 d  shows that port B is opened directing oil pressure to the top of the piston. Port A is connected to the drain and the piston moves to the left, moving the vanes in the closed direction. After some finite time, the system stabilizes in a balanced state with high current as shown in FIG. 9 e  with port A closed, port B closed and the vanes positioned as a function of the applied current. Full current applied to the solenoid results in port B being closed, oil pressure being directed to the top of the piston while port A is connect to the drain and the piston moves to the left until a full closed vane position is achieved. Removing current from the solenoid returns the actuation system to the state shown in FIG. 9 a  with the vanes fully open. 
     Having now fully described the invention as required by the patent statutes, those skilled in the art will be able to ascertain modifications and alterations to the specific embodiments disclosed herein. Such modifications and alterations are within the scope of the invention as defined in the following claims.