Abstract:
A turbocharger actuator and method of calibrating for a variable nozzle turbocharger. Included are an actuator housing having a diaphragm connected across it, a piston, and a compression spring arranged to be generally centered in the actuator housing biasing the piston. Three rivets connect the actuator housing to a bracket. The diaphragm is crimped to connect to the actuator housing, which is coated with an elastomeric bead. The bracket includes three plate sections, the first having a plurality of rivet holes, and second two each having an elongated hole to receive an attachment bolt and allow sliding movement of the actuator assembly relative to the turbocharger housing.

Description:
The present invention relates to a turbocharger actuator and a method of calibrating the actuator. It is particularly applicable to a variable nozzle turbocharger (VNT). 
   BACKGROUND OF THE INVENTION 
   Turbochargers are used extensively in modem diesel engines to improve fuel economy and minimize noxious emissions. Traditionally a turbocharger comprises a turbine wheel in a chamber within a turbine housing, a compressor wheel and housing, and a central cast bearing housing for journaling a shaft which connects the compressor and turbine wheels. The turbine wheel rotates when driven by exhaust gasses from an internal combustion engine and causes the compressor wheel to rotate and compress air for delivery to the engine at a rate that is greater than the rate the engine can naturally aspirate. The turbocharger pressure output is a function of component efficiencies, mass flow through the turbine and compressor and the pressure drop across the turbine. 
   A VNT typically comprises a substantially cylindrical piston received within the turbine housing concentrically aligned with the rotational axis of the turbine. The piston is longitudinally movable to set the area of the inlet nozzle to the turbine from the volute so as to modulate the performance of the turbocharger for different operating conditions. The piston is moved by an actuator which is usually pneumatically operated and which is attached to the turbine housing by a bracket. It is necessary to calibrate the actuator when it is fitted. 
   Traditionally a VNT is calibrated using two fixed end points with a manually adjustable connecting rod and end. The rod and end is held in place by a locknut and the actuator assembly is held by two bolts and nuts. Conventional parts of a VNT are difficult to fit and adjust in confined spaces, and the manual calibration process reduces assembly line productivity, increases costs and tends to be relatively unreliable. 
   There is a need for a more robust actuator design and calibration process to enable automatic calibration and compact turbocharger installations, as well as to increase assembly line productivity and reduce the cost of an actuator. It is also desirable to make the calibration process more reliable and reduce the warranty returns, for example for loss of calibration. 
   BRIEF SUMMARY OF THE INVENTION 
   According to one aspect of the present invention there is provided an actuator for a variable nozzle turbocharger, comprising: an actuator housing; a piston; a diaphragm, connected across the actuator housing; at least one compression spring arranged to be generally centred in the actuator housing and to bias the piston; a spaded rod, connected to the piston, for calibrating a turbocharger, and a bracket comprising a first planar portion for fixedly connecting to the actuator assembly, and at least one second portion extending generally perpendicular to the first portion and having an elongate hole formed therein to receive means for attaching the bracket to the turbocharger housing, the elongate hole allowing a sliding movement of the actuator assembly relative to the turbocharger housing. 
   Preferably the actuator housing is connected to the bracket using at least one, and preferably three, rivets. The diaphragm may be crimped to connect it to the actuator housing and it may be coated with elastomer bead to improve and control the crimping process. 
   Advantageously the shape of the piston in the actuator is modified to reduce the overall length of the actuator. 
   According to a preferred embodiment the bracket comprises a third portion extending perpendicular to the first portion and being generally parallel to the second portion and the third portion having an elongate hole formed therein to receive a bolt to attach the bracket to the turbocharger housing, the elongate hole allowing a sliding movement of the actuator assembly relative to the turbocharger housing. 
   Preferably the elongate holes allow around 4 mm of sliding movement (+/−2 mm). 
   According to a second aspect of the present invention there is provided a method of calibrating a variable nozzle turbocharger comprising the steps of:
         a) using an actuator assembly which has a spaded rod;   b) using at least one bolt to attach the actuator assembly to an end housing (of either a compressor or a turbine) which has a pin crank so that the spaded rod is adjacent to the pin crank;   c) applying a predetermined vacuum to the actuator, through an actuator port to allow the actuator to take a calibrated position determined by gravity;   d) keeping the pin crank in contact with the flow screw of the turbocharger;   e) tightening the or each bolt, at a predetermined torque, to tighten the attachment of the actuator assembly to the end housing;   f) controlling the actuator calibration in accordance with predetermined process instructions;   g) determining whether the calibration process is correct and if it is not correct then repeating the process from step c) using a different predetermined vacuum value.       

   According to a preferred embodiment of the second aspect of the invention the method is conducted using the actuator assembly of the first aspect. 
   The compact design of the new actuator and the novel calibration procedure enable application of a VNT in confined spaces where conventional parts would be difficult or impossible to fit and adjust. In addition, automation of the calibration process is enabled, providing increased production line capacity. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made to the accompanying drawings, in which: 
       FIG. 1  is a cross-section of an actuator for a variable nozzle turbocharger according to one embodiment of the invention; 
       FIG. 1A  is a cross section of an actuator for a variable nozzle turbocharger showing a design according to the prior art; 
       FIG. 2  is a perspective view of part of the known actuator of  FIG. 1A . 
       FIG. 3  is a perspective view of part of the actuator of  FIG. 1 , according to one embodiment of the invention; 
       FIG. 4  is a side view of a known bracket for fixing the known actuator of  FIG. 2  to a variable nozzle turbocharger; 
       FIG. 5  is a perspective view of one embodiment of a new bracket for fixing the new actuator of  FIG. 3  to a variable nozzle turbocharger. 
       FIG. 6  is a side elevation view of the known actuator of  FIG. 2  attached by the known bracket of  FIG. 4  to a variable nozzle turbocharger. 
       FIG. 7  is a side elevation view of the new actuator of  FIG. 3  attached by the new bracket of  FIG. 5  to a variable nozzle turbocharger. 
       FIG. 8  is a cross-sectional view of the new actuator of  FIG. 3  illustrating the new calibration method. 
       FIG. 9  is a perspective view of the new actuator and another embodiment of a new bracket. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1A  the known actuator assembly comprises a diaphragm  1 A crimped at  2 A into the side wall of an actuator assembly  3 A. A spring  4 A holds the diaphragm  1 A taut and controls the position of actuator piston  8 A. Two sets of bolts and nuts, of which one is shown at  9 A, are used to hold the bottom wall of the actuator assembly  3 A to a bracket assembly  18 A which in turn will be connected to a turbine housing (not shown). A calibration rod  5 A extends through a gimball  11 A and is held in place by a locknut  6 A and is fixed at one end to the actuator piston  8 A. A heat shield  12 A protects the actuator. A stud  13 A passes through the bottom wall of the actuator assembly  3 A and a double plate  17 A. 
   The rod  5 A has an adjustable rod end  15 A and a bolt hole  21 A for fixing to either the compressor or the turbine housing of the turbocharger. 
   By contrast, in  FIG. 1 , a modified actuator assembly is shown according to the invention. The two bolts and nuts  9 A are replaced by three rivets, of which two are shown at  7 , and the actuator assembly  3  combines the functions of actuator assembly and bracket assembly. The rod end  5 A and the locknut  6 A are replaced by a rod  5  with spaded (flattened) end portion  15  shown in profile in  FIG. 1 . This new shape for the rod end assists the calibration process as will be described later. A spaded rod is a design known for use in wastegated turbochargers but has not hitherto been used in variable nozzle technology because the calibration process is not the same. Specifically the spaded rod  5  has a flat portion at one end formed by cold forging with a hole to be connected to the pin crank of the turbocharger. A compression spring  4 , in the inventive modification, is centered in the actuator assembly  3  and this reduces the hysteresis, ie the inaccuracies, particularly in calibration, due to the imperfections in the spring  4  itself. The diaphragm  1  is crimped into the side wall  3  of the actuator assembly at 2 and this is improved in the invention by a crimping control achieved by the addition of elastomer bead  46  on the diaphragm  1 . Elastomer bead can accept more variation in compression during the crimping process used to close the actuator than a flat shape which is traditionally used by the applicant, or a metal to metal contact as traditionally used by other people in the field. 
   The elastomer bead  46  also improves the seal capability. The convolution of the diaphragm  1  has a reduced width to reduce the diaphragm stress and the overall diameter of the actuator. 
   In addition, the piston  8  has a shape modification which reduces the overall length of the actuator assembly, as can be seen by comparing  FIG. 1  with  FIG. 1A . The new bracket is shown at  18  and the gimble is shown unchanged at  11 . 
   The piston  8  must withstand 1.7 NM torque, with respect to the rod end  5 , without relative motion. The engineering requirements are 0.15 SCCM max under 1.5 bars and a pull test of 100 Kg. 
     FIG. 2  is a perspective view from below of a traditional design of a turbocharger actuator assembly, ie a view from below of the assembly in the left hand side of  FIG. 1 . The heat shield  12 A is shown part cut-away and the side wall of the actuator assembly  3 A is attached to the bracket assembly  18 A by two nuts  9 A. The rod end  15 A is held in place by a locknut  6 A and is adjustable. Thus, traditionally, calibration is effected by two fixed end points with a manually adjustable connecting rod and end. 
   By contrast, the inventive actuator assembly of  FIG. 3  has a side wall of actuator  3  held to the bracket assembly  18  by the three rivets  7  and no locknut is needed because the rod  5  is spaded at the end  15  and of fixed length. Thus, the actuator end-point is allowed to move, and the rod and the second end point are fixed. When a calibrated vacuum is applied to the actuator, the actuator body is moved towards the fixed end point until forces are equalized. The actuator  3  is then in the calibrated position and is fixed to the compressor or the turbine housing by accessible bolts and bracket. 
   The traditional shape of the bracket  18 A is shown in detail in the plan drawing of  FIG. 4  which also shows the positions of two bolts  10 A which hold the bracket  18 A to a traditional turbocharger body. Such an arrangement is shown in the side view of  FIG. 6  where a traditional turbocharger  20  is attached to a traditional actuator  30 A by the traditional bracket  18 A which is attached to the actuator by two bolts and nuts  19 A. The traditional adjustable rod end  15 A is shown. 
   In  FIG. 5  the shape of the new bracket  18  is shown with a generally triangular plate section  31  having three rivet holes  32 , and two bent sections  33  and  34  having elongate bolt holes  35  and  36  respectively. A central hole  37  accommodates the fixed length new shaped rod  5  with end  15 . As shown in the side view of  FIG. 7 , the new bracket  18  is used to connect the new actuator body  30  to a turbocharger  20 . The plate section  31  is riveted to the actuator housing by three rivets  7  and the bent portions  33  and  34  are connected to the turbocharger  20  either to the turbine housing or the compressor housing by two bolts  38  through the slot shaped holes  35  and  36 . The elongate shape of the holes  35 ,  36  allows adjustment during calibration and obviates the need for the rod end  15  on the actuator  30  to be adjustable. 
     FIG. 6  shows a traditional actuator assembly  30 A, such as that shown in  FIG. 2  and of  FIG. 1A , attached to a turbine housing  20  by means of the bracket of  FIG. 4  by means of bolts and nuts  19 A. The rod end  15 A is shown. 
     FIG. 7  shows a new actuator assembly  30 , such as that shown in  FIG. 3  and  FIG. 1 , attached to a turbine housing  20  by means of the bracket of  FIG. 5 . The attachment is by rivets  7  through the first portion of the bracket  31  and bolts  38  through at least the second portion of the bracket allowing a sliding movement of the actuator  30  relative to the turbine housing  20  as shown by the arrow  39 . 
     FIG. 8  illustrates the new calibration method and comprises a cross sectional view of the inventive actuator. 
   The new calibration process comprises attaching the actuator  30  and bracket assembly  18  onto the turbocharger  20  in a vertical position with the actuator head down and the spaded rod  5  adjacent to the pin crank  40 . Vacuum is applied to the actuator port  42 . The actuator will naturally take its calibrated position under the influence of gravity. The pin crank  40  is put in contact with the VNT flow screw  45  as shown by the arrow  41 . The attachment bolts  38  ( FIG. 7 ) are then tightened at the required torque and the actuator calibration is controlled according to normal process instructions. If the actuator calibration is not correct, then the bolts  38  are unscrewed and the process is repeated from step  2  with a modified vacuum value. 
     FIG. 9  shows the new actuator  3  assembled to the bracket  18  and shows the rod  5  and spaded rod end  15  together with the rivet holes  32  and the slot holes  35 ,  36  in the bent portions  33 ,  34  respectively. The slot-type holes  35 ,  36  accept a sliding movement. The heat shield  12  is also shown.