Abstract:
A wastegate valve for a turbocharger system in an engine of a work machine, vehicle or the like particularly suitable for operation at changing altitudes. The wastegate valve includes a spring operating against an adjustable spring seat. The adjustable spring seat is adjusted in response to ambient pressure changes to alter the installed length of the spring.

Description:
TECHNICAL FIELD 
     The present invention relates generally to turbocharged internal combustion engines, and, more specifically, to turbocharger systems having a wastegate control valve for controlling exhaust flow to a turbocharger. 
     BACKGROUND 
     A limiting factor in the performance of an internal combustion engine is the amount of combustion air that can be delivered to the intake manifold for combustion in the engine cylinders. Atmospheric pressure is often inadequate to supply the required amount of air for efficient operation of an engine. 
     It is known to use turbochargers in the intake air supply of internal combustion engines to increase the combustion air supplied to the combustion cylinders. Each turbocharger typically includes a turbine having a turbine wheel driven by exhaust gases from the engine, and one or more compressors having compressor wheels driven by the turbine through a common turbocharger shaft carrying both the turbine wheel and the compressor wheel. The compressor receives the fluid to be compressed, and supplies the compressed fluid to the combustion chambers. The fluid compressed by the compressor may be in the form of combustion air only, or may be a mixture of fuel and combustion air. Through the use of a turbocharger, the power available from an engine of given size can be increased significantly. Thus, a smaller, less expensive engine may be used for a given power requirement, and power loss due to, for example, changes in altitude, can be compensated for. 
     Under some conditions, a turbocharger can provide combustion air at too great of pressure for the intake manifold or combustion cylinders, leading to possible engine damage. Overspeed operation of a turbocharger can lead to damage to the turbocharger as well. It is known to use a wastegate control valve in the exhaust flow stream to the turbocharger. A branch line of the exhaust system bypasses the turbine wheel of the turbocharger. Operation of the wastegate valve can direct exhaust flow through the bypass line, thereby reducing the exhaust gas flow to the turbine wheel, reducing turbine wheel speed and thereby the boost or pressure of air supplied by the turbocharger compressor. 
     It is known to use both mechanical and electrical control systems for wastegate valve operation. U.S. Pat. No. 6,012,289 entitled “Apparatus and Method for Utilizing a Learned Wastegate Control Signal for Controlling Turbocharger Operation”, assigned to the assignee of the present invention, discloses a method for controlling an engine turbocharger having a wastegate control valve. The turbocharger is controlled by an electronic controller, which is capable of delivering a wastegate control signal to the wastegate control valve. 
     Turbocharged internal combustion engines having wastegate control valves can experience additional difficulties in operation at high altitude, due to the reduced atmospheric pressure. The reduced atmospheric pressure can result in unfavorable pressure differences across the wastegate diaphragm. The wastegate may not be able to open under the given control system, or may open less than required, causing higher than acceptable turbine inlet pressures. Machines operated at both high and low altitude locations are not easily outfitted with control strategies that will take into consideration the effects of changing altitudes on the wastegate control valve operation. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In one form thereof, the present invention provides an internal combustion engine with a combustion cylinder; an exhaust system in flow communication with the combustion cylinder, to receive exhaust gases from the combustion cylinder; a combustion air system connected in flow communication to the combustion cylinder, to supply air to the combustion cylinder for supporting combustion; and a turbocharger. The turbocharger includes a compressor having an inlet and an outlet, a turbine having an inlet connected to receive a flow of exhaust gases from the combustion cylinder, and a wastegate valve for controlling the flow of exhaust gases to the turbine. The wastegate valve includes a valve housing, and a valve diaphragm in the valve housing separating the valve housing into first and second valve compartments having a first valve compartment pressure and a second valve compartment pressure. One of the first and second valve compartment pressures is ambient pressure. A valve rod is connected to the valve diaphragm. A spring is operatively connected to exert a spring force against the valve rod, the spring having an installed spring length. An adjustable spring seat is adjustable in height, for varying the installed spring length of the spring in response to changes in the ambient pressure. 
     In another form thereof, the present invention provides a wastegate with a valve housing, a valve diaphragm in the valve housing separating the valve housing into first and second valve compartments having a first valve compartment pressure and a second valve compartment pressure. One of the first valve compartment pressure and the second valve compartment pressure is ambient pressure. A valve rod is connected to the valve diaphragm. A spring is operatively connected to exert a spring force against the valve rod, the spring having an installed spring length. An adjustable spring seat is adjustable in height, for varying the installed spring length of the spring in response to changes in the ambient pressure. 
     In yet another form thereof, the present invention provides a method for controlling operation of a wastegate valve, the method comprising steps of: providing a wastegate valve having a valve housing, a valve diaphragm separating the valve housing into first and second valve compartments, a valve rod connected to the valve diaphragm and extending through one of the compartments, and a spring operatively connected to exert a spring force against the valve rod, for urging the rod in a direction, the spring having an installed spring length; providing an adjustable spring seat for altering the spring force applied against the rod; detecting ambient pressure changes; and adjusting the spring seat in response to changes in ambient pressure. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     FIG. 1 is a partial cross-sectional view of an internal combustion engine having an altitude compensated wastegate for a turbocharger according to the present invention; 
     FIG. 2 is an enlarged cross-sectional view of the adjustable wastegate shown in FIG. 1; 
     FIG. 3 is an enlarged cross-sectional view of an actuator for the adjustable wastegate; and 
     FIG. 4 is a plan view of an alternative embodiment of an adjustable spring seat for the wastegate. 
    
    
     DETAILED DESCRIPTION 
     Referring now more specifically to the drawings, and to FIG. 1 in particular, there is shown a wastegate control valve  10  in accordance with the present invention. Wastegate control valve  10  operates in a turbocharger system  12  of an internal combustion engine  14 . 
     Engine  14  is of known design, and includes a plurality of combustion cylinders  16 , one combustion cylinder  16  being shown in FIG. 1. A piston  18  is operatively disposed in each combustion cylinder  16 , and is connected by a piston rod  20  to a crankshaft  22 . At least one intake valve  24  and at least one exhaust valve  26  are provided in each combustion cylinder  16 . Intake valve  24  controls flow communication between a combustion air system  28  and combustion cylinder  16 , and exhaust valve  26  controls flow communication between an exhaust system  30  and combustion cylinder  16 . As those skilled in the art will understand readily, engine  10  can be one of spark ignition operating design, compression ignition, or other common or less common design. The particular design for engine  10  shown and described herein is merely one suitable configuration. 
     Turbocharger system  12  includes a compressor  32  having a compressor inlet  34  in flow communication with a source of combustion air, such as ambient air, received through an air cleaner  36 . A compressor outlet  38  is connected in flow communication to an inlet air duct  40  of combustion air system  28 , which may further include an aftercooler  42 . A compressor wheel  44  is operatively disposed, in known manner, between compressor inlet  34  and compressor outlet  38 . Compressor wheel  44  is carried on a turbocharger shaft  46 . 
     Turbocharger system  12  further includes a turbine  52  having a turbine inlet  54  in flow communication with exhaust system  30  via an exhaust duct  56 . A turbine outlet  58  is connected inflow communication to an exhaust line  60  of exhaust system  30 , which may further include an exhaust muffler  62 . A turbine wheel  64  is operatively disposed, in known manner, between turbine inlet  54  and turbine outlet  58 . Turbine wheel  64  is carried on turbocharger shaft  46 , at an opposite end thereof from compressor wheel  44 . 
     Wastegate control valve  10  is provided in a bypass line  70  connected in flow communication between exhaust duct  56  and exhaust line  60 . Bypass line  70  provides a parallel path to that through turbine  52 , and wastegate control valve  10  controls the flow of an exhaust gas stream reaching turbine wheel  64  by controllably opening and closing the path through bypass line  70 . 
     As can be more clearly seen in FIG. 2, wastegate control valve  10  includes a valve housing  72  and a valve diaphragm  74  disposed in valve housing  72 . Valve diaphragm  74  separates the interior of valve housing  72  into separate first and second valve compartments  76  and  78 , respectively. First and second valve compartments  76  and  78  are isolated from each other, to separately contain first and second valve compartment pressures. Valve diaphragm  74  is a rubberized or other flexible body, the position of which can vary as the relative pressure differential changes between first and second valve compartment pressures in first and second valve compartments  76  and  78 . 
     A valve rod  80  has a first end  82  connected to valve diaphragm  74 , and a second end  84  (FIG. 1) having a valve head  86  operating in a valve opening  88  of bypass line  70 . Valve rod  80  moves in response to movement of valve diaphragm  74 , to open and close opening  88 . A spring  90  is operatively connected to exert a spring force against valve rod  80 , biasing valve rod  80  in a direction. In the embodiment illustrated in FIG. 2, spring  90  is disposed in first valve compartment  76 , and first valve compartment  76  is connected openly to the ambient environment so as to remain at ambient pressure. Spring  90  operates between an fixed spring seat  92  on valve diaphragm  74 , and an adjustable spring seat  94  in first valve compartment  76 . Adjustable spring seat  94  is controllable to reposition a plate  96 , to alter the installed height of spring  90 , in response to changes in the ambient pressure. 
     In a first embodiment of adjustable spring seat  94 , a cam means includes first and second angular blocks  98  and  100 , respectively. Angular blocks  98  and  100  are reverse positioned, wedge-shaped ramps disposed one on top of the other. Relative movement between blocks  98  and  100  brings thicker or thinner portions of each in superimposed engagement, thereby making the overall thickness of adjustable spring seat  94  thicker or thinner, as desired. To accomplish the relative movement therebetween, at least one of the blocks  98  and  100  is linearly translatable relative to the other block  98  or  100 . In the embodiment shown, linear translation of block  98  is achieved through movement by a control rod  102 . Block  100  is secured to plate  96 . 
     An alternative embodiment of adjustable spring seat  94  is shown in FIG. 4, wherein a cam means includes a disk  110  rotatably secured around a pivot connection  112 . A peripheral portion  114  of disk  110  has a ramp  116 . Control rod  102  is tangentially connected to disk  110  by a pin  118 , such that substantially axial movement of control rod  102  cause rotation of disk  110  about pivot connection  112 . 
     Axial movement of control rod  102  is achieved through an actuator  130  that may be passive or active in design. Active actuators  130  can be electric, hydraulic or pneumatic prime movers controlled by the engine ECM (not shown) in response to the receipt of operating and performance data of engine  14  and/or turbocharger  12 . As illustrated in FIG. 4, a pneumatic actuator  132  includes a return spring  134  operating against a piston  136  in a pressurizable chamber  138 . 
     A suitable passive actuator  130  is shown in FIG. 3, in the form of an actuator pot  140  that moves control rod  102  automatically in response to ambient pressure changes. Actuator pot  140  includes an actuator housing  142  and an actuator diaphragm  144  disposed in actuator housing  142 . Actuator diaphragm  144  separates the interior of actuator housing  142  into separate first and second actuator compartments  146  and  148 , respectively. First and second actuator compartments  146  and  148  are isolated from each other, to separately contain first and second actuator compartment pressures. Actuator diaphragm  144  is a rubberized or other flexible body, the position of which can vary as the relative pressure differential changes between first and second actuator compartment pressures in first and second actuator compartments  146  and  148 . 
     Control rod  102  extends through first actuator compartment  146 , which is open to the ambient environment, and thereby maintained at ambient pressure. Second actuator compartment  148  is maintained at a controlled pressure, so that changes in ambient pressure in first actuator compartment  146  cause a movement of actuator diaphragm  144 , and corresponding movement of control rod  102 . 
     The controlled pressure in second actuator compartment  148  can be achieved in several ways. For example, second actuator compartment  148  can be a sealed compartment, provided with a desired controlled pressure at the time of manufacture and assembly. As another example, second actuator compartment  148  can be connected to a regulated pressure source, with an appropriate pressure regulator valve (not shown) controlling the pressure supplied to second actuator compartment  148 . Adjustment also can be achieved in a variety of structural variations, such as a pivotable frame structure (not shown) holding diaphragm  144 , to vary the position of diaphragm  144 . A return spring  134  also may be incorporated with the various modifications discussed herein. 
     INDUSTRIAL APPLICABILITY 
     During operation of engine  14 , fuel and air are combusted in known manner in combustion cylinder  16 . Exhaust gases from the combustion process flow from cylinder  16 , through exhaust duct  56  to turbine  52  of turbocharger system  12 . Exhaust gas flow along turbine wheel  64  from turbine inlet  54  to turbine outlet  58  causes rotation of turbine wheel  64  and turbine shaft  46  connected thereto. Turbine shaft  46  rotates compressor wheel  44 . Air drawn in to compressor inlet  34  from air cleaner  36  is compressed and supplied to inlet air duct  40  and combustion cylinder  16 . 
     Under some operating conditions, it is desirable to reduce the flow of exhaust gas to turbine  52 , slowing rotation turbocharger shaft  46  and lowering the boost obtained from compressor  32 . This can be achieved by operating wastegate  10  to open valve opening  88 , allowing exhaust gas flow through bypass line  70 , directly from exhaust duct  56  to exhaust line  60 . 
     As the ambient pressure changes, due, for example, to changes in altitude, the pressure in first actuator compartment  146  of actuator pot  140  also changes. Since the pressure in second actuator compartment  148  is fixed, any change in pressure in first actuator compartment  146  causes movement of actuator diaphragm  144 , and corresponding axial movement of control rod  102 . As control rod  102  moves axially, adjustable spring seat  102  is caused to become thicker or thinner, through linear movement of block  98  in the embodiment illustrated in FIG. 2, or through rotation of disk  110  in the embodiment illustrated in FIG.  4 . 
     The present invention for a wastegate valve compensates for changes in operation of the valve resulting from ambient pressure changes. The installed spring length of the wastegate spring is adjusted through adjustment of an adjustable spring seat provided in the wastegate valve. An actuator is provided for adjusting the adjustable spring seat automatically, as the ambient pressure changes. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.