Abstract:
Engines having turbochargers with a mechanically actuated wastegate typically control the wastegate in response to the air pressure at an outlet of a compressor portion of the turbocharger. Some engine configurations don&#39;t provide enough compressor outlet pressure variation to suitably control the wastegate. In the present invention, a control strategy is provided for opening and closing a wastegate based on exhaust gas pressure.

Description:
TECHNICAL FIELD 
     The present invention relates generally to an internal combustion engine having an exhaust driven turbocharger and more particularly to control a wastegate in response to pressure in an exhaust system. 
     BACKGROUND 
     Due to desired performance characteristics of internal combustion engines, exhaust gas driven turbochargers must be regulated to achieve desired charge-air pressures over a wide range of engine speeds. Charge air pressure is related to turbocharger speed and turbocharger speed is related to the flow of an exhaust gas stream through a turbine portion of the turbocharger. Many exhaust driven turbochargers include a wastegate that permits a portion of the exhaust gas stream of the engine to bypass the turbine portion. 
     Typical exhaust driven turbochargers have a pressure responsive canister control module that is operably connected to the wastegate. The canister control module includes a movable diaphragm (or piston) having a linkage and a spring or biasing member. The piston is exposed to atmospheric pressure and the spring on one side and a charge air pressure on the other side. As the charge air pressure increases beyond a predetermined value, the piston and linkage are moved toward the biasing member, causing the wastegate to open, in turn slowing the turbocharger. 
     However, some internal combustion engines, such as those used in some large work machines, are configured to operate in a manner that may prevent this type of control strategy from working well. One such example is, an internal combustion engine configured to have a high torque rise in relation to engine speed. In other words, the engine is configured so that as the engine speed is decreased, the output torque of the engine is increased at a faster than normal rate. To help increase the torque at a faster rate, the turbocharger is configured to provide higher charge air pressure at lower engine speed. 
     One disadvantage with this type of engine configuration is that the charge air pressure does not vary much over the normal operating range of engine speed. Due to the lack of charge air pressure variation, wastegate control strategies based on charge air pressure may not provide enough control of the turbocharger. This may cause the turbocharger to operate at extremely high speeds, resulting in damage or reduced turbocharger life. 
     One example of a control system that does not use charge air to control the wastegate is U.S. Pat. No. 5,205,125 issued to General Motors Corporation on Apr. 27, 1993. In this system the wastegate is controlled by the pressure of the exhaust pushing the wastegate open. Additionally, the wastegate assembly includes an adjustable biasing mechanism to control how much pressure is required to open the wastegate. 
     One possible problem related to using exhaust pressure to control the wastegate is that exhaust pressure fluctuates greatly as each exhaust valve opens. Also, the temperature of exhaust gas is much higher than that of charge air exiting the compressor portion. Existing canister control modules may not operate with the extreme temperatures of exhaust gas. Particulates in the exhaust gas may build up in a control mechanism and reduce dependability of the control system. 
     This invention is directed to overcoming one or more of the above identified problems. 
     SUMMARY OF THE INVENTION 
     In an aspect of the present invention, a mechanism is provided for controlling the wastegate of a turbocharger. The mechanism includes a canister control module, a conduit having a first end in fluid communication with an exhaust system and a second end in fluid communication with the canister control module. An actuator is positioned in the canister control module and is responsive to pressure from the exhaust system. The actuator being adapted to move the wastegate between a first and a second position, the first position allowing fluid communication between the exhaust system and a turbine portion of the turbocharger and the second position allowing partial bypassing of the turbine portion. 
     In another aspect of the present invention, a method for controlling a wastegate of a turbocharger is provided. The method includes directing a portion of exhaust gas from an exhaust system to an actuator, exerting a force with the portion of exhaust on the actuator and moving the wastegate to the open position when exhaust gas is above a predetermined pressure. 
     In yet another aspect of the present invention, is an internal combustion engine having a control mechanism for controlling the wastegate of a turbocharger. The control mechanism includes a canister control module having a pressure region, a conduit in fluid communication with the canister control module and an exhaust system, and an actuator positioned in said canister control module. The actuator is adapted to move the wastegate between a first and a second position, in the first position the wastegate allows fluid communication between an exhaust system and an inlet to a turbine in the turbocharger. In the second position the wastegate permits partial bypassing of the turbine portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of an internal combustion engine having a turbocharger in accordance with the present invention. 
     FIG. 2 is an illustration of a turbocharger and the interconnection of a canister control module of the present invention. 
     FIG. 3 is a sectional view of a canister control module and related pressure communication components as embodied in the present invention. 
    
    
     DETAILED DESCRIPTION 
     With reference to FIG. 1 an internal combustion engine  10  includes a conventional exhaust driven turbocharger  12  having a compressor portion  14  and a turbine portion  16 . The compressor portion  14  includes a compressor wheel (not shown) and the turbine portion  16  includes a turbine wheel (not shown). The compressor wheel and turbine wheel are rotatably coupled by a shaft  18 . The compressor portion  14  is fluidly coupled to an intake manifold  20  on the engine and the turbine portion  16  is fluidly coupled to an exhaust system  22  on the engine. The exhaust system  22  typically includes an exhaust manifold  23  and exhaust tube  24 . 
     With reference to FIG. 2 the turbocharger  12  includes a housing  25  surrounding the compressor portion  14  and a turbine portion  16 . The shaft  18  is disposed within the housing  25 . The compressor portion  14  further includes an air inlet  26  and an air outlet  28 . The air inlet  26  is open to the atmosphere, but an air filter system (not shown) may be provided near the air inlet  26 . The air outlet  28  is fluidly coupled to the intake manifold  20 . An aftercooler (not shown) may be provided at a location between the air outlet  28  and the intake manifold  20 . The turbine portion  16  further includes a turbine inlet  30 , a turbine outlet  32  and a conventional wastegate assembly  34 . Typically, the turbine inlet  30  is in fluid communication with the exhaust manifold  23 , and the turbine outlet  32  is coupled to the exhaust tube  24 . 
     The wastegate assembly  34  is pivotally mounted within the housing  25  on a pin  36  and is moveable between an first (open) position and a second (closed) position. The pin  36  extends outside of the housing  25  and a bell crank  38  is externally coupled to the pin  36 . The bell crank  38  includes a first bore  40  that engages the pin  36  and second bore  42  positioned at a predetermined distance from the first bore  40 . The bell crank  38  is movable between a first position  44  and a second position  46 . First position  44  relates to, wastegate assembly  34  closed, and second position  46  relates to wastegate assembly  34  open. 
     A canister control module  48  is mounted on the engine  10  or the turbocharger  12 . The canister control module  48  includes a body  50 , an actuator  49  or a piston  51 , a control linkage  52  attached to the piston  51 , and an inlet port  53 . The body  50  includes a cylindrical wall portion  54 , a first end  56  and a second end  58 . The first end  56  is closed and includes the inlet port  53 . The second end  58  is open to the atmosphere and may include a pair of mounting studs  60 . The mounting studs  60  are adapted to fasten to a common mounting bracket (not shown). It should be noted, that any conventional mounting arrangement may be substituted for the one described without departing from the scope of the present invention. The control linkage  52  extends through the second end  58  of the canister control  48  and is adapted on a first end  64  to pivotally engage the second bore  42  of the bell crank  38 . 
     With reference to FIG. 3, a sectional view of the canister control  48  is illustrated. The control linkage  52  has a second end  66  attached to the piston  51 . The piston  51  is disposed within the cylindrical wall portion  54  of the canister control  48 . The piston  51  is moveable between a first position  70  and a second position (not shown) near the second end  58  of the body  50 . A diaphragm  72  or seal is disposed between the piston  51  and the cylindrical wall portion  54  of the body  50 . The diaphragm  72  or seal isolates the first end  56  of the body  50  from the second end  58 . A spring  74 , or alternate biasing member, is positioned between the second end  58  of the body  50  and the piston  51 . The inlet port  53  of the canister control  48  is adapted to engage a hose  76  or tube in a conventional manner. 
     As shown in the previous figures, the inlet port  53  of the canister control  48  is fluidly coupled to a hose  76  or tube at a first end  78 . A second end  80  of the hose  76  is fluidly coupled to the exhaust system  22 . 
     Within the hose  76 , a replaceable porous filter  82  may be disposed. The porous filter  82  may be constructed of stainless steel, ceramic, or any other media capable of withstanding engine exhaust gases. Additionally, a dampening volume  84  and cooling apparatus  86  may be provided within the hose. The dampening volume  84  may be a cylindrical member  88  positioned between the first end  78  and second end  80  of the hose  76 . Alternately, the dampening volume  84  may consist of an enlarged diameter portion (not shown) of the hose  76 . The cooling apparatus  86  may be provided in a number of conventional manners. One example is through the use of a heat exchanger positioned in the hose, possibly in conjunction with the dampening volume  84 . The heat exchanger may be as simple as a tube connected to a supply of engine coolant at a first end and connected to a radiator return line at a second end. Alternately, the cooling apparatus may be provided by having an extended portion of the hose  76  or tube exposed to an air stream having a cool temperature relative to the exhaust. An orifice  90  is additionally positioned in line with the hose  76 , preferably located between the filter  82  and dampening volume  84 . 
     INDUSTRIAL APPLICABILITY 
     In operation, exhaust gas from the engine  10  is directed to the turbine portion  16 , additionally exhaust gas is directed to the canister control  48  by way of the hose  76  (or conduit). The exhaust gas enters the canister control  48  through the inlet port  53  and acts on the piston  51 . As the pressure of the exhaust gas increases sufficiently to overcome the combined force of the spring  74  and atmospheric pressure, the piston  51  moves toward the second end  58  of the canister control  48 . The control linkage  52  moves with the piston  51  and causes the bell crank  38  to rotate, which in turn opens the wastegate assembly  34 . Opening of the wastegate  34  allows a portion of the exhaust gas to bypass the turbine portion  16 , thus slowing the speed of the turbocharger  12 . 
     To compensate for fluctuations of exhaust gas pressure due to the opening of and closing of exhaust valves, an orifice  90  and dampening volume  84  may be included in the hose  76  between the exhaust system  22  and inlet port  53 . The orifice  90  acts to resist the fluctuations in exhaust gas pressure and the dampening volume  84  serves to absorb fluctuations. 
     The filter  82  is preferably positioned in the hose  76  nearest to the exhaust system  22  as reasonably possible, the filter  82  prevents particulate matter from entering and further restricting the orifice  90  or other components. 
     The cooling apparatus  86  functions to cool the exhaust gas temperature down stream of the cooling apparatus  86 . Reduced exhaust gas temperature may help prevent damage or wear to components such as the canister control  48  module.