Abstract:
The present invention provides a two-stage turbocharger unit having a valve that will help to create a smooth transition of exhaust gas energy from the high-pressure turbine (HP) turbine to the low-pressure (LP) turbine. The LP and HP turbines are positioned such that the valve can be in one position to force all of the exhaust gas to flow through the HP turbine and when in another position to force all of the exhaust gas through the LP turbine. When the valve is placed in an intermediate position, the exhaust gas can be variably directed to flow through both turbines, with the percentage of exhaust gas flowing through each turbine being dependent on the position of the valve.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the use of control valves in a two-stage turbocharger, more specifically, the regulation of controlling the transition from a high-pressure turbine to a low-pressure turbine. 
   BACKGROUND OF THE INVENTION 
   Two-stage turbochargers are commonly known and are used in all kinds of engines. They consist of a high-pressure (HP) turbine, and a low-pressure (LP) turbine, with each turbine having its own compressor. During normal operating conditions, when the engine runs at lower speeds, the only turbine typically in use is the HP turbine. When the engine is running at lower speeds, it creates less exhaust gas energy. This lower amount of exhaust gas energy is typically not enough to power the LP turbine, but it does provide enough energy to power the HP turbine. During operation, as the engine begins to increase speed, the HP turbine is typically operated by the lower energy exhaust gases, but after the engine reaches a certain speed and load, the HP turbine begins to operate in series with the LP turbine until the HP turbine provides enough flow capacity to have any effect on engine performance. When this occurs, the LP turbine begins to operate and generate the higher level of boost pressure than the HP turbine cannot generate in series with the LP turbine. Increasing engine speed also increases the exhaust gas energy, which is necessary to operate the LP turbine. 
   Another common problem with two-stage turbochargers occurs at higher engine speed, when the HP turbine is not cut off from the air flow of the exhaust gas. During this condition there is the possibility of “overspeed,” i.e., the increased exhaust gas energy can cause the HP turbine to spin at speeds which may cause damage. Control valves of two-stage series turbocharger systems have been applied to modulate the amount of exhaust gas pressure flowing into the LP turbine. These valves typically have been used for closing off exhaust gas flow to the LP turbine thereby only allowing the exhaust gas to flow only to the HP turbine until the HP turbine is no longer effective, at which point the valve opens a pathway to allow exhaust to flow to the LP turbine. This is beneficial in providing boost pressure at low engine speeds, but does not aid preventing overspeed of the HP turbine. 
   Accordingly, there exists a need for an improvement in transitioning from the HP turbine to the LP turbine in a two-stage turbocharger system, as well as an improvement in the prevention in overspeed in a HP turbine. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a valve regulation assembly for a two-stage turbocharger which provides a smooth transition for exhaust gas flow from a HP turbine to a LP turbine during acceleration. 
   It is another object of the present invention to prevent overspeed in a HP turbine by directing all of the exhaust gas flow directly to the LP turbine, by using the present invention. 
   The present invention is an addition to the two-stage turbine concept, including a valve that allows for the closure of the high-pressure stage outlet to avoid high-pressure stage overspeed and also improves control characteristics. 
   According to the present invention, the LP and HP turbines are positioned such that the valve can be in one position to force all of the exhaust gas to flow through the HP turbine, and when in another position to force all of the exhaust gas through the LP turbine. When the valve is placed in an intermediate position, the exhaust gas can be variably directed to flow through both turbines, with the percentage of exhaust gas flowing through each turbine being dependent on the position of the valve. 
   The present invention also overcomes the problem of overspeed. The present invention can close off the flow of exhaust gas energy to the HP turbine, thereby eliminating the chance for overspeed to occur. 
   In accordance with a first embodiment of the present invention, a valve regulation assembly for a two-stage turbocharger is provided, comprising: (1) a high-pressure turbocharger unit having a high-pressure turbine portion operable to receive an exhaust gas flow; (2) a low-pressure turbocharger unit having a low-pressure turbine portion, and located downstream from said high-pressure turbocharger unit; and (3) a valve operably associated with said turbine portions of said high-pressure and said low-pressure turbocharger units, wherein said valve can direct said exhaust gas flow from a source of said exhaust gas flow to either said high-pressure turbocharger unit, said low-pressure turbocharger unit, or distribute said exhaust gas flow therebetween. 
   In accordance with a second embodiment of the present invention, a two-stage turbocharger for use in a motor vehicle is provided, comprising: (1) an exhaust conduit; (2) a high-pressure (HP) turbocharger unit operably associated with said exhaust conduit and operable to receive an exhaust gas flow; (3) a low-pressure (LP) turbocharger unit connected to said exhaust gas conduit and is located downstream of said high-pressure turbine; and (4) a valve located operably associated with said high-pressure turbine through said exhaust gas conduit, wherein said valve can be in a position to restrict all of said exhaust gas flow through said high-pressure turbine only, or said valve can be moved to another position to inhibit said exhaust gas flow from entering the high-pressure turbine, thereby directing all of said exhaust gas to flow to said low-pressure turbine. 
   In accordance with a third embodiment of the present invention, a method for directing exhaust gas flow in a two-stage turbocharger for use in a motor vehicle is provided, comprised of: (1) providing a high-pressure turbine; (2) providing a low-pressure turbine located downstream from said high-pressure turbine; (3) providing a conduit for exhaust gas flow from said high-pressure turbine to said low-pressure turbine; and (4) providing a valve located in said conduit, wherein said valve is used for directing exhaust gas flow from said high-pressure turbine to said low-pressure turbine. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a schematic view of a two-stage turbocharger unit having the present invention used in an engine with one exhaust bank; 
       FIG. 2  is a schematic view of a two-stage turbocharger unit having the present invention used in an engine with two exhaust banks; 
       FIG. 3  is a top view of the valve assembly portion of the present invention; 
       FIG. 4  is a bottom view of the valve assembly portion of the present invention; 
       FIG. 5  is a side view of the valve assembly portion of the present invention; 
       FIG. 6  is a cut-away side view of the valve assembly portion of the present invention with the valve in a position to block off the exhaust gas inlet port; 
       FIG. 7  is a cut-away side view of the valve assembly portion of the present invention with the valve in a position to block off the HP turbine inlet port; and 
       FIG. 8  is a cut-away side view of the valve assembly portion of the present invention with the valve in an intermediate position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   Referring to  FIG. 1 , a two-stage exhaust gas turbocharger unit is generally shown at  10 , comprised of a high-pressure (HP) turbocharger unit  12 , and a low-pressure (LP) turbocharger unit  14 . The HP turbocharger unit  12  includes a HP turbine  16 , and an HP compressor  18  having an outlet port  20 . Similarly, the LP turbocharger unit  14  includes a LP turbine  22  and a LP compressor  24  having an outlet port  26 . The LP turbine  22  is mounted on an exhaust manifold  28 . The LP compressor  24  is connected to an intake line  30 , which is connected at the center of LP compressor  24 . An intake conduit  32  is connected to outlet port  26  on a first end, and is connected to the center of HP turbine  18  on a second end. 
   The HP turbine  16  and the LP turbine  22  are connected by a valve assembly  34  having a valve  36 , shown in  FIG. 1 , and in  FIGS. 3-8 . The valve assembly  34  is mounted on the exhaust manifold  28  and receives exhaust gases from either the second exhaust manifold outlet  40  or the HP turbine outlet  42 . The valve assembly  34  is also comprised of a lever  44 , a first valve plate  46  that works in conjunction with a first contact surface  48 , and second valve plate  50  that works in conjunction with a second contact surface  52 . The first valve plate  46  and the second valve plate  50  face in opposite directions of each other, and are connected by a pin  54 , and are mounted onto a valve stem  56 . The valve stem  56  is fixed for rotation upon a hinge assembly  58 . The valve assembly  34  also includes an exhaust gas inlet port  60 , an HP turbine inlet port  62 , an LP turbine outlet port  64 , and a rotatable connector  66 . The rotatable connector  66  is connected to an actuator (not shown) which can be hydraulic, pneumatic, or some other type of device controlled by the vehicle&#39;s electronic control unit. 
   The operation of the present invention configured for a single-bank exhaust system as shown in  FIG. 1  will now be described. During low engine speed operation, the valve  36  is used to close off the exhaust gas inlet port  60  when the vehicle is first beginning to accelerate, and exhaust gas pressure is low, forcing all of the exhaust gas through the HP turbine  16 . When the valve  36  is configured in this manner, the exhaust gas flows from the exhaust manifold  28 , through the first exhaust manifold outlet  38 , through the HP turbine  16 , through the HP turbine outlet  42 , through the HP turbine inlet port  62  and into the valve assembly  34 . The valve assembly  34  then directs the exhaust gas into the LP turbine  22 , where it is then passed into the remaining components of the exhaust system (not shown). As all of the exhaust gas is being forced through the HP turbine  16 , fresh air flows through the intake line  30 , passing through the LP compressor  24 , and through outlet port  26 . The air then flows through the intake conduit  32 , and into the HP compressor  18 . The HP compressor  18  compresses the fresh air received from the intake conduit  32 , and forces it into the intake manifold of the engine (not shown). 
   During the process where all of the exhaust gas is being directed toward the HP turbine, the LP compressor  24  is not activated because it is controlled by the LP turbine  22 , which is also not activated. The LP turbine  22  is larger in size compared to the HP turbine  16 , and the LP compressor  24  is larger than the HP compressor  18 . Neither are activated during this process because at lower engine speeds the volume of exhaust gas flow is not high enough to activate the LP turbine  22 , and the volume of fresh air flowing into the system is not high enough for LP compressor  24  to effectively compress it. Directing all of the exhaust gas flow into the smaller HP turbine  16  allows the HP compressor  18  to provide the necessary amount of compressed air to flow into the intake manifold of the engine, increasing engine power at low engine speeds. 
   As the engine speed increases and the vehicle accelerates, the smaller HP turbine  16  and HP compressor  18  become less and less effective. When the engine speed increases to a certain predetermined value, the vehicle&#39;s electronic control unit commands the actuator (not shown) to open the valve  36 , lifting the second valve plate  50  away from the second contact surface  52 , allowing exhaust gas from the exhaust manifold  28  to flow through the second exhaust manifold outlet  40 , through the exhaust gas inlet port  60 , and then through the valve assembly  34 . The exhaust gas then exits through the LP turbine outlet port  64  and flows into the LP turbine  22 , the exhaust gas then flows into the remaining exhaust system components. As the LP turbine  22  is activated from the increased exhaust gas pressure, the LP compressor  24  will begin to compress air coming in from the intake line  30 . The compressed air is then forced through the outlet port  26  and into the intake conduit  32 , where it then flows through the HP compressor  18 , through the outlet port  20 , and into the intake manifold of the engine. During this portion of operation, the air coming into the HP compressor  18  has already been pressurized by the LP compressor  24 , and the LP compressor  24  does not compress the air any further. 
   As the engine speed continues to increase, the valve  36  continues to rotate further away from the exhaust gas inlet port  60 , and moves closer to the HP turbine inlet port  62 . When it becomes necessary to direct all of the exhaust gas to flow directly into the LP turbine  22 , the valve  36  moves into a position where the first valve plate  46  comes in contact with the first contact surface  48 . When the valve  36  is in this position, exhaust gas cannot flow from the HP turbine  16  into the valve assembly  34 . All of the exhaust gas flows from the exhaust manifold  28 , through the second exhaust manifold outlet  40 , and into the valve assembly  34 . The valve  36  can be controlled by an actuator, or some other device, connected to the rotatable connector  66 , which rotates the lever  44 , thereby rotating the valve  36 . 
   When closing off the second exhaust manifold outlet  40  or the HP turbine outlet  42 , the valve  36  provides a smooth transition from the exhaust gas flowing through the HP turbine  16  to the LP turbine  22 , and can be moved to any position therebetween to direct the flow of exhaust gas as driving conditions mandate. 
   It should also be noted that another advantage of the present invention is the orientation of the valve assembly  34  in relation to the HP turbine  16  and the LP turbine  22 . The valve  36  is located in a position where the flow of exhaust gas pushes on the valve  36  when the first valve plate  46  is pressed against the first contact surface  48  and when the second valve plate  50  is pressed against the second contact surface  52 . This also occurs when the valve  36  is located in any position therebetween. Also, the hinge assembly  58  is located in a position between the HP turbine outlet  42 , and the second exhaust manifold outlet  40 . Locating the hinge assembly  58  in this position allows for a single valve to be used for directing exhaust gas flow to either the HP turbine  16  or the LP turbine  22 . Also, the valve assembly  34  is not only used for directing exhaust gas flow to each of the turbines, but the valve assembly  34  can also stop the flow of exhaust gas into the HP turbine  16 , preventing overspeed and damage. Additionally, locating the valve  36  in the aforementioned position allows for greater control of the exhaust gas flow than compared to, for example, if the valve  36  were positioned in front of the second exhaust manifold outlet  40  or in front of the HP turbine outlet  42 . 
   The present invention can also be used with engines having two exhaust banks, such as with a “V-6” or “V-8” engine. This embodiment is shown in  FIG. 2 , and is similar to the embodiment shown in  FIG. 1 , wherein like numbers refer to like elements. In addition, this embodiment also includes a first exhaust tube  68  connected to a first exhaust bank (not shown) and a first opening  70 , as well as a second exhaust tube  72  connected to a second exhaust bank (not shown) and a second opening  74 . In this embodiment, exhaust gas flows from the first exhaust tube  68  into the first opening  70 , and from the second exhaust tube  72  into the second opening  74 . The exhaust gas then flows into the exhaust manifold  28  where it is directed to flow into either the HP turbine  16  or the LP turbine  22  through the use of the valve assembly  34 . The remaining operations of the HP turbocharger unit  12 , the LP turbocharger unit  14  and the valve assembly  34  remain the same as mentioned in the previous embodiment. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.