Apparatus, system, and method for preventing overspeed of a turbocharger

An apparatus, system, and method are disclosed for preventing overspeed of a turbocharger. The apparatus includes a two-stage turbocharger system with a high pressure and a low pressure turbocharger. A bypass valve that divides an exhaust flow into a primary exhaust flow and a bypass flow. A relief valve vents a portion of the primary exhaust flow around the high pressure turbocharger. The low pressure turbocharger receives the bypass flow, the primary exhaust flow, and the vented portion of the primary exhaust flow. The apparatus includes a controller having a protection condition module that determines a protection indicator, and a relief valve control module that controls the relief valve according to the protection indicator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to turbocharger systems and more particularly relates to turbocharger systems with two turbocharger stages in series.

2. Description of the Related Art

Emissions regulations on internal combustion engines have become quite stringent and now impose significant constraints on engine design. Various features have been added to engines to respond to new emissions regulations, and to provide operational freedom to pursue the competing goals of meeting emissions and maintaining engine performance. Recent engine development cycles are increasingly using advanced turbocharger systems, such as variable geometry turbos and two-turbo systems. Two-turbo systems allow increased charge density by staging air compression. Further, they allow an engine to exhibit both responsiveness with a small, high pressure turbo stage, and high capacity with a large, lower pressure turbo stage.

One drawback of the two stage turbo system is that at fully rated operation, the high pressure (smaller) turbo is not able to accept the entire exhaust flow of the engine or the turbocharger will overspeed. One solution in the current art is to install a bypass line around the high pressure turbo and direct a portion of the exhaust directly to the lower pressure turbo. In many cases, a significant majority of the exhaust is flowing through the bypass line when the engine is operating at fully rated power. It is desirable to have a large flow capacity difference between the high pressure turbo and the low pressure turbo, to maximize the responsiveness of the high pressure turbo while maximizing the flow capacity of the low pressure turbo. However, the greater the flow capacity difference between the high pressure turbo and the low pressure turbo, the larger the bypass valve must be. Therefore, the bypass valve controlling the bypass line is typically large and has a relatively slow response time to go from open to closed. By contrast, the engine is preferably quite responsive. Therefore, in the current art, the engine and/or the turbocharger flow targets must have artificially reduced response to avoid overspeeding the high pressure turbo in transient situations.

Additionally, with a two-stage system in the current art, the high pressure compressor may have a bypass valve because at high inlet air flow rates, the high pressure compressor becomes a restriction in the intake air system. When the compressor bypass valve opens, the compressor then stops absorbing work from the high pressure turbocharger, which can cause instability or overspeed of the high pressure turbocharger, as well as reduce operator satisfaction with inconsistent engine performance.

SUMMARY OF THE INVENTION

From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that prevents overspeed of a turbocharger. Beneficially, such an apparatus, system, and method would prevent overspeed of the turbocharger without limiting the responsiveness of the engine.

The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available turbocharger speed control systems. Accordingly, the present invention has been developed to provide an apparatus, system, and method for preventing overspeed of a turbocharger that overcomes many or all of the above-discussed shortcomings in the art.

An apparatus is disclosed to prevent overspeed of a turbocharger. The apparatus includes a bypass valve that divides an exhaust flow between a bypass flow and a primary exhaust flow. The apparatus further includes a first turbocharger comprising a high pressure charging stage and a second turbocharger comprising a low pressure charging stage. The first turbocharger receives the primary exhaust flow and the second turbocharger receives the bypass flow and the primary exhaust flow. The apparatus further includes a relief valve that vents at least a portion of the primary exhaust flow when the relief valve is open.

In one embodiment, the relief valve opens according to an exhaust manifold pressure indicator, a first turbocharger speed indicator, a compressor bypass indicator, a primary exhaust flow indicator, and/or an engine transient event indicator. The engine transient event indicator may be an indication of whether an engine speed-load change amount is greater than a first threshold value, and/or whether a user input request change amount is greater than the first threshold value. The relief valve may be a spring-actuated mechanical valve, or an electronically actuated valve. The apparatus may include a protection condition module that functionally executes determining the protection indicator, and a relief valve control module that functionally executes controlling the relief valve according to the protection indicator.

A method is disclosed for preventing overspeed of a turbocharger. The method includes providing a bypass valve that divides an exhaust flow between a bypass flow and a primary exhaust flow. The method further includes providing a first turbocharger comprising a high pressure charging stage and a second turbocharger comprising a low pressure charging stage. The first turbocharger receives the primary exhaust flow and the second turbocharger receives the bypass flow and the primary exhaust flow. The method further includes providing a relief valve that vents at least a portion of the primary exhaust flow when the relief valve is open, and opening the relief valve according to a protection indicator.

In one embodiment, the method includes opening the relief valve according to the protection indicator by determining an engine transient event indicator and opening the relief valve according to the engine transient event indicator. The method includes determining the engine transient event indicator by determining whether an engine speed-load change, or a target engine speed-load change, is greater than a first threshold value. The method may include determining the engine transient event indicator by determining whether a user input request change is greater than a second threshold value. In one embodiment, the method includes determining the protection indicator by determining: a first turbocharger overspeed indicator, a compressor bypass indicator, a primary exhaust flow indicator, and/or an exhaust manifold pressure indicator.

A system is disclosed to prevent overspeed of a turbocharger. The system includes an internal combustion engine producing an exhaust flow, and a bypass valve that divides the exhaust flow between a bypass flow and a primary exhaust flow. The system further includes a first turbocharger comprising a high pressure charging stage and a second turbocharger comprising a low pressure charging stage. The first turbocharger receives the primary exhaust flow and the second turbocharger receives the bypass flow and the primary exhaust flow. The system further includes a relief valve that vents at least a portion of the primary exhaust flow when the relief valve is open.

In one embodiment, the system includes a controller comprising a protection condition module and a relief valve control module. The protection condition module determines a protection indicator, and the relief valve control module controls the relief valve according to the protection indicator. The protection indicator may be an engine transient event indicator.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic illustration depicting one embodiment of a system100to prevent overspeed of a turbocharger in accordance with the present invention. The system100may comprise various sensors for monitoring operating conditions within a given embodiment. Sensors may be strategically disposed within the system100and may be in communication with a controller. Sensors for the system100may include temperature sensors, pressure sensors, and mass flow sensors. One of skill in the art may determine the preferred placement and the preferred types of sensors useful for a particular application. Furthermore, sensors may comprise virtual sensors for detecting operating parameters of the system100based on other information, such as engine speed (rpm) for example.

The system100comprises an internal combustion engine102producing an exhaust flow104. The system100further includes a bypass valve106that divides the exhaust flow104between a bypass flow108and a primary exhaust flow110. The system100further includes a first turbocharger112comprising a high pressure charging stage that receives the primary exhaust flow110. The first turbocharger112includes a turbine112A and a compressor112B, mechanically coupled with a turbocharger112shaft. The compressor112B may have a compressor bypass valve113in a compressor bypass line. In one embodiment, when the intake air flow to the engine102exceeds a threshold flow amount, the compressor bypass valve113opens. In alternate embodiments, the compressor bypass valve113may open at a set engine102speed, intake manifold pressure, low pressure compressor114B pressure outlet, or under similar conditions known in the art.

The system further includes a relief valve116that vents at least a portion of the primary exhaust flow110when the relief valve116is open. Venting of at least a portion of the primary exhaust flow110may include sending a portion of the primary exhaust flow110around the first turbocharger112, or venting the primary exhaust flow110to the bypass flow108(refer to the embodiment ofFIG. 1B). When the relief valve116vents a portion of the primary exhaust flow110, the first turbocharger112receives the remainder110A of the primary exhaust flow110after venting117. The system100further includes a second turbocharger114comprising a low pressure charging stage that receives the bypass flow108and the primary exhaust flows110. The second turbocharger114includes a turbine114A and a compressor114B, mechanically coupled with a turbocharger114shaft. If the relief valve116vents117a portion of the primary flow110around the first turbocharger112, the second turbocharger114receives the recombined primary flow110B and the bypass flow108. Referring toFIG. 1B, if the relief valve116vents117a portion of the primary flow110to the bypass flow108, the second turbocharger114receives the primary flow110and the bypass flow108, as the bypass flow remainder110B combined with the bypass flow108and vented portion117of the primary flow110.

The system100may further include a controller118having modules configured to execute preventing overspeed of the turbocharger112. The controller118may include a protection condition module120and a relief valve control module122. The protection condition module120determines a protection indicator, and the relief valve control module122controls the relief valve116according to the protection indicator. The protection indicator may be an engine transient event indicator. The engine transient event indicator may be an indication of whether an engine speed-load change is greater than a first threshold value, and/or whether a user input request change is greater than a second threshold value. For example, the protection condition module120may detect an engine transient event has occurred when an engine speed change over 1,000 rpm/second occurs, and the protection condition module120may determine the protection indicator is TRUE based on the engine transient event. In the example, the relief valve control module122may command the relief valve116to open until the engine transient event is completed and the protection condition module120determines the protection indicator is FALSE.

FIG. 2is a schematic block diagram illustrating one embodiment of a controller118in accordance with the present invention. The controller118includes a protection condition module120that determines a protection indicator202. The protection indicator202may include any indicator from the list of indicators including an exhaust manifold pressure indicator204, an intake manifold pressure indicator220, a first turbocharger speed indicator206, a compressor bypass indicator208, a primary exhaust flow indicator210, and/or an engine transient event indicator212.

The exhaust manifold pressure indicator204may be an indication of whether an exhaust manifold pressure204exceeds a threshold. The first turbocharger speed indicator206may be an indication of whether the first turbine112A speed exceeds a speed threshold and/or may imminently exceed a speed threshold. The compressor bypass indicator208may be an indication of whether a compressor bypass valve113has opened, and/or whether other conditions exist—for example an intake manifold pressure—that indicate the compressor bypass valve113may be open or may imminently open. The primary exhaust flow indicator210may be an indication of whether the primary exhaust flow110has exceeded a threshold. The engine transient event indicator212may be an indication of whether an engine transient event has occurred or is in progress. For example, the engine transient event indicator212may be an indicator that a user input request change is greater than a second threshold value. In the example, the user input request change may be the change accelerator position with respect to time, and the second threshold value may be 80%/second. In the example, a user request change of accelerator position greater than 80% per second (for example—a transition from 0-100% accelerator request in less than 0.8 seconds) may set the engine transient event indicator212to TRUE, and the protection condition module120may set the protection indicator202to TRUE based on the engine transient event indicator212. In one embodiment, all indicators204-212in the system100may work together, for example causing the protection condition module120to set the protection indicator202to TRUE if any indicator204-212indicates that protection is needed.

The controller118further includes a relief valve control module122that controls the relief valve116according to the protection indicator202. For example, if the protection indicator202is TRUE, the relief valve control module122may command the relief valve116OPEN. The relief valve control module122may send a relief valve command214, which may be an electrical voltage, a datalink signal, or the like. In the example, the relief valve control module122commands the relief valve116CLOSED when the protection indicator202is FALSE.

FIG. 3Ais a schematic diagram depicting one embodiment of a bypass valve assembly300to prevent overspeed of a turbocharger in accordance with the present invention. In one embodiment the bypass valve assembly300comprises an exhaust flow104entering the bypass valve assembly300. The bypass valve106directs flow to the primary exhaust flow110in a first position304, and directs flow to the bypass flow108in a second position306. The bypass valve106appears in the schematic ofFIG. 3Aas a flapper valve106to show the logical arrangement of flows104,108,110with the valve positions304,306, but any type of valve106known in the art is contemplated within the scope of the invention. It is a mechanical step for one of skill in the art to select a valve type based upon the flow rates, temperatures, and pressures experienced within a given system100, and to arrange the flows104,108,110and valve106accordingly.

The bypass valve assembly300further includes a relief valve116. The relief valve116may be a spring-actuated mechanical valve, an electronically actuated valve, or any other type of valve known in the art. The indicators204-212selected for a given embodiment may determine which valve types are appropriate for the relief valve116. For example, if the exhaust manifold pressure indicator204is used in a given embodiment, the relief valve116may be spring-actuated, (E.g. where a pressure in the exhaust manifold applies force to an actuator arm overcoming a bias spring and opening the valve—not shown), or electronic where a controller118detects the exhaust manifold pressure through a sensor and the relief control module122commands214the relief valve116open when the exhaust manifold pressure exceeds a threshold. The relief valve116vents117at least a portion of the primary exhaust flow110, either around the first turbine112A back into the primary exhaust flow110(e.g. as depicted inFIG. 1A) or into the bypass flow108(e.g. as depicted inFIG. 1B). The relief valve116may be placed upstream of the bypass valve106(e.g. as depicted inFIG. 3A) or downstream of the bypass valve106(e.g. as depicted inFIG. 1A).

FIG. 3Bis a schematic diagram depicting one embodiment of a bypass valve assembly300to prevent overspeed of a turbocharger in accordance with the present invention. In the embodiment ofFIG. 3A, the relief valve116vents117at least a portion of the primary exhaust flow110to the bypass flow108when the valve116is open. The bypass valve106is depicted in the first position304such that no flow occurs in the bypass flow108except as the relief valve116may allow venting117into the bypass flow108if the valve116is open.

FIG. 4is an illustration of a duty-cycle map400with engine transient events in accordance with the present invention. The duty-cycle map400includes a first region502at relatively low engine speeds and loads where the bypass valve106is scheduled to remain closed. The duty-cycle map400includes a second region504at relatively high engine speeds and loads where the bypass valve106is scheduled to be fully open. The duty-cycle map further includes a transition region506at medium engine speeds and loads wherein the bypass valve106is scheduled to be in an intermediate state between fully open and closed. The duty-cycle map400further includes a compressor-bypass line508, wherein a compressor bypass valve113opens above and to the right of the line508, and closes below and to the left of the line508. The regions502,504,506and compressor-bypass line508of the duty-cycle map400are shown for purposes of illustration only, and the positions and inclusion of each of these features will vary depending upon particular aspects of a given embodiment of the system100.

A further consideration of the present invention may include providing an indication that the bypass valve106is malfunctioning and adjusting components of the system100to compensate. For example, an indicator may determine that the bypass valve106is stuck closed, and therefore the relief valve116may be further configured, under such circumstances, to be opened at considerably higher engine speeds and engine loads than it would under otherwise normal operating parameters.

The duty-cycle map400illustrates a first engine transition510from the first region502to the second region504. The first engine transition510takes the engine from a position on the duty cycle map400where the bypass valve106is closed to a position where the bypass valve106is scheduled to fully open. If the transition510occurs quickly, one or more indicators204-212may exceed a threshold causing the relief valve control module122to command214the relief valve116open. In one embodiment, the velocity of the transition510is calculated (e.g. in units of (rpm-(lb-ft))/second) and if the velocity of the transition510exceeds a threshold, the engine transient event indicator212is set to TRUE.

The second engine transition512takes the engine from a position on the duty cycle map400where the bypass valve106is closed to a position where the bypass valve106is scheduled to fully open, and additionally transitions the engine102to a position on the duty cycle map400where the compressor bypass valve113opens. The second transition512is generally more aggressive than the first transition510, and the second transition512causes even greater problems in the current art than the first transition510. If the transition512occurs quickly, one or more indicators204-212may exceed a threshold causing the relief valve control module122to command214the relief valve116open. In one embodiment, the velocity of the transition512is calculated (e.g. in units of (rpm-(lb-ft))/second) and if the velocity of the transition512exceeds a threshold, the engine transient event indicator212is set to TRUE. In one embodiment, the second transition512causes the compressor bypass indicator208to be TRUE, and/or may cause the first turbocharger speed indicator206to be TRUE.

FIG. 5is an illustration500of a bypass valve position and a relief valve position during an engine transient event in accordance with the present invention. One curve shows a desired bypass valve position502, and another curve shows an actual bypass valve position504. At a given time506, a rapid change occurs in the desired bypass valve position502, which may occur due to an engine transient event. The actual bypass valve position504is less responsive than the desired, and at some point a gap508between the desired position502and the actual position504causes the protection indicator202to be set where the relief valve116opens—as indicated by the step change on the bypass valve position510. In one embodiment, the gap508is measured directly and utilized to open the relief valve116. However, the gap508may also just cause another indicator204-212to set the protection indicator202, or the gap508may cause a physical change—for example a raised exhaust manifold pressure, that forces a mechanical relief valve116to open. At some point the actual bypass valve position504may approach the desired bypass valve position502such that a second gap512is narrow enough such that the relief valve116closes. The closing conditions may vary as the opening conditions vary as described above. The time scale in the illustration500varies with the responsiveness of the bypass valve106—for example the amount of time shown inFIG. 5may be several hundred milliseconds.

FIG. 6is a schematic flow chart diagram illustrating one embodiment of a method600to prevent overspeed of a turbocharger in accordance with the present invention. The method600includes providing602a bypass valve that divides an exhaust flow between a bypass flow and a primary exhaust flow. The method600further includes providing604a high pressure turbocharger comprising a high pressure charging stage and receiving the primary exhaust. The method600further includes providing606a low pressure turbocharger comprising a low pressure charging stage and receiving the bypass flow and the primary exhaust flow. The method600further includes providing608a relief valve that vents at least a portion of the primary exhaust flow when the relief valve is open. The method600further includes a relief valve control module122opening610the relief valve according to a protection indicator.

FIG. 7is a schematic flow chart diagram illustrating one embodiment of a method for opening610a relief valve according to a protection indicator in accordance with the present invention. The method610includes opening the relief valve according to the protection indicator by determining an engine transient event indicator, and opening the relief valve according to the engine transient event indicator. In one embodiment, the method610includes determining the engine transient event indicator by determining whether an engine speed-load change is greater than a first threshold value. In one embodiment, the method610includes determining the engine transient event indicator by determining whether a target engine speed-load change is greater than a first threshold value. In one embodiment, the method610includes determining the engine transient event indicator by determining whether a user input request change is greater than a second threshold value.

The method610begins by selecting702whether an engine transient detection method is USER or SPEED-LOAD. If the engine transient detection method is USER, the method610includes a protection condition module checking704whether a change (Δ) in an user input request is greater than a second threshold value. The method610includes opening706the relief valve (check704with a YES resolution) or closing708the relief valve (check704with a NO resolution). In one embodiment, if the engine transient detection method is SPEED-LOAD, the method610includes checking710whether the SPEED-LOAD check is a check against the TARGET speed-load or the ACTUAL speed-load. If the check is for the ACTUAL speed load, the method610includes checking712whether a Δ-engine speed-load is greater than a first threshold value. If the check is for the TARGET speed-load, the method610includes checking714whether a Δ-engine speed-load target is greater than the first threshold value. The method610includes a relief valve control module122opening706the relief valve (check712and/or714with a YES resolution) or a relief valve control module122closing708the relief valve (check712and/or714with a NO resolution).

FIG. 8is a schematic flow chart diagram illustrating an alternate embodiment of a method610for opening a relief valve according to a protection indicator in accordance with the present invention. In one embodiment, the method610includes opening the relief valve according to the protection indicator by determining a first turbocharger overspeed indicator, and opening the relief valve according to the first turbocharger overspeed indicator. In one embodiment, the method610includes opening the relief valve according to the protection indicator by determining a compressor bypass indicator, and opening the relief valve according to the compressor bypass indicator. In one embodiment, the method610includes opening the relief valve according to the protection indicator by determining a primary exhaust flow indicator, and opening the relief valve according to the primary exhaust flow indicator. In one embodiment, the method610includes opening the relief valve according to the protection indicator by determining an exhaust manifold pressure indicator, and opening the relief valve according to the exhaust manifold pressure indicator.

In one embodiment, the method610includes a protection condition module checking802whether a compressor bypass indicator is OPEN or CLOSED. If the compressor bypass indicator is OPEN, the method610includes a relief valve control module122opening706the relief valve. If the compressor bypass indicator is CLOSED, the method610includes a protection condition module checking804whether a turbocharger overspeed indicator is TRUE or FALSE. If the turbocharger overspeed indicator is TRUE, the method610includes a relief valve control module122opening706the relief valve. If the turbocharger overspeed indicator is FALSE, the method610includes a protection condition module checking806whether a primary exhaust flow indicator is HIGH. If the primary exhaust flow indicator is HIGH, the method610includes a relief valve control module122opening706the relief valve. If the primary exhaust flow indicator is not HIGH, the method610includes a protection condition module checking808whether an exhaust manifold pressure indicator is HIGH. If the exhaust manifold pressure indicator is HIGH, the method includes a relief valve control module122opening706the relief valve. If the exhaust manifold pressure indicator is not HIGH, the method includes a relief valve control module122closing708the relief valve.