Patent Application
20200116078
The field of technology generally relates to turbocharged internal combustion engines and, more particularly, to such engines equipped with a twin-scroll turbocharger.
Turbochargers can be used with internal combustion engines to improve engine performance and/or efficiency by recovering some of the otherwise wasted energy downstream of the combustion chambers. A turbine is positioned in the flow of engine exhaust gas and is coupled with a compressor positioned at the air intake of the engine. The flowing exhaust gases turn the turbine and, in turn, the compressor, which increases air intake pressure and the fuel-burning capacity of the engine. In a twin-scroll turbocharger, exhaust gases from different cylinders of a multi-cylinder engine reach the impeller of the turbine via two separate flow channels. For a variety of reasons, these flow channels do not have identical swallowing capacities—i.e., one of the two channels has a greater capacity to flow gases through it than does the other. While this does not negate the benefits of a twin-scroll turbocharger relative to a single-scroll design, it results in an imbalance in certain gas flow characteristics between the separate flow channels and can cause a corresponding imbalance among the associated combustion chambers.
According to one embodiment, an internal combustion engine includes a first combustion chamber, a second combustion chamber, a turbocharger, a first exhaust valve, and a second exhaust valve. The turbo charger includes a first scroll and a second scroll having a swallowing capacity different from the first scroll. The first exhaust valve is configured to open and close according to a first periodic cycle and to allow combustion gases to pass from the first combustion chamber to the first scroll when open. The second exhaust valve is configured to open and close according to a second periodic cycle and to allow combustion gases to pass from the second combustion chamber to the second scroll when open. The first periodic cycle is different from the second periodic cycle to at least partially compensate for the different swallowing capacities of the first and second scrolls.
In some embodiments, the first scroll has a larger swallowing capacity than the second scroll, and the second periodic cycle includes a valve-open period that is longer than a valve-open period of the first periodic cycle.
In some embodiments, the valve-open period of the second periodic cycle is 5 or more crankshaft degrees longer than the valve-open period of the first periodic cycle.
In some embodiments, the first scroll has a larger swallowing capacity than the second scroll and the second periodic cycle includes a valve-open period that begins before a valve-open period of the first periodic cycle relative to a top dead center condition for each of the combustion chambers.
In some embodiments, the valve-open period of the second periodic cycle begins 5 or more crankshaft degrees before the valve-open period of the first periodic cycle.
In some embodiments, the second periodic cycle includes a valve-open period that begins before a valve-open period of the first periodic cycle relative to a top dead center condition for each of the combustion chambers, and the valve-open period of the second periodic cycle is longer than the valve-open period of the first periodic cycle.
In some embodiments, the engine includes a first cam lobe that rotates to define the first periodic cycle and a second cam lobe that rotates to define the second periodic cycle.
In some embodiments, the first scroll has a larger swallowing capacity than the second scroll and the cam lobes are shaped such that the second exhaust valve is open longer than the first exhaust valve.
In some embodiments, the first scroll has a larger swallowing capacity than the second scroll and the cam lobes are shaped such that the second exhaust valve opens before the first exhaust valve relative to a top dead center condition for each of the combustion chambers.
In some embodiments, the cam lobes are shaped such that the second exhaust valve opens before the first exhaust valve relative to a top dead center condition for each of the combustion chambers, and the cam lobes are shaped such that the second exhaust valve is open longer than the first exhaust valve.
According to another embodiment, an internal combustion engine includes a cam shaft configured to periodically open and close combustion chamber exhaust valves of the engine such that one exhaust valve is held open longer than another exhaust valve and/or one exhaust valve opens before another exhaust valve relative to respective combustion chamber top dead center conditions.
In some embodiments, the exhaust valve that is held open longer than and/or opens before the other exhaust valve controls flow of combustion gases to the smaller of two scrolls of a twin-scroll turbocharger.
In some embodiments, the engine further includes a first combustion chamber, a second combustion chamber, a first exhaust valve, and a second exhaust valve. The first exhaust valve is configured to open and close according to a first periodic cycle and to allow combustion gases to pass from the first combustion chamber to a first scroll of a twin-scroll turbocharger when open. The second exhaust valve is configured to open and close according to a second periodic cycle and to allow combustion gases to pass from the second combustion chamber to a second scroll of the twin-scroll turbocharger when open. The first scroll of the turbocharger has a swallowing capacity that is larger than a swallowing capacity of the second scroll of the turbo charger. The cam shaft includes a first cam lobe that rotates to define the first periodic cycle and a second cam lobe that rotates to define the second periodic cycle. Each periodic cycle includes a valve-open period having a duration and a beginning relative to a top dead center condition of the respective combustion chamber. One or both of the following conditions is satisfied:
whereby the engine includes differential exhaust valve timing to at least partially compensate for the different swallowing capacities of the first and second scrolls of the turbocharger.
It is contemplated that any of the features listed above, illustrated in the drawings, and/or described below can be combined with any one or more of the other features except where there is an incompatibility of features.
Illustrative embodiments will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:
As described herein, differential exhaust valve timing can be implemented to at least partially compensate for the imbalanced gas flow through an internal combustion engine that can result when the engine is equipped with a twin-scroll turbocharger. Due to a variety of differences between the separate exhaust flow paths through the turbine of a twin-scroll turbocharger (e.g., flow length, area, shape, direction and location of impingement on turbine impeller, shape of engine exhaust manifold, etc.), it is nearly impossible to design the two turbine scrolls to have identical gas flow characteristics in a practically sized package. Stated differently, a twin-scroll turbocharger places a different amount of back pressure on different cylinders of the engine.
An engine equipped with differential valve timing operates with valve opening time, valve closing time, valve open duration, and/or valve lift being different among different cylinders of the engine. This is distinguished from variable valve timing in which one or more valve timing parameters vary with engine speed for all of the cylinders. Differential valve timing can be implemented independently from engine speed such that the valve timing of one cylinder is different from that of another cylinder at all engine speeds. Both differential valve timing and variable valve timing may also be used together in the same engine.
The illustrated engine 10 is a four-cylinder engine with four combustion chambers A-D. Combustion chambers A and D are intermittently fluidly connected with a first scroll 14 of the turbine 12 via a pair of first exhaust valves 16, which open and close according to a first periodic cycle to allow combustion gases to pass from the associated combustion chambers to the first scroll when open. Combustion chambers B and C are intermittently fluidly connected with a second scroll 18 of the turbine 12 via a pair of second exhaust valves 20, which open and close according to a second periodic cycle to allow combustion gases to pass from the associated combustion chambers to the second scroll when open. The first scroll 14 and the second scroll 18 have different swallowing capacities, and the first and second periodic cycles of the respective exhaust valves 16, 20 are different from each other to at least partially compensate for the different swallowing capacities of the scrolls.
As used herein, swallowing capacity is a term of art that refers to the amount of gas a turbine scroll is capable of allowing to pass through the scroll per unit time. While there are no specific units associated with the swallowing capacity, it is most closely associated with mass flow rate, normalized by other gas flow variables such as temperature and density, and is used in a relative sense to compare flow capabilities of different flow channels. As such, one of the scrolls 14, 18 may be referred to as the large scroll, and the other may be referred to as the small scroll.
Referring again to
In order to at least partially compensate for the different swallowing capacities of the first and second scrolls 14, 18 of the turbine 12, the first and second periodic cycles 36, 38 are different from each other. In this particular example, the second periodic cycle 38 has a valve-open period 40 that is longer than a valve-open period 42 of the first periodic cycle 36. Additionally, the valve-open period 40 of the second periodic cycle 38 begins before the valve-open period of the first periodic cycle 36. The valve-open periods may also be referred to as valve-open “durations” but are measured in degrees of crankshaft rotation rather than time to normalize for engine speed. Accordingly, with the exhaust valve timing illustrated in
Each valve-open period 40, 42 is the period between the crankshaft angle at which the respective valve opens (EVO) and the crankshaft angle at which the same valve closes (EVC). In the example of
In some embodiments, the timing of the second exhaust valves 20 is advanced relative to the first exhaust valves 16 while the respective valve-open durations 40, 42 are the same. For example, the first cam lobes 28 and the second cam lobes 30 may have substantially identical cam profiles but be affixed to a central shaft of the cam shaft 26 such that the second valves 20 open sooner than the first valves 16 relative to TDC. This is illustrated in
In some embodiments, the second valves 20 open at the same EVO angle as the first valves 16 and have a greater valve-open duration 40 than do the first valves. This is illustrated in
In other examples, the valve-open period 40 of the second periodic cycle 38 is longer and begins relatively sooner than that of the first periodic cycle 36 without the respective EVC angles being the same. For instance, the second exhaust valves 20 may be advanced by 10° relative to the first exhaust valves 16 and close less than 10° before the first exhaust valves close. Or the second exhaust valves 20 may be advanced by 5° relative to the first exhaust valves 16 and close more than 5° after the first exhaust valves close. Various other combinations of EVO angles and valve-open durations are possible in which the valve-open period is longer and/or begins sooner for exhaust valves associated with the small turbine scroll than for exhaust valves associated with the large turbine scroll. In other variations, the amount of valve lift for exhaust valves associated with the small turbine scroll is greater than that of exhaust valves associated with the large turbine scroll. This can be combined with differential valve timing or employed independently to help compensate for the different swallowing capacities of the first and second turbine scrolls.
As used herein, relative terms such as greater, lesser, longer, shorter, sooner, later, etc. as used to describe the EVO angle, valve-open duration, and amount of valve lift are intended to refer to amounts that are beyond normal manufacturing tolerances. For example, where cam lobe manufacturing is performed with tolerances such that EVO angle varies by ±3° from nominal design intent, then the EVO angle of one valve is said to be lower than the EVO angle of another valve if it is more than 3 degrees lower. It is contemplated that manufacturing tolerances will decrease over time as manufacturing techniques are improved.
Differential valve timing employed in an internal combustion engine equipped with a twin-scroll turbocharger as disclosed above has now been computer-modeled in order to evaluate its effect on the gas flow imbalance caused by turbine scrolls having different swallowing capacities. It is noted that the differential exhaust valve timing described herein does not equalize or otherwise change the swallowing capacity of the turbine scrolls. Swallowing capacity is an intrinsic characteristic of the scrolls and is not considered alterable absent variable scroll geometry. But the different swallowing capacities of the two scrolls causes measurable differences in certain other engine operating parameters.
The heavy solid line in each of
In the simulations used to generate
In embodiments where there is a valve-open duration differential among the exhaust valves, at least a portion of the additional duration of the longer duration may occur at a lower relative crankshaft angle, as in the example of
In various embodiments, the exhaust valves feeding the small turbine scroll open at a relative crankshaft angle that is less than that of the valves feeding the large turbine scroll by an amount in a range between 3 and 20 crankshaft degrees. In some embodiments, the EVO angle differential is between 5 and 20 crankshaft degrees, or between 5 and 15 crankshaft degrees. In embodiments where there is an EVO angle differential among the exhaust valves, the valve-open duration of the earlier-opening valve may be at least as long as the valve-open duration of the later-opening valve.
While presented in the context of a four-cylinder, four-stroke engine with one twin-scroll turbocharger and with one exhaust valve per cylinder, it should be understood that the benefits of the disclosed differential valve timing may be realized with other types of combustion engines equipped with multi-scroll turbochargers. Variations include engines with any number of cylinders greater than one and any number of intake and/or exhaust valves per cylinder. Additionally, while the above description is presented using cam shafts to define the valve timing, it is contemplated that other valve timing systems, such as electric actuator-controlled systems, could be configured to operate with differential valve timing as described herein to reap the same benefits as cam-controlled valve timing.
It is to be understood that the foregoing description is not a definition of the invention but is a description of one or more exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.
As used in this specification and claims, the terms “for example,” “e.g.,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
