Patent Application
20230014159
This invention relates to internal combustion engines, and more particularly to turbocharged air intake systems for such engines.
A supercharger is an air compressor that increases the pressure or density of air supplied to an internal combustion engine. This gives each intake cycle of the engine more oxygen, letting it burn more fuel and do more work, thus increasing the power output. Supercharging is a well understood method of increasing the performance of internal combustion engines.
Power for the supercharger can be provided mechanically by means of a belt, shaft, or chain connected to the engine's crankshaft. Common usage restricts the term supercharger to mechanically driven units; when power is instead provided by a turbine powered by exhaust gas, the supercharger is known as a turbocharger.
Superchargers having a centrifugal compressor (such as turbochargers) are typically used when high compressor efficiency is desired. The usable flow range of centrifugal compressors is limited by surge and choke conditions, encountered when the air flow at a given pressure ratio is too low or too high, respectively.
When the engine has unsteady intake flow characteristics, such as a four-stroke engine with four or fewer cylinders, surge behavior is exacerbated. As internal combustion engine vehicles become more efficient there is a need to reduce the engine size. Such engine downsizing is often accomplished by reducing cylinder count.
Another engine condition that can result in unsteady intake to the intake manifold is an engine operating strategy known as cylinder deactivation (CDA). With CDA, fuel and valve actuation are shut off to one or more cylinders at low loads to reduce engine pumping losses and to increase exhaust temperature. As cylinders are deactivated, intake flow is reduced and the flow rate becomes unsteady. This can lead to compressor surge behavior.
A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:
The following description is directed to improving performance of turbocharged internal combustion engines. A positive displacement blower is placed in the air intake path between the turbocharger's compressor and the engine's intake manifold. As explained below, the blower is operated in a manner that reduces the likelihood of engine surge.
In the example of this description, engine 10 is a four-stroke diesel engine. However, the invention is useful with other engine configurations, such as engines fueled with other fuels or with two-stroke engines.
An intake manifold 12 provides intake air to the cylinders 11. Exhaust from combustion within the cylinders 11 exits the engine 10 via an exhaust manifold 13.
Engine 10 is equipped with a turbocharger 14. The turbine 14a of the turbocharger is driven by exhaust from the engine. Turbine 14a drives a centrifugal compressor 14b, which compresses intake air entering the compressor 14b. The compressed air is then cooled by a cooler 15.
A positive displacement blower 16 is placed on the air intake path between compressor 14b and the intake manifold 12. An example of a suitable positive displacement blower 16 is a Roots-type blower. In the example of
In the embodiment of
Referring to the embodiments of both
A controller 16b or 21 controls the speed of blower 16, based on air flow demands of the engine. This air flow demand data may be measured directly using a delta pressure sensor across blower 16. Alternatively, air flow demand data may be obtained indirectly based on air flow data already measured or calculated by an engine control system. Controller 16b or 21 receives the air flow demand data and determines the blower speed that will maintain an engine cycle average of 1.0 across the blower.
Because the speed of blower 16 is modulated such that the cycle-average pressure ratio across it is 1.0, blower 16 provides no additional compression. Used in this manner, blower 16 smooths out the intake flow. It instantaneously compresses air to the intake manifold during periods in the engine cycle when intake valves are closed. It instantaneously expands air from the compressor when an intake valve is open and air is free to flow from the intake manifold and into the cylinder.
When intake flow is low, blower 16 compresses the intake. When intake flow is high, blower 16 expands the flow. The engine cycle average pressure ratio is 1.0.
More specifically, at some instantaneous moments in the engine cycle, the blower 16 is compressing the air flow (above the dotted line) at which point work is done to the air by the blower. At other moments in the cycle, the air flow is expanding across the blower 16, at which point work is being done by air to the blower. Averaged out over an engine cycle, the power required to run the blower at a cycle average pressure ratio of 1.0 is low because the net work done to the air flow is near zero. Only friction losses plus some thermodynamic inefficiencies in the compressor need be overcome by input power to the blower 16.
Thus, because blower 16 can expand as well as compress gases flowing through it, the net power required to operate blower 16 at a cycle-average pressure ratio of 1.0 is only its mechanical friction. In practical application, there are some thermodynamic inefficiencies in both the compression and expansion processes to be overcome, in addition to the mechanical friction. Nevertheless, the power consumption of blower 16 is quite low. This particularly distinguishes the use of blower 16 from conventional superchargers.
If blower 16 is equipped with independent speed control, such as by being electrically driven, it can confer additional benefits on the engine. These benefits may include reduction in transient boost lag, adding boost at speeds and loads where the turbocharger in ineffective, and recovering energy during engine throttling.
The intake system of
