Patent Publication Number: US-11384681-B2

Title: Control of an opposed-piston engine with a mass airflow sensor located after a charge air cooler

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     This Project Agreement Holder (PAH) invention was made with U.S. Government support under Agreement No. W15KQN-14-9-1002 awarded by the U.S. Army Contracting Command-New Jersey (ACC-NJ) Contracting Activity to the National Advanced Mobility Consortium. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The field is internal combustion engines, particularly uniflow-scavenged, opposed-piston engines. More specifically, the field is related to location of a mass airflow sensor in the air handling system of an opposed-piston engine. 
     BACKGROUND OF THE INVENTION 
     In a conventional four-stroke cycle, internal combustion engine, a single piston in a cylinder completes a cycle of operation during two complete revolutions of a crankshaft. During an intake stroke, movement of the piston from top to bottom dead center creates a low pressure environment that draws air into the cylinder in preparation for the following compression stroke. In this manner, the flow of gas through the engine is aided by the pumping action of the piston during the intake stroke. 
     In a two-stroke cycle, opposed-piston engine, two oppositely-disposed pistons in a cylinder complete a cycle of operation during a single revolution of a crankshaft. The cycle includes a compression stroke followed by a power stroke, but it lacks a distinct intake stroke during which the cylinder is charged with fresh air by movement of a piston. Instead near the end of the power stroke, pressurized fresh air enters the cylinder through an intake port near one end of the cylinder and flows toward an exhaust port near an opposite end of the cylinder as exhaust exits. Thus, gas (charge air, exhaust, and mixtures thereof) flows through the cylinder and the engine in one direction, from intake port to exhaust port. The unidirectional movement of exhaust gas exiting through the exhaust port, followed by pressurized air entering through the intake port, is called “uniflow scavenging”. The scavenging process requires a continuous positive pressure differential from the intake ports to the exhaust ports of the engine in order to maintain the desired unidirectional flow of gas through the cylinders. Without this continuous positive pressure differential, combustion can falter and fail. At the same time, a high air mass density must be provided to the intake ports because of the short time that they are open. All of this requires pumping work in the engine, which is unassisted by a dedicated piston pumping stroke as in a four-stroke cycle engine. 
     The pumping work required to maintain the unidirectional flow of gas in an opposed-piston engine is done by an air handling system (also called a “gas exchange” system) which moves fresh air into and transports combustion gases (exhaust) out of the engine&#39;s cylinders. The air handling elements that do the pumping work may include one or more gas-turbine driven compressors (e.g., a turbocharger) and/or a pump, such as a supercharger (also called a “blower”), which may be mechanically or electrically driven. In one example, a compressor is disposed in tandem with a supercharger in a two-stage pumping configuration. The pumping arrangement (single stage, multi-stage, or otherwise) drives the scavenging process, which is critical to ensuring effective combustion, increasing the engine&#39;s indicated thermal efficiency, and extending the lives of engine components such as pistons, rings, and cylinders. Manifestly, in a two-stroke cycle, opposed-piston engine, airflow is one of the most fundamental factors by which engine operation is controlled. 
     For effective control of airflow, information regarding the mass of incoming air (“mass airflow”) is vital to measurement of airflow conditions and to determination of precise and accurate control parameter values with which the air handling devices are actuated. Additionally, mass airflow measurement is important to controlling fuel provisioning in an opposed-piston engine equipped for fuel injection. Mass airflow measurement also plays an important role in control of exhaust gas recirculation (EGR). Parametrically, mass airflow is often expressed in SI units, for example kg/s (kilograms per second). In many instances, measurement of air mass entering the air handling system of an opposed-piston engine is enabled by an electronic mass airflow (MAF) sensor positioned in a charge air channel of the air handling system, through which charge air is transported to the intake ports of the engine&#39;s cylinders, at a point where fresh air first enters the air handling system. In a turbocharged opposed-piston engine this places the MAF sensor in the charge air channel, upstream of the compressor inlet. In cases where the charge air channel may include a supercharger as well as a turbocharger, the MAF sensor is located upstream of both charge devices. One example of such an arrangement is described in US publication 2018/0223750 A1. An alternative approach to measuring mass airflow in an opposed-piston engine is by means of a virtual mass airflow sensor, usually an algorithmically-based control routine that calculates a mass airflow value to generate a mass airflow signal, using inputs from other engine sensors. Examples of calculations used for determining mass airflow as would be used in designing a virtual MAF sensor are found in US publication 2014/0373814 A1. A virtual sensor is not a component or an element of the invention to be described. 
     Other means and/or locations for monitoring and measuring mass airflow in an opposed-piston engine may provide advantages related to increased precision in determination of fuel quantities, rail pressures, and start of injection that need to be commanded to a fuel injection system so as best to meet a torque demand, while controlling emissions and minimizing fuel consumption. 
     SUMMARY OF THE INVENTION 
     According to the invention, an opposed-piston engine includes an electronic sensor located in a charge air channel, at position between an outlet of a charge air cooler and an air intake component for distributing charge air to cylinder intake ports of the engine. The electronic sensor is configured and disposed to measure a rate of mass airflow between the outlet of the charge air cooler and the intake component and generate electronic signals indicative of the rate of mass airflow from the charge air cooler. 
     In other aspects of the invention, a control mechanization of the opposed-piston engine is electrically connected to the electronic sensor for controlling air handling devices, fuel provisioning devices, and/or EGR devices in response to the electronic signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a uniflow-scavenged, two-stroke cycle, opposed-piston engine. 
         FIG. 2  is a schematic diagram illustrating a fuel injection system embodiment for the opposed-piston engine of  FIG. 1 . 
         FIG. 3  is a schematic diagram illustrating an air handling system embodiment for an opposed-piston engine according to the invention. 
         FIG. 4  is a schematic diagram illustrating a control mechanization embodiment for an opposed-piston engine according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a schematic representation of a uniflow-scavenged, two-stroke cycle opposed-piston engine  8  of the compression-ignition type that includes at least one cylinder. Preferably, the engine  8  has two or more cylinders. In any event, the cylinder  10  represents both single cylinder and multi-cylinder configurations of the opposed-piston engine  8 . The cylinder  10  includes a bore  12  and longitudinally displaced intake and exhaust ports  14  and  16  machined or formed in the cylinder, near respective ends thereof. An air handling system  15  of the engine  8  manages the transport of charge air into, and exhaust out of, the engine. Each of the intake and exhaust ports includes one or more circumferential arrays of openings in which adjacent openings are separated by a solid portion of the cylinder wall (also called a “bridge”). In some descriptions, each opening is referred to as a “port”; however, the construction of a circumferential array of such “ports” is no different than the port constructions in  FIG. 1 . Fuel injectors  17  include nozzles that are secured in threaded holes that open through the sidewall of the cylinder. A fuel handling system  18  of the engine  8  provides fuel for direct side injection by the injectors  17  into the cylinder. Two pistons  20 ,  22  are disposed in the bore  12  with their end surfaces  20   e ,  22   e  in opposition to each other. For convenience, the piston  20  is referred to as the “intake” piston because it opens and closes the intake port  14 . Similarly, the piston  22  is referred to as the “exhaust” piston because it opens and closes the exhaust port  16 . Preferably, but not necessarily, the intake piston  20  and all other intake pistons are coupled to a crankshaft  30  disposed along one side of the engine  8 ; and, the exhaust piston  22  and all other exhaust pistons are coupled to a crankshaft  32  disposed along the opposite side of the engine  8 . 
     Operation of the opposed-piston engine  8  is well understood. In response to combustion the opposed pistons move away from locations in the cylinder  10  where they are at their innermost positions, toward their respective associated ports. While moving outwardly from their innermost locations, the pistons keep their associated ports closed until they approach respective BDC locations where they are at their outermost positions in the cylinder and their associated ports are open. The pistons may move in phase so that the intake and exhaust ports  14 ,  16  open and close in unison. Alternatively, one piston may lead the other in phase, in which case the intake and exhaust ports have different opening and closing times. Charge air  34  enters the cylinder  10  through the intake port  14  and flows in the direction of the exhaust port  16 . Turbulence of the charge air  34  promotes air/fuel mixing, combustion, and suppression of pollutants. 
       FIG. 2  shows the fuel provisioning system  18  embodied as a common rail, direct injection fuel handling system. The fuel handling system  18  delivers fuel to each cylinder  10  by injection into the cylinder. Preferably, each cylinder  10  is provided with multiple fuel injectors mounted for direct injection into cylinder space between the end surfaces of the pistons. For example, each cylinder  10  has two fuel injectors  17 . Preferably, fuel is fed to the fuel injectors  17  from a fuel source  40  that includes at least one rail/accumulator mechanism  41  to which fuel is pumped by a fuel pump  43 . A fuel return manifold  44  collects fuel from the fuel injectors  17  and the fuel source  40  for return to a reservoir from which the fuel is pumped. Elements of the fuel source  40  are operated by respective computer-controlled actuators that respond to fuel commands issued by an engine control unit. Although  FIG. 2  shows the fuel injectors  17  of each cylinder disposed at an angle of less than 180°, this is merely a schematic representation and is not intended to be limiting with respect to the locations of the injectors or the directions of the sprays that they inject. In a preferred configuration, best seen in  FIG. 1 , the injectors  17  are disposed for injecting fuel sprays in diametrically opposing directions of the cylinder  8  along an injection axis. Preferably, each fuel injector  17  is operated by a respective computer-controlled actuator that responds to injector commands issued by an engine control unit. 
       FIG. 3  shows an exemplary embodiment of an air handling system  15  according to the invention. The air handling system  15  manages the transport of charge air provided to, and exhaust gas produced by, the opposed-piston engine  8 . The air handling system construction includes a charge air subsystem  38  and an exhaust subsystem  40 . In the air handling system  15 , a charge air source receives fresh air and processes it into charge air. The charge air subsystem  38  receives the charge air and transports it to the intake ports of the engine  8 . The exhaust subsystem  40  transports exhaust products from exhaust ports of the engine for delivery to other exhaust components. 
     The air handling system  15  includes a turbocharger arrangement that may comprise one or more turbochargers. For example, a turbocharger  50  includes a turbine  51  and a compressor  52  that rotate on a common shaft  53 . The turbine  51  is disposed in the exhaust subsystem  40  and the compressor  52  is disposed in the charge air subsystem  38 . The turbocharger  50  extracts energy from exhaust gas that exits the exhaust ports and flows into the exhaust subsystem  40  directly from engine exhaust ports  16 , or from an exhaust collector  57  that collects exhaust gases output by the opposed-piston engine. In this description the exhaust collector  57  may comprise an exhaust manifold assembly attached to a cylinder block  75  of the opposed-piston engine or an exhaust plenum or chest formed with the cylinder block  75  that communicates with the exhaust ports  16  of all cylinders  10 , which are supported in the cylinder block  75 , The turbine  51  is rotated by exhaust gas passing through it to an exhaust outlet  58 . This rotates the compressor  52 , causing it to generate charge air by compressing fresh air. 
     Exhaust gases from the exhaust ports of the cylinders  50  flow from the exhaust collector  57  into the inlet of the turbine  51 , and from the turbine&#39;s outlet into an exhaust outlet channel  55 . In some instances, one or more after-treatment devices (not shown) may be provided in the exhaust outlet channel  55 . The air handling system  15  may be constructed to reduce NOx emissions produced by combustion by recirculating exhaust gas through the ported cylinders of the engine by way of an exhaust gas recirculation (EGR) loop  59 . If the air handling system is equipped with EGR, exhaust gas transported through the EGR loop  59  is mixed with charge air in a mixer  63  positioned in the charge air subsystem, downstream of the outlet of the compressor  52   
     The charge air subsystem may provide ambient inlet air to the compressor  52  via an air filter  81 . As the compressor  52  rotates it compresses the ambient inlet air. The compressed air flows into the inlet of the supercharger  60 . Air pumped by the supercharger  60  flows through the supercharger&#39;s outlet to an inlet of a charge air cooler  67 , and from the outlet of the charge air cooler  67  into an air intake component  68 . Pressurized charge air is distributed by the air intake component  68  to the intake ports  14  of the cylinders  10 . In this description the air intake component  68  may comprise an intake manifold assembly attached to the cylinder block  75 , or an intake plenum or chest formed with the cylinder block  75  that communicates with the intake ports  14  of all cylinders  10 , which are supported in the cylinder block  75 . 
     The charge air subsystem includes at least one cooler coupled to receive and cool charge air before delivery to the intake ports of the engine  8 . In this regard, the charge air cooler  67  is provided between the outlet of the supercharger  60  and the air intake component  68 . In some instances, charge air output by the compressor  52  may flow through another cooler  69 , positioned in the charge air channel downstream of a mixer in which charge air flowing from the outlet of the compressor  52  is mixed with whence it is pumped by the supercharger  60  to the intake ports. 
     With further reference to  FIG. 3 , the exemplary air handling system  15  is equipped for control of gas flow at various control points in the charge air and exhaust subsystems. In the charge air subsystem, charge air flow and boost pressure are controlled by operation of a shunt path  80  coupling the outlet of the supercharger to the supercharger&#39;s inlet. The shunt path  80  includes a shunt valve  82  that governs the flow of charge air into, and thus the pressure in, the intake component  68 . More precisely, the shunt valve  82  shunts the charge air flow from the supercharger&#39;s outlet (high pressure) to its inlet (lower pressure). Note that the shunt path  80  may shunt the outlet of the charge air cooler  67  to the inlet of the supercharger  60 , as seen in  FIG. 3 , or may omit the charge air cooler  67  and shunt the outlet of the supercharger  60  to its inlet; the precise configuration of the shunt loop  80  would be a matter of design choice. Sometimes those skilled in the art refer to the shunt valve  82  as a “bypass” valve or a “recirculation” valve. A backpressure valve  90  in the exhaust channel  55  governs the flow of exhaust out of the turbine and thus the backpressure in the exhaust subsystem for various purposes, including modulation of the exhaust temperature. As per  FIG. 3 , the backpressure valve  90  is positioned in the exhaust channel  55 , between the output  58  of the turbine  51  and the after-treatment devices  79 . A wastegate valve  92  diverts exhaust gases around the turbine blade, which enables control of the speed of the turbine. Regulation of the turbine speed enables regulation of the compressor speed which, in turn, permits control of charge air pressure. An EGR valve  92  controls the amount of exhaust gas that is recirculated by the EGR loop  59  to the charge air channel. The valves  82 ,  90 ,  91 , and  92  are opened and closed by respective computer-controlled actuators that respond to rotational commands issued by an engine control unit. In some cases, these valves may be controlled to two states: fully opened or fully closed. In other cases, any one or more of the valves may be variably adjustable to a plurality of states between fully opened and fully closed. 
     In some instances, additional control of gas flow and pressure is provided by way of a variable speed supercharger. In these aspects, the supercharger  60  is coupled by a drive mechanism  95  to a crankshaft  30  or  32  of the engine  8 , to be driven thereby. The drive mechanism  95  may comprise a stepwise transmission device, or a continuously variable transmission device (CVD), in which cases charge air flow, and boost pressure, may be varied by varying the speed of the supercharger  60  in response to a speed control signal provided to the drive mechanism  95 . In other instances, the supercharger may be a single-speed device with a mechanism to disengage the drive, thus giving two different drive states. In yet other instances, a disengagement mechanism may be provided with a stepwise or continuously variable drive. In any event, the drive mechanism  95  is operated by a computer-controlled actuator that responds to drive commands issued by an engine control unit. 
     In some aspects, the turbine  51  may be a variable-geometry turbine (VGT) device having an effective aspect ratio that may be varied in response to changing speeds and loads of the engine. Alteration of the aspect ratio enables control of the speed of the turbine. Regulation of the turbine speed enables regulation of the compressor speed which, in turn, permits control of charge air boost pressure. Thus, in many cases, a turbocharger comprising a VGT may not require a wastegate valve. A VGT device is operated by a computer-controlled actuator that responds to turbine commands issued by an engine control unit. 
     As seen in  FIG. 3 , the invention concerns placement of an electronic sensor  100  disposed to measure a rate of mass airflow between the outlet of the charge air cooler  67  and the intake component  68  and generate electronic signals indicative of the rate of mass airflow. The electronic senor is a mass airflow (MAF) sensor  100  that is disposed, placed, installed, located, or positioned in the charge air channel  38  between the outlet of the charge air cooler  67  and the inlet of the intake component  68 . Thus the mass airflow measured by the MAF sensor  100  is in the portion of the charge air channel  38  that is downstream of a compressor disposed in tandem with a supercharger in a multi-stage pumping configuration operative to provide charge air to an inlet of the charge air cooler  67 . In essence, the MAF sensor, at the location shown in  FIG. 3 , measures a mass flow rate of charge air delivered to the intake ports of the opposed-piston engine  8 . This parameter should reflect the mass flow rate of fresh air entering the engine; if EGR is employed, the parameter should reflect the mass flow rate of fresh air entering the engine, plus the mass flow rate of recirculated exhaust gas. In either case, the airflow parameter measured by the MAF sensor  100  has many uses. Such uses may include: determination of an amount of fuel to be injected by the fuel injection system (see US 2017/0204790); diagnosis of air handling components (see US 2016/0160781); control of EGR flow (see US 2014/0373814); and other uses. These and other functions are carried out by an engine control mechanization and employed thereby to control the air handling and fuel provisioning systems, as well as other engine systems. 
     In this disclosure, and with reference to  FIG. 4 , an engine control mechanization  93  is a computer-based system that governs the operations of various engine systems, including the fuel provisioning system, the air handling system, a cooling system, a lubrication system, and other engine systems based on inputs from the MAF sensor  100  and other engine sensors. The engine control mechanism  93  includes one or more electronic control units coupled to associated sensors, actuators, and other machine devices throughout the engine. As per  FIG. 4 , control of the fuel handling system of  FIG. 2  and the air handling system of  FIG. 3  (and, possibly, other systems of the opposed-piston engine  8 ) is implemented by the engine control mechanization  93 , based on electrical signals from the MAF sensor  100  indicative of a rate of mass airflow between the outlet of the charge air cooler  67  and the intake component  68 . In response to signals from the MAF sensor and one or more of the other engine sensors, commands are generated for actuation of one or more air handling devices and/or fuel provisioning devices. The control mechanization  93  includes a programmable engine control unit (ECU)  94  programmed to execute air handling algorithms and fuel provisioning algorithms under various engine operating conditions. Such algorithms are embodied in control modules that are part of an engine systems control program executed by the ECU  94  while the engine is operating. 
     For the air handling system, the ECU  94  controls one or more air handling devices by issuing backpressure (Backpressure), wastegate (Wastegate), EGR, and shunt (Shunt) commands to actuate the exhaust backpressure valve  90 , the wastegate valve  91 , the EGR valve  92 , and the supercharger shunt valve  82 , respectively. In cases where the supercharger  60  is operated by a variable drive, the ECU  94  also controls this air handling device by issuing drive (Drive) commands to actuate the supercharger drive  95 . And, in those instances where the turbine  51  is configured as a variable geometry device, the ECU  94  also causes actuation of this air handling device by issuing VGT commands to set the aspect ratio of the turbine. 
     For the fuel provisioning system, the ECU  94  controls injection of fuel into the cylinders by issuing rail pressure (Rail) commands to actuate the fuel source  40 , and by issuing injector (Injector) commands to actuate the injectors  17 . 
     When the opposed-piston engine  8  runs, the ECU  94  determines the current engine operating state based on engine load and engine speed, and governs the amount, pattern, and timing of fuel injected into each cylinder  10  by control of the common rail fuel pressure and injection duration, based on the current operating state. For this purpose, the ECU  94  may receive signals from other engine sensors which may include an accelerator sensor, a speed governor, or a cruise control system, or equivalent means that detects accelerator position, an engine speed sensor that detects the rotational speed of the engine, and a pressure sensor that detects rail pressure. The ECU  94  configures the air handling system  15  to provide the optimal AFR for the current operational state. For this purpose, in addition to the MAF sensor  100 , the ECU receives electrical signals from other engine sensors that may include pressure and temperature sensors that detect ambient air pressure and temperature upstream of the inlet of the compressor  52 , pressure and temperature sensors that detect charge air pressure and temperature upstream of the inlet of the supercharger  60 , intake pressure and temperature sensors that detect charge air pressure and temperature at the inlet of the air intake component  68 , exhaust pressure and temperature sensors that detect exhaust pressure and temperature at the outlet of the exhaust collector  57 , exhaust pressure and temperature sensors that detect exhaust pressure and temperature downstream of the outlet of the turbine, and, possibly other sensors. 
     As will be evident to the reasonably skilled craftsman, although the invention has been described with reference to presently preferred examples and embodiments, it should be understood that various modifications can be made without departing from the scope of the following claims.