Engine with a piston heating system and method for operation thereof

Methods and systems are provided for actively heating pistons in combustion chambers to decrease a torque imbalance in an engine. In one example, a method for operation of an engine includes determining a variation between compression ratios in a first combustion chamber and a second combustion chamber and operating a piston heating system to apply a targeted amount of heat to a first piston assembly based on the variation between the compression ratios, the first piston assembly including a first piston positioned within the first combustion chamber.

FIELD

The present description relates generally to an engine with a piston heating system designed to adjust compression ratios in combustion chambers in an engine and a method operation of an engine with a piston heating system.

Variations in cylinder compression ratios may arise in engines due to the manufacturing tolerances of different components as well as stack-up tolerances in groups of components. For instance, the tolerances in components influencing piston squish height and bowl volume can cause variations in cylinder compression in multi-cylinder engines. Often the compression ratio can vary cylinder to cylinder by +/−1.0%, for instance, which can cause variations in the power produced by each cylinder. Consequently, the power and fuel consumption of the engine may be reduced and the drivability of a vehicle in which the engine resides may be negatively affected. These problems may be particularly prevalent in compression ignition engines. However, variations in compressions ratios can also have negative impacts on spark-ignition engines.

One example approach shown by Cannata, in U.S. Pat. No. 7,827,943 B2, includes a system that varies a compression ratio in a cylinder via a mechanical assembly that adjusts the position where the connecting rod and the piston are attached. However, Cannata's system achieves compression ratio adaptability at the expense of engine reliability. For example, Cannata's mechanical compression ratio adjustment system may be prone to malfunction and failure due to the complexity of the mechanical components used to adjust the compression ratios.

The inventors have recognized the aforementioned problems with previous engines and facing these challenges developed a method for operation of an engine, in one example, to address the problems. The method includes determining a variation between compression ratios in a first combustion chamber and a second combustion chamber and operating a piston heating system to apply a targeted amount of heat to a first piston assembly based on the variation between the compression ratios, the first piston assembly including a first piston positioned within the first combustion chamber. In this way, the compression ratio of each cylinder may be adjusted to reduce variations between the compression ratios in the engine and stabilize the amount of torque produced by the cylinders, if desired, through a robust and reliable compression ratio adjustment system. Consequently, engine efficiency can be increased while reducing noise, vibration, and harshness (NVH) caused by the torque imbalance. Such compression ratio adjustment is also carried out using a dependable system that is not prone to malfunction. As a result, the drivability as well as the reliability of the vehicle may be increased, thereby increasing customer satisfaction.

In one example, operating the piston heating system may include activating a heater coupled to a lubrication line, the lubrication line including a nozzle directing lubricant to a first piston rod coupled to the first piston and a crankshaft during engine operation. In this way, a piston assembly heater can be incorporated into a lubrication system to induce compression ratio adjustment in an efficient and reliable manner.

In another example, the amount of heat delivered to combustion chambers in the engine may be varied based on engine load. In such an example, during low load conditions (e.g., when the engine load is below a predetermined threshold value) piston assembly heaters coupled to the first and second combustion chambers may be activated or operated to increase an amount of heat delivered to the combustion chambers to increase the compression ratios in the combustion chambers. Consequently, the piston heating system can also be used to increase combustion efficiency in the engine during low load conditions, for instance.

DETAILED DESCRIPTION

The following description relates to a piston heating system and a method for operating the piston heating system to adjust the compression ratio in one or more combustion chambers in an engine. The piston heating system includes piston assembly heaters providing independent targeted heating to engine piston assemblies (e.g., pistons and piston rods), enabling the compression ratio of associated combustion chambers to be varied. As defined herein, a compression ratio is a value that represents a ratio of the volume a combustion chamber from its largest capacity to its smallest capacity. It will be appreciated that heating or cooling of the piston assembly can increase or decrease the compression ratio of the combustion chamber due to the material properties of the piston, piston rod, cylinder block, and cylinder head. Specifically, temperature affects the piston volumetrically. If the piston is heated isothermally, the volumetric shape of the piston expands in all directions. However, in real engines, the piston temperature is not isothermal, so the expansion along any axis X (width, height, radius) may vary as a function of Cexp=dT/dX, where Cexp is the thermal expansion coefficient for the piston material. When a variance in compression ratios is ascertained, from pressure or proximity sensors signals for instance, the piston assembly (e.g., piston and piston rod) corresponding to the combustion chamber with the smaller compression ratio may be heated to reduce the compression ratio variance. Consequently, engine efficiency can be increased while reducing noise, vibration, and harshness (NVH) in the engine. Moreover, it will be appreciated that the piston heating system is more reliable than previous mechanical systems for adjusting cylinder compression ratios. Additionally, the piston heating system may also be designed to heat the pistons and/or piston rods during low load and cold start conditions to further increase engine efficiency.

FIG. 1shows a schematic depiction of an engine employing a piston heating system designed to vary combustion chamber compression ratios in the engine.FIG. 2shows a first example of a piston heating system with lubricant heaters.FIG. 3shows a second example of a piston heating system with an induction heater.FIGS. 4 and 5show methods for operation of engines and piston heating systems to adjust compression ratios in the engine.FIG. 6shows a timing diagram of an exemplary piston heating system control strategy for reducing torque imbalances in an engine as well as increasing engine efficiency.

Turning toFIG. 1, an engine10with a piston heating system12in a vehicle14is schematically illustrated. Although,FIG. 1provides a schematic depiction of various engine and piston heating system components, it will be appreciated that at least some of the components may have a different spatial positions and greater structural complexity than the components shown inFIG. 1. The structural details of the components are discussed in greater detail herein with regard toFIGS. 2-3.

An intake system16providing intake air to a first combustion chamber18and a second combustion chamber20, is also depicted inFIG. 1. A first piston17is positioned in the first combustion chamber18and a second piston19is positioned in the second combustion chamber20. The pistons17and19are coupled to a crankshaft21via mechanical components23(e.g., piston rods). Each pair of pistons and associated mechanical components (e.g., piston rods) may be referred to as a piston assembly. The combustion chambers,18and20, are formed by a cylinder block22coupled to a cylinder head24. Although,FIG. 1depicts the engine10with two combustion chambers. The engine10may have an alternate number of combustion chambers, in other examples. For instance, the engine10may include a single combustion chamber, three combustion chambers, six combustion chambers, eight combustion chambers, etc., in other examples. Moreover, the combustion chambers may be arranged in different banks, in some examples. For instance, the first combustion chamber18may be arranged in a first cylinder bank while the second combustion chamber20may be arranged in a second cylinder bank.

The intake system16includes an intake conduit26and a throttle28coupled to the intake conduit. The throttle28is configured to regulate the amount of airflow provided to the combustion chambers,18and20. In the depicted example, the intake conduit26feeds air to an intake manifold30. In turn, the intake manifold30directs air to a first intake valve32and a second intake valve34via a first intake runner36and a second intake runner38, respectively. However, in other examples, such as in the case of a single-cylinder engine, the intake conduit26may route intake air directly to an intake valve in one combustion chamber.

The intake valves32and34may be actuated by intake valve actuators,40and42, respectively. Likewise, exhaust valves,44and46, may be actuated by exhaust valve actuators48and50, respectively. In one example, the intake valve actuators40and42and the exhaust valve actuators48and50may employ cams coupled to intake and exhaust camshafts (not shown), respectively, to open/close the valves. Continuing with the cam driven valve actuator example, the intake and exhaust camshafts may be rotationally coupled to a crankshaft. Further in such an example, the valve actuators may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT), and/or variable valve lift (VVL) systems to vary valve operation. Thus, cam timing devices may be used to vary the valve timing, if desired. It will therefore be appreciated that valve overlap may occur. In another example, the intake and/or exhaust valve actuators,40,42,48, and50, may be controlled by electronic valve actuation. For example, the valve actuators,40,42,48, and50, may be electronic valve actuators controlled via electronic actuation. In yet another example, the engine10may alternatively include exhaust valves controlled via electric valve actuation and intake valves controlled via cam actuation including CPS and/or VCT systems or vice versa. In still other embodiments, the intake and exhaust valves may be controlled by a common valve actuator or actuation system.

The engine10further includes a lubrication system52providing lubricant to engine components such as the pistons,17and19, crankshaft21, mechanical components23, etc. The lubrication system52includes a lubricant reservoir54that receiving lubricant from the lubricated components (e.g., pistons, crankshaft, piston rods, etc.). Thus, the lubricant reservoir54in the lubrication system52may be designed to receive drain oil from the lubricated components such as the pistons17and19, crankshaft21, mechanical components23, etc. For instance, the lubricant reservoir54may be positioned below the lubricated components to receive oil that has been sprayed or otherwise delivered to the lubricated components. A lubricant pump56is positioned in the lubricant reservoir54in the illustrated example. However, in other examples, the lubricant pump56may be positioned external to the lubricant reservoir with a pick-up line extending into the reservoir. The lubricant pump56is configured to flow pressurized lubricant to a plurality of lubrication lines58. The plurality of lubrication lines58are schematically illustrated. However it will be appreciated that the lubrication lines may extend through different sections of the cylinder block22and/or cylinder head24to provide lubricant to the pistons,17and19, the crankshaft21, mechanical components23, etc. The lubrication system52may further include nozzles designed to spray or otherwise direct lubricant to the pistons, crankshaft, etc., and are discussed in greater detail herein with regard toFIGS. 2 and 3. The lubrication system52also includes valves that are designed to regulate the flowrate of the lubricant provided to the lubricated components, discussed in greater detail herein with regard toFIGS. 2 and 3.

The piston heating system12includes a first piston assembly heater62coupled to the first combustion chamber18and a second piston assembly heater64coupled to the second combustion chamber20. The piston assembly heaters,62and64, are configured to provide varied amounts of heat to the pistons,17and19. Varying the amount of heat provided to the pistons enables the compression ratios in the combustion chambers to be adjusted. In this way, the compression ratios in specific cylinders may be tuned to reduce torque imbalances in the engine as well as increase combustion efficiency in the engine10. Control strategies used to vary the compression ratios in the engine are discussed in greater detail herein. The first piston assembly heater62and/or the second piston assembly heater64may be electrical heaters designed to heat lubricant directed to the first piston17, the second piston19, and/or the mechanical components23(e.g., piston rods) connected to the pistons, in one example. In such an example, an energy storage device66may deliver electrical power to the first piston assembly heater62and the second piston assembly heater64. However, in other examples, the first piston assembly heater62and/or the second piston assembly heater64may be induction heaters designed to provide targeted amounts of heat to the first piston17, the second piston19, and/or the mechanical components23(e.g., piston rods) via induction heating. Specifically, the induction heaters may be designed to heat piston rods when the rods drop below a combustion chamber liner, in one example. Further in other examples, the first piston assembly heater62and/or the second piston assembly heater64may include a heat exchanger configured to transfer heat from engine coolant to lubricant that is delivered to the first piston17, the second piston19, and/or mechanical components23(e.g., piston rods) coupled to the pistons and the crankshaft21. In this way, excess heat in the engine cooling system may be transferred to the piston heating system, to increase engine efficiency. Other types of piston assembly heaters that may be used in the piston heating system include electrical heating elements, heat pump devices, a coolant to oil heat exchanger, etc. It will be appreciated that heating of the piston assemblies (e.g., pistons and/or piston rods) allows the pistons and/or piston rods to thermally expand to increase the combustion ratio of the corresponding combustion chamber. The thermal expansion of the pistons and piston rods may be proportional to their vertical length. In some examples, the piston rods may be taller (e.g., three times taller) than the piston. Therefore, heating the piston rod may have a significant impact on the compression ratio growth.

The piston heating system12may be designed to vary the heating delivered to targeted pistons and/or piston rods to decrease compression ratio variances in the engine10. By decreasing compression ratio variance NVH in the engine decrease while combustion efficiency is increased. For instance, if it is determined that one of the combustion chambers has a smaller compression ratio than the other combustion chamber, the piston within the combustion chamber and/or the piston rod having the smaller compression ratio may be heated to increase the compression ratio of the combustion chamber. Consequently, the compression ratio variance can be decreased. The piston heating system12may also be configured to deliver heat to the pistons17and19during low load and/or cold start conditions to further increase engine efficiency, in one example. A low load condition may be a condition where engine load is less than a threshold value and a cold start condition may be a condition where engine temperature is less than a threshold value. The engine load threshold pressure may be 10 bar brake mean effective pressure (BMEP), in one example. However, it will be appreciated that the engine load threshold may be dependent on the size and application of the engine. In another example, the low load conditions threshold may be approximately equal to the maximum BMEP the engine experience during a city or highway drive cycle, in one instance. It will also be appreciated that the engine load threshold may also be highly dependent on the vehicles transmission or axle ratios. The engine temperature threshold value, in one instance, may be equivalent to the engines coolant temperature where the controller changes operating modes at approximately 65° C., in one example. Alternatively, the engine temperature threshold value may be determined based on whether the exhaust manifold temperature or the catalyst out temperatures exceeds the catalyst's T80 temperature which is the temperature where the catalyst converts 80% of the NOx or total hydrocarbon emissions (THC) exhaust emissions.

The engine10additionally includes an engine cooling system68configured to remove heat from the engine10and specifically the cylinder block22and the cylinder head24. The engine cooling system68includes an engine coolant jacket70. The engine coolant jacket70is shown positioned in the cylinder head24. However, it will be appreciated that in other examples, the cylinder block22may additionally or alternatively include a coolant jacket. Moreover, it will be appreciated that the engine coolant jacket70may include a plurality of passages directing coolant around high temperature areas in the engine such as the combustion chambers. The engine coolant jacket70includes an inlet72receiving coolant from a coolant pump74and an outlet76delivering coolant to a heat exchanger78(e.g., radiator) designed to remove heat from the coolant flowing therethrough. In this way, a coolant loop may be formed in the engine cooling system68. Coolant lines80with valves82positioned in the coolant lines may also be included in the engine cooling system68. However, in other examples, only one of the coolant lines80may include a valve. The coolant lines80may be configured to direct heated coolant through lubrication lines in the lubrication system to heat lubricant. In such an example, the engine coolant may be used to heat lubricant directed at the pistons,17and19. Thus, the coolant lines80may be included in the piston assembly heaters,62and64, in one example.

A fuel delivery system84is also shown inFIG. 1. The fuel delivery system84provides pressurized fuel to fuel injectors86. In the illustrated example, the fuel injectors86are direct fuel injectors coupled to the first and second combustion chambers,18and20, respectively. Additionally or alternatively, the fuel delivery system84may also include a port fuel injector designed to inject fuel upstream of the combustion chambers into the intake system16. The fuel delivery system84includes a fuel tank88and a fuel pump90designed flow pressurized fuel to downstream components. The fuel delivery system84may include conventional components such as a high pressure fuel pump, check valves, return lines, etc., to enable fuel to be provided to the injectors at desired pressures.

An exhaust system92configured to manage exhaust gas from the combustion chambers,18and20, is also included in the vehicle14depicted inFIG. 1. The exhaust system92includes the exhaust valve44and46designed to open and close to allow and inhibit exhaust gas flow to downstream components from the combustion chambers. The exhaust system92also includes exhaust runners93providing fluidic communication between an exhaust manifold94and the first and second combustion chambers18and20. The exhaust system92also includes an emission control device96coupled to an exhaust conduit98downstream of the exhaust manifold94. The emission control device96may include filters, catalysts, absorbers, etc., for reducing tailpipe emissions.

An exhaust gas recirculation (EGR) system140is also shown inFIG. 1. The EGR system140includes an EGR conduit142fluidically coupled to the intake system16and the exhaust system92. Thus, the EGR system140may be designed to flow exhaust gas from the exhaust system92to the intake system16. The EGR system140further includes an EGR valve144configured to adjust a flowrate of exhaust gas flowing through the EGR conduit142. An EGR cooler146is also included in the EGR system140. The EGR cooler146is configured to remove heat from exhaust gas flowing through the EGR conduit142. For instance, the EGR cooler146may include coolant conduits circulating coolant near exhaust gas conduits. However, numerous EGR cooler designs have been contemplated.

During engine operation, the combustion chambers18and20typically undergoes a four stroke cycle including an intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, generally, the exhaust valves close and intake valves open. Air is introduced into the combustion chamber via the corresponding intake conduit, and the piston moves to the bottom of the combustion chamber so as to increase the volume within the combustion chamber. The position at which the piston is near the bottom of the combustion chamber and at the end of its stroke (e.g., when the combustion chamber is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). During the compression stroke, the intake valves and exhaust valves are closed. The piston moves toward the cylinder head so as to compress the air within combustion chamber. The point at which the piston is at the end of its stroke and closest to the cylinder head (e.g., when the combustion chamber is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process herein referred to as injection, fuel is introduced into the combustion chamber. In a process herein referred to as ignition, the injected fuel in the combustion chamber is ignited via compression, resulting in combustion. However, in other examples, spark from an ignition device may be used to ignite the air fuel mixture in the combustion chamber. During the expansion stroke, the expanding gases push the piston back to BDC. A crankshaft converts this piston movement into a rotational torque of the rotary shaft. During the exhaust stroke, in a traditional design, exhaust valves are opened to release the residual combusted air-fuel mixture to the corresponding exhaust passages and the piston returns to TDC.

FIG. 1also shows a controller100in the vehicle14. Specifically, controller100is shown inFIG. 1as a conventional microcomputer including: microprocessor unit102, input/output ports104, read-only memory106, random access memory108, keep alive memory110, and a conventional data bus. Controller100is configured to receive various signals from sensors coupled to the engine10. The sensors may include engine coolant temperature sensor120, exhaust gas composition sensor122, exhaust gas airflow sensor123, an intake airflow sensor124, combustion chamber temperature sensors126, pressure transducers128coupled to the combustion chambers18and20, engine speed sensor130, knock sensor132, etc. In other examples, the sensors may additionally include proximity sensors coupled to the combustion chambers18and20. The pressure transducers and/or the proximity sensors may be used to ascertain the compression ratios of the associated combustion chamber. In other examples, proximity sensors may be used instead of pressure transducers. Additionally, the controller100is also configured to receive throttle position (TP) from a throttle position sensor112coupled to a pedal114actuated by an operator116.

Additionally, the controller100may be configured to trigger one or more actuators and/or send commands to components. For instance, the controller100may trigger adjustment of the throttle28, lubrication system52, intake valve actuators40and42, exhaust valve actuators48and50, piston heating system12, engine cooling system68, EGR system140, and/or fuel delivery system84. Specifically, the controller100may be configured to send signals to the first piston assembly heater62and the second piston assembly heater64to adjust amounts of heat provided to the pistons. The controller100may also be configured to send control signals to the lubricant pump56to adjust a flowrate of heated lubricant provided to the pistons, in one example. Additionally, the controller100may be configured to send control signals to the valve82to vary the amount of coolant flow provided to the lubrication system52. Furthermore, the controller100may be configured to send control signals to the fuel pump90and the fuel injectors86to control the amount and timing of fuel injection provided to the combustion chambers18and20. The controller100may also be configured to send command signals to the EGR valve144and the EGR cooler146, in one example.

Therefore, the controller100receives signals from the various sensors and employs the various actuators to adjust engine operation based on the received signals and instructions stored in memory (e.g., non-transitory memory) of the controller. Thus, it will be appreciated that the controller100may send and receive signals from the piston heating system12.

For example, adjusting the first piston assembly heater may include adjusting a piston assembly heater actuator to adjust the piston assembly heater. In yet another example, adjusting the amount of heat delivered to the pistons via the piston assembly heaters,62and64, may be empirically determined and stored in predetermined lookup tables and/or functions. For example, one table may correspond to determining an amount of piston heating delivered to a piston when there is a variance in combustion chamber compression ratios, one table may correspond to determining an amount of piston heating delivered to pistons in the engine based on changes in engine load. The tables may be indexed to engine operating conditions such as engine temperature and engine load, among other engine operating conditions. Furthermore, the tables may output an amount of fuel to inject via the fuel injectors to the combustion chambers at each cylinder cycle.

FIG. 2shows a first example of an internal combustion engine200and piston heating system202in cross-section. A z-axis and x-axis are provided inFIG. 2as well asFIG. 3, for reference. In one example, the z-axis may be parallel to a gravitational axis. However in other examples, other z-axis orientations have been contemplated. It will be appreciated that the engine200and the piston heating system202, shown inFIG. 2, are examples of the engine10and the piston heating system12shown inFIG. 1. Therefore, features in the engine10and piston heating system12shown inFIG. 1may be included in the engine200and piston heating system202, shown inFIG. 2, or vice versa.

FIG. 2shows the engine200including a cylinder block204coupled to a cylinder head206forming a combustion chamber208. Although only one cylinder is depicted inFIG. 2, it will be appreciated that the engine200may include additional combustion chambers and piston heating system components similar to those depicted inFIG. 2. Thus, other combustion chambers in the engine may include similar piston assembly heaters, lubrication lines, etc. Additionally, an exhaust valve210and an intake valve212are shown coupled to the combustion chamber208. Correspondingly, intake conduit214and exhaust conduit216providing fluidic communication between upstream intake system components and downstream exhaust system components, are also depicted inFIG. 2.

A piston218is positioned within the combustion chamber208. The piston218include piston rings220designed to seal the combustion chamber208. A piston rod222is attached to the piston218and a crankshaft224. The piston218and piston rod222may be included in a piston assembly.

The piston heating system202includes a lubrication line226and a valve228coupled to the lubrication line. The valve228is configured to adjust an amount of lubricant flowed to the lubrication line226. The valve228as well as other lubricant valves described herein may be an on/off electrically actuated solenoid valve, an on/off pneumatically actuated solenoid valve, an on/off electrically actuated piezoelectric stack valve, an electrically actuated proportioning valve, or a pneumatically actuated proportioning valve.

A nozzle230is positioned at the end of the lubrication line226. The nozzle230is designed to direct lubricant spray towards an underside232of the piston218. The piston heating system202also includes a piston assembly heater234coupled to the lubrication line226. The piston assembly heater may be an electric heater, in one example. However, in other examples the piston assembly heater may receive heated coolant from the engine cooling system68, shown inFIG. 1, to heat the lubricant flowing through the lubrication line226. The piston heating system202may also include a lubricant conduit236and a valve238coupled to the lubricant conduit. The valve is configured to adjust an amount of lubricant flowed to lubrication lines240. Nozzles242are positioned at the end of the lubrication lines240. The nozzles242are designed to spray lubricant towards the piston rod222. Another piston assembly heater244may be coupled to the lubrication lines240. However in other examples, only one of the piston assembly heaters,234and244, may be included in the piston heating system202. Again the piston assembly heater244may be an electrical heater, in one example, or in other examples may receive heated coolant from the engine cooling system, as previously discussed. When the piston assembly heaters receive heated coolant from the engine cooling system the coolant flow to the heater may be varied to adjust the amount of heating provided by the piston assembly heater to the lubricant flowing therethrough.

A pressure sensor246(e.g., pressure transducer) is also shown inFIG. 2. The pressure sensor246extends through the cylinder head206into the combustion chamber208. The pressure sensor246is configured to sense the pressure in the combustion chamber208. A pressure signal from the pressure sensor246may be used to determine the combustion chamber's compression ratio. In other examples, the engine200may additionally or alternatively include a proximity sensor that senses the proximity of the piston to an upper portion of the cylinder head206to enable the compression ratio of the combustion chamber208to be determined. In such an example, the proximity sensor may extend through the cylinder head in a similar manner to the pressure sensor. A temperature sensor248is also shown extending through the cylinder block204into the combustion chamber208. The temperature sensor248is configured to determine the temperature in the combustion chamber208. The engine200also includes an engine speed sensor250coupled to the crankshaft224designed to sense the rotational speed of the crankshaft.

A direct fuel injector252is also shown coupled to the combustion chamber208. However, a port fuel injector may additionally or alternatively be included in the engine. It will be appreciated that the valve228, valve238, piston assembly heater234, and piston assembly heater244may receive control signals from the controller100, shown inFIG. 1. Therefore, the amount of heat delivered to the lubricant flowing through the lubrication lines226and240as well as the flowrate of the lubricant traveling through the lubrication lines may be varied. Variation in lubricant heating and/or lubricant flowrate enables the heat delivered to the piston and/or piston rod to be varied to induce an adjustment in the compression ratio in the combustion chamber. For instance, when the piston is heated the axial length253of the piston increases, thereby reducing the compression ratio in the combustion chamber208. In one example, the piston may be constructed out of a metal such as steel, aluminum, etc. The growth of the piston may be dependent on the thermal expansion coefficient, thermal conductivity, and heat transfer coefficient (e.g., conductive and/or convective heat transfer coefficient) of the piston. The thermal expansion coefficient and thermal conductivity are properties of the piston material and can vary along the height of the piston if the piston is not composed of a single material such as an assembly of smaller components with different materials (i.e., aluminum, steel, etc.,) or alloys. The heat transfer coefficient is a function of the pistons surface area, roughness, and material. In one example, the bottom of the piston could be roughened to increase surface area and increase convective heat transfer which would increase the sensitivity of the compression ratio to the cooling/heating jets and heaters. Furthermore, the cross sectional shape of the piston will affect the thermal gradients within the piston which will impact the sensitivity of the compression ratio to the cooling/heating jets and heaters.

FIG. 3shows another example of an internal combustion engine300and piston heating system302in cross section. The engine300and the piston heating system302are examples of the engine10and the piston heating system12shown inFIG. 1. Therefore, features in the engine10and piston heating system12shown inFIG. 1may be included in the engine300and piston heating system302, shown inFIG. 3, or vice versa. Furthermore, the internal combustion engine300and piston heating system302may have similar features to the internal combustion engine200and piston heating system202, shown inFIG. 2. Therefore, redundant description is omitted.

The engine300includes a cylinder block304coupled to a cylinder head306forming a combustion chamber308. The engine300also includes a combustion chamber liner310. Additionally, an exhaust valve312and an intake valve314are shown coupled to the combustion chamber308. Correspondingly, an intake conduit316and an exhaust conduit318providing fluidic communication between upstream intake system components and downstream exhaust system components, are also depicted inFIG. 3.

The piston heating system302include an induction heater320. The induction heater320may at least partially extend around a piston rod322coupled to a piston324positioned in the combustion chamber308. In one example, the induction heater320may include an insulated wire that is repeatedly looped to form a ring commonly referred to as an induction coil. The inside diameter of the induction coil may be no smaller than the engines cylinders bore diameter, in some instances. Further in such an example, the induction coil may be attached to the bottom of the cylinder liner or bore such that the piston rod passes through the center of the induction coil. In one example, the induction coil may be wrapped around the liner. In another example, the induction coil may be imbedded in the block material. However, in these examples, the liner and engine block are typically constructed of metal and would therefore interfere with the induction heating of the piston rod. Continuing with the induction coil example, alternating current may be applied to the induction coil with an electrically conductive piece of metal positioned inside the induction coil. The alternating current in the induction coil generates eddy currents inside the electrically conductive piece of metal which heats the electrically conductive piece of metal. It will further be appreciated that the induction heater320may heat the piston rod322as the rod drops below the combustion chamber liner310, in one example. In such an example, the induction heater320may not directly heat the piston but heat the piston rod that in turn heats the piston. Therefore, the induction heater320may be positioned vertically below the combustion chamber liner310to avoid directly heating the liner, in one example. However, other induction heater positions have been contemplated.

The piston rod322is also shown rotationally attached to a crankshaft326. The induction heater320also extends through the combustion chamber liner310. The induction heater320may be configured to heat the piston rod and/or piston via induction. The induction heater320may therefore include components such an electromagnet, an electronic oscillator, coils, etc., that enable eddy currents to be generated in the piston rod and/or piston to generate heat therein, as discussed above. Using induction heaters to heat the pistons has the benefit of heating the piston independent of lubrication system operation. Furthermore, induction heaters can provide targeted heating of the piston, to avoid unwanted heating of surrounding components, if desired.

An energy storage device328(e.g., battery, flywheel, capacitor, etc.,) is configured to provide energy to the induction heater320. It will be appreciated that the energy storage device328may provide energy to other engine systems, in some examples. Further in some examples, the energy storage device328may be recharged via an alternator coupled to the crankshaft326.

A lubrication line330is also depicted inFIG. 3. The lubrication line330includes a nozzle332positioned at one end. The nozzle332is configured to spray lubricant towards the piston rod322. A valve334is also coupled to the lubrication line330. The valve334is designed to enable adjustment in the flowrate of lubricant through the lubrication line. The valve334, induction heater320, and energy storage device328may receive control signals from the controller100, shown inFIG. 1, to adjust operation of the components.

FIG. 3also shows a direct fuel injector336. A pressure sensor338(e.g., pressure transducer) is also shown inFIG. 3. The pressure sensor338extends through the cylinder head306into the combustion chamber308. The pressure sensor338is configured to sense the pressure in the combustion chamber308. A temperature sensor340is also shown extending through the cylinder block304into the combustion chamber308. The temperature sensor340is configured to determine the temperature in the combustion chamber308. The engine300also includes an engine speed sensor342coupled to the crankshaft326designed to sense the rotational speed of the crankshaft.

Additionally, in some examples, it will be appreciated that the engine300may include one set of pistons that have corresponding induction heaters, such as the induction heater shown inFIG. 3, and one set of pistons with corresponding lubrication line piston assembly heaters, such as the piston assembly heaters shown inFIG. 2.

FIG. 4shows a method400for operation of an engine with a piston heating system. Method400as well as the other methods described herein may be implemented by engines and piston heating systems described above with regard toFIGS. 1-3or may be implemented by other suitable engines and piston heating systems, in other examples. Instructions for carrying out the method400and the other methods described herein may be executed by a controller based on instructions stored in memory (e.g., non-transitory) executable by the controller and in conjunction with signals received from sensors of in the engine and corresponding systems, such as the sensors described above with reference toFIGS. 1-3. The controller may employ engine actuators of the engine systems to adjust engine operation, according to the methods described below.

At402the method includes determining engine operating conditions. The engine operating conditions may include combustion chamber pressures, intake flowrate, engine temperature, exhaust gas flowrate, exhaust gas composition, engine speed, engine load, combustion chamber temperatures, piston position, etc.

Next at404the method includes determining if there is a deviation in compression ratios of multiple combustion chambers. Specifically in one example, it may be determined if the difference between a first compression ratio and a second compression ratio is greater than an acceptable value. In one example, the threshold value may be correlated to engine size, engine speed, and/or engine load. Further in one example, the threshold value may be strongly correlated to the coefficient of variation (COV) of indicated mean effective pressure (IMEP). In such an example, for a given speed and load point for an engine, the COV of mean effective pressure (MEP) can be calculated and used to calculate the cycle to cycle +/−3 sigma spread for each cylinder. Continuing with such an example, the maximum variation of MEP cylinder to cylinder due to compression ratio should not exceed the 3 sigma cycle to cycle 3 sigma spread. As a result, testing of different compression ratios may have to be conducted on the engine to quantify the effect of compression ratio on MEP at identical calibration and boundary condition settings. Based on these measurements, the maximum compression ratio variance may be calculated for the given engine, speed, and load. In one example, the equation 1, shown below, may be used to determine the compression ratio variance between combustion chamber.

σMEP,cycle-cycle⁡(rpm,⁢load)μMEP,cycle-cycle⁡(rpm,⁢load)>σMEP,compresion⁢⁢Ratio⁡(rpm,⁢load)μMEPcompersion⁢⁢Ratio⁡(rpm,⁢load)(Equation⁢⁢1)
However, other suitable techniques for ascertaining compression ratio variance have been contemplated. The compression ratio in each of the combustion chambers may be determined based on signals from pressure sensors coupled to the combustion chambers, signals from proximity sensors coupled to the combustion chambers, and/or signals from temperature sensors coupled to the combustion chambers, in one example.

If it is determined that there is not a deviation between the compression ratios (NO at404) the method advances to406. At406the method includes maintaining engine operating parameters. Maintaining engine operating parameters may include sustaining shutdown of the piston assembly heaters and operating the lubrication system according to a predetermined control strategy.

On the other hand, if it is determined that there is a deviation between the compression ratios (YES at404) the method advances to408. At408the method includes operating a piston heating system to apply a targeted amount of heat to a piston assembly based on the compression ratio deviation, the piston assembly including at least a piston positioned within the combustion chamber. In another example, step408may include actively heating the first piston assembly including at least the first piston to decrease a torque imbalance between a first combustion chamber and a second combustion chamber, the first combustion chamber having the first piston positioned therein and the second combustion chamber having a second piston positioned therein. Further in one example, operating the piston heating system to apply the targeted amount of heat to the piston assembly may include operating a piston assembly heater to initiate piston and/or piston rod heating. Operation of the piston assembly heater may include sending electrical power to an electrical heater coupled to a lubrication line spraying lubricant towards a piston rod and/or an underside of the piston, in one example. In other examples, operation of the piston assembly heater may include sending electrical power to an induction heater designed to inductively heat the piston and/or piston rod. In another example, operation of the piston assembly heater may include increasing an amount of heated coolant provided to a piston assembly heater. In such an example, heat from the coolant flowing through the piston assembly heater is transferred to lubricant flowing through the piston assembly heater. As previously discussed the piston heating will increase the compression ratio in the corresponding combustion chamber. Further in one example, the piston may only be heated when the engine coolant temperature is below a threshold value. In one example, the threshold temperature may be determined based on a temperature used to indicate a transition from a catalyst light off mode to a standard operating mode. However, other techniques for determining the aforementioned threshold have been contemplated.

Next at410the method includes inhibiting heating of a second piston via the piston heating system, the second piston positioned in the second combustion chamber. For instance, activation of a second piston assembly heater designed to heat the second piston may be prevented. In other words, deactivation of the second piston assembly heater may be sustained. In this way, one piston assembly heater may be activated while the other is deactivated to enable the deviation between the compression ratios to be reduced. Consequently, a torque imbalance in the engine can be reduced, thereby reducing NVH in the engine. A reduction in torque imbalance also enables combustion efficiency to be increased. Further in other examples, an amount of heating of the second piston may be reduced rather than inhibited.

At412the method includes determining if there is an increase or decrease in engine load. If there is an increase in engine load the method advances to414. At414the method includes operating the piston heating system to decrease the amount of heat provided to the pistons in the engine. Operating the piston heating system to decrease the amount of heat provided to the piston includes deactivating the first and second piston assembly heaters corresponding to the first and second combustion chambers, respectively. In other examples, an output of the piston assembly heaters for each of the combustion chambers may be decreased to decrease an amount of heat provided to the pistons via the piston heating system. Decreasing the compression ratios of the combustion chambers during high load conditions can increase combustion efficiency.

However, if there is a decrease in engine load the method advances to416. At416the method includes operating the piston heating system to increase the amount of heat provided to the pistons in the engine. Operating the piston heating system to increase the amount of heat provided to the piston includes activating or increasing the heat output by the first and second piston assembly heaters corresponding to the first and second combustion chambers, respectively. Heating the pistons during a low load condition enables the compression ratios of the combustion chambers to be increased to increase combustion efficiency.

FIG. 5shows another method500for operation of an engine with a piston heating system. As discussed above, the method may be implemented by the engines and piston heating systems described above with regard toFIGS. 1-3or may be implemented by other suitable engines and piston heating systems.

At502the method includes determining engine operating conditions. The engine operating conditions may include combustion chamber pressures, intake flowrate, engine temperature, exhaust gas flowrate, exhaust gas composition, engine speed, engine load, combustion chamber temperatures, piston position, etc.

Next at504the method includes determining if there is a torque imbalance in the engine. The torque imbalance in the engine may be ascertained based on combustion chamber pressure signals, in one example. For instance, if the compression ratios in two combustion chamber vary by an amount greater than a threshold value it may be ascertained that there is a torque imbalance in the engine. The threshold value may be determined using the techniques described above with regard toFIG. 4, in one example. However, other strategies for determining if a torque imbalance is occurring have been contemplated. For instance, the torque imbalance may be determined based on a comparison between temperatures and/or pressures in the first combustion chamber and the second combustion chamber. Furthermore, it will be appreciated that during some conditions the engine may be operating with a torque imbalance and without a torque imbalance during other conditions.

If it is determined that there is not a torque imbalance in the engine (NO at504) the method proceeds to506. At506the method includes maintaining engine operating parameters. Maintaining engine operating parameters may include sustaining shutdown of the piston assembly heaters and operating the lubrication system according to a predetermined control strategy.

On the other hand if it is determined that there is a torque imbalance in the engine (YES at504) the method advances to508. At508the method includes operating a piston heating system to apply a targeted amount of heat to a piston assembly corresponding to the combustion chamber to decrease the torque imbalance. For instance, electric or induction heaters providing heating to the piston and/or piston rod may be powered to increase an amount of heat provided to a piston to increase the compression ratio of the combustion chamber in which the piston resides.

At510the method includes determining if a knock condition is occurring in the engine. A knock condition may include one or more engine operating conditions that generate knock such as engine temperature, engine speed, engine load, etc. Specifically in one example, signals from a knock sensor coupled to the engine may be used to determine if engine knock is occurring. For instance, if a signal indicating vibration from a knock sensor exceeds a threshold value it may be determined that knock is occurring. Furthermore, it will be appreciated that the engine may be operated with a knock condition. If a knock condition is not occurring in the engine (NO at510) the method advances to512. At512the method includes maintaining engine operating parameters. For instance, predetermined valve timing and or injection timing strategies may be maintained.

On the other hand, if it is determined that a knock conditions is occurring in the engine (YES at510) the method proceeds to514. At514the method includes adjusting engine operating parameters to reduce (e.g., stop or prevent) engine knock. Adjusting engine operating parameters to reduce (e.g., stop or prevent) engine knock may include retarding or advancing valve timing, retarding injection timing, and/or reducing an amount fuel injection. In this way, combustion efficiency in the engine can be increased through a reduction in engine knock. In one example, the EGR flowrate may be adjusted to reduce engine knock. For instance, a flowrate of cooled EGR gas may be increased when knock is detected. Such a knock control strategy, may be implemented in a compression ignition engine. In another example, in a spark ignition engine, the spark timing may be retarded to reduce (e.g., stop or prevent) knock. Continuing with the spark ignition example, spark timing may be advanced when the engine is below the knock limit to increase combustion efficiency. In another example, the temperature of the oil sprayed onto the piston assembly may be decreased to reduce (e.g., stop or prevent) knock. In another example, a pilot injection quantity may be increased to reduce (e.g., stop or prevent) knock. A pilot injection may be an injection event occurring prior to a primary fuel injection event. In yet another example, injection timing may be retarded to reduce (e.g., stop or prevent) knock. Further in some examples, a combination of the knock reduction strategies may be used in conjunction to stop or prevent knock. Next at516the method includes determining if the engine is below a threshold temperature. The threshold temperature may corresponding to a cold start threshold temperature (e.g., 80° C.). An engine temperature sensor may be used to determine the engine temperature, in one example. If it is determined that the engine is not below the threshold temperature (NO at516) the method advances to518. At518the method includes maintaining engine operating parameters, such as maintaining current piston heating strategies. However, if it is determined that the engine is below the threshold temperature (YES at516) the method moves to520. At520the method includes operating the piston heating system to increase an amount of heat applied to the pistons in the engine. For instance, amounts of heat generated by piston assembly heaters providing heat to the first and second pistons may be increased to decrease a cold start duration. Specifically, the piston heating system may be operated to increase an amount of heat delivered to the combustion chambers until the engine temperature surpasses the threshold temperature. Consequently, engine emissions are reduced.

Now turning toFIG. 6, graphs600depict example piston heating system control signals in conjunction with engine load and compression ratios of different combustion chambers plots, such as described inFIGS. 1-5. The example ofFIG. 6is drawn substantially to scale, even though each and every point is not labeled with numerical values. As such, relative differences in timings can be estimated by the drawing dimensions. However, other relative timings may be used, if desired. Furthermore, each of the curves and plots time is represented in the x axis.

Continuing withFIG. 6, curve602depicts the compression ratio of a first combustion chamber and curve604depicts the compression ratio of a second combustion chamber (along the y axis). Signal606indicates a control signal sent to a first piston assembly heater and signal608indicates a control signal sent to a second piston assembly heater. Curve610depicts the engine load in the engine (along the y axis). The control signals for the piston assembly heaters shown inFIG. 6are intended for electrical heaters or induction heaters. However, it will be appreciated that in other examples, control signals may be sent to piston assembly heaters that utilized heated engine coolant to warm engine lubricant directed to pistons.

At t0, the compression ratio curves602and604have a variation612therebetween. Specifically, the compression ratio corresponding to the first combustion chamber is less than the compression ratio corresponding to the second combustion chamber. When such variation is recognized, the first piston assembly heater is turned on at t1. Turning on the first piston assembly heater generates piston heating. When the first piston is heated the compression ratio of the first combustion chamber is increased, to reduce the variance between the compression ratios. Once the compression ratios are substantially equivalent or within an acceptable range, the first piston assembly heater is turned off, as illustrated at t2. Therefore, when there is a deviation between compression ratios in different combustion chambers, a piston in the combustion chamber with the smaller compression ratio is heated to decrease the deviation between the compression ratios to decrease a torque imbalance in the engine. Consequently, NVH in the engine is reduced and engine efficiency is increased. Thus, the technical effect of heating a piston to reduce compression ratio variations is a reduction in NHV in the engine and an increase in combustion efficiency.

Additionally, the engine load curve610is above a threshold value614until it reaches t3. When the engine load decreases below the threshold value614both the first piston assembly heater and the second piston assembly heater are turned on. In this way, the compression ratio of the combustion chambers in the engine may be increased during low load conditions to increase engine efficiency.

Further in some examples, the piston assembly heaters may be designed to output a variable amount of heat such as in a stepwise or continuous manner. In such an example, the degree of piston assembly heater output may be determined based on the difference between the compression ratios of the combustion chambers, engine load (e.g., rate of change of engine load), engine temperature, etc. In this way, the degree of piston heating may be fine-tuned based on engine operating conditions. Moreover, it will be appreciated that the plots shown inFIG. 6are exemplary in nature and that, in other examples, the compression ratios and piston heating system control scheme may differ.

The invention will further be described in the following paragraphs. In one aspect, a method for operation of an engine is provided. The method includes determining a variation between compression ratios in a first combustion chamber and a second combustion chamber and operating a piston heating system to apply a targeted amount of heat to a first piston assembly based on the variation between the compression ratios, the first piston assembly including at least a first piston positioned within the first combustion chamber.

In another aspect, an internal combustion engine is provided. The internal combustion engine includes a first combustion chamber with a first piston positioned therein, the first piston coupled to a crankshaft via a first piston rod, a second combustion chamber with a second piston positioned therein, the second piston coupled to the crankshaft via a second piston rod, a piston heating system including a first heating device designed to provide heat to the first piston and a second heating device designed to provide heat to the second piston, and a controller including code stored in non-transitory memory executable by a processor to: determine a variation between compression ratios of the first combustion chamber and the second combustion chamber, and operate the piston heating system to apply a targeted amount heat to at least one of the first piston, the first piston rod, the second piston, and the second piston rod based on the variation between the compression ratios.

In another aspect a method for operation of an engine system is provided. The method includes actively heating a first piston assembly including at least a first piston to decrease a torque imbalance between a first combustion chamber and a second combustion chamber, the first combustion chamber having the first piston positioned therein and the second combustion chamber having a second piston positioned therein.

In any of the aspects herein or combinations of the aspects, operating the piston heating system may include activating a heater coupled to a lubrication line, the lubrication line including a nozzle directing lubricant to a first piston rod coupled to the first piston and a crankshaft during engine operation.

In any of the aspects herein or combinations of the aspects, operating the piston heating system may include activating a heater coupled to a lubrication line, the lubrication line including a nozzle directing lubricant to an underside of the first piston during engine operation.

In any of the aspects herein or combinations of the aspects, operating the piston heating system may include activating an induction heater coupled a section of a cylinder block adjacent to the first piston.

In any of the aspects herein or combinations of the aspects, the method may further include inhibiting heating of a second piston assembly based on the variation between the compression ratios, the second piston assembly including at least a second piston positioned in the second combustion chamber.

In any of the aspects herein or combinations of the aspects, the method may further include in response to identifying a knock condition, increasing a pilot injection quantity into at least one of the first combustion chamber and the second combustion chamber to reduce knock. In any of the aspects herein or combinations of the aspects, the method may further include in response to identifying a knock condition, increasing a flowrate of cooled exhaust gas recirculation in the engine to reduce knock.

In any of the aspects herein or combinations of the aspects, the variation between the compression ratios may be determined based on at least one of combustion chamber pressures and combustion chamber temperatures.

In any of the aspects herein or combinations of the aspects, the first heating device may be a heater coupled to a lubrication line.

In any of the aspects herein or combinations of the aspects, the lubrication line may include a nozzle directing lubricant to the first piston rod coupled to the first piston and the crankshaft during engine operation.

In any of the aspects herein or combinations of the aspects, the first heating device may be an induction heater coupled to a portion of a cylinder block adjacent to the first piston.

In any of the aspects herein or combinations of the aspects, the internal combustion engine may be configured to implement compression ignition in the first combustion chamber and the second combustion chamber.

In any of the aspects herein or combinations of the aspects, the first piston may be included in a first cylinder bank and the second piston is included in a second cylinder bank.

In any of the aspects herein or combinations of the aspects, the method may further include determining a knock condition in the combustion chamber and in response to determining the knock condition, advancing spark timing in the first combustion chamber to prevent knock.

In any of the aspects herein or combinations of the aspects, the torque imbalance may be determined based on a comparison between at least one of temperatures and pressures in the first combustion chamber and the second combustion chamber.

In any of the aspects herein or combinations of the aspects, the method may further include inhibiting heating of a second piston assembly based on the torque imbalance, the second piston assembly including at least the second piston.

In any of the aspects herein or combinations of the aspects, heating the first piston assembly may include actuating a heater coupled to a lubrication line with a nozzle jetting lubricant at a first piston rod coupled to the first piston.

In any of the aspects herein or combinations of the aspects, heating the first piston assembly may include actuating a heater coupled to a lubrication line with a nozzle jetting lubricant at an underside of the first piston.

In any of the aspects herein or combinations of the aspects, the method may further include adjusting an amount of active heating of the first piston and actively heating the second piston based on a change in engine load.

In any of the aspects herein or combinations of the aspects, the torque imbalance may be determined based on a comparison between temperatures in the first combustion chamber and the second combustion chamber.

In any of the aspects herein or combinations of the aspects, the method may further include increasing the amount of heat delivered to the combustion chambers by the piston heating system during a low load to increase the compression ratios of the combustion chambers.

In any of the aspects herein or combinations of the aspects, the method may further include decreasing an amount of heat delivered to the combustion chambers during a high load condition to decrease the compression ratios of the combustion chambers.

In any of the aspects or combinations of the aspects, the method may further include increasing an amount of heat delivered to the combustion chambers when the engine is below a threshold temperature.

In any of the aspects or combinations of the aspects, the first piston assembly may include a first piston rod.