Patent Grant
10337419
This application relates to diesel engine fuel management techniques. and provides a method and system for extending cylinder deactivation to mid-range engine loads.
It is possible to control combustion processes in diesel engines to limit the number of cylinders providing torque output. One technique is cylinder cut-out. The technique eliminates fuel to a cylinder while continuing to cycle the intake and exhaust valves. The piston also cycles. The technique results in fuel economy losses.
At very low loads and idle conditions, an engine runs with poor fuel efficiency. All cylinders are firing, but little to no torque output is needed. Even in a loaded idle condition, the engine could provide more torque than necessary. Fuel is wasted, and the fuel economy is poor.
The low, and inefficient, fuel use is not effective to heat the aftertreatment system, and so pollution is high.
It would be beneficial to improve fuel economy and fuel efficiency in a diesel engine. It is beneficial to reduce pollution.
The disclosure overcomes the above disadvantages and improves the art by way of a system and method for cylinder deactivation in a multi-cylinder diesel engine, comprising pumping air in to an intake manifold of the diesel engine using a turbocharger. Air is pumped in to the intake manifold using an intake air assisting device. And, fuel injection is selectively deactivated to at least one of the cylinders in the diesel engine. An intake valve and an exhaust valve is selectively deactivated for the at least one of the cylinders of the diesel engine.
A multiple cylinder diesel engine system comprises a multiple cylinder diesel engine comprising a respective intake valve and a respective exhaust valve for each of the multiple cylinders. An intake manifold is connected to supply air to the multiple cylinders of the diesel engine. An exhaust manifold is connected to receive exhaust from the multiple cylinders of the diesel engine. An intake air assisting device is connected to pump air in to the intake manifold. A valve control system is connected to selectively deactivate a respective intake valve and a respective exhaust valve for a cylinder of the multiple cylinder diesel engine. A fuel injection control system is connected to selectively deactivate fuel injection to the cylinder. The multiple cylinder diesel engine enters a cylinder deactivation mode whereby the valve control system deactivates the respective intake valve and the respective exhaust valve for the cylinder. The valve control system deactivates fuel injection to the cylinder while other cylinders of the multiple cylinder diesel engine continue to fire.
A pollution management system for a diesel engine, comprises a diesel engine comprising a plurality of combustion cylinders. Each of the plurality of combustion cylinders comprises a respective piston connected to a crankshaft, a fuel injector connected to an injection controller, an intake valve connected to an intake valve controller, and an exhaust valve connected to an exhaust valve controller. An exhaust system is connected to the exhaust valves. The exhaust system comprises a catalyst for filtering pollution from an exhaust stream and a sensor for measuring a pollution level in the exhaust stream. A control unit comprises a processor, a memory device, and processor-executable control algorithms stored in the memory. The control algorithms are configured to receive pollution level sensor data from the sensor, determine a pollution level in the exhaust stream, and determine whether the pollution level exceeds a pollution threshold. When the pollution level in the exhaust stream exceeds a pollution threshold, the control system selects at least one of the plurality of combustion cylinders for deactivation, commands the injection controller to deactivate the respective fuel injector for the at least one of the selected combustion cylinders, commands the intake valve controller to deactivate the respective intake valve for the at least one of the selected combustion cylinders, and commands the exhaust valve controller to deactivate the respective exhaust valve controller for the at least one of the selected combustion cylinders.
A method for operating a multiple cylinder diesel engine system in a cylinder deactivation mode comprises determining that the diesel engine system is operating within at least one threshold range. Cylinder deactivation mode is entered in at least one cylinder of a multiple-cylinder diesel engine when the diesel engine system is operating within the at least one threshold range. An air fuel ratio is adjusted to at least one firing cylinder of the multiple-cylinder diesel engine based on the entering of cylinder deactivation mode in the at least one cylinder. Entering cylinder deactivation mode comprises deactivating fuel injection to the at least one cylinder and deactivating intake valve actuation and exhaust valve actuation to the at least one cylinder.
Additional objects and advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosure. The objects and advantages will also be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claimed invention.
Reference will now be made in detail to the examples which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Directional references such as “left” and “right” are for ease of reference to the figures.
Cylinder deactivation (CDA), where the intake valve, exhaust valve, and fuel injection are shut off for a selected cylinder cycle, is not obvious for diesel engines for several reasons. Many benefits inure and can be used to improve fuel economy and pollution control. Contrary to prior research, CDA can be used to benefit fuel economy and pollution control in heavy machinery and light auto. For example, low load cylinders can be deactivated to yield a fuel economy increase. The efficiency of the engine increases because of a reduction in friction via elimination of valve motion. Further, turning off in-efficient cylinders to increase the efficiency of other cylinders improves fuel economy over-all.
Cylinder deactivation differs from “cylinder cut-out,” which merely turns off fuel injection to a chosen cylinders, but leaves affiliated valves in motion. Cylinder cut-out results in measurable and detrimental system losses. Cylinder deactivation, however, achieves measurable system gains. As cylinders are deactivated, other firing cylinders must increase their torque output (load) to maintain the user experience. Increasing the load on the firing cylinders increases their fuel efficiency & brake thermal efficiency. Deactivating the intake and exhaust valves on the deactivated cylinders reduces energy losses to move those valves, which increases fuel economy.
CDA can be used during certain duty cycles. For example, when on the highway, heavy duty trucks can turn off CDA for high speed or cruising duty cycles. But, for example, a garbage truck can use CDA throughout the pickup duty cycle. The same can be applied to a bus for a transport versus a pick-up duty cycle.
Normal operation of a 3, 4, 5, 6, 8, or 10 cylinder diesel engine involves inducing air into the intake manifold, closing valves on the cylinders, injecting fuel, igniting the fuel for combustion, and emptying the cylinder for the next cycle.
When the operating conditions do not require full torque output, it is possible to limit which cylinders receive fuel, and it is further possible to tailor the amount of fuel injected in to the individual cylinders. For example, it is possible to run the engine at 50% load capacity by deactivating fuel injection to half of the cylinders while using the remaining cylinders at full torque capacity. An even number of cylinders can be deactivated to balance torsion across the engine, but it is also possible to deactivate a single cylinder, or another odd number of cylinders, to receive fuel efficiency benefits. The fuel efficiency of the fully used cylinders is extremely high, while there is no fuel use in the deactivated cylinders. The overall fuel efficiency for the motive device is improved, and fuel consumption is reduced. The strategy permits tailoring the torque output to the driving conditions. Using a six cylinder engine as an example, it is possible to deactivate 2 or 4 cylinders while fully or partially using the torque output capacity of the remaining cylinders.
Turning to
Fuel is injected to individual cylinders via a fuel injection controller 300. The fuel injection controller 300 can adjust the amount and timing of fuel injected in to each cylinder and can shut off and resume fuel injection to each cylinder. The fuel injection for each cylinder 1-6 can be the same or unique for each cylinder 106, such that one cylinder can have more fuel than another, and one cylinder can have no fuel injection, while others have fuel.
A variable valve actuator (VVA) 200 also couples to the cylinders 1-6 to actuate intake valves 130 and exhaust valves 150. The VVA 200 can change the actuation of the intake valves 130 and exhaust valves 150 so as to open or close the valves normally, early, or late, or combinations thereof, or cease operation of the valves. Early Intake Valve Opening (EIVO), Early Intake Valve Closing (EIVC), Late Intake Valve Opening (LIVO), Late Intake Valve Closing (LIVC), Early Exhaust Valve Opening (EEVO), Early Exhaust Valve Closing (EEVC), Late Exhaust Valve Opening (LEVO), Late Exhaust Valve Closing (LEVC), a combination of EEVC and LIVO or Negative Valve Overlap (NVO) can be implemented by the VVA 200. VVA 200 can cooperate with a hydraulic, electric, or electric solenoid system to control the intake and exhaust valves 130, 150. The engine 100 can be cam or camless, or a hybrid “cam-camless VVA.” So, the intake and exhaust valves 130, 150 can either couple to a cam system for actuation, as the camshafts 801, 802 example of
A diesel engine works by compressing intake fluid in a cylinder 1-6 using a piston 160. Fuel is injected via fuel injector 310. The high heat and compression ignites the fuel, and combustion forces the piston from top dead center (TDC) to bottom dead center (BDC) and torque is thereby directed to the crankshaft 101. Diesel operation can be referred to as “4 stroke,” though other operation modes such as 2-stroke and 8-stroke are possible. In 4-stroke, the piston moves from TDC to BDC to fill the cylinder with intake fluid (stroke 1). The start of the cycle is shown in
Exhaust gases leave cylinders through exhaust ports 155 in engine block 102. Exhaust ports 155 communicate with an exhaust manifold 105. An exhaust manifold sensor 175 can monitor the pressure, flow rate, oxygen content, nitrous or nitric oxide (NOx) content, sulphur content, other pollution content or other qualities of the exhaust gas. Exhaust gas can power a turbine 510 of a variable geometry turbocharger (VGT) 501 or other turbocharger. The turbocharger 501 can be controlled via a turbocharger controller 500 to adjust a coupling 514 between the turbine 510 and the compressor 512. The VGT can be adjust so as to control intake or exhaust flow rate or back pressure in the exhaust.
Exhaust gas is filtered in an aftertreatment system. The aftertreatment system can include a variety of pollution management mechanisms such as a hydrocarbon, fuel or urea doser. Several filters can be alone or in combination, such as DOC, DPF, SCR, NH3, Cu-Ze SCR, among others. One or more catalyst 800 filters pollution, and can comprise a diesel particulate filter (DPF), Diesel catalysts typically comprise a variety of rare earth metals to filter pollution, including NOx. At least one exhaust sensor 807 is placed in the aftertreatment system to measure exhaust conditions such as tailpipe emissions, NOx content, exhaust temperature, flow rate, etc. The exhaust sensor 807 can comprise more than one type of sensor, such as chemical, thermal, optical, resistive, velocity, pressure, etc. The exhaust sensor 807 can comprise an array of sensors, with sensor distribution options including before, after, or within the catalyst 800. A sensor linked with the turbocharger 501 can also be included to detect turbine and compressor activity.
Exhaust can exit the system after being filtered by the at least one catalyst 800. Or, exhaust can be redirected to the intake manifold 103 via a variety of pathways, some of which are illustrated in
Variant engine system 12 in
Using a very small intake assist device 601 extends the operating range of cylinder deactivation (CDA) by boosting the available oxygen. A small air pump, supercharger, or fan is connected to an oxygenating source, such as intake system 700, The intake system can supply fresh air to increase the air fuel ratio in the intake manifold of the diesel engine. Instead of limiting CDA to low load or idle conditions, the intake assist device 601 can increase air flow to the intake manifold and can increase the air to the cylinders. This can provide a more lean burn engine by raising the air portion of the AFR. While it is possible to lower the AFR during cylinder deactivation (CDA) mode, the intake assist device makes it possible to increase the AFR by adding flow against a low pressure intake manifold. This is contrary to the prior art, which seeks to eliminate energy drains during CDA mode. EGR does not need to be suspended to limit CO2 contributions, but it can be regulated.
By controlling the air fuel ratio to the cylinders 1-6, it is possible to eliminate the turbocharger 501, thus simplifying the control algorithm outputs and reducing system outlay. In
Intake and exhaust valves 130, 150 move as controlled by VVA 200 for firing cylinders 1-3. However, intake and exhaust valves 150 are not actuated for cylinders 4-6.
Increasing the fuel to cylinders 1-3 makes the mixture in the cylinders 1-3 more “rich.” The air fuel ratio for the cylinder is lower, because there is less air and more fuel. The resulting exhaust is hotter, as shown in
Unlike gasoline engines, which must be a stoichiometric 17:1 AFR (seventeen parts air to one part gasoline), diesel systems can vary the AFR and still work. The AFR in a firing cylinder can range from 17:1-100:1 (seventeen parts air to one part diesel fuel up to 100 parts air to one part diesel fuel). Soot is an issue at low AFR, and so it is beneficial to keep the AFR 22:1-24:1 when high temperature operation is desired. To avoid soot, adjusting the air fuel ratio to a firing cylinder comprises adjusting one or both of the intake gases and the fuel injection to maintain an air fuel ratio of seventeen parts air to one part fuel or greater. CDA mode can operate with an AFR between 17:1-70:1, or 20:1-50:1. Another AFR range is 24:1-45:1. One AFR range for providing an aftertreatment catalyst bed temperature around 300 degrees Centigrade is 30:1-45:1 AFR.
Because of the polynomial relationship between AFR and TOT, it is possible to develop a control algorithm for sensing a low temperature condition and adjusting the air fuel ratio to bring the exhaust temperature to a desired range. Using the above exhaust gas recirculation (EGR) controller 400, fuel injection controller 300 and intake assist controller 600 is one aspect of regulating the exhaust temperature. Entering cylinder deactivation (CDA) mode on select cylinders is another aspect of adjusting AFR and TOT.
Entering CDA mode reduces air flow through the engine 100. This is shown in
Material selection limits at what temperature the catalyst is efficient, at what temperature the catalyst is ruined via sintering effects, and at what temperature the catalyst can conduct diesel particular regeneration (DPR). Regeneration processes burn off pollutants at a high heat, which limits the pollutant's atmospheric entry and environmental pollution. Burning off the pollution renews the catalyst 800 to capture pollution anew.
In certain load modes for the engine system, exiting normal mode and entering CDA mode can raise exhaust temperature 100 degrees Centigrade. The impact can be seen by turning to
Off-highway vehicles, such as forklifts, graders, pavers, harvesters, mowers, construction equipment, farming equipment, etc. operate for a significant amount of time at a load insufficient to heat the catalyst to its ideal temperature. But, one cannot simply adjust the catalyst to a different material because the vehicles have excursions to higher temperatures, and thus the catalyst 800 need to withstand higher temperatures without damage.
The unloaded idle mode (point UI) can have a high tailpipe pollution emission because the engine exhaust is far below the ideal catalyst temperature. Entering CDA mode to deactivate at least one cylinder adds instant heat to the exhaust by increasing the fuel efficiency of the engine. By adjusting the AFR to the firing cylinders, an additional 100 degrees Centigrade of heat can be instantly added to the exhaust. Recalling the curve of
The instant heat-up via CDA mode can be applied to diesel particulate filter (DPF) regeneration techniques. Instead of idling a vehicle to run a DPF regeneration cycle, computer control can initiate CDA mode during select operation modes or at select operation times. Further tailoring of the AFR augments the heat added to the exhaust. And, point R, an ideal DPF regeneration point, is more easily achieved without the use of a fuel doser or idle cycle.
It is possible to implement a method for monitoring exhaust temperature, wherein the air fuel ratio to a firing cylinder is adjusted to raise the exhaust temperature or to maintain the exhaust temperature above a threshold temperature. It is possible to monitor a pollution level exhausting from the diesel engine and to adjust the number of cylinders entering cylinder deactivation mode to reach a target pollution level. It is further possible to adjust the air fuel ratio to the at least one firing cylinder based on reaching the target pollution level.
It is possible to monitor an exhaust flow rate through the aftertreatment system, and to adjust the number of cylinders entering cylinder deactivation mode to reach a target exhaust flow rate.
The method of
Memory device 1401 is a tangible readable memory structure, such as RAM, EPROM, mass storage device, removable media drive, DRAM, hard disk drive, etc. Signals per se are excluded. The algorithms necessary for carrying out the methods disclosed herein are stored in the memory device 1401 for execution by the processor 1403. When optional variable geometry turbocharger control is implemented, the VGT control 1415 is transferred from the memory 1401 to the processor for execution, and the computer control system functions as a turbocharger controller. Likewise, the computer control system 1400 implements stored algorithms for EGR control 1414 to implement an EGR controller; implements stored algorithms for intake assist device control 1416 to implement intake assist controller; implements stored algorithms for fuel injection control 1413 to implement fuel injection controller. When implementing stored algorithms for VVA control 1412, various intake valve controller and exhaust valve controller strategies are possible relating to valve timing and valve lift strategies, as detailed elsewhere in this application,
While the computer control system 1400 is illustrated as a centralized component with a single processor, the computer control system 1400 can be distributed to have multiple processors, or allocation programming to compartmentalize the processor 1403. Or, a distributed computer network can place a computer structure near one or more of the controlled structures. The distributed computer network can communicate with a centralized computer control system or can network between distributed computer structures. For example, a computer structure can be near the turbocharger 501 for VGT control 500, another computer structure can be near the EGR valve 410 for EGR controller 400, another computer structure can be near the intake and exhaust valves for variable valve actuator 200, yet another computer controller can be placed for fuel injection controller 300, and yet another computer controller can be implemented for intake assist controller 600. Subroutines can be stored at the distributed computer structures, with centralized or core processing conducted at computer control system 1400.
If the engine system meets CDA criteria, as by having an appropriate load or crankshaft RPM, or both, the computer control system selects the number of cylinders that can be deactivated while meeting current load and RPM requirements in step S403. Additional factors to consider are one or more of whether the exhaust temperature is within a threshold range or at a target temperature, whether the brake thermal efficiency (BTE) is above a BTE threshold, or whether the tailpipe emissions are within a range or at a target level. One strategy deactivates as many cylinders as possible without impacting the torque output of the engine. Another strategy deactivates as many cylinders as possible to maintain as high an exhaust temperature as possible. Another strategy deactivates as many cylinders as possible to have as fuel-efficient operation as possible.
Once the number of cylinders for deactivation are selected in step S403, the fuel injection controller 300 shuts off fuel to the selected cylinders in step S405. A concurrent or consequent adjustment of air fuel ratio (AFR) to the firing cylinders can be made in step S413. The amount of fuel injected in to the cylinders ranges from 0-100%, and is computer controllable by appropriate mechanisms, including sensors, transmitters, receivers, and actuators. Step S413 can additively or alternatively comprise adjusting one or more of the timing or quantity of fuel injection, intake flow, exhaust gas recirculation (EGR), valve opening or valve closing profile (lift or timing) for the firing cylinders. This can comprise the AFR tailoring strategies detailed above and can comprise compressor 512 or intake assist device 601 or exclude turbocharger 501 as appropriate.
With fuel adjustments made, the intake and exhaust valve actuation is shut off for the selected, deactivated, cylinders in step S407. The system monitors one or more of exhaust temperature, brake thermal efficiency, pollution level, exhaust flow rate through the catalyst, etc. in step S409. If it is not possible to adjust the number of deactivated cylinders, the monitoring in step S409 continues, But, if it is possible to deactivate additional cylinders, step S411 determines to do so. For example, the thresholds for temperature, pollution or flow rate could indicate that an increase or decrease in the number of cylinders in CDA would improve exhaust conditions. So, if the thresholds indicate that adjusting cylinders in CDA mode would benefit the target exhaust conditions, the method checks whether other parameters, such as load and RPMs, permit CDA mode by returning to step S401.
In one aspect, and returning to
Returning to the flow diagram, the results of step S409 can be analyzed and a determination can be made in step S415 to decide whether to adjust the exhaust profile. As above, to adjust aspects of the exhaust and its ability to heat the catalyst 800 or have pollution filtered from it, it can be necessary to adjust the engine activity at the cylinder level. And so, if the exhaust profile is to be adjusted, the algorithm returns to step S413. Otherwise, the system continues to monitor as in step S409.
It may be necessary to exit CDA mode altogether, in step S417, as when the load on the engine increases above a threshold. Or, as when the brake thermal efficiency or pollution control is better outside of CDA mode. The system checks whether the engine still meets criteria for implementing CDA mode by returning to step S401. If base criteria are not met, step S417 triggers an exit from CDA mode. The deactivated cylinders receive valve actuation control and fuel injection to return to firing mode. However, the algorithm can continue to check whether AFR adjustments or valve profile adjustments benefit the exhaust profile, as by continuing the flow through steps S413, S409, & S415.
Triggering conditions for entering or exiting CDA mode, or for combining variable valve actuation techniques with normal or CDA mode cylinders, are outlined in
A bold line in
The threshold range can comprise an exhaust temperature range below an ideal catalyst bed temperature. The ideal catalyst bed temperature can be between 200-300 degrees Centigrade, above 200 degrees Centigrade, above 300 degrees Centigrade, or can be an exhaust temperature beneath a diesel particulate filter regeneration temperature. In this last instance, the diesel particulate filter regeneration temperature can be around or above 500 degrees Centigrade. Outside the temperature threshold range, it is possible to exit CDA mode.
An exhaust temperature sensor 807 in combination with the control system 1400 can receive and process exhaust temperature data from the exhaust temperature sensor. Based on the exhaust temperature data, commands can be adjusted to the fuel injector to adjust the quantity of fuel injected to active combustion cylinders of the plurality of combustion cylinders. Also, commands can adjust the number of combustion cylinders selected for deactivation.
Turning to
The triggering conditions of
The catalyst 800, when 96% efficient, can receive exhaust having 5.0 grams per horsepower hour NOx and remove enough NOx to stay under the 0.2 g/hp-hr upper limit. Likewise, when the catalyst is 96% efficient, the catalyst can receive 7.5 g/hp-hr NOx from the exhaust manifold, yet filter pollution to stay under the 0.3 g/hp-hr upper limit. The amount of NOx pollution from the engine that can be filtered decreases as the catalyst efficiency decreases. So, by using the catalyst temperature as a determinative threshold, and maintaining the catalyst temperature within a target threshold range, or at a target temperature, the firing cylinders can be run in high fuel efficiency mode (high temperature, high NOx output) without increasing pollution at the tailpipe. The algorithm of
Returning to
A load monitoring sensor such as crankshaft sensor 107 can determine a load on the engine. The control algorithm can receive load data from the crankshaft sensor 107 and determine a load on the engine. The control system 1400 can determine an engine output requirement based on the load on the engine. When a load on the engine is below a first load threshold LT1, the control system 1400 can adjust the number of the plurality of combustion cylinders selected for deactivation to meet engine output requirements. When a load on the engine is above the first load threshold LT1, the control algorithm is configured to boost intake flow to the intake manifold. When the load on the engine is above a second load threshold LT2, the control algorithm exits CDA mode.
The load on the engine can impact the decision to enter CDA mode in a variety of ways. Comparing
The control system 1400 can monitor the engine operating mode. A threshold range for entering CDA mode can comprise one or more of an idle engine operating mode threshold LTA, a loaded idle engine operating mode threshold LTB, and a loaded engine operating mode threshold LTC. The number of cylinders of the multiple-cylinder diesel engine entering cylinder deactivation mode is adjusted based on whether the engine operating mode is the idle engine operating mode, the loaded idle engine operating mode, or the loaded engine operating mode.
Engine operating modes can comprise a lightly loaded mode, a medium load mode, and a heavy duty load mode, and the threshold range for entering CDA can comprise the lightly loaded mode and the medium load mode. An engine operating mode can also comprise a start-up mode, and the threshold range for entering CDA can comprise the start-up mode.
Determining whether to enter CDA can comprise monitoring an engine crankshaft speed via crankshaft sensor 107. When a threshold range comprises a high speed threshold range above ST and a low speed threshold range below ST, the number of cylinders entering cylinder deactivation mode is adjusted based on whether the engine crankshaft speed is within the high speed threshold range of the low speed threshold range.
A normal operating mode can be used in Zone 4, especially when an engine is optimized for operation in Zone 4, such as a cruising mode. An augmented mode can be used in Zones 1-3, in Zones 2 & 3 only, or in Zone 3 only. The augmented mode applies the principles of steps S409, S415, & S413 to adjust the valve opening or valve closing profile to impact fuel efficiency. Above threshold speed ST, Zone 3 is used. Below threshold speed ST, Zone 4 techniques are used.
The techniques of the augmented mode can adjust the valve profiles, as summarized in
Cylinder deactivation requires an implementation strategy for optimal trade-offs between BSFC (Brake Specific Fuel Consumption) & NOx & TOT (turbine out temperature). Early Intake Valve Closing (EIVC) and Late Intake Valve Closing (LIVC) yield good BSFC. It is possible to use these techniques at high speed and high load conditions. While NOx is higher for EIVC and LIVC, the catalyst is heated to an ideal filtering range via the CDA at start-up and low load. The catalyst can filter the increased NOx for a net tailpipe emission within the desired regulatory limits.
As
Other triggering events for entering or exiting CDA mode can include monitoring an accelerator position, and wherein the threshold range comprises a subset of accelerator positions. A certain rate of acceleration causes a load on the engine, and so CDA mode can be linked to the accelerator as it can be linked to the load. Other user inputs, such as buttons, levers and other user inputs can trigger a threshold range for entering CDA mode. For example, the user can select DPF regeneration mode, which causes the engine system to enter CDA to reach a target DPF regeneration temperature, such as point R in
Exiting CDA mode can comprise deselecting the combustion cylinders selected for deactivation, commanding the injection controller to activate the respective fuel injector for the at least one of the deselected combustion cylinders, commanding the intake valve controller to activate the respective intake valve for the at least one of the deselected combustion cylinders, and commanding the exhaust valve controller to activate the respective exhaust valve controller for the at least one of the deselected combustion cylinders. The control algorithm is further configured to adjust commands to the fuel injector to adjust the quantity of fuel injected to active combustion cylinders of the plurality of combustion cylinders based on the engine output requirement. As the cylinders exit CDA mode, the fuel injector 310 is controlled to redistribute fuel based on engine load requirements.
The control algorithm can comprise instructions to receive air flow data from an air flow sensor such as intake manifold sensor 173. The control system 1400 can determine an air flow amount to respective intake valves, determine an air fuel ratio for each of the plurality of combustion cylinders based on the determined air flow amount and based on the fuel injector commands, and, based on the determined air fuel ratio, command the intake assisting device to increase air flow to the plurality of combustion cylinders when the load on the engine is within a predetermined range. Based on the determined air fuel ratio, the control system can adjust commands to the fuel injector 310 to adjust the quantity of fuel injected to active combustion cylinders of the plurality of combustion cylinders.
Returning to
The air assisting device acts to supply fresh air in lieu of, or to supplement, the air supplied via turbocharging to raise the ratio of oxygen to fuel. Instead of using CDA only at very low load or idle conditions, CDA use is extended to higher load conditions. The air assisting device is used to raise the air fuel ratio (AFR) from 20:1 to 23:1 or 24:1. For example, using an air pump permits CDA at 25-35% load. A larger range is 25-50% load. This allows a diesel engine to benefit from reduced emissions over a larger operating range and at loads where turbocharging otherwise wouldn't suffice to raise the AFR. The low fuel use and low emissions is possible over a greater engine operating range because the oxygenating source is not dependent on the turbocharger. The intake assist device 601 can be an air pump, a supercharger or even a fan.
Because the duty cycle of the intake air assisting device is very small, for example, 2%, and because the intake air assisting device size is kept very small, for example, 15% the size of the engine or less, there is a net fuel savings. For example, a 15 L, 7 L, or 2 L engine can be paired with a 0.3 L supercharger, a fan, or an air pump. Using an 2 L engine again as an example, the intake air assisting device supplies approximately 0.5 kg/min air flow or less to increase the AFR for the 25-50% load operation. The low, 140-150 kPA intake manifold pressure in this load range permits a low capacity intake air assisting device and results in a low power use.
CDA mode can be used on a six cylinder engine or an eight cylinder engine. CDA can be entered on half of the cylinders, two of the cylinders, etc. The engines can operate with only two firing cylinders. The use of CDA mode creates “an engine within an engine,” because a great capacity can be installed on a device or vehicle for high load operation, but computer control strategies reduce the engine fuel use and pollution to that of a much smaller engine for small loads and idle conditions. That is, CDA mode can be used to selectively reduce the engine displacement. But, CDA can also be used to double the load per cylinder, increasing torque output from each cylinder over a normal mode. These assets can reduce emissions, improve fuel economy, and increase TOT.
Yet another benefit of CDA mode is the ability to recover energy of compression. Because charge air or other intake flow is captured in a CDA cylinder, and because the piston 160 is not deactivated, the piston continues to cycle up and down in the deactivated cylinder. The piston follows its stroke cycle, and work is done to compress the charge of air. But the piston springs back, which can augment torque output from the diesel engine by coupling compression spring-back from the piston 160 to the crankshaft 101. This “air spring” effect can return more energy to the crankshaft than friction losses would otherwise rob from a normal mode-activating cylinder. Using CDA mode puts less wear on the engine than engine braking, regular combustion, positive power, or braking loads. Shutting off cylinders preserves them, and running the remaining firing cylinders efficiently is less wear across the engine than running all cylinders inefficiently. To augment the spring-back, it is possible to boost the intake flow to the cylinder prior to deactivating the valves.
NOx Adjustment Strategies Using CDA
A fuel efficient combustion cycle has increased NOx emission. Consumers want good fuel economy, but Federal Regulations require low NOx output. The goals are at odds.
One compromise has been to make the engine less fuel efficient to reduce NOx output, as by adjusting engine timing to retard the engine, or as by exhaust gas recirculation (EGR). Redesigning other system components attempts to increase fuel economy to make up for the loss of fuel efficiency. The other components make up for fuel economy losses in the engine by being more aerodynamic, having less drag, etc. But, in the end, the engine is fuel inefficient.
One issue is that a fuel-efficient diesel (one having low BSFC—brake specific fuel consumption) has increased NOx output. For example, a fuel efficient diesel can output 6-9 grams NOx/engine hour. However, regulations require output of 0.2, and soon to be 0.02 grams NOx/engine hour. Only by having an efficient aftertreatment system can the goal be reached while satisfying consumer demand for fuel efficiency. And so it becomes necessary to heat the catalyst quickly for efficient filtering.
For example, being 8% more fuel-efficient, as measured by BSFC, increases NOx 2 g/hp-hr. Another 8% fuel efficiency increase does the same, and so fuel efficiency/fuel economy can increase 16%, but at a cost of moving from 1 g/HP hr to 5 g/Hp hr NOx. If the catalyst can stay in its most efficient filtering range, the NOx is captured, and the tailpipe emission meets the necessary standards.
In a gasoline engine, CDA would work to reduce pumping losses, and to reduce need for an intake throttle. The benefits would be limited to flow and drag losses. A gasoline engine must be run stoichiometric fuel:air (AFR), and so CDA mode's benefits are more limited.
On a diesel engine, which lacks a throttle, CDA is less about pumping losses, and more about efficient combustion. The diesel engine can have a range of air-fuel ratios. The AFR can be adjusted to conditions, and so CDA works to run each cylinder at a higher load, which increases that cylinder's brake thermal efficiency, which improves fuel economy. CDA permits fuel economy benefits by deactivating one or more cylinders to conserve fuel to that cylinder and to conserve energy expenditures to actuate that cylinder. Fuel economy is increased in the remaining active cylinders, because the fuel to those cylinders is adjusted in response to the deactivated cylinder and in response to the load or idle conditions. The amount of fuel can be metered for the circumstances.
Pollution is reduced in one aspect by deactivating cylinders in CDA mode. Turning off one or more cylinders causes reduction in inefficient fuel use, which lowers pollution and fuel consumption. So, CDA causes instantaneous benefits. Because the AFR is adjusted to the active cylinders, the amount of air necessary for optimal combustion is also tailored to the active cylinder. In a low load condition, the amount of torque output needed is quite small. Pushing air in to all cylinders, and pushing fuel in to all cylinders puts out too much torque and uses too much energy and fuel. Deactivating one or more cylinders permits one or more remaining firing cylinders to use more fuel or less air, resulting in a hotter combustion. The higher heat combustion has lower tailpipe pollution because the catalyst bed can be heated and pollution can be better filtered. In one aspect, the NOx emissions reduce because less quantity of exhaust output generates less NOx. However, higher fuel economy increases NOx, because efficient combustion increases NOx. Thus, there are tradeoffs between increased fuel efficiency, decreased exhaust amount, and the ability of the catalyst to heat to optimum NOx filtering temperature.
Just using CDA, absent adjustments to AFR or fuel to other cylinders, increases the fuel efficiency by 5%, because there is less fuel use with cylinders deactivated. Friction losses to the CDA piston are far outweighed by gains from not running the valves and injector(s).
But, adjusting AFR to the active cylinders can increase pollution by increasing the efficiency of combustion. Efficient fuel use in a cylinder can increase NOx. So with CDA, the amount of air necessary for optimal combustion is also tailored to the active cylinder. In a low load condition, the amount of torque output needed is quite small. Pushing air in to all cylinders, and pushing fuel in to all cylinders puts out too much torque and uses too much energy and fuel. Deactivating one or more cylinders permits one or more remaining cylinders to use more fuel or less air, resulting in a hotter combustion. The higher heat combustion has lower pollution because the catalyst bed can be heated and pollution can be better filtered by the aftertreatment system, which runs most efficiently when heated to between 200-300 Degrees Centigrade.
Adjusting the AFR with CDA instantly heats the exhaust. The higher heat exhaust warms the catalyst to its optimum filtering temperature. Using CDA, it is possible to remove the fuel doser that would otherwise be needed to raise exhaust temperature during low load or low temperature operation. This reduces aftertreatment fuel use and expenses. For urea pollution management systems, the need for urea is dramatically reduced.
On the one hand, NOx emissions reduce during CDA in low load conditions because there is a decrease in the amount of exhaust gas output. Fewer cylinders in use spew less exhaust. Less exhaust output generates less NOx. However, decreasing the exhaust via CDA reduces flow rate by half, which reduces the amount of exhaust for heating the catalyst. But, the reduced flow rate retains heat in the catalyst better, and the exhaust is hotter, which heats the catalyst quicker. However, higher fuel economy increases NOx, because efficient combustion increases NOx. With better catalyst heating, the catalyst is better able to absorb the NOx. Thus, there are tradeoffs between increased fuel efficiency, decreased exhaust amount, and the ability of the catalyst to heat to optimum NOx filtering temperature.
The exhaust heats instantly, because CDA can be turned on and off in one cam revolution, but the surrounding metal, such as cylinder-to-cylinder heat transfer and such as the catalyst itself, take longer to warm up from heat transfer. Meeting future emissions standards becomes an issue of heating the operating environment around the ideally heated exhaust.
Running the engine efficiently using CDA uses fuel more efficiently in the active firing cylinders, while using no fuel in the inactive cylinders. The reduced fuel use increases fuel economy, which is highly desired. The increased catalyst function versus low fuel use is also highly desired. Using less fuel more efficiently ultimately reduces NOx emissions for the engine.
Cylinder Deactivation Use Strategy (Exhaust Temperature On-Demand)
Cylinder deactivation is extremely beneficial to fuel economy and aftertreatment pollution management and can be implemented when the full engine torque output is not required. CDA can be used to heat exhaust temperature, which heats the catalyst, which causes better NOx management. A heated catalyst is better able to filter NOx.
CDA deactivates the intake valve, exhaust valve, and fuel injection to a cylinder, while increasing the torque output of the remaining cylinders, as by running the other cylinders in a more fueled condition, or in a more stoichiometric air-fuel ratio. Unlike a gasoline engine, a diesel engine can have variations in the air-fuel ratio (AFR) such that the amount of air can be varied with respect to the amount of fuel to adjust the torque output. Adjusting the AFR to adjust the torque output also adjusts the heat output of the cylinder.
One control technique implements CDA mode only when the exhaust temperature is below 250 degrees Centigrade. Below this temperature, NOx is poorly filtered. Above this temperature, the catalyst is efficient. Fuel economy ordinarily closely tracks this phenomenon. But, CDA increases fuel economy by more efficiently using fuel in each cylinder, as by adjusting the air-fuel ratio (AFR).
In diesel, a fuel efficient cylinder increases both NOx output and exhaust temperature. So, it is thought that CDA is bad: it increases NOx. But, the temperature increase improves the ability of the catalyst to filter pollution. This ultimately filters more NOx than the fuel economy increase adds, resulting in a net reduction in pollution.
Note that the 250 degree line for implementing CDA can be adjusted to 200 or 300 degrees Centigrade, depending upon catalyst material and goal NOx output.
A large portion of a diesel engine's operation map outputs torque with the exhaust temperature below 250 Centigrade as shown in
Studying the engine map reveals that the need for CDA mode decreases as engine RPMs increase. The engine is more able to output exhaust at target aftertreatment temperatures as load and speed increase. Restricting CDA by temperature makes CDA use less detectable to the driver, who has ordinary operation experience above the low-load temperature band.
Cylinder Deactivation for Catalyst Regeneration
It is difficult to design the catalyst for optimal operation for the full temperature range of 0-600 degrees Centigrade. At some point, the low temperature NOx filtering materials cannot withstand the heat of DPF catalyst regeneration, yet higher temperature filtering materials perform poorly at low temperatures. So, capturing NOx is difficult.
Using CDA, it is possible to remove the fuel doser that would otherwise be needed to raise exhaust temperature during low load or low temperature operation. This reduces aftertreatment fuel use and expenses. For urea pollution management systems, the need for urea is dramatically reduced.
One issue is that a fuel-efficient diesel has increased NOx output. For example, a fuel efficient combustion diesel can output 6-9 grams NOx/engine hour. However, regulations require output of 0.2, and soon to be 0.02 grams NOx/engine hour. Only by having an efficient aftertreatment system can the goal be reached while satisfying consumer demand for fuel efficiency. And so it becomes necessary to heat the catalyst quickly for efficient filtering and for efficient burn-off.
The exhaust heats instantly, for example, an additional 100-110 degrees Centigrade can be added to the exhaust temperature by switching from normal operation to CDA operation. This contrasts sharply with EEVO and other prior art strategies that must cycle for some time to bring exhaust temperature up. Current heavy machinery can take all 20 minutes of its FTP (Federal Testing Procedure) emissions test to come up to the correct temperature for emissions standards, if at all. Certain machinery never generates enough heat to pass emissions tests. Other strategies require 7 minutes to warm up to reach emissions test. CDA mode can heat an aftertreatment system within 3 minutes. The increased exhaust temperature available through CDA mode is greater than competing strategies, and requires less fuel to reach that temperature than competing strategies.
Because CDA can be turned on and off in one cam revolution, the ability to switch cylinders between normal and CDA modes permits fast tailoring of the exhaust temperature. Meeting future emissions standards becomes an issue of ideally heated and filtered exhaust.
Catalyst regeneration heats the catalyst to a particular temperature, for example 500-600 degrees Centigrade. NOx is burnt off, along with other pollutants, to clean the catalyst so that it can filter pollution once again. Because CDA can so instantly heat the exhaust, it is an asset for particulate filter regeneration techniques. Using CDA can reduce vehicle down time for regeneration, and provide more on-demand regeneration. So, instead of pulling road-side to run the engine at high RPMs with the parking brake on, CDA mode can activate during vehicle operation to regenerate the catalyst.
Using CDA, it is possible to remove the fuel doser that would otherwise be needed to clean the catalyst during low load or low temperature operation. This furthers the goal of redesign of the aftertreatment for one temperature band for efficient operation. Ideally, the catalyst operates from 200-600 degrees Centigrade, but from a materials science perspective, it is difficult to design the catalyst for the whole temperature operating range 0-600 C. Thus, using CDA to instantly heat the exhaust to 200 or more degrees Centigrade alleviates some of the material burden of including a low temperature filtering material in the catalyst. The optimal temperature band of the aftertreatment can be moved, and the materials within adjusted accordingly.
Other implementations will be apparent to those skilled in the art from consideration of the specification and practice of the examples disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims.
| Filing Document | Filing Date | Country | Kind |
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| PCT/US2016/013863 | 1/19/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/118482 | 7/28/2016 | WO | A |
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