Patent Application
20060168945
The present invention pertains to internal combustion engines, and particularly to engines with aftertreatment systems. More particularly, the invention pertains to NOx reduction in the exhaust stream of an engine.
The present system may use a cylinder cutout system for regeneration of a lean NOx trap or adsorber in the exhaust of an internal combustion engine.
Diesel engines may offer a 30 to 50 percent improved fuel economy over conventional gasoline engines in automobiles, but at a potential cost of increased emissions. However, a lean NOx trap system may be used to reduce NOx emissions. NOx traps generally require periodic regeneration by raising the temperature of the exhaust stream. A related-art, full flow lean NOx trap achieves regeneration through enriched operation of the engine, an approach that has several disadvantages including a high fuel penalty
A cylinder cutout system may be used in lieu of an enriched operation to overcome the fuel economy penalty. In a conventional gasoline engine, the intake charge may be throttled under partial load on the engine in order to control the air flow, fuel flow and power generated by the engine. In an engine employing cylinder cutout, instead of throttling to control air flow, one or more cylinders may be “cut-out” in a controlled fashion by using, for example, a variable valve actuation mechanism. This approach may reduce or eliminate pumping work losses of the engine. The cylinder cut-out approach may be applied specifically to diesel engines for potentially controlling exhaust temperature and achieving increased fuel economy.
In
Manifolds 15 and 23 may be attached to the head 13 having ports 19 and 22 which connect the manifolds to their respective valves 25 and 26. The valves 25 and 26 may be round but appear oval in
The intake valve 25 and exhaust valve 26 may be opened and closed by the movement of lobes 29 and 33 on camshafts 31 and 32, respectively. Although engine 11 may have a dual overhead camshaft arrangement in
Valve springs 47 and 48 may be situated between components 43 and 44 and spring base supports 51 and 52. Supports 51 and 52 may be secured top head 13. Under conventional operation and with no actuation, springs 47 and 48 may keep valves 25 and 26 normally closed.
Camshafts 31 and 32 may be linked to a crankshaft 24 for rotation by one of several ways. For examples, the camshafts may be mechanically connected to the crankshaft or the camshafts may be electronically and/or hydraulically actuated with movement in accordance with a sensed position or angle of the crankshaft. Various devices such as solenoids may be utilized to actuate the valves. Other intake and exhaust approaches, even those without valves, may be alternatively incorporated in the engine.
When the cams 31 and 32 rotate, the lobes 29 and 33 may turn toward and push the stems 35 and 36 to open the valves 25 and 26, respectively. Rollers 45 and 46 may be attached to the ends of the valve stems 35 and 36 to remove contact and friction between the stem ends and the cam surfaces during actuation of valves 25 and 26, respectively. The valves 25 and 26 may generally be opened and closed at different times. The camshafts 31 and 32 may rotate at about one-half the rotation rate of the crankshaft 24. Various other kinds of mechanisms, besides valves and injectors, may be utilized for bringing air and fuel to the engine and for removing exhaust gases from the engine.
As piston 21 approaches its closest position (TDC 41) to head 13 which is highest point of a connecting rod 38 from the center of crankshaft 24, the compressed mixture of air 16 and fuel 27 may ignite (due to the heat of a highly compressed mixture in a diesel engine or the spark of a plug in a gasoline engine) and expand thereby providing much pressure on the piston 21 and pushing the piston down the sealed cylinder 17 and away from the head 13. Piston 21 may be connected via the connecting rod 38 to the crankshaft 24 that is rotated by the force of the burning mixture upon the piston. The piston 21 being forced down by the burning and expanding mixture of air 16 and fuel 27 may be regarded as a power cycle.
As the piston approaches its farthest position from the head (i.e., bottom dead center—BDC 42, which is the lowest position of the connecting rod 38 relative to the center of the crankshaft), the exhaust valve 26 may open and the piston 21 return back up the cylinder 17 and push a burnt mixture or exhaust gas 14 out of the cylinder 17 through the exhaust valve 26 into the exhaust manifold 23 via an exhaust port 22, resulting in an exhaust cycle.
The exhaust valve 26 may close and the intake valve 25 open thereby permitting the piston 21 to draw in another amount of air 16 into the cylinder 17 during its next intake cycle as the piston 21 moves down cylinder 17 away from the head 13.
The sequence of intake, compression, power and exhaust cycles may repeat themselves for a given piston 21 and cylinder 17 over the next two rotations of the crankshaft 24. Each of the pistons 21 of the other cylinders 17 may proceed through the same process. However, each piston may have its sequence of cycles offset from the other pistons in the engine by somewhere from one-half to one-and-one-half revolutions of the crankshaft 24. Thus, in the case of the four cylinder engine 11 shown in
Engine 11 may instead have a different number of cylinders and configuration such as an in-line, “V” or opposed cylinder arrangement. The engine may be an internal combustion engine of another kind not having pistons in cylinders. An example of such engine may be a Wankel engine.
The present system 10 may incorporate a cylinder 17 cutout mechanism tailored for regeneration of a lean NOx trap 50 (i.e., NOx adsorber) in
Several benefits may result from the NOx trap or adsorber 50 regeneration approach of the present system 10. Relative to a first benefit, when regeneration of NOx trap 50 is triggered, a cylinder 17 cutout may be employed. One or more cylinders 17 may be cutout. Cutout may be rotated among cylinders to maintain mechanical (e.g., rotational) balance and thermal balance in the engine. For instance, an engine having a cutout applied sequentially to all of the cylinders may run smoother than if a cutout is constantly applied to the same cylinder or cylinders. Also, the heat in the engine may be more evenly distributed in it with a sequenced cutout. The rotation of the cutout among the cylinders may be of various sequences, patterns or forms. Cutout may raise the load on the remaining cylinders 17 of engine 11, and consequently raise exhaust 14 temperature and reduce oxygen concentration (i.e., NOx reduction). Any variable valve actuation mechanism may be employed for a regeneration-driven cylinder cutout.
Additional control of exhaust 14 temperature, oxygen and CO/hydrocarbon concentration may be achieved by secondary post-injection of fuel 27 in the cylinder 17, supplementary injection in the exhaust 14 and/or injection duration control. Fuel injection systems may be designed to provide injection events, such as the pilot event 65, pre-event 66, main event 67, after event 68, post event 69 and a second post event 70 injections, in that order of time and crankshaft position, as shown in the graph of fuel 27 injection rate control in
All of the combustion of the injected fuel 27 does not necessarily take place in cylinder 17. After-event injection 68 and post-event injections 69 and 70 do not necessarily contribute to the power developed by engine 11, but may be used judiciously to heat the exhaust 14 and use up excess oxygen. In some cases when the temperature during an expansion (power) stroke in cylinder 17 is very low (e.g., while under light load conditions), the post event injection fuel may go out as raw fuel and become difficult to manage. Yet, there are times when two post event injections 69 and 70 may be used—one to raise the combustion and exhaust temperature early in the expansion stroke and the second to further raise the temperature later in the stroke for more effect in the downstream regeneration process. However, there may be an impact on the fuel economy of the engine 11 due to the post event injections or fuel injection duration. These added fuel injection events, if utilized, may be implemented to merely tweak the cylinder 17 cutout approach for the NOx adsorber 50 aftertreatment, not to replace the cutout.
Relative to a second benefit, regeneration may be triggered based on an NOx sensor or sensors 54 or on a model-based calculation of NOx emissions. This calculation may be used to estimate the total NOx adsorbed since the last regeneration event and/or determine the current adsorption efficiency. Either of these results may be used to trigger regeneration and cutout.
Relative to a third benefit, cylinder 17 cutout may be used to maintain an exhaust 14 operating temperature within the optimum or desired adsorption temperature window, for trapping and storing emissions, thereby extending the period over which the NOx adsorber 50 can operate before needing regeneration.
An integrated sensing and control system may be used, including a calculation module in an ECU 40 that determines when cylinder 17 cutout is to be employed. Calculations by the module may be based on sensor readings, in particular, exhaust 14 temperatures from sensor 55 and sensor 56, NOx emission measurements from sensor 54, and the adsorber state as known or estimated from sensed data or calculations. Other variables such as current engine 11 load and speed may also be incorporated in the calculation.
In the case where accurate NOx sensors are not available, a mathematical or NOx emissions model may be incorporated within or connected to the calculation module. This model may also be used in a predictive capacity, for forecasting future emission levels based on projected operating conditions of the engine.
The calculation module may render a cylinder 17 cutout decision based on a heuristic or model-based algorithm. An example of a heuristic algorithm may be a simple rule that dictates cylinder 17 cutout when the adsorber state is below a predetermined threshold. Another example may be a rule that dictates cylinder 17 cutout when the adsorber state is acceptable but exhaust temperature has been too low for optimum adsorber operation for some predetermined duration. An example of a model-based algorithm may be a predictive calculation, based on current operation and sensed parameters of engine 11, indicating when the adsorber is likely to become saturated.
A provision may be included for a higher-level mode command from the central engine computer unit (ECU 40) that can override an aftertreatment-centered calculation. The ECU 40 may incorporate a processor, a computer, a controller, a calculation module and/or an emissions model. The output of the cylinder 17 cutout calculation may be routed to either a dedicated cylinder controller or the engine ECU 40. The fuel penalty for this additional control may be much less than for that without cylinder cutout.
If a cylinder 17 cutout is desired or needed, it may be actuated with the valve mechanism shown as an illustrative example. Other approaches may be implemented such as fuel 27 shut off to the particular cylinder 17 involved. In the present approach, the injector 12 may be turned off and additionally the valves 25 and 26 may be deactivated in a closed position. However, the valves may be deactivated in a combination of various positions, for example, a closed exhaust valve 25 and an open intake valve 26. The desired combination of deactivated positions may depend on other parameters such as oil leakage into the cylinder.
Injector 12 may be controlled with a signal along line 59 from ECU 40. For instance, a signal to activate or turn on injector 12 may be sent by ECU 40 at an appropriate time when the valves are activated to result in a power stroke. In a similar manner, injector 12 may be inactivated or shut off with appropriate timing.
In
If cylinder 17 is to be cutout, a signal from ECU 40 may go along line 61 to device 43 to effectively deactivate valve 25, which means that lobe 29 of cam 31 may push down on the upper portion of stem 35 without lower portion of stem 35 moving down to open valve 25. Without a signal along line 61 to device 43, the pushing down of the upper portion of stem 35 would result in similar downward movement of the lower portion of stem 35 thereby opening valve 25. Similarly, a signal from ECU 40 may go along line 62 to device 44 to effectively deactivate valve 26, which means that lobe 33 of cam 32 may push down on the upper portion of stem 36 without the lower portion of stem 36 moving down to open valve 26. Without a signal along line 62 to device 44, the pushing down of the upper portion of stem 36 would result in a similar downward movement of the lower portion of stem 36 thereby opening valve 26.
The times of the activation and non-activation of valves 25 and 26 may be electronically controlled by ECU 40. Similarly, the times of activation of injector 12 may be electronically controlled by ECU 40. Cylinder 17 cutout may be achieved by a variety of patterns of activation and deactivation of valves 25 and 26, with specific timing for each of the valves' activations and deactivations. For instance, it may be possible to deactivate only one of the valves for certain durations of time. Also, the deactivation and corresponding durations of injector 12 may be a part of cylinder 17 cutout. Various sorts of calculations and programs may be selected and executed by ECU 40, for effecting cylinder 17 cutout, depending on the various inputs to ECU 40.
Inputs to ECU 40 via line 71 from sensor 39 may include revolutions per minute (rpm) and positions at various times of crankshaft 24 with signals on line 71. Temperatures of the exhaust 14 before and after adsorber 50 may be detected by sensors 55 and 56, respectively. These pre-adsorber and post-adsorber exhaust 14 temperatures may be in the form of signals along lines 72 and 73 from sensors 55 and 56, respectively, to ECU 40. Also, a sensor 54, or the like, may be positioned near an exit of adsorber 50 to measure the amount of NOx in the exhaust 14. A signal indicating a measurement of the NOx may go along a line 74 from sensor 54 to ECU 40. Various other signals of operating parameters of the engine 11, such as cooling system temperature, oil pressure, exhaust oxygen, mass air flow, air/fuel ratio, detonation, and the like, may be conveyed to ECU 40 along lines from the corresponding sensors (not necessarily shown in the Figures).
Other inputs to ECU 40 may be entered from a user interface 63 and other engine sensors. Such other inputs may include engine throttle control, programs for the ECU 40, setpoints, selection among various modes of operation of the engine and the ECU, adjustments of performance and emissions related parameters, and so forth.
In the present specification, some of the material may be of a hypothetical or prophetic nature although stated in another manner or tense.
Although the invention has been described with respect to at least one illustrative embodiment, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.
