Control for controlling the ignition timing in a cold start condition for an engine in a vehicle drive system

Abstract

A method and controller for controlling ignition timing in a cold-start condition for an engine in a vehicle propulsion system. The method includes determining whether the engine is in a cold-start condition and advancing the ignition timing before top dead center in a combustion cycle so that combustion heat is primarily absorbed by a surface within a combustion chamber when the engine is in a cold-start condition.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a controller for controlling ignition timing in a cold start condition for an engine in a vehicle drive system. INTRODUCTION

[0002] This introduction generally sets forth the context of the disclosure. The work of the presently named inventors to the extent described in this Background section, as well as aspects of the specification not otherwise considered prior art at the time of filing, are expressly and by implication admitted as prior art to the present disclosure.

[0003] Catalytic converters can be used to reduce the gaseous emissions of an engine in a vehicle's propulsion system. Generally, catalysts are more efficient at higher temperatures. For example, a "light-off temperature" may be a temperature at which the conversion of combustion gases by the catalyst in the converter may have reached a desired level of efficiency. To increase the temperature of the catalyst more quickly, especially during a cold-start condition, the ignition timing retardation can be delayed so that the heat of combustion is primarily directed into the exhaust gases and toward the catalyst.

[0004] US 8 989 989 B2 shows a system comprising a temperature estimation module and a fuel control module. The temperature estimation module estimates the piston temperature based on the engine's operating conditions. The fuel control module controls various injection parameters (e.g., injection timing, pressure, location, and number of injections per cycle) depending on the piston temperature.

[0005] US 9 816 454 B1 shows a system for controlling an engine based on the piston temperature deviation, which system includes a module for estimating the piston temperature, a module for estimating the deviation of the piston temperature from the steady-state temperature and an engine control module that determines a control parameter for the engine based on the estimated temperature deviation.

[0006] US 2014 / 0 331 968 A1 describes a method for cold-starting an ethanol-fueled internal combustion engine. The engine temperature is determined, the drive shaft is rotated, the engine is phased, and the fuel pressure is ensured to exceed a certain threshold. In the first operating cycle after phasing, the ignition timing is increased by 21° to 50° before top dead center (TDC) if the engine temperature is below a certain value. In the following operating cycle, the ignition timing is controlled according to the ignition advance table.

[0007] DE 698 23 750 T2 relates to a control device for an internal combustion engine or, in particular, to a control device of an internal combustion engine for improving the stability of the idling state immediately after a cold start of the internal combustion engine.

[0008] JP 2006 - 63 857 A describes a method for quickly and reliably starting an engine, in which the ignition timing advance is determined based on engine temperature and fuel properties. These two factors influence the combustion rate at the time of engine start. SUMMARY

[0009] The object of the invention is to reduce the thermal stress on the piston surface in order to improve component durability and operational reliability of the engine. This object is achieved by the subject matter according to claim 1. Further developments can be found in the subclaims.

[0010] As explained above, during a cold start, an engine may undergo a "Cat Light-Off" mode (a catalyst light-off mode) in which the spark timing retardation may be delayed to allow primary combustion heat to reach the catalyst, allowing the catalyst temperature to quickly reach an efficient conversion temperature and / or "activation temperature." While this strategy addresses the conversion of gaseous emissions, it does not address the issue of particulate emissions. The inventors of the present disclosure understand that the impingement of fuel on cold combustion surfaces present during a cold start causes fuel to generate particulates. Generally, the colder the surface, the more particulates are present in the emissions.

[0011] The inventors of the present disclosure have recognized that particulate emissions can be significantly reduced by controlling ignition timing during a cold start so that combustion heat is primarily directed toward heating the surfaces of the combustion chamber. In stark contrast to conventional ignition timing, which tends to retard the timing during a cold start to direct combustion heat to a catalyst, an exemplary embodiment of the present disclosure advances the ignition timing so that combustion heat is primarily directed toward a surface within a combustion chamber in the engine during a cold start mode. In this way, particulate emissions can be significantly reduced during a cold start mode.

[0012] Furthermore, not only are particulate emissions significantly reduced, but heating the combustion surfaces in the combustion chamber improves combustion efficiency for subsequent operating modes, such as in a catalytic heating mode, by retarding the ignition timing. By first heating the combustion surfaces when the engine is in a cold-start condition according to the present disclosure, the time required to operate in a catalytic heating mode, where the ignition timing can be retarded, can be significantly reduced. Thus, particulate emissions can be reduced in the present disclosure while simultaneously reducing the time required to operate the catalytic heating mode before the desired catalyst temperature is reached, which can also further reduce gas emissions.

[0013] Additionally, an exemplary embodiment of the present disclosure provides improved combustion stability during cold-start conditions. During a cold start, any combustion instability may result in a combustion strategy that may be noticeable to a driver of a vehicle. The driver or passenger may notice that the engine is operating in a manner different from "normal" operation. The amount of time the engine must operate "abnormally" from the driver's perspective during a cold-start condition may be significantly reduced by an exemplary embodiment of the present disclosure.

[0014] In one exemplary aspect, a method and controller for controlling ignition timing in a cold-start condition for an engine in a vehicle propulsion system. The method includes determining whether the engine is in a cold-start condition and advancing the ignition timing before top dead center in a combustion cycle such that combustion heat is primarily absorbed by a surface in a combustion chamber in the engine when the engine is in a cold-start condition.

[0015] In another exemplary aspect, the ignition timing is about thirty degrees before top dead center.

[0016] In another exemplary aspect, the method includes determining when a combustion surface exceeds a predetermined threshold temperature and retarding the ignition timing to a time after the ignition timing at which the heat of combustion is primarily absorbed by the surface of the combustion chamber.

[0017] In another exemplary aspect, determining when a combustion surface exceeds a predetermined threshold temperature includes determining when a piston surface exceeds the predetermined threshold temperature.

[0018] In another exemplary aspect, the predetermined threshold temperature exceeds an evaporative temperature of a fuel for the engine.

[0019] In another exemplary aspect, the predetermined threshold temperature is greater than about one hundred and forty degrees Celsius.

[0020] In another exemplary aspect, retarding the ignition timing to a time after the ignition timing at which heat of combustion is primarily absorbed by the surface of the combustion chamber includes retarding the ignition timing to a time at which heat of combustion is primarily directed to an exhaust catalyst.

[0021] In another exemplary aspect, the method further includes adjusting fuel injection timing to correspond to ignition timing such that heat of combustion is primarily absorbed by a surface in a combustion chamber in the engine when the engine is in a cold start condition.

[0022] In another exemplary aspect, the method further includes determining whether the engine has reached a predetermined speed and advancing ignition timing before top dead center in a combustion cycle such that heat of combustion is absorbed primarily by a surface in a combustion chamber when the engine is in a cold start condition and the engine speed has reached the predetermined speed.

[0023] Further areas of applicability of the present disclosure will become apparent from the detailed description provided below. It should be understood that the detailed description and specific examples are provided for purposes of illustration only and are not intended to limit the scope of the disclosure.

[0024] The above features and advantages, as well as other features and advantages of the invention, are readily apparent from the following detailed description, including the claims and embodiments, when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present disclosure will become more fully understood with reference to the detailed description and the accompanying drawings, in which: Fig. 1 is a functional block diagram of an example embodiment of an engine system according to the present invention; Fig. Figure 2 is a graph of combustion chamber surface temperatures during different ignition timing strategies for an engine in a cold start condition; Fig. 3 is a graph illustrating particulate emissions for alternative cold start strategies, one of which is in accordance with the present invention; and Fig. 4 is a flowchart illustrating an engine control method in accordance with an example embodiment of the invention.

[0026] In the drawings, the same reference numerals are used for similar and / or identical elements. DETAILED DESCRIPTION

[0027] When fuel comes into contact with a cold surface, the fuel cannot fully mix with the charge air in the engine and evaporate. Combustion of liquid fuel creates locally rich combustion zones, which leads to the formation of undesirable soot emissions. As a result, the amount of particulate produced from cold surfaces in an engine can be greater than that from pistons operating at typical operating temperatures. The surfaces in the combustion chamber may be cold if the engine has been shut down for a period of time.

[0028] For example, further adjusting fuel injection based on a piston temperature deviation can reduce the formation of fuel puddles on the piston surfaces. This prevention of fuel puddles on the piston surfaces can reduce the amount of particulate matter produced by the engine.

[0029] With reference to Fig. 1 illustrates a functional block diagram of an exemplary engine system 100. The engine system 100 includes an engine 102 that combusts a fuel-air mixture to generate propulsion torque for a vehicle based on driver inputs from a driver input module 104. Driver inputs may include, for example, an accelerator pedal position, a brake pedal position, and inputs to a cruise control system. The driver input may be sensed by the cruise control system, which may be an adaptive cruise control system that regulates the vehicle speed to maintain a predetermined inter-vehicle following distance.

[0030] Air is drawn into the engine 102 through an intake system 108. The intake system 108 may include an intake manifold 110 and a throttle body 112, which may include a flap valve with a rotatable flap. An engine control module (ECM) 114 controls a throttle actuator module 116, which in turn controls the opening of the throttle body 112 to regulate the amount of air drawn into the intake manifold 110.

[0031] Air from intake manifold 110 is drawn into the cylinders of engine 102. Although engine 102 may include multiple cylinders, only a single representative cylinder 118 is shown here for illustrative purposes. For example only, cylinder 102 may include 2, 3, 4, 5, 6, 8, 10, and / or 12 cylinders. The ECM 114 may deactivate some of the cylinders, which may improve fuel efficiency under certain engine operating conditions.

[0032] The engine 102 can be operated according to the four-stroke cycle principle. The four strokes are the intake stroke, compression stroke, combustion stroke, and exhaust stroke. During each revolution of a crankshaft (not shown), two of the four strokes occur within cylinder 118. Consequently, two revolutions of the crankshaft are required for cylinder 118 to complete all four strokes.

[0033] During the intake stroke, air is drawn from intake manifold 110 through intake valve 122 into cylinder 118. The ECM 114 controls an injector actuator module 124 to regulate fuel injector 126 to achieve a desired air / fuel ratio. As shown, fuel injector 126 injects fuel directly into the cylinders. Additionally or alternatively, fuel may be injected into mixing chambers associated with the cylinders. Furthermore, fuel may be injected into intake manifold 110 centrally or at multiple locations, e.g., near intake valve 122 of each cylinder. The fuel actuator module 124 may stop injecting fuel into deactivated cylinders.

[0034] During the compression stroke, a piston 128 in cylinder 118 compresses the air-fuel mixture. The engine 102 may be a compression-ignition engine, in which case the compression in cylinder 118 ignites the air-fuel mixture. Alternatively, the engine 102 may be a spark-ignition engine (e.g., a gasoline direct injection (SIDI) engine), in which case an ignition actuator module 130, based on a signal from the ECM 114, applies voltage to a spark plug 132 in cylinder 118 to ignite the air-fuel mixture. The timing of the ignition spark may be set so that the piston is at its uppermost position, referred to as top dead center (TDC).

[0035] The ignition actuator module 130 can be controlled by a timing signal that determines how long before or after TDC the spark should be triggered. Because piston position is directly dependent on crankshaft rotation, the function of the ignition actuator module 130 can be synchronized with the crankshaft angle. In various applications, the ignition actuator module 130 can stop spark generation for deactivated cylinders.

[0036] The generation of the ignition spark is also referred to as a firing event. The ignition actuator module 130 may have the ability to vary the ignition timing for each firing event. The ignition actuator module 130 may even be able to vary the ignition timing for the next firing event if the ignition timing signal is changed between a last and the next firing event. In various implementations, the engine 102 may have multiple cylinders, and the ignition actuator module 130 may vary the ignition timing relative to TDC by the same amount for all cylinders of the engine 102.

[0037] During the combustion stroke, the combustion of the air-fuel mixture propels the piston downward, thereby driving the crankshaft. The combustion stroke can be defined as the period of time between the moment the piston reaches top dead center (TDC) and the moment the piston returns to bottom dead center (BDC). During the exhaust stroke, the piston begins to move upward from bottom dead center (BDC), expelling the byproducts of combustion through an exhaust valve 134. The combustion waste products are expelled from the vehicle via an exhaust system 136.

[0038] The exhaust system 136 may include a catalytic converter 152. The catalytic converter 152 may be located behind and adjacent to the exhaust manifold 150.

[0039] The engine system 100 may measure the position of the crankshaft with a crankshaft position (CKP) sensor 180. The temperature of the engine coolant may be measured with an engine coolant temperature (ECT) sensor 182. The ECT sensor 182 may be located within the engine 102 or at other locations where the coolant is circulated, such as a radiator (not shown).

[0040] The pressure in the intake manifold 110 may be measured with an intake manifold pressure (MAP) sensor 184. In various implementations, engine vacuum, consisting of the difference between ambient air pressure and the pressure in the intake manifold 110, may be measured. The mass flow rate of air flowing into the intake manifold 110 is measured with a mass air flow (MAF) sensor 186. In various implementations, the MAF sensor 186 may be positioned in a housing that also includes the throttle body 112.

[0041] The throttle actuator module 116 may monitor the position of the throttle valve 112 using one or more throttle position sensors (TPS) 190. The temperature of the ambient air drawn into the engine 102 may be measured with an intake air temperature (IAT) sensor 192. The air / fuel ratio of the exhaust gas from the engine 102 is measured with an air / fuel ratio (AFR) sensor 194. The ECM 114 uses signals from the sensors to make control decisions for the engine system 100. For example, the ECM 114 estimates a steady-state piston temperature and a deviation of the piston temperature from the steady-state temperature and then adjusts, for example, injection timing, injection pressure, injection location, and / or a number of injection pulses per engine cycle based on the piston temperature.

[0042] With reference to Fig. 2 is Fig. 2 shows a graph 200 of combustion chamber surface temperatures during various ignition timing strategies for an engine in a cold-start condition. The horizontal axis 202 of the graph represents time, and the vertical axis 204 of the graph represents a surface temperature in a combustion chamber of an engine. As shown in the graph 200, at time 206, the combustion chamber temperature is substantially the same for all three strategies at 208. The temperature at 208 represents a combustion chamber with a cold surface temperature. The impact of fuel on a cold surface results in a high amount of particulate emissions produced during combustion.

[0043] According to an exemplary embodiment of the present disclosure, ignition timing is advanced so that heat of combustion is directed to and absorbed by a surface within the combustion chamber, represented by line 210 in graph 200. As can be clearly seen, the surface temperature of the combustion chamber increases dramatically during application of an exemplary embodiment of the present invention, as represented by line 210. This dramatic increase in surface temperature contrasts sharply with the surface temperatures resulting from conventional ignition timing strategies, represented by lines 212 and 214, which tend to retard timing so that heat of combustion leaves the combustion chamber, enters the exhaust, and is directed to and absorbed by a catalyst.The difference in strategies leading to temperature / timing lines 212 and 214 is that the injection / ignition timing strategy for line 212 is later than the injection / ignition timing strategy for line 214.

[0044] According to the exemplary embodiment of the strategy leading to temperature / timing line 210, when the temperature reaches a predetermined temperature 216, the ignition / injection timing strategy may stop advancing the ignition timing and then enter a different ignition / injection timing strategy. In the instance represented by line 210, when the surface temperature reaches the predetermined temperature 216, the ignition / injection timing is retarded so that the heat of combustion is now directed to the catalyst to raise the temperature of the catalyst in the heater to an activation temperature.

[0045] With reference to Fig. 3, the dramatic reduction in particulate emissions that can be achieved with an exemplary embodiment of the present disclosure is illustrated by graph 300. The horizontal axis 302 of graph 300 represents the time course, and the vertical axis of graph 300 is divided into three sections: the vertical axis of section 304 represents the cumulative amount of particulates generated; the vertical axis of section 306 represents the instantaneous measurement of the particulate generation rate; and the vertical axis of section 308 represents the instantaneous measurement of the concentration of particulate emissions. The results for each section of graph 300 resulting from the application of advanced spark timing according to an exemplary embodiment of the present disclosure are illustrated by line(s) 310.These results contrast sharply with the significantly higher proportion of particles generated by applying a conventional ignition timing strategy, as illustrated by line(s) 312. In the example illustrated by graph 300, the particles generated by the advanced ignition timing strategy can be reduced by approximately 90% compared to conventional cold-start spark timing strategies.

[0046] Fig.4 illustrates a flowchart 400 of an exemplary method according to the present disclosure. The method begins at step 402 and continues to step 404. In step 404, control determines whether the engine is in a cold start condition. If control determines that the engine is not in a cold start condition in step 404, the method proceeds to step 412. However, if control determines that the engine is in a cold start condition in step 404, the method proceeds to step 406. In step 406, control advances the engine's ignition timing so that combustion heat is directed toward a surface of a combustion chamber and continues to step 406. In step 408, control determines whether a surface temperature of the combustion chamber exceeds a predetermined threshold.If control determines in step 408 that the surface temperature of the combustion chamber does not exceed the predetermined threshold, the method returns to step 406. However, if control determines in step 408 that a surface temperature of the combustion chamber exceeds a predetermined threshold, the method continues to step 410. In step 410, control changes the ignition timing so that the heat of combustion is no longer directed toward a surface of the combustion chamber and continues to step 412. The method ends with step 412.

[0047] While the present disclosure explains that ignition timing is advanced during a combustion cycle so that combustion heat is directed toward a surface of the combustion chamber, it is understood that the fuel injection strategy may need to be adjusted according to the advanced ignition timing strategy for it to be effective. Generally, when advancing ignition timing, the fuel injection timing also needs to be advanced to optimize the effect of the advanced ignition timing and achieve the most effective amount of combustion heat transfer to a surface of a combustion chamber.Furthermore, the overall spark strategy may be similarly adjusted, such as, but not limited to, the number of injections per combustion cycle, fuel pressure, and the like, which may affect the effectiveness of the advanced spark timing in directing the heat of combustion to a surface of a combustion chamber.

[0048] In an exemplary embodiment, ignition timing may be advanced relative to crankshaft angle in the combustion cycle to at least about 20 degrees before top dead center (TDC). Typical ignition timing strategies tend to reduce spark during a cold start condition. For example, a conventional cold start timing strategy may time the spark at about 10 degrees past top dead center (i.e., -10 degrees TDC). With advanced ignition timing, combustion occurs earlier in the combustion cycle and is shifted earlier in the combustion cycle such that at least a portion of that combustion occurs during the late compression stroke, resulting in an increase in the amount of combustion heat directed at a surface of a combustion chamber. In a preferred exemplary embodiment, ignition timing may be advanced between about 30 and 40 degrees TDC.

[0049] Conventional cold-start spark strategies may retard ignition timing to direct combustion heat to a catalyst, and / or the ignition timing may be based on another conventional metric, such as one based on optimizing an engine's mean base torque (MBD). In contrast to these conventional ignition timing strategies, an exemplary embodiment may advance ignition timing so that combustion heat is directed toward a surface of a combustion chamber, which may result in little to no torque being generated.

[0050] According to an exemplary embodiment of the present disclosure, the advanced timing strategy that directs combustion heat to a surface of the combustion chamber may be initiated after a controller determines that the engine is in a cold-start condition. The cold-start condition may be indicated by any number of factors, such as, without limitation, low engine coolant temperature and the like. Further, in an exemplary embodiment of the present disclosure, the advanced timing strategy may not be initiated until after combustion conditions have sufficiently stabilized during a cold start. For example, during a cold start, in an exemplary embodiment, the advanced spark timing strategy may not be initiated until the engine has reached a stabilized idle speed.Traditionally, an engine starting strategy, including a cold-start strategy, does not advance the ignition timing because advanced ignition timing reduces the amount of torque, which can lead to engine stalling. Therefore, conventional engine starting strategies have avoided advancing the ignition timing to prevent engine stalling.

[0051] In an exemplary embodiment of the present disclosure, the advanced timing strategy may continue until the surface temperature reaches a predetermined threshold. The predetermined threshold may, for example, correspond to a fuel vaporization temperature.

[0052] In an exemplary embodiment of the present disclosure, a controller may determine the temperature of a surface of a combustion chamber using, for example, a piston surface temperature model, a cylinder wall temperature model, or any other surface temperature determination systems and methods without limitation. Exemplary systems and methods for modeling piston surface temperature are disclosed in commonly assigned U.S. Patent Nos. 8,989,989 and 9,816,454, both of which disclosures are incorporated herein in their entirety.In an exemplary embodiment, when a piston surface temperature model indicates that a piston surface temperature exceeds a predetermined threshold, spark advance may be changed to direct combustion heat to a surface of a combustion chamber in a manner that may then direct the combustion heat to another location, such as a catalyst, to increase the temperature to an activation temperature.

[0053] In another exemplary embodiment, the predetermined threshold temperature may be selected based on factors other than fuel vaporization temperature, such as a temperature that may adversely affect combustion chamber components. In some engines, a combustion chamber surface may be made of an aluminum alloy, which may be sensitive to elevated temperatures. The predetermined threshold may be selected so that the aluminum alloy is not adversely affected in these engines.

[0054] In another exemplary embodiment of the present disclosure, the surface temperature may continue to be modeled and / or monitored even after the ignition timing strategy is no longer advanced to conduct heat to a combustion chamber surface, and the ignition timing strategy may be advanced again when the surface temperature drops below a minimum predetermined threshold. In this way, even after the initial cold start, particulate matter from combustion may continue to be minimized, and combustion efficiency may continue to be optimized. This strategy may be particularly useful in engines with a large mass that can quickly absorb heat from the combustion chamber surfaces until the engine warms up. As a result, the combustion chamber surface temperature may drop quickly and benefit from additional heating of the combustion surfaces to minimize particulate matter.

[0055] This description is merely illustrative and is in no way intended to limit the present disclosure, its embodiments, or uses. The broad teachings of the disclosure may be embodied in numerous forms. Thus, while the present disclosure includes specific examples, the true scope of the disclosure is in no way limited, and further modifications will become apparent from a study of the drawings, the specification, and the following claims.

Claims

[1] A controller for a vehicle propulsion system, the controller being programmed to: Determining whether the engine (102) is in a cold start condition; and advancing the ignition timing before top dead center in a combustion cycle so that the heat of combustion is absorbed mainly by a surface in a combustion chamber in the engine when the engine (102) is in a cold start condition, in which the control is further programmed to: to determine when a combustion surface exceeds a predetermined threshold temperature; and to delay the ignition point to a point after the ignition point at which the heat of combustion is mainly absorbed by the surface of the combustion chamber, wherein the controller is programmed to determine when a combustion surface exceeds a predetermined threshold temperature by determining when a piston surface exceeds the predetermined threshold temperature. [2] The control of claim 1, wherein the ignition timing is approximately thirty degrees before top dead center. [3] The controller of claim 1, wherein the predetermined threshold temperature exceeds an evaporative temperature of a fuel for the engine. [4] The controller of claim 1, wherein the predetermined threshold temperature is greater than about one hundred and forty degrees Celsius. [5] The controller of claim 1, wherein the controller is programmed to retard the ignition timing to a time after the ignition timing at which the heat of combustion is primarily absorbed by the surface of the combustion chamber by retardation of the ignition timing to a time at which the heat of combustion is primarily directed to an exhaust catalyst. [6] The controller of claim 1, wherein the controller is further programmed to adjust fuel injection timing to correspond to ignition timing such that combustion heat is absorbed primarily by a surface in a combustion chamber in the engine (102) when the engine (102) is in a cold start condition. [7] The controller of claim 1, wherein the controller is further programmed to determine whether the engine (102) has reached a predetermined speed and to advance the ignition timing before top dead center in a combustion cycle so that the heat of combustion is absorbed primarily by a surface in a combustion chamber when the engine is in a cold start condition and the engine speed has reached the predetermined speed.

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