Method for cold-start emissions diagnosis of a catalytic treatment device of an internal combustion engine

Abstract

A method for cold-start emissions diagnosis of a catalytic treatment device (28) of an internal combustion engine (10), the method comprising: Determining a torque reserve (102); Determining a light-off state (108) of the catalytic treatment device (28); Determining a time period until the starting state is reached (108); Integration of the total torque reserve over the previously determined period of time (106); Determining whether a value from the integration exceeds an integration threshold (110); Determining whether the previously determined time period until the light-off state is reached exceeds a minimum time threshold (114); and if the value from the integration exceeds the integration threshold and the time taken to reach the light-off condition exceeds the minimum time threshold, it is indicated that the cold start emissions diagnosis is positive (112); whereas in the event that either the value from the integration falls below the integration threshold or the time until the light-off condition is reached falls below the minimum time threshold, it is indicated that the cold-start emissions diagnosis is negative (116) if the time until the light-off condition is reached exceeds the minimum time threshold and the value from the integration falls below the integration threshold; and whereas in the event that either the value from the integration falls below the integration threshold or the time taken to reach the light-off condition falls below the minimum time threshold, it is indicated that the cold start emissions diagnosis is indeterminate (118) if the time taken to reach the light-off condition falls below the minimum time threshold and the value from the integration exceeds the integration threshold.

Description

INITIATIONThe present invention relates to a method for cold start emission diagnosis of a catalytic treatment device of an internal combustion engine.DE 10 2005 039 393 A1 describes a method for checking the functionality of heating up a catalytic converter arranged in an exhaust system of an internal combustion engine, wherein a diagnosis of the heating up of the catalytic converter is carried out by monitoring the actual ignition angle intervention. For this purpose, the current ignition angle is detected and transferred into a torque model used for catalyst heating. A degree of fulfilment of catalytic converter heating measures carried out is obtained by means of the torque model and a fault signal is generated by comparing the degree of fulfilment obtained with a limit value.Catalytic treatment apparatuses, generally referred to as catalysts, are of decisive importance for the emission reduction in internal combustion engines. In the case of catalytically active catalysts, the emissions of the engine are significantly reduced, and so the emission values after treatment by an active catalyst can be substantially inexplicable. However, when a converter is substantially catalytically inactive, emissions from the converter may be significant. The temperature of the catalytic converter of a catalytic converter must be increased significantly after a cold start of the engine before the converter becomes substantially catalytically active. A catalyst may be defined as a light-off condition when sufficiently catalytically active to oxidize fifty percent of an appropriate volume of hydrocarbons in the engine. Considerable efforts are being made to quickly increase the catalyst temperature to a temperature that assists deactivation after a cold start of the engine. A satisfactory functioning of the catalyst is a prerequisite for reducing emissions. Accordingly, any degradation in the performance of a catalyst must be diagnosed and quickly treated to minimize emissions. Existing catalyst deactivation strategies rely on an increased idling speed with a simultaneous delayed combustion phase to increase the enthalpy of the exhaust gas. The cold start emission diagnostic is performed at a stable engine speed. New converter deactivation strategies include non-idle conditions with spark retard to increase exhaust enthalpy.Although current cold start emissions diagnostic methods serve their purpose, a new and improved system and method is needed to meet emissions regulations.SUMMARYAccording to the invention, a method for cold start emission diagnosis of a catalytic treatment device of an internal combustion engine is presented, which method is distinguished by the features of claim 1.Further areas of applicability will become apparent from the description presented herein. It is to be understood that the specification and specific examples are for the purpose of illustration only.BRIEF DESCRIPTION OF THE DRAWINGSThe drawings described herein are for illustrative purposes only. FIG. 1 is a schematic diagram of an engine and engine diagnostic hardware in accordance with the principles of the present invention; and FIG. 2 is a flow chart for cold start emissions diagnostic in accordance with the principles of the present invention.DETAILED DESCRIPTIONThe following description is merely exemplary in nature.Referring to FIG. 1, the internal combustion engine 10 receives the intake air via the intake bore 12 in which is disposed a conventional thick film or hot wire mass flow sensor 16 that converts the mass flow of the intake air into the signal MAF 50. The intake air flow of the engine may alternatively be determined by the generally understood velocity density approach. The intake air is metered through the bore 12 with a manually or electronically controlled intake air valve of butterfly or rotary design. The air temperature downstream of the intake air valve 14 (in an intake plenum or manifold) is converted to the output signal MAT 52 by thermocouple or thermistor 18. The intake plenum is for distributing the intake air to a plurality of intake ports into which fuel is selectively injected to form an air-fuel mixture. Alternatively, the fuel may be directly injected into the cylinders of the engine. Each intake passage terminates at a ventilated engine cylinder intake passage for timed delivery to an engine cylinder for combustion therein. The products of combustion are carried out of the cylinders through an exhaust port opening into an exhaust conduit 26. The exhaust conduit 26 terminates at an opening of a commonly available catalytic treatment device 28 for directing the exhaust gas to the treatment device 28, where the treated engine exhaust gas exits the device 28 and is directed through the tail pipe 30 in which is disposed an exhaust gas sensor, such as a commercially available calorimeter sensor 34 or a hydrocarbon sensor, for converting the concentration of fuels (such as hydrocarbons HC) into the sensor output signal Qact 54.A conventional piston is accommodated in each cylinder of the engine 10 and reciprocated by the combustion reaction of the air-fuel mixture in the cylinder. Each piston is mechanically connected to a motor output shaft 22, the reciprocal piston actuation rotationally driving the output shaft. The Hall effect or variable reluctance type sensor 24 is disposed proximate the output shaft 22 to convert the rotation of the output shaft into the output signal RPM 56 at a frequency proportional to the speed of the output shaft 22 and with individual signal events indicative of the occurrence of motor events. Ambient barometric pressure is converted to output signal BARO 58 by a conventional pressure transducer external to the engine.The coolant is passed over a conventional coolant circuit in which a conventional temperature transducer 20 in the form of a thermocouple or thermistor is disposed for converting the coolant temperature into the output signal TEMP 60. The converter output signals are received by a conventional microcontroller 36 in a form generally understood in the art and include these known elements which is a central processing unit CPU 38 having arithmetic logic circuitry for performing logic and arithmetic logic operations and control circuits, and various memory devices such as RAM 40, read only memory ROM 42 and NVRAM 44, non-volatile random access memory.The controller is activated by manually applying the ignition power by an engine operator, and when activated, performs a series of operations stored in an instruction-by-instruction format in the ROM 42 for engine control, diagnosis and maintenance. These operations include fuel control and spark control operations for generating and issuing an engine fueling command in the form of an injector pulse width PW 62 to a fuel control module (not shown) for driving at least one fuel injector to supply fuel to the described cylinder intake ports for mixing with intake air, and for generating and issuing an ignition timing command EST 64 to an ignition control module for time-selectively activating spark plugs in active engine cylinders to ignite the air-fuel mixture. Any commercially available refueling and ignition timing controls may be used to generate and output the PW 62 and EST 64 signals.Among various other diagnostic methods that may be incorporated in accordance with the principles of the present invention, method 100 for cold start emission diagnostic of catalytic treatment device 28 is as shown in FIG. 2. Generally, this method 100 provides for monitoring the functionality of the catalytic treatment device 28 (also referred to herein as catalyst) at a time when the converter typically reaches a light-off and before a time when the converter should operate at its maximum efficiency to determine whether the beneficial emissions mitigation characteristic is achieved by the light-off to diagnose and thus avoid a longer inactivity time or a low efficiency of the converter.More specifically, these operations are initiated upon application of the ignition energy to a previously inactive controller 36 by the engine operator, such as by rotating an ignition cylinder to an "on" position, and general initialization actions are taken. These initialization actions include, among other things, setting pointers, counters, and flags to initial values, clearing RAM 40 blocks, and transferring data from ROM locations 42 to RAM locations 40.After general initialization actions, an ignition cycle time marking the start time of the current ignition cycle is cleared and, in a next step, a catalyst diagnostic is activated, e.g., by setting a diagnostic activation flag in RAM 40. Interrupts, including the time and event based interrupts, are next activated after predetermined time events. The routine proceeds to reference from memory or sample input signals and processes and stores the current values of the control input signals including signals RPM 56, TEMP 60, BARO 58, MAF 50, and MAT 52. The sampled signals are processed, if necessary, to representative values indicative of engine speed, ambient air pressure, engine intake mass flow, engine load, engine coolant temperature, and engine intake plenum temperature for use in the current diagnostic operations or other control and diagnostic operations. These values are stored in the RAM 40.Referring specifically to FIG. 2, method 100 begins to obtain a value for a torque reserve 102 and a catalyst light-off condition (CLO) 104 (i.e., the amount of spark retard). In a step 108, a period of time for heating the catalyst (i.e., a CLO activation time) is set. Subsequently, in a step 106, the torque reserve value 102 is integrated over a period of time defined by the CLO state 104. A decision step 110 determines whether the integrated value from step 106 exceeds a predetermined threshold. If the decision is yes, the method 100 indicates that the cold start diagnostic is positive in a step 112.Optionally, decision step 110 also evaluates whether the amount of time to warm up the catalyst exceeds a minimum time threshold. If the integrated value 106 exceeds the predetermined threshold and the amount of time to warm the catalyst exceeds the minimum time threshold, the method 100 again indicates that the cold start diagnostic is positive 112.If either of the criteria is not met at step 110, the method 100 proceeds to step 114 that determines whether the amount of time to warm the catalyst exceeds the minimum time threshold. If step 114 determines that the amount of time to warm the catalyst exceeds the minimum time threshold, method 100 indicates that the CLO diagnostic is negative (step 116). On the other hand, if step 114 determines that the amount of time to warm the catalyst does not exceed the minimum time threshold, then the method 100 indicates that the CLO diagnostic is indeterminate in a step 118.

Claims

A method for cold start emissions diagnosis of a catalytic treatment device (28) of an internal combustion engine (10), the method comprising: determining a torque reserve (102); determining a light-off condition (108) of the catalytic treatment device (28); determining a time period until the light-off condition (108) is reached; integrating the total torque reserve over the predetermined time period (106); determining whether a value from the integration exceeds an integration threshold (110); determining whether the predetermined time period until the light-off condition is reached exceeds a minimum time threshold (114); and if the value from the integration exceeds the integration threshold and the time period until the light-off condition is reached exceeds the minimum time threshold, indicating that the cold start emissions diagnosis is positive (112); whereas in the case where either the value from the integration falls below the integration threshold value or the time until the light-off state is reached falls below the minimum time threshold value, it is indicated that the cold start emission diagnosis is negative (116), if the time until the light-off state is reached exceeds the minimum time threshold value and the value from the integration falls below the integration threshold value; and whereas in the case where either the value from the integration falls below the integration threshold value or the time until the light-off state is reached falls below the minimum time threshold value, it is indicated that the cold start emission diagnosis is indeterminate (118), if the time until the light-off state is reached falls below the minimum time threshold value and the value from the integration exceeds the integration threshold value.The method of claim 1, wherein if the value of the integration does not exceed the integration threshold, the cold start emission diagnostic is negative.

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