Engine warm-up offsets

Details Engine warm-up offsets Engine warm-up offsets

2002-04-18

2003-07-08

Gimie, Mahmoud M (Department: 3747)

Internal-combustion engines

Spark ignition timing control

Electronic control

C123S491000, C701S113000

Reexamination Certificate

active

06588402

ABSTRACT:

The present invention generally relates to a method for controlling an internal combustion engine, and is in particular related to the control of such an engine during the warm-up period thereof.
Internal combustion engines typically exhibit relatively poor combustion stability during a warm-up period therefor, and particularly following a cold start of the engine whilst it is at a very low temperature. The combustion stability generally improves as the engine warms up towards its normal operating temperatures. In some engines which are controlled by an engine management system under the control of an electronic control unit (ECU), a warm-up period is defined as the initial operation of the engine until it reaches a predetermined engine operating temperature.
The combustion stability within the engine can be indicated by a coefficient of variance (COV) value. This COV value provides an indication of the degree of variation of the gross indicated torque within each cylinder of the engine. The gross indicated torque is directly related to the peak pressures within each cylinder and may graphically be represented by the area beneath a cylinder pressure trace. Variations in the gross indicated torque generally arise as a result of unstable combustion within each cylinder and hence the COV value is essentially a measure of how stable the engine is running. Typically, a decrease in the COV value would indicate an improvement in the combustion stability of the engine.
It is known practice, particularly in four-stroke engines, to try to improve the combustion stability during the engine warm-up period by running the engine using a richer than usual air/fuel mixture and/or by advancing the ignition timing during this period. These operating parameters have generally been controlled manually or automatically as a function of the engine coolant temperature during the warm-up period. However, tests conducted by the Applicant on it's direct injected engines have shown that there is no direct correlation between the coolant temperature and the degree of combustion stability for certain types of engines. For example, if an engine at start-up having a coolant temperature of say 20 degrees Celsius is compared to the same engine which had previously been started whilst having a lower coolant temperature and which had since been running for a period of time such that the coolant temperature was now at 20 degrees Celsius, the COV value for each situation could well be very different even though the coolant temperature was now the same.
Tests conducted by the Applicant on certain engines reveal that the COV value of the engine typically progressively decreases following cold start-up of the engine during a warm-up period until it reaches an at least substantially constant value. This constant or steady state COV value is generally the same as the COV value of the engine when the engine is running at normal operating temperatures (ie: the engine has effectively warmed up and a satisfactory level of combustion stability has been achieved).
During the warm-up period, both the average cylinder gas temperature (ACGT) within each combustion chamber of the engine and the temperature of the engine coolant progressively increase. The coolant temperature typically rises as a result of energy transfer in the form of heat from the combustion chambers and cylinder walls to the coolant passages of the engine. It has been found that with steady state running conditions after a period of time following start-up, the temperature difference between the ACGT and the coolant temperature becomes at least substantially constant. This may occur even while the combustion and coolant temperatures continue to increase. The point at which this temperature difference first reaches this substantially constant value generally corresponds to the point at which the COV reaches its low steady state value.
Accordingly, it is desired that certain engine operating parameters are modified during the warm-up period such that the ACGT increases so that the temperature difference between the combustion and coolant temperatures under steady state operating conditions attains the constant value referred to above. This would typically lead to the COV value being the same low steady state value as it would under normal running conditions which in turn would effectively result in the achievement of acceptable combustion stability during the warm-up period. This constant COV value would be achievable across any operating conditions.
Further to the above comments, the Applicant has noted that, for a particular engine configuration started from a given coolant temperature, whilst the time to achieve satisfactory combustion stability may differ depending upon engine operating conditions and more generally how the engine is run following start-up, substantially the same level of energy is always put into the engine to attain this satisfactory combustion stability. This energy is placed into the engine by the combustion of fuel within each combustion chamber of the engine during the warm-up period and therefore the amount of fuel delivered to the engine since start-up correlates to the amount of energy delivered to the engine since start-up. That is, for a particular configuration of engine, the point at which the abovementioned temperature difference and COV value reach a constant value also correlates to a certain amount of fuel being delivered to the engine.
It therefore follows that there is a correlation between the amount of fuel supplied to the engine since start-up and the degree of combustion stability of the engine. To reiterate, the total amount of fuel supplied to the engine since start-up (referred to as the “accumulated fuel”) required to reach the above noted low steady state COV value is substantially the same regardless of how long it takes to reach that point, provided that the engine at start-up has the same initial coolant temperature. It is therefore not relevant to the attainment of satisfactory stability whether the engine is operated at high speed or remains at idle until that point is reached as long as the same total amount of fuel from start-up is used.
Accordingly, it is possible to base the degree of offset or modification to individual engine operating parameters during the warm-up period on the accumulated fuel since start-up. That is, the offsets can be set on the basis of how much fuel has been delivered to the engine since start-up.
Alternatively, it should be noted that other means for estimating the amount of energy delivered to the engine during the warm-up period may be used. For example, the energy supplied to the engine may be estimated by way of an accumulated value of the load level of each combustion event during the warm-up period.
It is therefore an object of the present invention to operate with a low COV value during a warm-up period for an engine, this being achieved by the provision of operating parameter offsets based on a certain measure of the energy delivered to the engine during the warm-up period.
It is a further object of the present invention to operate with a low COV value during a warm-up period for an engine, this being achieved by the provision of operating parameter offsets based on the amount of fuel delivered to the engine during the warm-up period.
With this in mind, the present invention provides in one aspect a method of controlling an internal combustion engine during a warm-up period thereof including controlling at least one operational parameter of the engine as a function of at least a certain measure of the energy supplied to the engine during the warm-up period. Preferably, the at least one operational parameter of the engine is controlled as a function of at least the certain measure of energy supplied to the engine during the warm-up period of the engine to thereby provide improved combustion stability during said warm-up period.
Conveniently, control of the at least one operational parameter of the engine may be provided on the basis of a certain measure of the ener

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