Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2000-03-28
2001-12-25
Kwon, John (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S430000, C123S406450, C123S350000, C701S101000, C701S102000
Reexamination Certificate
active
06332452
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
Priority is claimed with respect to German Application No. 199 16 725.7-26 filed in Germany on Apr. 13, 1999, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a method for torque monitoring in the case of Otto engines in motor vehicles, in which a reference torque value is derived from the speed of the Otto engine and the air mass supplied and compared with a torque value specified by the driver, torque-reducing interventions in the control of the engine being performed if the reference torque value exceeds the torque value specified by the driver by a specifiable factor or value.
2. Discussion
SUMMARY OF THE INVENTION
Systems previously employed in practice for monitoring the torque desired by the driver in the case of Otto engines take account only of operation at a lambda value of 1, i.e. for an air/fuel mixture which is always in fixed association. To monitor the torque output by the engine, the parameters relevant for operation at lambda=1 are detected and evaluated. These are essentially the variables air mass flow, engine speed and possibly also the ignition angle. The torque of the engine is determined by means of characteristic maps and efficiencies (ignition angle). This calculated torque is compared with a maximum permitted torque desired by the driver. If a threshold is exceeded, fault responses, such as safety fuel cut-off or switching off of the throttle-valve output stages, are triggered.
The air mass is detected by an air-mass sensor or pressure sensor and its plausibility is assessed with the throttle valve. The ignition angle output is compared with a reference ignition angle at which the engine has the maximum torque, in the case of a lambda value of 1, and this is then used to form an ignition-angle efficiency which is multiplied directly with the reference torque (maximum torque at lambda=1).
This known monitoring system is not suitable for extended operating ranges of the Otto engine, especially of an Otto engine with direct injection, since here the torque-determining variables are not just the air mass and the ignition angle but, in addition, the fuel quantity or mass supplied or injected. For better efficiency, the engine is as far as possible unthrottled. For an Otto engine with direct injection, this results essentially in two additional ranges: homogeneous lean operation, in which lambda=1 to 1.4, and stratified operation, in which lambda is significantly greater than 1.4. In these operating modes, the known torque monitoring system leads to unsatisfactory and much too inaccurate results.
One object of the present invention is thus to provide a method for torque monitoring which allows more accurate torque monitoring, at least in homogeneous lean operation of the Otto engine.
The present invention concerns a method for torque monitoring in Otto engines disposed in motor vehicles. A reference torque value (Mo) is derived from the speed (n) of the Otto engine and the air mass (L) supplied and, in homogenous lean operation (lambda=1 to 1.4), this reference torque value is corrected by a signal derived from a signal (&lgr;ist) from a lambda probe and is then compared with a torque value (Mmax) specified by the driver. Torque reducing intervention means, such as safety fuel cut-off, switching off the throttle-valve output stages or a fault response are employed in control of the engine if the corrected reference torque value (Mo) exceeds the torque value (Mmax) specified by the driver by a specifiable amount. This method provides reliable and accurate torque monitoring when lambda values are greater than 1.
Since, according to the invention, the torque determined at a lambda value of 1 in homogeneous lean operation is multiplied by an efficiency dependent on the lambda value, accurate torque monitoring which includes automatic adaptation to different lambda values is possible, even in homogeneous lean operation.
Particularly simple and effective correction is achieved by virtue of the fact that the signal from the lambda probe is converted by means of a function stage or a characteristic map into a correction signal, and the latter acts by multiplication on the reference torque value.
Further improvements to torque monitoring are achieved by virtue of the fact that a reference ignition-angle signal and an actual ignition-angle signal and/or an exhaust-gas recirculation offset signal and/or an ignition-angle difference signal dependent on the lambda signal are used to form a correction ignition-angle signal which acts in the form of a correction factor on the reference torque value by multiplication. Since the optimum ignition value differs from that at a lambda value of 1 in the region of lambda values between 1 and 1.4, this additional corresponding correction increases the accuracy of torque monitoring in homogeneous lean operation considerably.
It is expedient if the correction ignition-angle signal is converted into the correction factor by means of a function stage or a characteristic map.
The reference ignition-angle signal is formed in a simple manner from the engine-speed signal and the air-mass signal by means of a characteristic map.
In stratified operation, the torque output by the engine depends almost exclusively on the engine speed and the fuel mass. In stratified operation, the ignition angle is almost completely dependent on the fuel mass and therefore does not play a significant part in a monitoring function. It is therefore particularly advantageous for torque monitoring in stratified operation to be performed by a method which has the features of claim
7
. The engine torque which is output, i.e. the reference torque value, is then preferably determined by means of a characteristic map as a function of the engine speed and the fuel mass supplied.
Since the methods for torque monitoring for homogeneous lean operation and stratified operation differ significantly, it is advantageous if a detection stage, designed as a function stage or characteristic map, is provided for these operating modes, a changeover between the respectively associated comparison methods for these operating modes being effected by this detection stage. A changeover characteristic map with a tolerance band above which stratified operation is permissible is particularly suitable here.
The torque value specified by the driver is likewise expediently determined as a function of the accelerator-pedal position by means of a characteristic map or a function stage.
A particularly advantageous configuration of the method according to the invention consists in plausibility-checking the actual lambda value in homogeneous lean operation and the desired fuel mass in stratified operation. This is intended to detect a faulty lambda probe or incorrect determination of the desired fuel mass. According to the invention, the respective operating state is disabled or prevented in the case of a specifiable amount by which the variable to be monitored (lambda value or desired fuel-mass value) exceeds the corresponding variable determined from the characteristic map.
In homogeneous lean operation, it is advantageous if a desired lambda value is determined by means of a characteristic map as a comparison variable obtained from the air mass value and the fuel mass value. An actual fuel-mass value is determined in a corresponding manner by means of a characteristic map as a comparison variable obtained from the actual lambda value and the air mass value. Since the fuel mass used to calculate the torque has to be assessed for plausibility as part of safety monitoring, it is necessary here, as with the lambda signal, to carry out suitable monitoring of the actually injected fuel mass. Similarly to the solution in the case of homogeneous lean operation, the lambda probe is used to monitor the air/fuel mixture. In this process, the inverse ratio of the actual lambda value to the air mass supplied is formed and the resulting fuel mass is determin
Debusmann Martin
Roulet Tobias
Crowell & Moring LLP
Daimler-Chrysler AG
Kwon John
Vo Hieu T.
LandOfFree
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