METHOD AND ARRANGEMENT FOR LIMITATION OF CONTROLLABLE OPERATING PARAMETERS IN AN ENGINE

Abstract: The invention relates to a method for limitation of at least one controllable operating parameter which can cause ageing of at least one component (17; 19; 20) or one material in connection with an engine (1), comprising determination of a maximum limit value allowed (T2; Ta, Tb, Tc; n1) regarding said operating parameter (T; n) and control of the engine (1) so that said limit value (T2; Ta, Tb, Tc; n1) is not exceeded, by means of which ageing of said component (17; 19; 20) or material is limited. The invention is characterized in that it comprises continuous determination of a measure (F) which corresponds to the degree of impairment of said component (17; 19; 20) which depends on ageing, wherein said determination of said limit value (T2; Ta, Tb, Tc; n1) is made depending on said measure (F). The invention also relates to an arrangement for accomplishing said method. By means of the invention, an improved method and arrangement is provided for limitation of ageing of components and materials which in particular are arranged in connection with a combustion engine in a vehicle, which provides an improved fuel consumption, improved emissions and an improved performance of the vehicle.

Description: Method and arrangement for limitation of controllable operating parameters in an engine TECHNICAL FIELD The present invention relates to a method for limitation of at least one controllable operating parameter which can cause ageing of at least one component or one material which is arranged in connection with an engine, according to the preamble of appended claim 1. The invention also relates to an arrangement for accomplishing such a method, according to the preamble of appended claim 7. BACKGROUND ART In the field of motor vehicles, e.g. passenger cars, various components are occasionally gradually impaired due to, among other things, ageing and wear. In order to prevent ageing and functional incapability of a certain component too early in the life cycle of a vehicle, limits are commonly defined for certain operating parameters during operation of the vehicle, so that the component in question can be protected. One example of a component which is exposed to ageing and impairment (and by that a risk of functional incapability) is an exhaust manifold which is intended to be arranged in connection with a combustion engine in order to guide exhaust gases out from the combustion engine to the environment via a rear exhaust system. Due to ageing and occasionally high temperatures, the exhaust manifold may be gradually subjected to disintegration and impaired function. In order to reduce the risk of functional incapability of the exhaust manifold, a limitation can be defined as regards the temperature of the exhaust gases that flow out from the engine and through the exhaust manifold. In this manner, a premature impairment of its function is prevented. In accordance with known technique, this limitation of the exhaust gas temperature can be achieved by limiting the output power from the engine or by limiting the supply of a rich fuel mixture to the engine. This can be controlled by means of a computer-based control unit which is available for the vehicle in question. One drawback as regards such a method is, however, that the maximum limit allowed for the exhaust gas temperature must be set with a wide margin so that the worst possible operating situation is taken into consideration. For example, one such extreme operating situation can be said to be the equivalent of when a particularly active driver frequently drives the vehicle at very high loads and engine speeds. Thus, the limitation as regards the exhaust gas temperature is in this case set with a very wide margin, so that no functional incapability occurs too early. Due to the fact that a limitation of the exhaust gas temperature requires a supply of fuel, a limitation with a wide safety margin results in a comparatively high fuel consumption for the vehicle, which is a drawback. As a similar example, it can be mentioned that the motor oil in a combustion engine is gradually impaired, particularly due to driving with comparatively high engine speeds and a high torque from the engine. In this case, a limitation of the risk of impairment of the motor oil can be achieved by means of a maximization of the engine speed, which also can be accomplished by means of a computer-based control unit. More precisely, a compulsory control of the engine speed is in this case made, so that it never exceeds a certain limit which corresponds to the fact that there is a risk of impairment of the motor oil. Such a method can, however, involve a drawback in the form of a perceived impaired performance of the vehicle. One additional vehicle component where a similar limitation of a functional incapability is relevant is an exhaust catalyst. This is due to the fact that the catalytic active surface of the exhaust catalyst decreases due to ageing. Therefore, in order to make sure that the function of the exhaust catalyst is not impaired unnecessarily early, it is previously known to limit the temperature of those exhaust gases which flow through the exhaust catalyst. Another operating parameter which can be limited in a vehicle is its output torque. According to what is previously known from the EP patent 0507500, the output torque of an engine can be limited if certain predetermined parameters (e.g. the level and the temperature of the coolant, the pressure and the temperature of the motor oil and the temperature of the air which flows into the engine) differ from certain predetermined limit values. DISCLOSURE OF THE INVENTION A primary object of the present invention is to provide an improved method for limitation of controllable operating parameters which can cause ageing of engine components and materials which are arranged in connection with an engine. Said object is accomplished by means of a method, the characterizing features of which will be apparent from appended claim 1. Said object is also accomplished by means of an arrangement, the characterizing features of which will be apparent from appended claim 7. The invention constitutes a method for limitation of at least one controllable operating parameter which can cause ageing of at least one component or one material in connection with an engine, comprising determination of a maximum limit value allowed regarding said operating parameter and control of the engine so that said limit value is not exceeded, by means of which ageing of said component or material is limited. The invention is characterized in that it comprises continuous determination of a measure which corresponds to the degree of impairment of said component which depends on ageing, wherein said determination of said limit value is made depending on said measure. Thus, one fundamental principle behind the present invention is that a limitation of a predetermined, controllable operating parameter in the engine or the vehicle which causes ageing of a certain component or a certain material is established for at least one component with the intention of limiting the ageing, and thereby also the risk of functional incapability of the component in question or the material in question. Due to the fact that this limitation is made depending on the degree of ageing of the relevant component and material, respectively, an improvement as regards the emissions, the fuel consumption and the performance of the vehicle is made possible by means of the invention. Other advantageous embodiments of the invention will be apparent from the appended dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described in the following with reference to a preferred embodiment and to the appended drawings, in which Fig. 1 is a principal diagram of an arrangement in which the present invention can be utilized, and Fig. 2 is a graph which illustrates the function of the invention. PREFERRED EMBODIMENTS Fig. 1 shows a slightly simplified, schematic view of an arrangement according to the present invention. According to a first preferred embodiment, the invention is arranged in connection with a conventional combustion engine 1 of a petrol engine type. According to an alternative embodiment, the combustion engine can be of a diesel engine type. According to the preferred embodiment, which is shown in Fig. 1 , a combustion engine 1 is in a conventional manner supplied with inflowing air via an air inlet 2. The engine 1 is provided with a number of cylinders 3 and a corresponding number of fuel injectors 4. Each injector 4 is connected to a central control unit 5 via an electrical connection 6. Preferably, the control unit 5 is computer based and is adapted in a known manner to control the fuel supply to each injector 4 with fuel from a (not shown) fuel tank so that a air/fuel mixture which in every given moment is adapted is fed to the engine 1. The engine 1 according to the embodiment is formed in accordance with the "multi-point" injection type, where the correct amount of fuel to the engine 1 can be supplied individually to each injector 4 in a known manner. The engine 1 that is shown in the drawing is of a five-cylinder type. However, it shall be noted that the invention can be utilized in engines having various numbers of cylinders and various cylinder configurations. Preferably, the injectors 4 are constituted by the type in which the fuel is directly injected into the respective cylinder 3, but the invention can also be utilized in so-called "port injected" engines. Furthermore, the invention can in principle also be utilized for a so-called "single point" injection, where one single fuel injector is arranged in the inlet to the engine. During operation of the engine 1 , the control unit 5 is adapted to control the air/fuel mixture to the engine 1 so that it in every given moment is adapted to the prevailing operating condition. The control of the engine 1 takes place in an essentially known manner depending on various parameters which reflect the operating condition of the engine 1 and the vehicle in question. For example, the control of the engine can take place depending on the prevailing degree of throttle application, the engine speed, the amount of injected air to the engine and the oxygen concentration in the exhaust gases. To this end, the engine 1 is provided with, for example, a position indicator 7 for an accelerator pedal 8 in the vehicle, an engine speed indicator 9 for detection of the engine speed n of the engine 1 and an air flow meter 10 for detection of the amount of supplied air to the engine 1 , all of which are connected to the control unit 5 via corresponding electrical connections 11 , 12 and 13, respectively. Furthermore, the system also comprises a gas throttle 14, which preferably is electrically controllable and, for this reason, is provided with a controllable shifting motor 15 by means of which the gas throttle 14 can be set in a certain desired position so that a suitable amount of air is fed into the engine 1 depending on the prevailing operating condition. Thus, the shifting motor 15 is connected to the control unit 5 via an additional connection 16. During operation of the engine 1 , its exhaust gases are guided out from the cylinders 3 via an exhaust manifold 17 and further to an exhaust pipe 18 which is connected to the manifold 17. Preferably, an exhaust catalyst 19 is provided further downstream along the exhaust pipe 18, which exhaust catalyst according to the embodiment is constituted by a conventional three- way catalyst. Furthermore, a pre-catalyst 20 is arranged upstream of the exhaust catalyst 19. The pre-catalyst 20 is particularly adapted for rapid heating during cold starts of the engine 1 , i.e. so that its catalytic coating becomes active rapidly. This results in a considerable elimination of HC, CO, and NO* compounds in the exhaust gases, particularly during low idle flows. Also, by means of the fact that the flowing exhaust gases can be heated rapidly by means of the pre-catalyst 20, a comparatively short ignition time is provided for the subsequent exhaust catalyst 19, i.e. a comparatively short time that passes until the exhaust catalyst 19 has been heated to a temperature at which it is capable of reducing a predetermined part of the harmful substances in the exhaust gases. This results in a more effective exhaust purification for the engine 1 , particularly during cold starts. Furthermore, the arrangement according to the embodiment comprises a sensor 21 for detection of the oxygen concentration in the exhaust gases. Preferably, the sensor 21 is of the linear lambda sond type and is connected to the control unit 5 via an electrical connection 22. Preferably, the sensor 21 is arranged in the exhaust pipe 18, upstream of the pre-catalyst 20. However, other locations of the sensor 21 are possible, for example between the pre- catalyst 20 and the exhaust catalyst 19. In a manner which per se is previously known, the sensor 21 is utilized for generation of a signal which corresponds to the oxygen concentration in the exhaust gases. This signal is fed to the control unit 5 and is utilized for control of the air/fuel mixture to the engine 1. The system which has been shown in Fig. 1 and described above is considerably simplified. Several components in connection with the engine 1 which are not directly relevant as regards the function and the fundamental principle of the present invention have thus been omitted from this drawing. The function of the invention will now be described with reference to an example in which a certain operating parameter is limited so that the ageing of the above-mentioned exhaust manifold 17 can be limited. In this manner, the risk of functional incapability of the exhaust manifold 17 also can be decreased. More precisely, this is achieved by controlling an operating parameter in the form of the temperature T which prevails in the exhaust gases that flow out from the engine 1 and through the exhaust manifold 17. A similar limitation of the exhaust gas temperature T can be utilized for limiting a functional incapability of the pre-catalyst 20 and of the exhaust catalyst 19. In accordance with previously known technique, the exhaust gas temperature can be limited to a certain predetermined limit value with the intention of ensuring that the temperature of a certain component in connection with the engine never gets so high that there is a risk of damage or functional incapability of the component in question. As examples of such temperature- critical components can be mentioned the pre-catalyst, the exhaust catalyst critical components can be mentioned the pre-catalyst, the exhaust catalyst and the exhaust manifold. However, in accordance with what has been mentioned initially, such a previously known method results in a comparatively rigid delimitation as regards the exhaust gas temperature, which in turn can result in an unnecessarily high fuel consumption, increased HC and CO emissions and impaired performance of the engine. If a less rigorous limit instead should be set, the result would be a comparatively quicker ageing at the end of the life cycle, which limits the service life of the component. With the intention of achieving an improvement compared with known technique, the present invention is based on the knowledge that such a comparatively rigid limitation of, for example, the exhaust gas temperature not always is necessary, in particular not during the initial phase of the life cycle of a vehicle. For this reason, a fundamental principle behind the invention is that a continuous determination of a maximum limit value allowed as regards a predetermined operating parameter (e.g. the exhaust gas temperature) is made depending on a measure which corresponds to the continuous impairment of the component in question. In other words, according to the invention, a delimitation is made depending on to what extent the component can be considered to have aged in relation to a completely new component. According to the invention, a measure of the impairment or the ageing of the component in question can be estimated by means of a calculation of the number of driven kilometres, the number of starts, the number of operating hours or the amount of consumed fuel for the vehicle in question. Such a measure is provided by means of the control unit 5. Alternatively, said measure can be determined by means of methods which are based on measurements with indicators. The function of the invention will now be explained with reference to Fig. 2, which shows a graph of the connection between a predetermined limit value for a certain operating parameter (which is indicated on the y-axis), more precisely the exhaust gas temperature T, and a measure which corresponds to the ageing or the impairment F of a certain critical component (which is described by means of an "impairment factor", which for example can be said to correspond to a value between 0 and 100, where 0 corresponds to a completely new component which is fully capable of functioning whereas 100 thus corresponds to a worn-out component which is incapable of functioning. This is indicated along the x-axis in Fig. 2. In comparison with this, the graph shows a dashed line which indicates a limit value Ti which corresponds to previously known technique (i.e. a limit value which is defined with a very wide margin for the purpose of taking extremely hard conditions into consideration). Moreover, an unbroken line is shown which indicates how a limit value T 2 which depends on ageing or impairment can be defined in accordance with the invention. By means of the fact that the latter limit value T 2 is defined in a manner which depends on the degree of impairment of the component in question, it is for example possible to define and utilize a comparatively high limit value T 2 of the exhaust gas temperature in the beginning of the life cycle of a vehicle, i.e. before a noticeable ageing of the component in question (e.g. the exhaust catalyst 19 or the exhaust manifold 17) has occurred. This implies that only a low degree of cooling of the exhaust gas temperature needs to be done in the beginning of the life cycle of the vehicle. This, in turn, results in that a comparatively small amount of fuel needs to be utilized in order to cool the exhaust gases at this stage, which influences the emissions, the fuel consumption and the performance of the vehicle in a positive direction. Next, concurrently with the fact that ageing or impairment sets in the components in question, a gradually lowered limit value T 2 can be utilized. In this case, such a gradually lowered limit value corresponds to an increasingly evident cooling of the exhaust gases. This is indicated by means of the unbroken curve in Fig. 2. The limit value T 2 which is defined according to the invention can be selected in various ways concurrently with the ageing of the respective component. A continuous, gradually decreasing change of the limit value T 2 can be utilized, which also is shown in Fig. 2. Alternatively, the exhaust gas temperature T can be limited so that a first limit value T a is set when the impairment factor for example is between 0-10, a second, slightly lower, limit value T b is set for example is between 0-10, a second, slightly lower, limit value T b is set when the factor is between 10-50 and a third, additionally slightly lower, limit value T c is set when the factor is between 50-100. This results in a gradually decreasing limit value, which is shown by means of a dash dotted line in Fig. 2. The invention is not limited to the fact that the limit value T gradually drops to a value which corresponds to the limit value Ti which corresponds to previously known technique (cf. Fig. 2). For example, there might be applications where the limit value T 2 according to the invention approaches a value which is lower or higher than the limit value Ti according to known technique. Furthermore, the invention can be utilized for limitation of ageing of a material in the form of the motor oil which is present in the engine 1. In such a case, a limitation of the engine speed n of the engine 1 can be made. In this case, by analogy with what has been described above, a limit value ni is defined which depends on a measure related to the ageing or the impairment of the motor oil. For example, in the initial phase of the life cycle of the vehicle, a comparatively high limit value ni can be allowed, wherein the limit value ni gradually drops concurrently with an increasing "impairment factor" F. By making, for example, a comparatively insignificant limitation of the engine speed during the initial phase of the life cycle of a vehicle, an improvement of the perceived performance of the vehicle is provided. In connection with a motor oil change in the vehicle in question, some form of resetting to zero of the system is required, which suitably is made by a garage mechanic. The invention is not limited to the embodiments which are described above and shown in the drawings, but may be varied within the scope of the appended claims. For example, the engine may be of the type which is provided with a turbo device. In such an application, the exhaust manifold is particularly exposed to a risk of functional incapability, which is due to the fact that very high temperatures in this case may occur in the exhaust manifold. Furthermore, the invention can be utilized for limitation of functional incapability by controlling several different operating parameters in connection with a combustion engine. The invention is not limited to systems which comprise neither exhaust catalysts nor pre-catalysts, but may in principle also be applied to vehicles which are not provided with these components. Moreover, the invention may in principle be applied in connection with various types of engines, e.g. petrol engines, diesel engines or electric motors, and in propulsion systems which are based on a combination of a combustion engine and an electric motor. The invention is based on a control of operating parameters which result in ageing of components or materials. As examples of such operating parameters can be mentioned the temperature in or in connection with the engine, the temperature of the exhaust gases, the output or indicated torque of the engine, and the engine speed. In this manner, the invention is utilized in order to limit the rate of ageing of the component or the material in question. In connection with the determination according to the invention of the limitation of relevant operating parameters, several components or materials may be taken into consideration, i.e. the combined effects of the ageing of various components may be taken into account.

Claims: CLAIMS 1. Method for limitation of at least one controllable operating parameter which can cause ageing of at least one component (17; 19; 20) or one material in connection with an engine (1), comprising: determination of a maximum limit value allowed (T 2 ; T a , T b , T c ; ni) regarding said operating parameter (T; n), and control of the engine (1) so that said limit value (T 2 ; T a , Tb, T c ; ni) is not exceeded, by means of which ageing of said component (17; 19; 20) or material is limited, characterized in that it comprises: continuous determination of a measure (F) which corresponds to the degree of impairment of said component (17; 19; 20) which depends on ageing, wherein said determination of said limit value (T 2 ; T a , T, T c ; ni) is made depending on said measure (F). 2. Method according to claim 1 , c h a ra ct e r i z e d i n that said operating parameter (T) corresponds to the temperature of the exhaust gases which are emitted from the engine (1). 3. Method according to claim 1 or2, characterized in that said operating parameter (T) corresponds to the temperature in or in connection with the engine (1). 4. Method according to any one of the preceding claims, characterized in that said operating parameter corresponds to the torque of the engine (1 ). 5. Method according to any one of the preceding claims, characterized in that said operating parameter (n) corresponds to the engine speed of the engine (1 ). 6. Method according to any one of the preceding claims, characterized in that said limit value (T 2 ; T a , T b , T c ; ni) is selected gradually decreasing concurrently with the degree of impairment of said component (17; 19; 20). 7. Arrangement for limitation of at least one controllable operating parameter which can cause ageing of at least one component (17; 19; 20) or one material in connection with an engine (1 ), comprising a control unit (5) which is adapted for determination of a maximum limit value allowed (T 2 ; T a , Tb, T c ; ni) regarding at least one said operating parameter (T; n) and for control of the engine (1 ) so that said limit value (T ; T a , T b , T c ; ) is not exceeded, wherein ageing of said component (17; 19; 20) or material is limited, c h a r a c t e r i z e d i n that said control unit (5) furthermore is adapted for a continuous determination of a measure (F) which corresponds to the degree of impairment of said component (17; 19; 20) which depends on ageing, wherein said determination of said limit value (T 2 ; T a , T b , T c ; n is made depending on said measure (F).

Inventors: LITORELL MARTIN, SANDBERG LARS, LITORELL, MARTIN, SANDBERG, LARS
Applicants: LITORELL MARTIN, SANDBERG LARS, VOLVO PERSONVAGNAR AB, LITORELL, MARTIN, SANDBERG, LARS
Application year: 2000
Main classification: F02D41
IPC codes: F02D41