Abstract:
To modify engine operation and reduce the tendency of the engine to knock or ping, a knocking signal is generated which is representative of knocking intensity and/or frequency of knocking occurrence, and compared with a permissible knocking signal. The result of the comparison is utilized to change an operating parameter of the engine, for example by injecting a fluid, e.g. water, into the engine, changing charge pressure, for example of a turbocharger or the like. The permissible engine knock signal can be modified in accordance with an engine operating parameter, for example at low temperature, or low speed, the permissible knocking limit can be raised since the damaging effect of knocking at low temperature or low speed is less than under different operating conditions.

Description:
REFERENCED TO PRIOR PATENTS 
     U.S. Pat. No. 4,002,155, Harned et al; U.S. Pat. No. 4,133,475, Harned et al; U.S. Pat. No. 4,153,020, King et al; British Pat. No. 2,001,130, Scherenberg; and, assigned to the Assignee of this application: German Patent Disclosure Document DE-OS No. 30 09 046, Schramm. 
     The present invention relates to a system and method to control the operation of an internal combustion (IC) engine which is equipped with knock sensors to sense combustion conditions resulting in knocking or pinging of the engine, and which includes signal processors to receive the signals from the knock sensor, to then control the engine operation to prevent knocking or pinging. 
     BACKGROUND 
     Various types of knocking or pinging prevention and control systems have been proposed--see the referenced patents and patent documents listed above. The systems, as proposed, control operation of the engine by adjusting the position of an operating control element thereof if an evaluation circuit, connected to a knock sensor, senses that the engine is operating under knocking conditions, or has a tendency to knock. Typical changes to prevent knocking of the engine are: changing the fuel-air ratio to provide a somewhat richer mixture, that is, one which has more fuel therein; providing additives to the fuel-air mixture to insure operation without knocking, by increasing the resistance to knocking of the engine. Typical additives are water, alcohols, aniline compounds, lead, or similar metallic compounds, as well as combinations thereof. Other changes which can be made are changes in the extent of exhaust gas recirculation (EGR), by controlling the gas being returned in a return loop; controlling the temperature of the air which is charged into the engine, for example by heating or cooling the intake air; controlling the temperature of the combustion mixture or the combustion components thereof, controlling the cooling of the engine, and, most importantly, controlling ignition timing and/or fuel injection timing in a fuel injected engine. An additional change suitable for turbocharged engines is to change the turbo charging pressure. Readily changed parameters are the introduction of additives, for example by injecting components which have a tendency to decrease knocking, and to control the charge pressure of induction air, for example the charge pressure of a turbocharger. 
     The various steps taken to decrease knocking can be carried out in dependence on actual sensing of knocking, and especially by counting the sequence and the number of knocking events, and the intensity thereof, which occur--see, for example, the referenced U.S. Pat. No. 4,153,020, King et al. Knock control systems are subject to the problem that, if the knocking is slight, or occurs only from time to time, the control loop may overreact. Such overreaction can be avoided by making the control loop operate slowly. Yet, slow operation of the control loop prevents rapid reaction to substantial knocking which suddenly occurs. 
     THE INVENTION 
     It is an object to improve the control effects of a control loop which reacts to knocking of the engine to provide smooth response which, however, is rapid. 
     Briefly, in accordance with the invention, knocking signals are generated by knock sensors or the like, and distinguished from engine noise signals. A standard, or permissible knock signal is generated which is compared in a comparator, receiving the actual knocking condition signals, as well as the permissible signals and providing a control output signal to the engine control to change the operating conditions of the engine in a non-knocking operating direction if the comparison by the comparator exceeds a predetermined or preset value. 
     The particular change of engine control can be selected in accordance with design requirements to change a suitable engine parameter which affects knocking, as discussed above. The comparison can be carried out with respect to frequency of occurrence of knocking events, and/or intensity thereof, or a combination of both. If the knocking recognition system is sensitive, so that even under normal operating conditions, unusual combustion events or irregular combustion is recognized, a suitable value can then be commanded to respond to a predetermined number of sensed knocking events, so that the operating conditions of the engine can be controlled into the non-knocking region before actual knocking occurred, that is, as soon as a tendency to knocking operation has been recognized. 
     The system has the advantage that, by providing a standard, or permissible knocking signal, a certain degree of tendency to knocking can be permitted, so that, if only occasional, or very weak knocking events occur, the system need not react at all, and will not react; yet, at heavy knocking operation, the system will react rapidly. This provides for overall smoother engine operation, yet rapid control upon deviation from normal operation, so that overall deviation from an optimum operating point is reduced. 
     In accordance with a particularly desirable feature of the invention, the standard or permissible knocking signal can be changed in relation to engine parameters, or may have a modifying signal, for example representative of interference signals applied thereto. The permissible knocking signal, thus, can permit knocking operation for a larger number of sequential knocking events than otherwise, with the number being selected in accordance with design of the engine, which may permit several knocking events to occur without damage to the engine under certain engine operating conditions, for example at low engine speed or low engine, or ambient temperature. 
     In accordance with a particularly preferred feature of the invention, an adding circuit is included in the system which, in dependence on a control signal value, changes one operating parameter of the engine with long-time effective changes in a direction to reduce knocking combustion; a second parameter adjusting element is also provided and controlled, the second element having a short-time effect, and introducing, for example, rapidly acting changes which, however, do not persist over a long period of time. One such change is, for example, injection of water to the IC engine which will rapidly reduce knocking, but will not have a persistent effect. 
    
    
     DRAWINGS 
     The single FIGURE is a schematic block diagram of a combustion control system, operating in accordance with the method for an internal combustion engine. 
    
    
     DETAILED DESCRIPTION 
     An internal combustion (IC) engine 10 has a knock sensor 11 associated therewith in order to recognize combustion conditions which result in knocking or pinging. The output signal from the knock sensor is applied to an evaluation circuit 12 in order to filter out and remove the noise signals, so that the actual knocking signals can be distinguished from the number of pulses and frequencies which are mixed in with the signal derived from the sensor 11. Usual knock sensors sense more than actual knocking or pinging signals, and it is necessary to distinguish the knocking or pinging signals from overall engine noises. 
     The knocking signals recognized in the knocking recognition stage 12 are applied to an evaluation stage 13 in which the knocking signals are evaluated and provide an output signal which has certain characteristics in dependence on, for example, the frequency of occurrence of knocking signals, the intensity of the knocking signals, or a combination of both. The evaluation stage 13 thus provides an output signal evaluating the combustion events as sent by the knocking sensor, with respect to frequency of occurrence of unusual combustion conditions or the intensity thereof, or a combination, to provide an output signal representative of the respective selected parameter, or combination. Knocking recognition stages and evaluation stages are well known, and reference is made to the aforementioned patents and literature. 
     The output from the evaluation stage is an actual signal I K . This actual knocking value signal I K  is compared in a comparator 14 with a reference, or permissive knocking signal S K . The comparator 14, in its simplest form, may be an algebraic adder, which has positive and negative inputs. The output from the comparator 14, and representative of control deviation, is applied to a controller 15, the output of which is connected to a second comparator 17 which, again, may be an algebraic adder, for application to a knock prevention positioning element 18. The second comparator or algebraic adder 17 combines the output from the controller 15 with a desired value of a working point, represented by a signal Sa. Such a desired value of the working point, for example, may relate a specific working point or event of the IC engine to a predetermined value. For example, a suitable working point may be a predetermined ignition timing instant, or a predetermined charge pressure, derived, for example, from a turbocharger. The particular working point can be derived by manually setting a suitable control element, by inherent engine adjustment of a control element, for example by setting of engine vacuum, or in form of a signal derived from an engine operating computer which provides the respective predetermined parameter in dependence on engine operating and operation characteristics, stored in the form of characteristic curves within the engine operating computer in memory elements, for example programmable read-only memories (PROMs). Such engine operating computers are well known and in commercial use. The control deviation required to reduce pinging or knocking is applied to a first knock prevention positioning element 18, which controls the setting or timing of one of the parameters affecting engine operation. 
     The output of the controller 15 is additionally connected to a second knock prevention positioning element 19, which affects another parameter of operation of the engine. The controllers 15,16 may operate in accordance with any desired control algorithms, and have proportional and/or integral, and/or differential control characteristics. 
     To distinguish between the positioning elements 18 and 19, the positioning element 19 may also be termed a knock prevention stage. 
     The operation of the IC engine will depend on the applied engine operating parameters, for example temperature T, speed n, loading L, air number λ, type of fuel K, and the like. The engine operating parameters are applied singly or in combination to a knock-effect signal generating stage 20, as well as to the engine 10. The knock-effect signal generating stage 20 receives the respective engine parameters and provides, in accordance with engine operating characteristics stored, for example, in PROMs, a modifying signal, S&#39; K , which has, in dependence on the particular parameter, certain influence on the operation of the engine, the stage 20 being controllable so that a desired influence in dependence on change of the various parameters can be provided in form of an output signal therefrom. The output signal can be applied directly to the comparator 14 as an additional comparison input to modify the comparison level of the comparator 14 with respect to the permissible knocking signal S K , or can be applied to the permissible knocking signal S K  to modify it before comparison, as schematically illustrated by the broken line S&#39; K , or a combination of both direct and modifying connection may be made. 
     The output signal applied by the stage 20 thus changes the permissible knocking signal S K  in dependence on the desired parameter which is to be influenced. For example, the parameter may be speed, and at low speed of the engine, or at low temperature, the value S K , that is, permissible knocking, can be increased since under low temperature or low-speed conditions, knocking or pinging operation is relatively harmless to the engine. Similarly, changes of the permissible knocking or pinging signal S K  can be made in dependence on other engine parameters, selected in relation to the respective harm which can result to the engine if knocking or pinging persists under the respective conditions. 
     OPERATION 
     Basically, the method and system compares sensed and evaluated combustion conditions in the comparator 14 with a permissible value which provides a signal representative of a permissible degree of knocking or pinging events, and which, preferably, is changeable in dependence on then pertaining engine operating conditions, for example speed or temperature. A permissible value may be, for example, one pinging or knocking combustion event during sixteen combustion events in a specific cylinder; another permissible value may be a certain intensity of knocking combustion. 
     If the frequency of occurrence of knocking events is sensed, then the evaluation stage 13 can be constructed as an average value circuit, which provides, in dependence on frequency of occurrence, a digital or analog signal to the comparator 14. If the comparator 14 determines that the permissible value S K  is exceeded, the controller 15 will cause the knock prevention stage 19 to provide for rapid change of operating conditions of the IC engine to prevent pinging or knocking. One example would be the injection of water, or other substances which have the tendency to reduce knocking into the IC engine. The advantage of injecting water is that the ignition timing of the engine then need not be changed, and can be operated under optimum conditions, both with respect to fuel consumption and power output; as known, injection of water in certain operating ranges, provides for increased power output. 
     The water injection by the knock prevention stage 19 is operated in parallel with a quasi-stationary controller. For example, if the engine is turbocharged, the charge pressure can be controlled by the knock prevention positioning element 18. The optimum charge pressure is introduced in form of the signal S a  ; under ordinary, non-knocking operation, the optimum charge pressure is used. If knocking or pinging should result, as evaluated by the evaluation stage with respect to intensity and/or frequency of occurrence of knocking or pinging events, resulting in an output signal I a , charge pressure is changed so that the knock prevention stage 19 need not continue to inject water and thus introduce an excessive amount into the engine, which may lead later on to rusting. 
     In the simplest arrangement, the controller 16, positioning element 18, and comparator 17 can be omitted, and only a single knock prevention stage 19 is required. The influencing of a selected knock preventing engine operating parameter by the stage 19 can then be controlled directly from controller 15; in yet another alternative, the stage 19 is omitted and only the control path through elements 16,17,18 need be used. 
     Utilizing two parameter control positioning elements 18,19 has the advantage that a substantial number of combinations of the various methods to reduce knocking can be used. If, for example, as illustrated, two parameters are controlled, one immediately and quickly effective, and one more slowly effective but persistent, then it is desirable to so arrange the controller 16 that it operates, generally, slower than the controller 15, and to provide the controller 16 with a dead zone or dead band, so that rapid changes in the knock sensing signal derived from the evaluation stage 13 can be controlled by the rapidly acting knock prevention stage 19, for example by injection of water, whereas somewhat more stationary or slowly changing conditions in the operating level are controlled over the positioning element 18, for example by changing induction air pressure, charging pressure, or the like. 
     Various changes and possible arrangements thereof can be used with any of the others.