The present invention relates to a method of avoiding abnormal ccm- ^■ bustion, so-called knocking, in an internal combustion engine, prefer¬ ably of the Otto—type, there being a transducer arranged on the engine to sense a parameter responding to the engine combustion, e.g. prevail- ing pressure and/or teπperature conditions of the engine, and to transmit an output signal correspondi,ng to such a parameter value for controlling at least one means regulating the combustion. The invention alse relates to an arrangement on an internal combustion engine for carrying out the method. In Otto-type engines it is known that kno ing can occur in certain operating conditions, especially when the engine is heavily loaded. By knocking is meant an uncontrolled combustion of an explosive nature in the cylinders of an engine, and it is generated by inducted fuel-air mixture being locally ignited in the combustion chamber before a flame front starting from the spark plug has caused ignition. The engine is thus subjected to high temperature and pressure stresses which can lead to mechanical engine damage.

In Otto-type engines it is previously known to avoid knocking by ^{' '■} using a so-called knocking detector. A transducer incorporated in the detector is arranged to sense knocking in the form of high vibration level for the engine in question and in response thereto to generate an output signal controlling the engine ignition so that ignition of the fuel-air mixture is delayed. This results in that the abnormal course of ignition, i.e. the excessively high vibration level, ceases. Certai disadvantages accompany the known method however. Delayed ignition involves a deteriorated thermic efficiency, i.e. higher speci¬ fic fuel consurrption of the engine, which, frcm the point of view of air pollution, results in poorer exhaust gas composition than what is the case for optimum ignition. Higher exhaust gas temperature is also obtained, which puts increased demands on the material of the parts incorporated in the engine, as well as on engine cooling.

The present invention has the object of controlling the cαnbustion in an engine in response to the output signal of a transducer such that the above-mentioned disadvantages in the known technique do not occur. The invention is thus distinguished in that the output signal from a

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transdιcer of the land mentioned in the introduction is utilized for achieving a reduction of the engine induction pressure when the para¬ meter value sensed by the transducer represents abnormally high pressu ar /or temperature conditions during combustion in the engine. • In the inventive method, the induction pressure of the engine is thus controlled in response to the transducer output signal. As with already known techniques, the reduced induction pressure results in a reduction of engine performance, since the fuel-air quantity fed to the engine decreases. However, alteration in the thermic efficiency is avoided with the use of the invention, i.e. the specific fuel consump¬ tion can be maintained unchanged. Furthermore, the exhaust gas pollu¬ tants can be maintained substantially unchanged, as well as exhaust ga temperature and demands on'the engine cooling system.

In an advantageous embodiment of the invention, the output signal o the transducer is compared with a reference signal representing the parameter value for optimum combustion. A deviation signal generated from said cαrparation thereby affects the engine induction pressure in response to the magnitude of the deviation. This increases the accurac in .the control of the engine induction pressure and the engine perform ance loss caused by knocking sensed by the transducer can thus be kept down.

For carrying out the inventive method applied to en internal com¬ bustion engine, the invention is distinguished by an arrangsnent in which an electronic unit connected to the engine is disposed for pro- cessing the transducer output signal and that means affecting the engine induction pressure are connected to the electronic unit and adapted for controll g the engine induction pressure in response to the signal processed in the electronic unit.

Other distinguishing features of the invention are apparent from the description below and the following patent claims. The description is made with reference to the attached figures, of which

Figure 1 schematically illustrates an arrangement for applying the inventive method and Figure 2 shows in the same way an advantageous embodiment of the arrangsnent illustated in Figure 1.

During combustion in an engine 1 , a vibration level is obtained which is sensed by a transducer 2 connected to the engine 1. In respons

thereto, the transducer 2 gives an output signal which is amplified in a following amplifier 3 before it is applied to a comparator 4. The amplified output signal frcm the transducer 2 is compared in the comparator with a reference value frcm a reference value source 5, this value representing a vibration level in the engine corresponding to normal combustion. A possible deviation results in a corresponding output signal from the comparator, and after amplification in an ampli¬ fier 6 this signal is taken to an actuating means- 7 which in response thereto regulates the pressure in the engine induction syston 8. Com- bustion in the engine 1 is thus affected such that the vibration level subsequently sensed by the transducer 2 is successively reduced a d finally results in that the comparator 4 no longer registers devi¬ ations.

A more developed embodiment of the inventive arrangement for an Otto-type engine provided with supercharging is illustrated in Figure 2. Said Otto-type engine includes the engine unit 10, an induction systΘ-i 11 and an exhaust system 12. A turbo-type super-charger unit 13 includes a centrifugal compressor 14 incorporated in the induction system 11 , and an exhaust gas-driven turbine 15 incorporated in the exhaust gas system 12. A valve 16 is arranged to control the exhaust gas flow through a duct 17 leading past the turbine 15 and thus also controls the exhaust gas flow through the turbine 15. The rotational velocity of the turbine 15 is thus affected, and thereby the rotation¬ al velocity of the direct-driven compressor 14 also. Such alteration of rotational velocity causes variation in the pressure prevailing in ■ the induction systan 11 downstream of the compressor 14, and is denoted "siper-charging pressure" in continuation.

The valve 16 conventionally comprises an actuating means 18 by which opening and closing of the valve 16 is controlled. The valve 16, here of the dish-type, is provided with a valve rod 19 rigidly connec¬ ted to a diaphragm 20 arranged on the actuating means 18. The diaphragm 20 separates the actuating means 18 into an outer and inner chamber 22 and 23, respectively. The outer chamber 22 is supplied with super¬ charging pressure via a pipe 24. The inner chamber 23 is in cccmiunication with surrounding air, but also includes a helical spring 25 urging the valve 16 in closing direction. A pipe 26 provides ccπmunication between the pipe 24 and the induction air-system upstreamofthe compressor 14.

The portion of the pipe 24 between its connections to the induction air system 11 and the pipe 26 has a restricted through-flow area pro¬ vided by a constriction 27, this area being significantly smaller than the corresponding area in the pipe 26, when a timing valve 28 in the pipe 26 is in an open position as illustrated in Figure 2. The air-flew through the pipe 26 is regulated by the timing valve 28, and thereby the pressure which controls the valve 16 via the pipe 24. Eegulation of the timing valve 28 is in response to a signal applied to said valve, the value of the signal representing the deviation between the actual super-charging pressure and the maximum super- charging pressure which is allowable for the engine to work optimally, i.e. without abnormal combustion with knocking tendences.

The signal applied to the timing valve 28 is generated in an elec- tronic unit, in which there is incorporated a transducer 30 in the form of a so-called acceleroeter of a kind known per se. The trans¬ ducer 30 normally is of piezo-electrical type and senses vibrations present in the engine walls, said vibrations being directly attribut¬ able to the pressure conditions prevailing in the engine 10 during combustion. In response thereto, the transducer 30 generates an output signal, which is directly proportional to said pressure conditions. The output signal is sent via a connection ^' 31 to an amplifying circuit 32 and in amplified form to a comparator 33.

A reference signal is also applied to the comparator 33 via a connection 34. This signal is obtained by the distributor 35, con- ventionally mounted on the engine, generating a pulse train of a frequency directly corresponding to the engine revolution rate. The pulse train is fed via the connection 34 to a converter 36 in which the pulse train is converted into an output signal ^" with a voltage varying in response to the frequency of the train. The signal level is thus directly proportional to the engine speed, but also serves as a direct reference value for the pressure conditions which should prevail during ccmbustiαn in an Otto-type engine which is working optimally.

The comparison between the signal representing the actual pressure conditions in the engine and the signal representing the criterion value for said pressure conditions, carried out in the comparator 33, results in an output signal having a level representing the difference

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between said signals. This signal is taken via a connection 38 to an integrator 40 and the processed output signal therefrαn is taken via a connection 41 to a potentiometer 42. The latter allows the signal level to be manually adjusted to a predetermined level for a specific engine, before the signal is applied to one input terminal of a cαπparator 44. Via a connection 45, there is applied to the second input terminal of the comparator a signal frcm a pressure transducer 46 which senses the supercharging pressure in the induc¬ tion system 11 and transmits a signal corresponding thereto. The pressure transducer 46 is suitably adapted for transmitting an output signal within an upper super-charging range, within which range regu¬ lation of the super-charging pressure is significant frcm the point of view of knocking.

Depending on the difference between fed-in signals, the comparator 44 generates an output signal which is applied to a pulse modulator

48. In the latter the signal is converted to a pulse train of constant frequency, but where the relation between the positive and negative portion of the period is dependent on the level of the output signal of the comparator 44. The pulse train from the pulse modulator 48 is amplified in an amplifier 49, which constitutes .the driving step for ^' the timing valve 28. The latter functions in principle as a solenoid valve for opening and closing in pace with the changes be¬ tween the positive and negative period portions of the pulse train. The components in the electronic unit described above comprise simple and well-known circuits in electronics, and are therefore not described further.

When the engine works normally, the transducer 30 senses a similar normal vibration level in the engine 10. The level of the signal applied to the cαπparator 33 thereby falls belσw the level of the reference signal similarly applied to the comparator 33. The output signal of the comparator 33 thus assumes a level in proportion to the difference between the applied signal levels. Subsequent integra¬ tion of the signals in the integrator 40 results in an output signal therefrom to the connection 41 which signal after possible adjustment in the potentiometer 42 is applied to the comparator 44 and there serves as a criterion level for the signal which is applied to the comparator 44 from the pressure transducer 46. The latter signal

represents the actual super-charging pressure, while the signal functioning as a criterion represents the maximum permitted super¬ charging pressure for ensuring cαnbustion without knocking. As long as the engine 10 works at a normal vibration level as sensed by the transducer 30, the criterion level applied to the cαπparator 44 will be so high that the true level in the connection 45 will not exceed said criterion level. The output signal from the com¬ parator 44 has a relatively high level and after conversion in the pulse modulator 48 there is obtained a pulse train where the portion of the period causing the timing valve 28 to keep the pipe 26 open is great relative to the period portion actuating the timing valve 28 to keep the pipe 26 closed. In the latter case, absence of control pressure from the pipe 24 signifies that the super-charging pressure must achieve comparatively high values before said pressure, via the pipe 24, is capable of opening the valve 16 to decrease the exhaust gas flow through the turbine 15. The compressor 14 is thus permitted to create a high st er-charging pressure to the engine 10.

On the other hand, if the transducer 30 senses an abnormally high vibration level as a result of knocking during oαnbustion in the engine 10, it transmits a signal the level of which is higher than normal. The difference from the reference signal consequently decreases and this results in that the level of the output signal from the comparator 33 decreases as well as the output signal of the inte¬ grator 40. The latter signal represents a criterion level for the engine super-charging pressure, which furthermore corresponds to the maximum super-charging pressure permitted for current engine operating conditions. This results in that the level of the maximum permitted super-charging pressure is lowered relative to the normal case. The difference from the signal level in the connection 45 j representing true st_per-charging pressure is eliminated, and the out¬ put signal from the comparator 44 changes level. After conversion in the pulse modulator 48, also the relation between the period portions in the pulse train coming from the modulator has been changed. The time during which the timing valve 28 keeps the pipe 26 closed will be great relative to the time during which it is kept open. The control pressure drop from the pipe 24 will consequently be small and the valve 16 is thus supplied with a comparatively high control

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pressure which is capable of opening the valve 16 early, i.e. at relatively lew super-charging pressure. The exhaust gas flew through the turbine 15 decreases and thereby the super-charge created in the compressor 14. The decreases super-charging pressure reduces the ten- dency to knocking during cαnbusticn in the engine, which is sensed by the transducer 30, subsequent upon which there is a renewed regu¬ lation of the timing valve and so on.

In relation to the principle solution depicted in Figure 1 , the version illustrated in Figure 2 not only contains a comparison with respect to the engine vibration level, but also a second comparison with respect to the engine super-charging pressure. Said super¬ charging pressure cαπparison ensures that the engine is not supplied with a higher super-charging pressure than the criterion pressure set by the potentiometer 42, even if the engine is supplied with a fuel with a knocking tendency which is so low, i.e. the octane number is so high, that higher super-charging pressure per se could be supp¬ lied without knocking occuring during combustion. If the super-charging pressure comparison were not carried out, there would be no upper limit for the super-charging pressure in this case. Engine performance could thus reach.levels for which the engine is not designed.

In practice, an inventive embodiment according to Figure 2 includes further detail solutions, e.g. those having the task of ensuring that the engine is not ^' subjected to excessivesly high super-charging press¬ ure if a fault occurs in the system such as that the -transducer ceases to function or rupture occurs in the pipes 24,26, etc.

The invention can be modified in a plurality of alternative embodi¬ ments within the scope of the following patent claims. The number of transducers can thus be varied, and their output signal can be pro¬ cessed in different ways before it is permitted to actuate the means affecting the induction pressure. If more transducers are utilized, then different parameters can also be sensed. Said means can constitute an ordinary throttle in the induction systαn or a separate means directly or indirectly controlling the engine induction pressure.