DE3116753A1 - Device for adjusting the ignition timing of an applied-ignition internal combustion engine - Google Patents

Abstract

A device for adjusting the ignition timing of an applied-ignition internal combustion engine, especially a reciprocating-piston internal combustion engine, so as to retard it in the event of knocking combustion is described, the knock-detecting device of which is activated only when the internal combustion engine is running in excess of a predetermined load. In this way, the response threshold of the knock-detecting device can be set low since noises caused by the mechanics of the internal combustion engine and occurring especially in the lower partial load range and in idling, which can be distinguished only with difficulty from knocking noises occurring under higher load conditions, have no effect.

Description

Device for adjusting the ignition point of an externally ignited

Internal combustion engine The invention relates to an adjustment device the ignition point of a spark-ignited internal combustion engine according to the preamble of the main claim.

With a view to the lowest possible fuel consumption comes the ignition point of externally ignited internal combustion engines has recently increased in importance. In general, the earliest possible ignition point is beneficial for good power output the internal combustion engine and favorable specific. Consumption. As early as possible At the ignition point, however, there is a risk of knocking combustion caused by it which can lead to serious engine damage. The ignition timing is therefore as close as possible to the ElopEgronze cJewShlt or, as in more recent times common, if knocking combustion occurs, it is adjusted in the direction of retardation. Such Knock-regulated ignition timing devices are now widely known. A generic device is described in DE-OS 29 30 540, for example.

One problem that arises with these knock-controlled ignition systems is lies in the reliable detection of knocking combustion. When operating the internal combustion engine, in particular a valve-controlled reciprocating internal combustion engine, numerous occur parasitic noises, which are superimposed on the noise caused by the knocking and from this neither in terms of their amplitude nor in terms of their frequency spectrum for sure are distinguishable. This creates the risk of parasitic noises as knocking are evaluated and trigger an ignition timing adjustment or that a knocking Combustion is not recognized as such and does not trigger ignition timing adjustment.

The invention is based on the object of an adjustment device of the ignition point of a spark-ignited internal combustion engine, in which it is ensured that the ignition point in the event of knocking combustion and only with this is adjusted in the direction of late.

This problem is solved with the features of the main claim.

With a closer examination of the noises of a working, externally ignited internal combustion engine has been found that these noises qualitatively depending on the load condition in which.

the internal combustion engine is operated, change. With low loads, in which there is generally no risk of knocking burns, irregular, parasitic noises, which can be attributed, for example, to tilting of the pistons can be that in terms of amplitude and frequency of that occurring at high load Knocking noises can hardly be distinguished. These disappear with high loads irregular noises. The noise is a little larger in its amplitude but on the whole regularly and only superimposed by knocking combustion. The invention makes use of this knowledge by only using the knock detection device then activated, if the irregular, by the mechanics of the internal combustion engine conditional Operating noises disappear. This allows the response threshold that the knock detection device in the activated state has to be relatively low, so that knocking combustion is safely recognized.

Claim 2 characterizes an advantageous design of the load sensor.

The activation of the knock detection device above the predetermined Load condition can take place in many ways. For example, logical AND gates can be provided or the load sensor can be in series with the knock detection device be switched. Another embodiment is characterized in claim 3. In this embodiment, the response threshold is the knock detection device so high at low load that a knock signal is not recognized at all will.

The invention is illustrated below with reference to schematic drawings, for example and explained with further details.

The figures show: FIG. 1 the basic structure of the device according to the invention, FIG. 2 shows the control device contained in the device according to FIG. 1, FIG. 3 shows the control device in FIG the circuit according to FIG. 2 contained knock detection device, Fig. 4 details of a low-pass filter contained in the circuit according to FIG. 3 and FIG. 5 signal patterns at different points in the circuit according to FIG. 3.

According to Fig. 1, a four-cylinder reciprocating internal combustion engine 10 a suction pipe 14 provided with a throttle valve 12. Not the four individually illustrated spark plugs of the internal combustion engine 10 is the ignition pulse via a Distributor 16 is supplied, which receives the ignition pulse from an ignition device 18. the The timing of the ignition pulse generated by the ignition unit 18 is provided by a control unit 20 defines which reference pulses from a rotating component 22 of the distributor 16 cooperating HALL element 24 receives.

The control unit 20 is each connected to a speed sensor via a line 26 for detecting the speed of the internal combustion engine 10, a knock sensor 28 and a pressure sensor 30 for detecting the downstream of the throttle valve 12 in the intake manifold 14 prevailing pressure connected. The knock sensor 28 may be one attached to the engine block Piezo structure-borne sound sensor of the resonance or broadband type or another component which responds to vibrations.

As far as described so far, the structure of the device is on known and is therefore not explained in detail. In the control unit 20 are ignition times associated with the operating points of the internal combustion engine are stored, corresponding to which trigger pulses are delivered to the igniter 18. It understands that other ignition systems that respond to knock can also be used, for example a purely mechanical system with one Delay element which delays the ignition point in the event of knocking combustion.

FIG. 2 shows further details of the arrangement according to FIG. 1. Thereafter the knock sensor 28 via a knock detection circuit 32 is dashed with the overall control device 20 shown connected. The output of the knockdown detection circuit 32 is fed to one input of an AND gate 34, the other input of which is via a threshold switch 34 is connected to the pressure sensor 30. The control unit 20 contains a per se known microprocessor 35, for example a one-chip microprocessor of the type MC6805, which in a manner known per se corresponds to that at its inputs is programmed and a trigger pulse that is dependent on these signals supplies to the igniter 18. The threshold switch 36 is built so that it closes, as soon as a predetermined negative pressure in the intake manifold 14 is undershot.

Fig. 3 shows details of the knock detection circuit 32 according to FIG. 2.

The signal coming from the knock sensor 28 is first sent to a rectifier 38 and then fed to an amplifier 40. The amplified signal is on the one hand a smoothing stage 42 and, on the other hand, a low-pass filter 44. The ones from the Smoothing stage 42 and the low-pass filter 44 coming signals are in a comparator 46, which generates an output signal when the output signal of the smoothing stage 42 the output signal of the low pass 44 exceeds.

4 shows details of the low-pass 44 in a manner known per se a resistor -50 and a capacitor 52 which fill the actual low pass. The point of connection between the two is the positive input of an amplifier 54 connected downstream, the gain of which is normally through a ground connected to the negative input resistor 56 and a den negative input to the output connecting negative feedback resistor 58 is determined is.

To generate an offset voltage is known per se a network connected to a positive voltage source with the resistors 60, 62 and 64 are provided.

To reduce the gain of the amplifier is parallel to the Feedback resistor 58, a resistor 66 and a transistor 68 connected, its Base through a resistor 70 to ground and through a resistor 72 to the output of amplifier 54 is connected. The one from the high-value resistors 70 and 72 existing voltage divider determines the voltage at the base of transistor 68 and thus the turn-on voltage of transistor 68. When the transistor is turned on 68 is the resistance of the negative feedback path of amplifier 54 and thereby its Gain decreased.

The function of the described arrangement is explained with reference to Fig. 5: Diagram A shows the signal profile from the output of the knock sensor 28 at below low load running machine. This signal has a basic component, which through Given valve noises and the pairings of the friction partners of the internal combustion engine is. Superimposed on this are individual noises with a greater amplitude that may be on piston tilting and similar, undefined processes are caused. the Amplitudes these noises reach relatively large values.

The frequency spectrum of the signal curve changes at high speeds according to diagram A. The amplitudes of the basic spectrum increase. That of the individual Tips a little smaller. The basic structure of the signal curve changes nothing.

Diagram B shows the output signal of the knock sensor 28 at below high load running internal combustion engine. As can be seen, the individual tips are missing. Overall, the noise has a greater amplitude than the noise according to the diagram A on. There are no raised tips. The signal curve is more even than in the diagram A.

Diagram C shows the output signal of the knock sensor 28 at high Load with knocking combustion. Clearly visible are the individual through which knocking combustion caused excessive amplitudes. The size of the amplitude exaggeration of diagram C is not significantly different from that of diagram A, so that it is difficult for a detector circuit to detect amplitude peaks according to diagram A to be distinguished from the knocking combustion according to diagram C.

The diagrams A1, B1 and C1 show the rectifier 38 (Fig. 3 rectified) and amplified by the amplifier 40 with the input signals according to diagrams A, B and C.

The diagrams A2, B2 and C2 show the course of the signals according to the diagram A1, B1 and C1 at the output of the smoothing stage 42, which, for example, is an RC element with a time constant significantly smaller than that of the RC element 50, 52 according to FIG. 4 contains. The signal curves A2, B2 and C2 correspond in total the course of the signals according to the diagrams A1, B1 and C1. They are just somewhat smoothed, especially in their short-lasting tips, making a simpler one Further processing is possible.

Diagram D shows the output signal of the low-pass filter 44, superimposed of an offset voltage, which depends on the amplitude peaks of the signals is selected according to diagram C2. The signal curve according to diagram D is for the the signals fed to the low-pass filter 44 in accordance with the diagrams A1, B1 and C1 essentially the same, since the low-pass filter suppresses the brief amplitude increases in these signals.

In diagram E, the signal curves according to diagram C2 and D are superimposed the drawn. As can be seen, the signal according to diagram C2 exceeds the signal according to diagram D only with knocking combustion, so that the comparator 46 has an output signal generated according to diagram F.

As can be seen immediately from the foregoing, the comparator generates 46 even when the signals according to diagram A2 are superimposed on the signal according to diagram D an output signals corresponding to the amplitude peaks ~ in diagram A2. These output signals are suppressed because the threshold switch is activated when the load is low 36 (Fig. 2) is closed and the AND gate 34 thus blocks. At high load (diagram C2), on the other hand, the threshold switch 36 opens, whereby the AND element 34 receives the output signals the knock detection circuit 32 and thus the comparator 46 to the microprocessor 35 lets through.

The low-pass filter 44 forms a "dynamic threshold" of the comparator 46, because the signal according to diagram D because of the increasing amplitudes with increasing speed of the basic signal according to diagram B increases. Up to medium engine speeds the distance between the level of the signal according to diagram D and the basic signal is sufficient Diagram C2 in order to discriminate the knock signals. At higher speeds it will the course of the basic signal according to diagram B and thus also C increasingly more uniform, whereby the level of the signal D would be greatly increased and the knocking accordingly Diagram E would no longer be recognized. So that the level of the signal D is not impermissible is greatly increased, the transistor 68 opens at a predetermined by the Resistor 72 adjustable voltage, which leads to a flattening of the dependence of the Output of the amplifier 54 from the amplitude of the resistor 50 supplied Signal leads.

It will be understood that the output of the threshold switch 36 also directly to the comparator 46 or the open circuit associated with the amplifier 54 Circuit can be connected to the threshold of the knock detection circuit 32 in the partial load area and thereby the microprocessor 35 in this load area not to supply signals that simulate a knocking combustion. The AND element 34 can then be omitted.

It is further understood that, for example, in FIG. 2, the assembly from pressure sensor 30 and threshold switch 36 by a simple, with a predetermined. Vacuum closing switch can be replaced.

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Claims (4)

Device for adjusting the ignition point of an externally ignited Internal combustion engine P a t e n t a n s p r ü c h e: k 1.) Device for adjustment the ignition point of an externally ignited internal combustion engine, in particular a reciprocating piston internal combustion engine, in the late direction with knocking combustion, with a control device which in their position related to the rotational position of the crankshaft of the internal combustion engine generated trigger pulses dependent on the operating state of the internal combustion engine, one Ignition device, which generates an ignition pulse in response to a trigger pulse and a knock detection device, which detects knocking combustion of the internal combustion engine responds and the control device feeds a knock signal, which the late adjustment of the triggering impulse brings about that a known per se, more responsive to the load condition of the internal combustion engine (10) Load sensor (pressure sensor 30) is provided, which the knock detection device (28, 32) only activated above a predetermined load condition. 2. Internal combustion engine according to claim 1, d a d u r c h g e k e n n z e -i c h n e t that the load sensor is a pressure sensor (30) which on the prevailing in the intake manifold (14) of the internal combustion engine (10) downstream of a throttle valve (12) Pressure responds. 3. Internal combustion engine according to claim 1 or 2, d a d u r c h g e -k It is noted that the load sensor (30) with an input of a logical Linking element (AND element 34) that the knock detection device (28, 32) is connected to the other input of the logic element and that the output of the link. connected to a microprocessor (35) belonging to the control unit is. 4. Apparatus according to claim 1 or 2, d a'd u r c h g e k e n n -z e i c h n e t that the load sensor (pressure sensor 30) is above the predetermined load condition of the internal combustion engine (10) the response threshold of the knock detection device (28, 32) decreases.