GB2069601A - Method of and apparatus for automatically adjusting the ignition timing of controlled-ignition engines - Google Patents

Abstract

The apparatus comprises a detector 20 for detecting the position of the engine crankshaft, an accelerometer 18 for producing a signal representing the acceleration of the cylinder head, the signal being integrated by an integrator 45 and supplied to a zero valve detector in the form of an inverter 50, and means for adjusting the ignition timing in dependence on the crankshaft position at which the zero value of the integrated signal is detected. The signals from the sensors 18, 20 are supplied to a circuit 23 which adjusts the ignition timing so that the maximum pressure in the engine cylinders occurs at a preselected position of the crankshaft. <IMAGE>

Description

SPECIFICATION Methods of and apparatus for automatically adjusting the ignition timing of controlled ignition engines The present invention relates to methods of and apparatus for automatically adjusting the ignition timing of controlled-ignition engines.

With the operating conditions of an engine being known, for example by virtue of the values of characteristic parameters (speed of rotation of the engine, intake vacuum, temperature and richness of the mixture fed into the cylinders, the amount of burnt gases which are recycled to the intake, etc.), it is known that, under substantially normal engine operating conditions, there is a relationship between the moment of ignition in a cylinder and the moment at which the pressure in the cylinder is set at its maximum, which moments are generally identified by the corresponding angular positions of the crankshaft.

Thus, for example, when the setting or 'timing' of the ignition corresponds to the optimum advance for maximum power and maximum efficiency, it has been found that the maximum pressure in the cylinder in question occurs when the crankshaft is at a given position, namely about 15 30' after the top dead centre position. Therefore, the optimum advance setting can be achieved by modifying the timing of the ignition until the pressure maximum observed coincides with the above-indicated position of the crankshaft, that is to say, substantially 15= 30' after the top dead centre position.

One of the problems to be overcome is that of accurately determining the instantaneous value of the pressure in the cylinders of an engine, to identify the position of the crankshaft at which that pressure is at a maximum, and to modify the setting of the ignition system in consequence.

In French Patent No 2 109 698, the ignition advance is so set that the explosion always occurs at the optimum angular position of the engine shaft. The system uses a detector giving a more or less linear response, which will produce a signal having a straight rising edge. A disadvantage of this technique is that, in practice, as the explosion is not instantaneous, a noticeable degree of inaccuracy is found in the ignition advance setting, and the degree of inaccuracy increases in proportion to increasing engine speed.

French Patent Application No. 2 270 454 refer to studies concerning combustion in an internal combustion engine, which have shown that combustion occurs in two separate stages.

First of all, after the spark is first produced, there is a low-pressure stage in which the mixture is ignited and a flame begins to propagate in the combustion chamber. A substantial discontinuity in pressure is then observed, which marks the beginning of the second stage. In that case, the commencement of the second stage is detected, for example by means of a piezo-electric transducer which produces a signal as soon as the pressure rises above a predetermined threshold, and the moment of ignition is altered so that the commencement of the second stage occurs when the crankshaft is in a given position. Such a technique suffers from the disadvantage of requiring substantial modification of engines to permit installation of the piezoelectric transducer and in practice it is found that it is difficult to detect the beginning of the second stage with sufficient accuracy.

At an SAE Congress No. 750 883 which was held at Detroit, Michigan, U.S.A. from 1 3th to 1 7th October, 1975, it was proposed that detectors in the form of piezo-electric pressure transducers of annular shape be interposed between the spark plugs and the cylinder head of the engine. Such detectors can give good results, but replacing the spark plugs becomes a more difficult operation since it is necessary to avoid any damage to the detectors, while ensuring that a good seal is produced, when the spark plugs are refitted. However, in some cases, the electrical pulses corresponding to ignition may interfere with or even destroy the detectors unless precautions are taken which further increase the difficulty and the delicacy involved in repair or maintenance in regard to the spark plugs.

According to a first aspect of the invention there is provided a method of automatically adjusting the ignition timing of a controlled-ignition engine to an optimum value for operating conditions corresponding to maximum power and maximum efficiency of the engine, wherein the ignition timing is so adjusted that the maximum pressure in at last one cylinder of the engine occurs at a predetermined angular position of a shaft of the engine shaft, and wherein:: the angular position of the engine shaft is detected, acceleration effects to which a cylinder head of the engine is subjected are detected and a-first signal representative of said acceleration effects is produced during at least a portion of the rotation of the engine shaft; the first signal is integrated to produce a second signal, the zero value of which is detected with respect to the angular position of the engine shaft, and the ignition timing is adjusted in dependence on the angular value of the position of the engine shaft at which the second signal is zero in value.

According to a second aspect of the present invention there is provided apparatus for automatically adjusting the ignition timing of a controlled-ignition engine, the apparatus comprising: ignition control means, a rotation detector for detecting the rotational position of a shaft of the engine, an accelerometer which is fixed to a cylinder head of the engine and operative to produce a first signal representative of acceleration effects to which the cylinder head is subjected, an integrating means connected to the accelerator and operative to produce a second signal, zero value detection means connected to the integrating means for detecting a zero value of the second signal over at least a portion of the rotation of the engine shaft, angular position detecting means connected to the zero value detection means and to the rotation detector and operative to detect the angular position of the engine shaft corresponding to the zero value of the second signal, comparison means connected to the angular position detecting means to detect the spacing between said angular position and a reference position, and adjustment means connected to said comparison means to modify the action of the ignition control means in dependence on said spacing.

Embodiments of the invention can be designed to adjust the ignition timing in dependence on conditions which are to be obtained in respect of the engine. Such conditions may be, for example (but not exclusively), operation of the engine with optimum setting of the ignition advance, the engine then producing maximum power with maximum efficiency.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of an engine provided with an ignition timing control apparatus; Figure 2 is a diagrammatic view of an electronic control assembly for an ignition circuit; Figures 3 and 4 show more detailed views of the structure of the electronic assembly diagrammatically shown in Fig. 2; and Figure 5 shows a modification of the construction shown in Fig. 4 to form an apparatus embodying the invention Fig. 1 shows by way of example a four-cylinder engine 1 which is provided with an electronic ignition circuit 2.The ignition circuit diagrammatically comprises a voltage source 3 which supplies a main circuit comprising a capacitor 5 which is connected in series with a primary winding 9 of an ignition coil and a capacitor discharge circuit comprising a thyristor 4 which is connected in parallel with the main circuit. A secondary winding 10 of the ignition coil successively supplies each of spark plugs 13, 14, 1 5 and 1 6 of the engine 1 by way of a distributor 11, a rotor arm 1 2 of which is connected to a crankshaft 1 7 of the engine 1, for rotation therewith. by a drive member (not shown).

The engine 1 is provided with an accelerometer 18 which is fixed with respect to the cylinder head 1 9 of the engine 1, and means 20 for identifying at least one predtermined reference position of the crankshaft. The accelerometer 1 8 and the position identifying or detector means 20 produce information in the form of signals which are transmitted respectively by lines 21 and 22 to an electronic assembly 23 which is capable of automatically producing an ignition circuit control signal which is applied by way of a line 24 to the control electrode or trigger of the thyristor 4.

Fig. 2 shows in outline the arrangement of main electonic circuits of the assembly 23.

As can be seen from Fig. 2, the signal produced by the detector means 20 is passed to a circuit 25 which is capable of producing a signal which is representative of the angular rotation of the crankshaft 1 7. The signal from the accelerometer 18 and the signal produced by the circuit 25 are received by a circuit 26 which supplies a signal which is representative of the angular position of the crankshaft 1 7 when the pressure is at a maximum in at least one of the cylinders of the engine 1. The latter signal is compared to a reference signal in a circuit 27 where the ignition circuit control signal is automatically produced.

The accelerometer 1 8 can be of any known type and will not be described in detail herein.

Generally, it will comprise piezo-electric ceramic members and a seismic or vibration-sensitive mass which Is applied against the ceramic members by resilient means.

The means 20 operative to detect movement of the crankshaft 1 7 into a predetermined reference position may also be of any known type. In particular, the means 20 may comprise an optical detector such as a photoelectric cell and a wheel or disc carrying at least one optical marking which changes the state of the detector when it passes in front of the detector in the course of rotary movement of the wheel. The wheel may be fixed on the crankshaft 1 7 or preferably on a shaft (not shown) which is connected to the crankshaft for rotary movement therewith and which rotates at half the crankshaft speed. Mechanical systems can also be used, such as systems comprising a cam which is associated with crankshaft rotation and which periodically opens or closes a circuit breaker.

Fig. 3 shows an embodiment of the electronic circuit 25 which receives, from the detector 20, a signal which is formed by pulses 1" 12, etc., the space or time interval T between which is representative of an angle of rotation aR of the crankshaft 17. The value of that angle, which is preferably a sub-multiple of 360 and generally at most equal to 360 , essentially depends on the form of the detector 20.The time interval T between the above-mentioned pulses is inversely proportional to the speed of rotation N of the crankshaft 1 7 and directly proportional to aR, and is given by the equation aR T= 6 N in which: T is the period, measured in seconds, between two successive pulses; N, which is measured in r.p.m., is the average speed of rotation of the crankshaft during the time interval T; and aR is measured in degrees.

The apparent frequency F of production of the pulses 1,, 12, etc. is given by 1 F- T The output signal from the sensor 20 is applied to a first input terminal of an AND-gate 29.

An oscillator 30 (for example of resistance-capacitance type) having a frequency F, is connected to a divider circuit 31 which divides by K (an integer great than 1) and which is connected by a line 32 to a second input terminal of the AND-gate 29 to which it applies pulses at frequency F, F2 =- K and therefore with a period T2 = KT,. The output of the AND-gate 29 is connected to a counting input terminal C33 of an electrical pulse counter 33. The counter 33 may be of a conventional type which is known to those skilled in the art as 'Type 7493' and which is marketed by various manufacturers.

Upon receiving the pulse 11, and more particularly upon the occurence of the rising edge 34B of the pulse, the AND-gate 29 passes to its output terminal the pules which are produced by the circuit 31 and which are counted by the counter 33 until the falling edge 34A of the pulse 12 occurs, that is to say, during the time interval T between the pulse 1, and the pulse 12.

Flip-flops of the counter 33 are connected in parallel, by conductor lines, to the same number of independent elements of flip-flop type of a memory circuit 34. The circuit may be of a type which is known to those skilled in the art at 'Type 7474'.

The counter 33 has a zero resetting input RAZ33 which is connected to the detector 20 by a conductor 35 incorporating conventional delay means 35A (namely a pair of inerters) for delaying the transmission of the edge 34A of the pulses 1" 13.. . to the terminal RAZ33 of the counter 33.

The memory circuit 34 has a loading or read control input Ch34 which is connected to the detector 20 by a conductor line 36.

Under these conditions, when the pulse 13 is produced after a rotary movement at of the crankshaft 17, the edge 34A of the pulse 13 causes the digital content of the counter 33, equal to F2 X T, to be transferred into the memory circuit 34, and then the edge 33A which is received by the counter 33 with a certain delay with respect to the edge 34A (the delay is less than the duration of the pulse and is caused by the delay means 35A) causes the counter 33 to be reset to zero. The counter 33 is then ready to record fresh pulses from the AND-gate 29 during a fresh rotary movement aR of the crankshaft 1 7.

The memory or storage circuit 34 has output terminals which are respectively connected to set or initialisation terminals of a down-counter 37 (for example of Type 74 193).

The down-counter 37 has a down-counting input D37 which is connected by a line 38 to the output of the oscillator 30 of frequency F1. The circuit 37 also has a terminal Ro37 at which a signal appears each time that the down-counter 37 passes through zero.

The time interval Ts required for the resetting to zero of the down-counter 37, the initial digital content of which, as supplied by the memory circuit 34, is F2T and which receives the downcounting pulses at the frequency F1, is defined by the relationship Ts.F, = F2.T, and the frequency of the passages through zero of the down-counter 37 is therefore equal to: F, KF2 F, - = = KF F,xT F/F in which F is the frequency of the pulses I,.Ii, In other words, K pulses appear on the terminal Ro37 of the down-counter 37 in the course of each crankshaft rotation (YR and the periodicity of those consecutive pulses corresponds to a rotary movement aR of the crankshaft 1 7.

K The down-counter 37 has a loading or reset input Ch37 which is connected to its terminal Rio37 by a line 39. Under these conditions, each time that the down-counter 37 passes through zero, thereby producing a signal on the terminal Ro37, the down-counter 37 is automatically reset or returned to the loading position.

The output terminal Ro37 of the means 37 is connected by a line 40 to a counting terminal C- of a circuit which is diagrammatically shown at 28 and which may comprising m elementary circuits of the shift register type well known to those skilled in the art (for example Type 74 1 64), comprising eight output terminals, each of which produces a pulse which is the image of each unitary angle of rotation of the crankshaft and of a value etR/K, the arrangement of which outputs can permit differentiation or distinguishing of O to (8"-1) pulses supplied by the downcounter 37.

Each of the pulses produced by the down-counter 37 causes incrementation of the circuit 28 which, at any moment, will supply a signal which is representative of the number of pulses received during the time interval: (8-1) T' = (892- 1 JT = T, where K8"-1.

K In other words, the circuit 28, which constitutes an 'angular clock', behaves like a shift register circuit having 8t output terminals designated by O to (8"-1) in Fig. 3, which makes it possible to follow the rotation of the crankshaft 1 7 in a stepwise manner at successive angular spacings equal to a/K, from its reference position (as determined by the setting or timing of the wheel or disc carrying the optical markings), the speed of rotation of the crankshaft 1 7 being considered constant during a time interval T between two successive pulses 1,, 12 etc. It will be seen therefore that the choice of the values of at an K makes it possible to follow crankshaft rotation with accuracy.Generally, the selected values of ar and K will be such that the value of the angle (vR/K is for example between 0 30' and a few degrees, and the circuit 28 can then comprise three elementary circuits of shift register type, each having eight output terminals.

The counter 28 has a terminal RAZ28 for resetting it to zero, such terminal being connected to the detector 20 in such a way as to be reset to zero by each pulse 1,.

The shift register circuit 28 makes it possible to select an 'angular window', the purpose of which will be made apparent hereinafter. For this purpose, two output terminals of the shift register 28, corresponding to the two limit angles of the above-mentioned angular wndow, are respectively connected to the two input terminals of a flip-flop circuit 42 of the SET-RESET type.

Thus, the flip-flop 42 supplies on its output terminal a signal which is in the form of a square wave, between the two angular positions defining the selected 'angular window'. The square wave begins when a first signal appears at the output terminal of the register 28 corresponding to the first limit angle of the above-mentioned window (first change of state of the flip-flop 42), and the square wave is terminated when a second signal appears at the output terminal of the register 28 corresponding to the second limit angle of the window (secnd change of state of the flip-flop 42J Fig. 4 shows a diagrammatic view of the composition of the circuits 26 and 27 (see Fig. 2) which, with the circuit 25, form the electronic assembly 23.

The accelerometer 1 8 passes its signal to a low-pass filter 44, the cut-off frequencies of which are for example between 1 Hz and a few hundreds of Hz. The purpose of the filter 44 is to suppress the signals resulting from cylinder head vibration produced by other phenomena such as closing of the valves etc. and which generally result in the production of signals at frequencies which are higher than those resulting from the variations in pressure within the engine cylinders. The signal produced by the accelerometer 1 8 is successively integrated by a first integrating means 45 and then a second integrating means 46. The signal produced by the second integrating means 46 is passed to a threshold circuit 47 which supplies a pulse when the signal passes through its maximum value.The pulse from the circuit 47 is applied to a first input of an AND-gate 48 which transmits it to a flip-flop 49 when the gate 48 simultaneously receives two validation signals on two other input terminals. A first of these validation signals is supplied by an inverter 50 whose input is connected to the output of the first integrating means 45. Thus, when the signal from the first integrating means 45 is zero in value, the inverter 50 validates the signal of the threshold circuit 47 as actually being a maximum in respect of the signal supplied by the integrating means 46.

In the apparatus illustrated in Fig. 1, a choice has been made to observe only the portion of the signal from the second intetrating means 46 which corresponds to the maximum pressure in a given cylinder C, (see Fig. 1). It is then considered or assumed that the phenomena which occur in the other cylinders are similar and that the ignition setting will be identical for each cylinder.

For this purpose, the second validation signal used is the signal supplied by the flip-flop 42 which is connected to the circuit 28 (see Fig. 3) so that the second validation signal appears only for predetermined crankshaft positions in respect of which the maximum pressure in the cylinder C, is liable to occur in operation of the engine. For example, one of the input terminals of the flip-flop 42 is connected to the output of the circuit 28 which substantially corresponds to a first position of the crankshaft 17, at which the piston in the cylinder C, is at top dead centre, the other input terminal being connected to the output terminal of the circuit 28 which corresponds to a second position of the crankshaft after it has rotated through a further angle of 60'.

Besides the signal supplied by the AND-gate 48, the flip-flop 49 receives a synchronisation signal which may be formed by the pulses I produced by the detector 20 when the crankshaft is in a predetermined angular reference position. The reference position is so selected that the crankhaft 1 7 reaches that position before ignition occurs in the cylinder C1, irrespective of the engine operating conditions. For example, the abovementioned reference position will be located at 65 of crankshaft rotation before the piston in the cylinder C, reaches the top dead centre position.

It will be appreciated that the synchronisation signal may be that supplied by one of the outputs of the circuit 28 provided that, in all circumstances, the reference signal is produced before ignition of the spark plug in the cylinder C,.

The output of the flip-flop 49, being initially in logic state 0, is switched to logic state 1 upon reception of the synchronisation signal and reset to state 0 upon reception of the validated signal from the gate 48. This therefore produces a signal in the form of a square wave, the width of which depends on the angle 8 of rotation of the crankshaft 1 7 between the reference position and the position at which the maximum pressure occurs in the cylinder C,. That signal is transmitted to a first input of an AND-gate 51 which, at a second input, receives the output pulses of the circuit 28 or angular clock H. The output signal of a flip-flop 52, which is controlled by the synchronisation signal and by the output signal of a counter 53 of the shift register type (for example Type 74 164), is applied to a third input terminal of the circuit 51.

The counter 53 counts the synchronisation pulses and produces at once of its output terminals a signal which represents a number n of operating cycles of the engine 1.

When a first synchronisation signal occurs, the AND-gate 51 simultaneously receives the output signal from the flip-flop 49 and that from the flip-flop 52, which signals form the validation signals, and the gate 51 passes OK/aR pulses coming from the clock H throughout the duration of the signal produced by the flip-flop 49. The same phenomenon occurs during n engine operating cycles and the cycle counter 53 produces a signal which changes the state of the flip-flop 52.The number of pulses which have passed through the AND-gate 51 is divided by the number of cycles n in a circuit 54 which supplies a mean number of pulses rm = SmK/aR which is representative of the mean value of the angle Om of crankshaft rotation between the movement to the reference position and that corresponding to the maximum pressure in the cylinder C1.

Those pulses are applied to a down-counting terminal D55 of an up/down counter 55 (for example Type 74 193), which was initially set or initialised to the theoretical value r,h of the number of pulses which corresponds to the theoretical angular spacing 5th between the reference position of the crankshaft and the position at which the pressure in the cylinder C, is to be at a maximum.

The absolute value or modulus in respect of the difference r,,-r,, which is representative of the spacing E = /9th-6 m, appears on output terminals of the up/down counter55 which are connected to input terminals of a memory 56 (for example Type 74 174), while the sign of that difference is indicated by one of the outputs which are generally referred to as 'carry' or 'borrow' outputs, depending on whether the sign is positive or negative.

Transfer of the information E from the up/down counter 55 to the memory 56 is effected by the pulse produced by the cycle counter 53, which is delayed by a delay circuit 57a. The same pulse, delayed further in a delay circuit 57b, returns the up/down counter 55 to its initial condition by way of an input Ch55.The information c stored in the memory is applied to an adder-subtractor circuit 58 (Type 7483) to which is also applied the theoretical value ssth of the angle of crankshaft rotation between the reference position and the theoretical position in which ignition should occur in the cylinder C,, in order for the pressure in that cylinder to be at a maximum when the crankshaft has rotated through an angle 01h with respect to the reference position The circuit 58 supplies a signal which is representative of the angle ficom = ssth + E of crankshaft rotation between the reference position and the real position at which actuation of ignition in the cylinder C, is to occur This signal is applied to the set or initialisation terminals of an up/down counter 59 (Type 74 193), the down-counting terminal D59 of which is connected to the output of an AND-gate 60 which receives the synchronisation signal at one input terminal and the angular clock signal H at a second input terminal. Upon passing through zero, the circuit 59 produces at a terminal Rio59 thereof an ignition control signal which is transmitted by a suitable circuit 61 to the trigger electrode of the thyristor 4 and to a loading or reset terminal Ch59 of the up/down counter 59, thus permitting resetting or re-initialisation of the up/down counter 59.

Modifications may be made to the above-described apparatus. For example, it is possible to provide separate control of the ignition in each of the cylinders of the engine 1, by using as many circuits, comprising the circuit elements 48 to 61, as may be required.

Under certain engine operating conditions, the setting of the ignition will have to be different from optimum advance, over a period of greater or lesser length; for example if it is desired that the rise in temperature of the engine should be quicker when starting up. Generally, an addersubtractor circuit 62 (which is shown in broken lines in Fig. 4), which alters the value of ficorn by algebraically adding a corrective value y, is interposed between the circuits 58 and 59. This alteration may be effected permanently or only temporarily. In the latter case, the duration of the correction effect may be constant or may again depend on the value assumed by a parameter which is measured by a detector 63.

Such correction effects may also be produce when pinking occurs. or in order to ensure that the combustion gases are as non-polluting as possible, and so forth.

It will be appreciated that the values rth and Pth set up in the circuits 55 and 58 will be determined precisely for each engine. The setting up or display of such values, which are previously measured in dependence on the precies operating conditions of the engine, may be programmed in dependence on the same conditions.

Fig. 5 shows a diagrammatic view of a modification of the above apparatus forming an embodiment of the invention. The accelerometer 18 which is fixed on the cylinder head of the engine passes a signal to a low-pass filter 44, the cut-off frequencies of which are for example between 1 Hz and a few hundreds of Hz. The purpose of the filter 44 is to suppress signals resulting from vibration of the cylinder head produced by phenomena such as closure of the valves, etc. and which generally result in signals at frequencies which are higher than those resulting from the variations in pressure within the cylinders of the engine.

The signal produced by the accelerometer 1 8 is processed by an integrating means 45 whose output terminal is connected to the input terminal of a logic inverter 50 which produces a signal when the output signal from the integrating means 45 is zero in value. The output ot the inverter 50 is connected to an input terminal of an AND-gate 48 which at the same time receives on a second input terminal a signal which is representative of the angular position of the engine shaft, and which is produced by the arrangement illustrated in Fig. 3 above.

The signal produced by the AND-gate 48 is then processed as illustrated in Fig. 4.

Claims (4)

1. A method of automatically adjusting the ignition timing of a controlled-ignition engine to an optimum value for operating conditions corresponding to maximum power and maximum efficiency of the engine, wherein the ignition timing is so adjusted that the maximum pressure in at least one cylinder of the engine occurs at a predetermined angular position of a shaft of the engine shaft, and-wherein:: the angular position of the engine shaft is detected, acceleration effects to which a cylinder head of the engine is subjected are detected and a first signal representative of said acceleration effects is produced during at last a portion of the rotation of the engine shaft; the first signal is integrated to produce a second signal, the zero value of which is detected with respect to the angular position of the engine shaft, and the ignition timing is adjusted in dependence on the angular value of the position of the engine shaft at which the second signal is zero in value.

2. A method of automatically adjusting the ignition timing of a controlled-ignition engine, the method being substantially as herein described with reference to Figs. 1 to 5 of the accompanying drawings.

3. Apparatus for automatically adjusting the ignition timing of a controlled-ignition engine, the apparatus comprising: ignition control means, a rotation detector for detecting the rotational position of a shaft of the engine, an accelerometer which is fixed to a cylinder head of the engine and operative to produce a first signal representative of acceleration effects to which the cylinder head is subjected, an integrating means connected to the accelerator and operative to produce a second signal, zero value detection means connected to the integrating means for detecting a zero value of the second signal over at least a portion of the rotation of the engine shaft, angular position detecting means connected to the zero value detection means and to the rotation detector and operative to detect the angular position of the engine shaft corresponding to the zero value of the second signal.

comparison means connected to the angular position detecting means to detect the spacing between said angular position and a reference position, and adjustment means connected to said comparison means to modify the action of the ignition control means in dependence on said spacing.

4. Apparatus for automatically adjusting the ignition timing of a controlled-ignition engine, the apparatus being substantially as herein described with reference to Figs. 1 to 5 of the accompanying drawings.