AU488564B2 - High energy adaptive ignition via digital control - Google Patents

Description

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HIGH ENERGY ADAPTIVE IGNITION VIA DIGITAL CONTROL

Background of the Invention

This invention relates to automotive ignition systems

and, more particularly, to a digitally implemented, constant

dwell time version thereof.

Electronically controlled ignition systems are well

known in the art. Such systems are favored over their

mechanical counterpart since the electronic system is more

accurate and reliable. Basically, the purpose of any

ignition system is to generate a spark suitable for firing

the combustion chambers at a predetermined engine angular

position. In mechanical breaker point type systems it has

been found that spark energy falls off at increasing engine

RPM. This may result in inefficient fuel combustion or even

engine misfiring. The use of electronic circuitry in the

ignition can result in a constant spark energy level over

the entire range of engine active operation.

While fully electronic ignition systems have resulted

in enhanced engine performance, they have suffered certain

limitations. For example, in inductive storage type systems,

spark energy level is a function of battery voltage and

ignition coil resistance. Each of these parameters is

temperature dependent, and, in automotive applications,

temperature extremes are to be expected. Prior ignition

systems have not compensated for these variables.

A further failing in prior art ignition systems is

acceleration response. For proper engine operation, an

ignition system must respond to accelerations of up to 4,000 2 488,564

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have a time ?M per second. Electronic ignitions ncrmally suitably responsive. ig, which prevents them from being ignitions have required a In addition, fully electronic resulting in a very arge number of electronic components, of the components are xpensive system. Moreover, many degradation due to aging emperature dependent and suffer

ffects.

Summary of the Invention therefore, to provide It is an object of this invention, which compensates for the Sfully electronic ignition system of the ignition components. nvironmental and aging effects invention, sensors in the Briefly, according to the type types of pulses. The first ignition system provide two synchronous to the desired isan ignition pulse which occurs firing. Between ignition time of engine combustion chamber pulses is generated. The pulses, a sequence of position corresponds to a given engine instance of a position pulse

angular position. position pulses whereby First circuitry processes the of engine position is an output signal representative first of an ignition pulse, the produced. At the occurrence level from which it again circuitry is reset to a reference pulses. In the digital begins processing the position the first circuitry is implementation of the invention, counter. comprised of a resettable position

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Second circuitry also processes the position pulses to

produce at its output a signal representative of engine RPM.

In. the preferred embodiment of the invention, the second

circuitry is comprised of a clock, a speed counter, and a

speed register. The clock generates a signal of predeter-

mined time period which is suitable for activating the speed

counter. In its activated state, the speed counter produces

an output count representative of the number of position

pulses generated during each clock signal. At the conclu-

sion of a clock period, the total count from the speed

counter is transferred to the speed register.

A comparator monitors the output count from both the

first circuitry, e.g. position counter, and the second

circuitry, e.g. the speed register. The comparator produces

a trigger signal at a predetermined relationship between the

outputs from the first and second circuits. This rela-

tionship is such that once a trigger signal is generated, it

activates a switch which in turn maintains the ignition

system at a constant dwell time and thus a constant spark

energy level, provided there is a constant battery voltage

and ignition coil resistance.

To compensate for varying component values, such as

battery voltage and ignition coil resistance, a means moni-

tors the ignition energy level and generates a feedback

signal representative thereof. In a particular embodiment,

the feedback signal may be comprised of the synchronous

occurrence of a given current level in the ignition coil and

generated position pulses. In response to the feedback

signal, a control means alters the occurrence of the trigger

signal such that dwell time is adjusted to maintain a

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substantially constant ignition energy level. In the pre-

ferred embodiment, the control means responds to the feed-

Dack signal to vary the clock period interval. When, for

3xample, the control means detects an increasing current

limit feedback signal, such as might happen with decreased

:oil resistance or increased battery voltage, the clock time

period is decreased whereby the comparator institutes dwell

at a later time in the engine cycle. In so doing, the

feedback provides a fully adaptive constant energy ignition

system. Finally, in the preferred embodiment, each compon-

ent may be implemented by using digital technology, whereby

the resulting system comprises a minimum of external com-

ponents. Brief Description of the Drawings

Fig. 1 is a graphical representation of the operation

of a system according to the invention;

Fig. 2 illustrates the preferred embodiment of the in-

vention in block diagram form; and Fig. 3 is a more detailed diagram of the preferred em-

bodiment. .Detailed Description of the

Preferred Embodiment of the Invention

The present system utilizes both engine position and

speed information to maintain a constant ignition energy

level. Since the energy of an inductive storage type ig-

nition is a function of dwell time the time during dwell which battery current is passed through the coil),

control may be utilized to provide the desired operation.

Fig. la represents the angle offset required at con-

stant engine speed to yield a constant dwell time, Tdo.

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Plotted vertically is engine position angle and horizontally 0 is time. max represents the maximum allowable angle in a

given engine cycle, e.g. 450 of the distributor for an 8

cylinder engine. T represents the time corresponding to 0mmax

or the angle predictor, represents the angle with respect P to Omax which corresponds to the time Tp with respect to the T cycle time T such that dwell time do T Tp) remains

constant. Thus, it is seen that

Op Omax 10 do'

where w 0 is the angular velocity of the engine.

Fig. lb plots the desired angle offset as a function of

.time under engine acceleration. Note that the angle increases

exponentially with time while the angle predictor 0p

decreases linearly, since it is proportional to speed which

increases linearly under acceleration. Given an accelera-

tion a, it can be seen that

Op 00 Tdo 80 [0O a (d)

A predictor line can be constructed originating at the 0 T of the angle 00 O do and extending to the intersection

parabolic angle plot with the coordinate Op. The horizontal

coordinate of the intersection corresponds to the time Tp T such that T T do (a constant).

Thus, it should be observed that a constant dwell time

can be determined based on information as to engine position

and a predictor line which originates from the offset angle

corresponding to initial engine angular velocity, and descends

at a rate dependent upon engine acceleration. In substance

then, to maintain a constant dwell time the ignition system

must respond to engine position, speed, and acceleration. Fig. Ic illustrates a digital approximation to a constant

dwell type system. The approximation assumes that a sequence

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of digital pulses is generated between ignition pulses.

Each digital pulse corresponds to a particular engine angu-

lar position. Thus, engine angular position may be deter-

mined by counting the number of received position pulses

following an ignition pulse. For an accelerating engine,

the pulse count will rise at the parabolic rate previously

shown in Fig. lb. In turn, engine speed may be determined

by counting the number of position pulses generated during a

clock interval Tclk. For a given clock period Tclk the

number of pulses counted by the speed counter will increase

under engine acceleration. Thus, assuming the speed counter

starts at an initial count and counts down for each received

position pulse during the clock interval, it can be seen

that the final decremented count in the speed counter at the

end of a clock period traces the angle predictor line. At

a given number of clock intervals, the final count in the

speed counter will equal the count of the position counter.

This corresponds to the angle p and the time Tp that dwell

should be initiated if a constant dwell time Tdo is desired.

Hence, the time at which the output from the position counter

exceeds the output from the speed counter corresponds to the

time at which dwell should be initiated.

Fig. ld illustrates the desired angle offset 0 for a

system under acceleration and subject to a changing ignition

component, such as battery voltage or coil resistance. As-

suming that coil resistance decreases, or that battery

voltage increases, a corresponding correction to the pre-

dicted time Tp is easily made by decreasing the clock time

Tclk to T'clk This results in a new predicted time Tp

and a new desired dwell time Tdo' 7 488,564

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Fig. 2 illustrates a block diagram implementation of

the system described with respect to Fig. Id. A first

engine sensor (not shown) generates a sync pulse at the

desired time of engine firing. The sync pulses are routed

to the ignition system via channel I. A series of position

pulses are generated by a second sensor (also not shown) and

routed to the system via channel II. Each position pulse

occurs at a particular engine angular position.

The position pulses are processed through a position

output counter 20, which begins at an initial value and

increments one count for each received position pulse. A

-reset input terminal 22 connects to channel I whereby a

subsequently received sync pulse resets the counter to its

initial value. Thus, the position output counter 20 produces

at its output terminal 24 a signal of the form Y K1 8,

where Y is representative of the output signal, K 1 represents

a constant, and 0 is the engine angular position. The

generated signal Y increases at a linear rate when the

engine is at constant velocity, and at a parabolic rate fo.*

engine acceleration. Hence, output signal Y may be used as

representative of the engine position signal indicated in

Figs. la-ld.

Engine speed is determined in a speed output counter

Speed counter 30 has a first input 32 which connects

to channel II and a second input 34 which connects to a

clock 36. At its output 38 the speed output counter

produces a signal which is representative of the number of

position pulses generated during each clock 36 time period.

For a given clock period, the number of position pulses

counted increases, thereby increasing the output signal Z.

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Y signal A comparator 40 accepts at its first input 42 the second input output from the position counter 20, and at its When the 44-the speed output Z from speed counter 30. the signal Z comparator senses the signal Y is greater than

it activates its output 46. The output 46 of comparator 50. The connects to the "set" terminal 52 of a flip-flop to channel flip-flop has a "reset" input 54 which connects output 46 I, and a Q output 56. An activated comparator a trigger causes the Q output 56 of flip-flop 50 to produce terminal 62 of signal which is coupled to the trigger input

a switch 60.. Switch 60 has a first terminal 64 which connects 68. A in series through an ignition coil 66 to a battery a current sense second switch terminal 70 connects through 74. resistor 72 to a reference, or ground, potential by a Feedback from the ignition output is provided to the load resis- current limit amplifier 80 which connects The current tor 72 for sensing the current therethrough. 82 a signal repre- limit amplifier 80 produces at its output 66 is passing a sentative of the time during which the coil drop across the given current level, i.e. a given voltage T lim is fed back load resistor 72. This current limit time input 33. to the speed output counter 30 its Tdo adjust output 46 In operation, comparator 40 activates its count Z. Refer- when the position of count Y exceeds speed time that dwell ring to Fig. i, this corresponds to the dwell time. An should be initiated to maintain a constant the flip-flop 50 to activated comparator output 46 causes activates switch 60 to create a trigger signal which in turn builds up from its conductive state. Thereafter, current

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to ground potential 74. When an ignition pulse is generated,

it travels via channel I to the reset input 54 of flip-flop

thereby deactivating flip-flop output 56 and actuating

switch 60 to the nonconductive state. Coil 66 thereby

combustion produces a high voltage output which fires the

chamber. A change in battery 68 voltage, or the resistance of

at which ignition coil 66 can significantly alter the rate of the the coil 66 reaches a given current representative

desired ignition energy level. To compensate for these

a feed- variables, the current limit amplifier 80 generates

back signal representative of the total time the output coil

signal is 66 is at the desired current, which feedback

applied to the speed output counter 30. In turn, the speed

thus varying. output counter alters its clock period to T'clk time at the speed count output Z and thereby altering the This, in turn, which the comparator output 46 is activated. constant adjusts dwell time to maintain a substantially

ignition energy level. A more detailed block diagram of the preferred embodi-

ment of the invention is given in Fig. 3, wherein similar

numbers have been used to identify identical components.

Position pulses are routed via channel II to the position

counter 20. Counter 20 is of the "up" type whereby each

subsequently received position pulse increments the counter

output 24. to the next higher count state. At the end of a

position pulse sequence, a sync pulse via channel I is

applied to the counter reset terminal 22, thereby returning

the counter to its initial state in preparation for subse-

quent counting.

The speed output counter 30 is comprised of a series of

individual blocks including a modulus M counter 110, a

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modulus M divider 120, a time delay 130, a speed counter

140, a preset N memory 150 and a speed count register 160.

Speed output counter operalion may be understood as

follows. The clock 36 provides a clock signal rclk having a

frequency f0 This in turn is fed to the input. 122 of the

modulus M divider 120. Modulus M divider 120 frequenqy_-

divides signals at its input 122 by the value of modulus M

it receiVes at its input 124 from the modulus M counter 110.

This divided output T'elk appears at the modulus M divider

output 126. There it is fed both to a time delay 130 and to

the strobe input 162 of the speed count register 160. After

the time delay 130 the count appears at Lhe first input.142

of speed counter 140, whose second input 144 connects to

channel II. A third input 146 connects to the preset memory

150. Speed counter 140 produces at its output 148 a count

representative of the number of position pulses received at

counter input 144 during the time counter input 142 is

activate, i.e. during the T' time. Since the output

from the speed output counter 30 is only significant at the

endof the T'clk period, the speed count register 160 is

strobed via the trailing edge of the T'clk signal to accept

the final count from the output 148 of speed counter 140.

Once speed counter 140 senses the conclusion of the T'clk

signal, it activates its third input 146 to preset the

counter 140 to the value dictated by preset N memory 150.

The preset number N is the'maximum number of position pulses

that may occur during a cycle. To prevent speed counter 140

from transferring the preset number N to the speed count

register 160 on the conclusion of every T'clk signal, the

time delay 130 provides a slight time lag, whereby when the 11 488 564

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speed count registers strobe 162 is activated, the speed

counter output 148 is at or near its maximum value during a

T'clk interval. The speed count register 160 produces the

stored total speed count Z at its output 164.

A comparator 40 couples the Y output from output terminal

24 of position counter 20 to its first input 42, and the Z

output of the speed output counter 30 to its second input

44. The comparator 40 logic is such that when the Y count

output exceeds the Z count output the comparator activates

its output 46.

The comparator output 46 feeds to the first input 172

of an AND gate 170. The AND gate second input 174 connects

to the output 182 of a maximum dwell comparator 180. Maximum

dwell comparator 180 has its first input 184 connected to

the output 24 of position counter 20, and its second input

186 connected to the output of an N/4 memory 190. At the

highest desired engine RPM the system should be automatically

set to a 75% dwell time. Since N is the total number of

pulses per engine cycle, N/4 pulses should be encountered

prior to initiating maximum dwell time. Thus, gate 170

produces an activated output 176 over the active RPM range,

i.e. 300-5000 rpm, when Y is greater than Z, and when Y is

greater than N/4.

The output 176 from gate 170 connects to the set input

52 of flip-flop 50. As discussed with respect to Fig. 2,

once input 52 is activated the flip-flop output 56 produces

a trigger signal, which is amplified by drive circuitry 200

and applied to the control terminal 62 of a switch

Thereafter the switch 60 passes current from the battery 68

through the coil 66 and current sense resistor 72 to ground

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potential 74. When the reset input 54 of flip-flop

receives a sync, or ignition, pulse, the trigger signal at

output 56 ceases, whereby the switch 60 opens thus generat-

ing the ignition spark via coil 66.

A current limit amplifier 80 monitors the voltage

created by coil 66 current through current sense resistor

72. Current limit amp 80 produces at its output 82 a pulse

whose width Tli m is representative of the length of time a

predetermined current passes through ignition coil 66. The

Tlim signal is applied to one input 212 of an AND gate 210,

whose second input 214 connects to channel II. The gate 210

produces at its output 216 a signal representative of the

synchronous occurrence of the Tlim signal and the input

position pulses. Thus as the current limit time increases,

as' it will for increased battery 68 voltage or decreased

coil resistance 66, a greater number of position pulses

appears at the gate output 216.

The output of gate 216 is connected to the count down

input 112 of the modulus M counter 110. Connected to the up

count terminal 114 of modulus M counter 110 are the sync

pulses on channel I. During one cycle the modulus M counter

110 up counts via a received sync pulse, and down counts via

the number of pulses from gate 210. In stable operation

there is one T im pulse per cycle, whereby the modulus M

output remains constant. However, should the number of

feedback pulses from gate 210 change for a given cycle, the

modulus number M from the counter 110 will vary, whereby the

modulus M divider 120 will create a correspondingly changed

TI signal. Referring to Fig. id, as the number of feed- clk back pulses from gate 210 increases per cycle, indicating

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increased battery voltage or decreased coil resistance, the

modulus M is decremented whereby the divider 120 produces a

shorter T' clk signal at its output 126. As Fig. Id illus-

trates, this causes the system to initiate dwell at a later

point in the cycle, whereby the desired ignition energy

level is maintained. In general, the feedback provided by

gate 210 and modulus M counter 110 is sufficient to cause desired the system to always return to a state providing the

ignition energy.

In summary, an ignition system has been described which variations maintains a given ignition energy level despite effects on in engine acceleration, or temperature, or aging

ignition components. Moreover, the entire system may be

implemented by digital circuitry, thereby avoiding a large

number of age and temperature sensitive components.

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Claims (1)

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The claims defining the invention are as follows:-

1. A system for controlling the ignition dwell

of an internal combustion engine comorising an ignition pulse generating means, coupled

to the engine, and-producing ignition pulses suitable

for ignition firing, a position pulse generating means coupled to

the engine and producing position pulses representative

of engine angular position, a first circuit means for processing the

position pulses and producing an output signal

representative of engine position. the first means

resettable to an initial state prior to the occurrence

of the first position pulse following a trigger pulse, a second circuit means processing the position

pulses and producing an output representative of engine

RPI'I, a comparator means for comparing the first

circuit means output with the second circuit means

output and producing a trigger signal in response to a

predetermined relationship between the two outputs, switch means initiating dxwell time in response

to a trigger signal from the comparator means and firing

the ignition in response to an ignition pulse, means for generating a feedback signal

representative of the ignition energy level and, control means for predeterminedly altering the

occurrence of the trigger signal in response to the

.feedback signal, whereby the dwell time is adjusted to maintain

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a, substantially constant ignition energy level. 2. The system of' claim 1 wherein each structural element is imrlemented using di-ital circuitry. 3. The system of claim 1 or claim 2 wherein the first circuit means includes an angle counter for counting the number of position pulses generated between ignition pulses. 4j. The system as claimed in any one of' the preceding claims wherein the second circuit means includes clock means for generating a clock signal ~r~od~tczirn~time period, havng and speed counter means for counting the number of' position pulses generated during each clock signal period. The system of' claim 4~ wherein the second circuit means further comprises speed register means, responsive to the clock signal, for registering the count of' the speed counter means immediately prior to the conclusion of the cnlock signal, and applying the registered count to the comparator means. 6. The system of' claim 5 wherein the second circuit means further comrises means for presetting the speed counter to a predetermined count prior to its reception of rosition pulses generated during each clock signal period, and wherein the speed counter fLurther cocori- ses means for decrementing the predetermined count by the number of received position pulses during each clock-

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signal period.

7. The system as claimed in any one of the

preceding claims wherein the comparator means produces a trigger pulse when the output of the first circuit

means is greater than or equal to the output of the

second circuit means.

8. The system as claimed in any one of the coil preceding claims in combination with an ignition wherein the feedback signal generating means includes

means for generating a circuit limit pulse whose width is is representative of the time during which the coil

conducting a predetermined current and, gating means for generating a pulse train the representative of the synchronous occurrence of current limit pulse and the position pulses.

9. The system of claim 8 wherein the control

means comprises a modulus N register for generating a modulus

number M, the register incrementing the number for each

ignition pulse and decrementing its count for each pulse in the pulse train, and means for varying the clock signal period

responsive to the modulus number M. The system of claim 9 wherein the control means

further comprises an oscillator producing a signal of constant

frequency fo, and a modulus P programmable divider, responsive

to the modulus register, for dividing the frequency fo

by the modulus number H and applying the output clock 17 488.5 64

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signal to-the Specd counter means. 11. The system of claim 1 further comnris ig means for fixing.- a maximum allowable dwell time. 12. The systemi for controlling the ignition dwell of an internal conbustion engine substantially as hereinbefore described with reference to the accompanying- drawings.

DATED: 22nd July, 1976. 0D MOTOROLA, IN~C. 4(9 4 By their P--atent attorneys: PHII.LIF"P OR-'IC'I--'DE ';FdZATIC

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POSITION PULSES CHAN.2

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